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Monitoring of the degradation of chlorinated organic impurities in water by automated flow injection… Que, Amy Hong 1994

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MONITORING OF THE DEGRADATION OFCHLORINATED ORGANIC IMPURITIES IN WATERBY AUTOMATED FLOW INJECTION ANALYSISby Amy Hong QueB. Sc., Jilin University, 1984M. Sc., Jilin University, 1987A THESIS SUBMITTED iN PARTIAL FULFILLMENT OFTHE REQUREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinTHE FACULTY OF GRADUATE STUDIESDEPARTMENT OF CHEMISTRYWe accept this as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAMarch 1994© Amy Hong Que, 1994In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that theLibrary shall make itfreely available for reference and study. I further agree that permission for txtensivecopying of this thesis for scholarly purposes may be grantedby the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowedwithout my writtenpermission.__________________________Department of -The University of British ColumbiaVancouver, CanadaDate 44’A/ icy79DE-6 (2/88)ABSTRACTChlorinated organics are a major concern because of their persistence in theenvironment, possible toxicity and carcinogenicity. One of the substances of mostconcern, chloroform, has been classified as a priority pollutant by U.S. EnvironmentalProtection Agency. It is present at trace levels in man-made drinking water and in wastewater from industries such as pulp and paper. The scope of this thesis has been to developinstrumentation and methods for destruction and detection of chloroform and relatedcontaminants in such samples.Attack of chloroform by free radicals (e.g., HO.) can result in completemineralization: i.e., quantitative liberation of the innocuous free chloride and generation ofcarbon dioxide. Free radicals are formed when a suspension of a semiconductor materialsuch as titanium dioxide is illuminated with ultraviolet light. They are also formed whenaqueous solutions are subjected to a high intensity ultrasonic field. In this thesis we reportuse of both UV and ultrasound to degrade chloroform, and have monitored the rate andextent of conversion via real-time on-line measurement of free chloride concentration andconductivity. The technique used for these studies is Flow Injection Analysis.Specific objectives of this research were as follows:(i) To develop a photo-reactor within which to carry out the degradationexperiments. This contained two mercury lamps and used either suspended titaniumdioxide powder (anatase) or titania glass as photocatalyst. The two UV lamps weredirectly immersed in the solution to provide the most efficient UV irradiation. A 23 kHzsonicator probe was situated in the centre of the vessel for those experiments whichrequired it.(ii) To develop an automated sampling system by which the progress of thereaction within the reactor could be followed. This was comprised ofpolytetrafluoroethylene (Teflon®) tubing and contained an in-line microfiltering system to11remove catalyst solids. It was used to take samples from the reactor and deliver them tothe detection system.(iii) To develop an automated Flow Injection Analysis system to detect productsfrom the photodegradation of the organic species. A flow-through conductivity detectorwas constructed and used to monitor the change in total free ions. A chloride ion selectiveelectrode with its flow-through cell was used to quantitatively monitor the change inconcentration of free chloride ion. In both cases the output was observed as a series ofskewed Gaussian peaks.(iv) To characterize the instrumentation developed and to use it to study thedegradation of chlorinated organics - specifically chloroform. The instrumentation wasable to monitor the progress of reactions over a period of several hours without humansupervision. With the presence of UV light and titania powder catalyst it was found thatchloroform was totally degraded after about 50 mm. The chlorine was quantitativelyrecovered as chloride ions. A kinetic analysis showed that the reaction curve followedA—B--*C reactions. A mechanism for the reaction is proposed in the thesis. When usinga heterogeneous chloroform system, introduction of power ultrasound into the reactorimproved the yield after 20 mm by 41 % based on the detection of chloride ions. Apreliminary investigation of a glassy form of titanium dioxide showed a reaction rate whichwas four times slower than for the anatase form, given equal masses. This rate differencemay be due to decreased contacting surface area. However, the glassy form is mucheasier to use.The system developed has strong potential for rapid, semi-automatic developmentof optimal catalytic treatments to detoxify industrial waste water and purify municipaldrinking water. As such it has significant economic and environmental applications.111TABLE OF CONTENTSpageABSTRACT iiTABLE OF CONTENTS ivLIST OF FIGURES viiLIST OF SCHEMES ixLIST OF TABLES ixACKNOWLEDGMENTS xChapter 1 INTRODUCTION 11.1 Degradation of chlorinated organics 31.1.1 Photodegradation using titanium dioxide 31.1.2 Sonolysis with power ultrasound 71.1.3 Other possible methods 111.2 Real-time reaction monitoring by FIA 131.2.1 Principles of flow injection analysisand function of a flow system 131.2.2 Process monitoring by FIA 171.3 Monitoring degradation of chlorinated organics by FIA 221.4 Objectives 24Chapter 2 INSTRUMENTATION 262.1 Development of ph6to-reactorfor photodegradation of aqueous chlorinated organics 262.1.1 Reagents 262.1.2 Apparatus 26ivpage2.2 Development of automated FIA manifoldfor monitoring the degradation of chloroform 302.3 Components of FIA system 322.3.1 Computer for control and data acquisition 322.3.2 Pumps and tubing 332.3.3 Injection valve 342.3.4 Detectors 362.3.5 Signal recording 412.4 Characterization monitoring system 412.4.1 Characterization of FIA-conductivity detector andFIA-chloride ISE detector 412.4.2 Reproducibility of photodegradation-FIAmonitoring system 45Chapter 3 MONITORING PHOTODEGRADATION OFCHLOROFORM BY FIA 473.1 In-line monitoring of chloride ion formation by FIA 473.2 Effect of titanium dioxide concentrationon rate and efficiency of degradation 503.3 Study of two different types of Ti02 catalysts 523.4 Comparison of efficiencies of photodegradation byusing different conditions in the reactor cell 553.5 Off-line quantitative analysis of residual chloroform 603.6 Mechanism and kinetics of photocatalytic degradation 65VpageChapter 4 FURTHER WORK 734.1 Optimization of photo-reactor 734.2 Application to more compoundsand classes of compounds 744,3 Improvements to operating software 744.4 Improvements to the FIA manifold 75Appendix PRELIMINARY WORK 79Al Experimental - Decomposition of 4-chlorophenol 81A2 Results and discussion 82A3 Potential to continue the study of 4-chiorophenol withnew degradation and monitoring system 87REFERENCES 88viLIST OF FIGURESpageFigure 1.1 Sound frequencies. 8Figure 1.2 Schematic diagram of an ultrasonic probe system. 10Figure 1.3 Single-line FIA manifold. 14Figure 1.4 Schematic representation of the effect of dispersionon an injected sample zone. 15Figure 1.5 A typical recorder output. 16Figure 1.6 Analyzer response vs. time. 19Figure 1.7 Continuous monitoring based on sample injection. 21Figure 2.1 Reactor for sono/photolytic degradation ofchlorinated organics in water. 28Figure 2.2 Monitoring the degradation of chloroformby flow injection analysis. 31Figure 2.3 Internal workings of a six-port injection valve. 35Figure 2.4 Flow-through cell with chloride ion selective electrode(Cl-ISE). 37Figure 2.5 Circuit of amplifier for chloride ion selective electrode. 38Figure 2.6 Flow-through conductivity detector. 39Figure 2.7 Circuit of conductivity-to-voltage converter. 40Figure 2.8 Calibration plots for FIA-conductivity detector. 42Figure 2.9 Calibration plot for FIA-chloride ISE detector. 44Figure 2.10 Reproducibility of photodegradation-FIA monitoring system. 46Figure 3.1 Chloride ion peaks recorded with an in-line FIA-chiorideISE detector. 48Figure 3.2 Variation of chloride ion concentration with UV irradiation time. 49viipageFigure 3.3 The effect of titanium dioxide concentrationon rate and efficiency of degradation. 50Figure 3.4 Comparison of the efficiencies of two different formsof Ti02 catalyst. 54Figure 3.5 Recorded FIA peaks after 20 minute degradationunder each of the different conditions.(a) FIA-conductivity responses,(b) FIA-chloride ISE responses. 56Figure 3.6 (a) Total ion current chromatogram of partially degraded sample.(b) Mass spectrum of chloroform. 61Figure 3.7 Calibration curve for chloroform. 63Figure 3.8 Disappearance of chloroform. 64Figure 3.9 Variation of the concentration of CHCI3 and C1 vs.UV irradiation time. 66Figure 4.1 (a) FIA sampling system with proposed interface to HPLC.Sequential FIA detectors used are conductivity,C1-ISE, pH and UV absorbance (spectra). 77(b) Sequential detectors presently available. 78Figure Al Chemical structures of chlorinated phenolics. 80Figure A2 Photodegradation of 4-chlorophenol. 82Figure A3 Degradation of 4-chiorophenol with Fenton’s reagent. 84Figure A4 Mechanism of decomposition of chlorophenol. 85Figure A5 UV spectra of 4-chiorophenol and a photodegraded sample. 86Figure A6 Calibration curve of 4-chlorophenol. 87VIIILIST OF SCHEMESpageScheme 1.1 Proposed mechanism of production of HO radicals. 5Scheme 3.1 Decomposition reaction of chloroform. 57Scheme 3.2 Decomposition of water by power ultrasound. 59Scheme 3.3 Three steps of photocatalytic degradation of chloroform. 65Scheme 3.4 Proposed mechanism of decomposition of chloroform. 72LIST OF TABLESTable 3.1 Degree of mineralization of chloroform. 49ixACKNOWLEDGMENTSI would like to thank my supervisor, Dr. A. P. Wade for his advice andencouragement. I am grateful to Dr. Larry E. Bowman for his assistance withinstrumentation development. Thanks are also due to Natural Sciences and EngineeringResearch Council of Canada (NSERC Research Grant 5-80246) and the NationalNetworks of Centres of Excellence (NCE Grant 5-55331) for sponsoring this excitingwork. I appreciate the contributions of Dr. Bob Moody (Tioxide, UK) and ProfessorH. D. Gesser (Chemistry Department, University of Manitoba) for providing the anatasepowder and glassy forms of titanium dioxide catalyst.I would also like to thank colleagues in my group and the staff of the Departmentalworkshops for their frequent help. Many thanks also go to Tim Ma (UBC Civil EngineerDepartment) who ran the GC-MS analysis and Irene Hwang (UBC Chemical EngineerDepartment) who determined the surface areas of the catalyst materials used in thisresearch.In particular, I would like to express my utmost, heartfelt thanks to my family andfriends, especially my husband, Ziyi, and my parents for their dedication, help, support andtireless encouragement.xCHAPTER 1INTRODUCTIONChlorinated organics are a major concern to the environment. One problem withsome of these chlorinated organics, and the reason why they are termed persistent, is thatit can take decades or even centuries for them to break down naturally. Because of thispersistence and their high solubility in fat, they tend to accumulate in the tissues of someanimals (a process called bioaccumulation). The contamination is then passed through thefood chain and can reach very high concentrations in the tissues of predators [1].Chlorinated organics enter ecosystems by many pathways, including industrialdischarges and leakage, municipal and consumer wastes, and run-off from agricultural andforestry applications. They are used as insecticides, such as DDT(dichlorodiphenylfrichloroethane), and in various industrial applications, such as PCBs(polychiorinated biphenyls). Other important sources are the by-products of certainchlorination processes. Chlorination is widely used to disinfect waste water, drinkingwater [21 and swimming pools. Industrial uses of chlorine include bleaching of wood pulp[3]. Water chlorination does more than eliminate unwanted color and destroy bacteria;chemical reactions take place between chlorine and organic materials present in water toform chlorinated organics. Some of the chioro-organic compounds formed exhibit acuteand chronic toxicity to aquatic organisms. Chloroform, for example, is toxic andcarcinogenic. It is a common synthetic product arising at ppb (parts per billion) levelsduring municipal chlorination of drinking water supplies [4-7]. Although it is not an acutehazard to humans at the levels detected (the minimum lethal dose (MLD) of chloroform toa human being is 15 ml /70 kg person [8]), its presence suggests the need to monitor and1to determine whether there may be a chronic long-term threat to the populace. The U.S.Environmental Protection Agency (US EPA) has classified chloroform as a “prioritypollutant” [9] and has set a recommended maximum concentration of 100 ig/l in drinkingwater [101.One possible mechanism for the formation of chloroform can be deduced from thecompounds detected in tap water. Trihalogenated methanes and ethanol were found in tapwater but mono- and dihalogenated compounds could not be detected [6]. Ethanoloxidizes to acetaldehyde, which in turn, reacts with free chlorine to form chloral. Watercombines with chioral to form chioral hydrate, which then decomposes to formchloroform. The reaction scheme is:Cl2CH32O CH3HO CI3CHO (chioral)H20Cl3CCH(OH)2 CHC13Using chlorine to bleach pulp results in the formation and subsequent discharge ofchlorinated organic matter. Chloroform is one of the most abundant volatile chlorinatedcompounds found in effluent from the C-stage (chlorine) of bleaching of wood pulp[3, 11-13]. This stage has been identified as the major source of chloroform release to theatmosphere [13). Therefore, chloroform has been of significant interest to the pulp andpaper industry in British Columbia and elsewhere. The industry is switching more of itsproduction to chlorine dioxide bleaching, which results in far less chlorinated material inthe waste stream (effluent).21.1 DEGRADATION OF CHLORINATED ORGANICS IN WATERConcern over chloroform and other chioro-organic compounds in the aqueousenvironment has prompted research into methods for their degradation. Catalyst-assistedphotodegradation, biodegradation, chemical degradation and ultrasonic degradation aresome of the more common methods.Ideally, a water treatment process for degradation of trace halocarboncontaminants should yield innocuous products such as carbon dioxide, hydrochloric acidand water. This is referred to as “complete mineralization”. Since toxicity of chlorinatedaliphatic hydrocarbons decreases with chlorine content [14], partial degradation withdehalogenation may result in partial detoxification. Hydroxylation of carbon-chlorinebonds (with release of free chloride) is usually the important step in the degradation and isparticularly effective at detoxification. In part this is because the addition of a hydroxylgroup into the molecule makes the compound more polar and hence more soluble inwater, and makes the substance biologically more reactive [15]. From anotherperspective, the resulting products from hydroxylation tend to be excreted more readily byliving organisms. The following sections will briefly describe degradation methods whichhave been commonly investigated.1.1.1 PIIOTODEGRADATION USING TITANIUM DIOXIDERecently, a method for destroying organic impurities has attracted much attentionbecause of its possible use in puriijing drinking water and waste water. This method isbased on the powerful catalytic ability of the semiconductor titanium dioxide (anataseform) when exposed to near-ultraviolet (UV) light. It is fast and does not necessarilyrequire addition of liquid reagents. Titanium dioxide is activated only by photons ofwavelength 350 nm [16]. Heterogeneous photo-assisted catalysis has been shown tobe an effective method for complete mineralization (to dissolved CO2 and HC1) of dilute3aqueous solutions of many common chlorinated organic compounds [17]. Completedecomposition of aliphatic polychlorinated compounds, such as chloroform (CHC13)[16,18], dichloromethane (CH2C12) [16], carbon tetrachioride (CC14) [16] andtrichioroethylene (CI2C HC1) [14] has been reported. Rate parameters for degradation ofthese polychlorinated compounds have been obtained by Ollis [19]. Most aromaticcompounds and chlorine substituted aromatics are more intractable than aliphatics.Complete mineralization requires cleavage of the aromatic rings. Titanium dioxidesuspensions illuminated with UV light have been used for this purpose [17]. According toBarbeni et at, aqueous solutions of 4-chlorophenol (4-CP) [20] and pentachlorophenol(PCP) [21] are almost completely decomposed to CO2 and HC1. Kinetics of suchreactions have been actively studied by Matthews [17, 22] and Ollis [19].MechanismIn the presence of oxygen, several n-type semiconductor powders have beenshown to behave as photo-catalysts and promote the oxidation of substances. Powders ofsemiconductors such as Ti02 offer many advantages for desorptive decomposition. Toxiccompounds can be readily adsorbed to their surface, which can then be activated throughUV irradiation or attachment of reactive species. Irradiation of a semiconductor such asTi02 with light of energy higher than the band-gap results in creation of positive holes(hj in the valence band and electrons (e) in the conduction band of the semiconductor[23]. These charge carriers can recombine without further reaction. Alternatively, theholes can be scavenged by oxidizable species (for example H20, H202, or a hydrocarbonRH), and the electrons by reducible species (for example, 02 or H+) in the solution.Scheme 1.1 shows the reactions which occur [23].4hvTi02 > Ti02” (h + e)H20 + h -* H0 +HO- + h -* HO•H + e —* H•02 + e —* O2 >HO2O2 -2H0•-*02+ 11202 > HO• + HO- +02Scheme 1.1 Proposed mechanism of production of HO. radicalsThe hydroxyl radical, HO., produced as an intermediate, plays an important role inthe oxidation process. It is an indiscriminate, electrophilic, highly reactive species whichdegrades organic components of any water system. The hydroxyl radical is more reactivethan its parent and is responsible for the major pathway to the hydroxylation of organics.Organics may be quantitatively oxidized, stepwise, by such reactions— eventually to C02 and HC1.Tokumaru and coworkers [24] have demonstrated that hydroxyl radical, HO. isformed via the oxidation of water by a positive hole (h) of Ti02 with concurrent removalof the electron by molecular oxygen. Bard et al [25] demonstrated the formation of HO.radical on Ti02 photocatalyst under illumination by using spin-trapping. The probablerole of HO. in oxidation reactions is also supported by the reaction of Fenton’s reagentwith benzoic acid [26] and chlorophenols [27]. Fenton’s reagent is a mixture of hydrogenperoxide and a reducing agent such as ferrous ion which gives hydroxyl radicals, HO..Fe2 +11202 —* Fe3 + HO. + 0H5The hydroxyl radicals produced oxidize benzoic acid and chiorophenols completely tocarbon dioxide, hydrochloric acid and water.The mechanism of decomposition of chlorinated hydrocarbons is summarized asfollows: in aqueous solution, the surface of Ti02 is covered with OH- as well as H20.These species may react with the photo-generated hole (hj to produce HO. Chlorinatedorganics in aqueous media are adsorbed onto the surface of the catalyst. The carbon-chlorine bond may then be attacked and chlorine substituted by the electrophilic species(HO.) to form an alcohol. The alcohol may be oxidized by photo-generated holes andhighly reactive, reducible hydroxyl radicals to form aldehydes or ketones. These are easilyoxidized further to carboxylic acids. Carboxylic acids can be decomposed to C02 via the“photo-kolbe” reaction [26, 28, 29]. Chlorine radicals are converted to chloride ions bycapture of electrons. The presence of molecular oxygen and water are essential to thisreaction scheme [14, 20, 21].If the intensity of the light is sufficiently high, the photocatalytic powders cannotabsorb all of the incident photons. Thus, this radiation can cause homogeneous photolysisreactions, in addition to the desired heterogeneous photocatalytic degradation processes.This renders detailed mechanistic studies of such systems very difficult.The effect ofnwlecular oxygen on photodecoinpositionMolecular oxygen is required stoichiometrically for complete mineralization oforganic impurities. For example,Ti02/hvCHCI3 + H20 + 1/202 > CO2 + 3 HCI6Molecular oxygen acts as an electron acceptor to scavenge the photo-generatedelectrons during formation of HO. via oxidation of water by the photo-generated holes.This serves as a competition reaction for the recombination of photo-generated holes andelectrons.1120+ h -* HO• + H02 + e— [O21T,o[O2iTio2 + e —* [O22]Tjo2Hydroxyl radicals and peroxides are important intermediates involved in thedecomposition process because they are powerful oxidizing agents. The fact that someorganics degrade slowly or are incompletely degraded could be due to the amount ofhydroxyl radicals and peroxo groups generated on the surface being a limiting factor.Molecular oxygen is a very convenient oxidizing agent for most photocatalyticoxidations since it is readily available in air. Oxygen may enter into solution by severalroutes: (1) from fresh liquid, (2) by exposure of powder-containing solution to air,(3) through the walls of the reaction vessel which may be porous to oxygen, and (4) bydeliberate aeration of the solution.1.1.2 SONOLYSIS WITH POWER ULTRASOUNDUltrasonic oxidation has been reported as a method of degrading toxic materialssuch as phenols and chlorophenols in waste water in general, and in bleach plant effluent inparticular [30]. When an aqueous medium containing organic halogen compounds such asCH2I,CHC13 or CCI4, is irradiated with ultrasound, the carbon-halogen bond is cleaved[31]. Sonication of solutions results in localized extreme reaction conditions. Cavitationbubbles form and collapse. The localized pressures and temperatures generated are7sufficient to cause rupture of the 0-H bond of water with the formation of hydroxylradicals and hydrogen peroxide [31, 32]. Ultrasound irradiation also increases the activityof powder catalysts [331 since it causes remarkable changes in particle aggregation,surface morphology and (for powdered metal catalysts) thickness of oxide coatings. It isincreasingly used to initiate and promote chemical reactions [31, 32, 34]. Turai [35]reported that ultrasound improved the biological activity of bacteria used in waste watertreatment by increasing the availability of oxygen and mass transfer of the pollutants toand from the bacteria.The sound spectrumThe normal frequency range of human hearing is between 16 Hz and 16 kHz.Ultrasound is defined as the sound having higher frequency than that to which the humanear can respond. It is generally considered to lie between 20 kHz and 500 MHz(Figure 1.1) [36].100 101I Iio6 8Frequency (Hz)10[Ran][Uses]Power Ultrasound(20kHz- 100kHz)CleaningPlastic WeldingChemical ReactivityHigh FrequencyUltrasound(1MHz- 10MHz)Medical DiagnosticsChemical AnalysisFigure 1.1 Sound frequenciesHuman Hearing(16Hz- 16kHz)8The use of ultrasound within this large frequency range may be divided into twoprinciple areas: (1) power ultrasound and (2) high frequency ultrasound. Powerultrasound involves relatively higher power and low frequency waves between 20 kHz and100 kHz. Applications include cleaning, plastic wielding, and more recently to affectchemical reactivity. High frequency ultrasound involves high frequency, low amplitudepropagation. It is used in medical scanning, chemical analysis and studies on relaxationphenomena.UltrasoundproductionFor economic reasons mainly, 20-50 kHz is the region most commonly used. Therequired power and frequency range usefbl for chemical purposes is generally produced byan ultrasonic transducer or converter which converts either mechanical or electrical energyinto high frequency sound. Commonly used transducers which produce power ultrasoundare piezoelectric crystals and magnetostrictive devices. The operation of the former isnow described.A piezoelectric crystal, such as quartz, is coupled to suitable electrodes, and whenan alternating current of ultrasonic frequency is applied, the crystal vibrates (expands andcontracts) producing ultrasound. The transducer crystal vibrates in the longitudinaldirection and transmits this motion to a microtip (Figure 1.2). The material used for thetip should have high dynamic fatigue strength, low acoustic loss, be resistant to cavitationerosion and be chemically inert. The best material by far is titanium alloy.9POWERSUPPLYELECTRODEPIEZOELECTRICCRYSTALELECTRODETIP - - - - -— —— REACTION VESSELwrreAr(ajFigure 1.2 Schematic diagram of an ultrasonic probe systemChemical effects ofpower ultrasoundMost chemists who have an interest in sonochemistry concentrate on powerultrasound, since this type of sound provides sufficient energy to affect chemical reactivity[31].The physical phenomenon caused by power ultrasound which is responsible formost of the chemical effects is cavitation [34]. Like any sound wave, ultrasound istransmitted as a pressure wave through a medium. During each “stretching” phase a fluidmedium can literally be torn apart, provided that the negative pressure is strong enough toovercome intermolecular binding forces. Cavitation produces tiny micro-bubbles(cavities) of approximately 100 nm in diameter. In succeeding compression expansioncycles, these cavities grow until they become unstable, whereupon they collapse violentlyCONVERTERHORN GENERATOR10in less than a microsecond with the release of large amounts of energy in the immediatevicinity of the micro-bubbles. The likelihood of cavitation occurring increases withaeration and power applied, and decreases at high frequencies (> 50 kHz) [36].It has been estimated that transient local temperatures of up to several thousandKelvin (> 5000 K) [37] and local pressures of up to one hundred atmospheres areproduced during this collapse. In the immediate vicinity of the imploding bubble thepowerful shock wave produced on collapse will create a jet at roughly 400 km/h throughthe solution [34]. It is the violent implosion of unstable cavities which generates thesemomentarily extreme local temperatures, pressures and shock waves, and which providesa unique environment for chemical reactions.1.1.3 OTHER POSSIBLE METHODSChemical oxidations by dO2,H20and Fenton’s reagent (H20+ Fe2j [38] havealso been studied for the purpose of disinfecting and bleaching. High chemical demand,the consequent high cost, and the chemical contaminants introduced externally canpreclude the use of such chemical degradation as a viable treatment alternative in somecircumstances. Nevertheless, C102 has replaced (or partially replaced) Cl2 bleaching inmany kraft mills.The metabolism of chlorinated molecules by bacteria can also contribute toenvironmental detoxification. Two reports have dealt with the aerobic biodegradation ofpentachlorophenol (PCP) [39, 40]. Hydrocarbons are now known to be biodegraded bynumerous environmental microorganisms. However, many halogenated compounds arebiodegraded poorly and the most highly halogenated molecules appear to be metabolizedexceeding slowly.Other possible approaches to disinfect drinking water [41] and ground water [42]include ozonation and irradiation by ultraviolet light. Ozone is now being used instead of11free chlorine in production of bleached kraft pulp [43]. Ozone, short-lived in water, is anextremely strong disinfectant, second only to fluorine. It is also a chlorine-freedisinfectant and may one day lead to complete elimination of man-made chlorinatedsubstances from effluents. Two types of ozone reactions occur in natural waters: directozonation reactions and free radical ozonation reactions [41]. Direct ozonation reactions,which involve the ozone molecule, are highly selective and relatively slow. The freeradical ozonation reactions involve the autocatalytic decomposition of ozone, whichresults in the production of the same highly reactive but unstable intermediate mentionedpreviously - the hydroxyl radical. This free radical has been observed to be a less selectiveand more powerful oxidant than ozone itself.Ozonation has its own problems. Ozone reacts selectively with organiccompounds and usually cannot decompose the organics completely to carbon dioxide andwater [44]. Also ozone is very unstable, with a half-life of just 15 minutes at roomtemperature. This means it must be produced on-site, using processes which require highconsumption of electrical energy.High temperature processes such as incineration [45] may be used satisfactorily totreat waste hydrocarbon liquids or vapors which contain difficult chlorinated components.However, such high temperature treatments of very dilute halocarbon aqueous solutionsare economically impractical.121.2 REAL-TIME REACTION MONITORING BY HAReal-time monitoring of the reactions described above requires either in-situsensors (within the reaction vessel) or analytical systems which sample the contents of areaction vessel at regular intervals, and track the concentrations of key species present.Flow injection analysis (FIA) has been proven to be a suitable methodology. It is an idealtool for liquid sample handing, pretreatment of samples prior to their determination, andselective detection of analytes. Separation techniques such as in-line filtration can beimplemented and provide reproducible results. FIA systems provide fast, precise, andaccurate analyses. They are simple to operate and straightforward to automate; the latterproperty results in decreased labor expenses. The small volumes of solution required peranalysis minimize reagent volumes used, sample costs and waste disposal problems. Anautomated FIA system provides a means of carrying out an analysis in a closed system,thus materials which are toxic or unstable in air may be more conveniently and safelyanalyzed than by a manual method.1.2.1 PRINCIPLES OF FLOW INJECTION ANALYSIS (FIA)Principles offlow injection analysis andfunction ofaflow systemFlow injection analysis is based on injection of a liquid sample into a moving,non-segmented continuous carrier stream of a suitable liquid. The injected sample forms azone, which is then transported towards a detector that continuously records theabsorbance, electrode potential, or some other physical parameter(s) of the stream as itcontinuously changes due to the passage of the sample through the detector flow cell[46, 47].A simple flow injection analyzer (Figure 1.3) consists of a pump, which is used topropel the carrier/reagent stream through a narrow tube; an injection port, which13introduces a well-defined volume of sample solution into the carrier stream in areproducible manner; a reaction coil in which the sample zone disperses and possiblyreacts with the components of the carrier stream; a flow-through detector whichquantitatively detects the chemical species of interest; and a recording device [46]. FIA isbased on the combination of three principles: sample injection, controlled dispersion of theinjected sample zone, and reproducible timing of its movement from the injection pointtowards and through the detector.Pump SampleCarrier___________To WasteFigure 1.3 Single-line FIA manifoldA well-designed FIA system has an extremely rapid response: the residence time tr,which is the time between the injection and the peak maximum is in the range of 5-20 s.The residence time also defines the period for chemical reaction, if any. A sampling cycleis typically less than 30 s. The injected sample volumes are usually between 10 and250 j.tl. Thus, FIA is a simple, microchemical analytical technique, capable of having ahigh sampling rate (120 cycles/h), minimal sample and reagent consumption, and canproduce results in near real-time.ReactionCoilInjection PortFlow-throughDetector14Dispersion of the sample zoneA sample solution contained within the injection valve prior to injection ishomogeneous and has original concentration 0’. If it could be scanned by a detector, asquare signal would be produced, the height ofwhich would be proportional to the sampleconcentration (Figure 1.4, left). When the sample zone is injected, it follows themovement of the carrier stream and forms a dispersed zone whose shape depends on thegeometry of the channel, the flow velocity, time of sample residence in tube, viscosity andthe diffusion coefficient of analyte solution [48]. Hence a concentration gradient isformed and the peak-shaped response curve reflects a continuum of analyte concentrationsand dispersion (D) values (Figure 1.4, right).Transport conduit cross-section - top;No dispersion - left;Concentration profile - bottomDispersion - rightTwo physical processes, convection and difihision, are responsible for sampledispersion. The former is induced by flow and causes the sample zone to acquire aparabolic head and tail; the latter causes the concentration profile across the zone to takeFigure 1.4 Schematic representation of the effect of dispersion on an injected samplezone.15on a Gaussian shape. Combination of convection and diffusion results in FIA peakstypically being described as skewed Gaussian peaks.In FIA, excessive dispersion results in loss of sensitivity. Sufficient dispersion isrequired for mixing and reaction to take place and (usually) for the production of aconcentration gradient. In order to design an FIA system rationally, the dispersioncoefficient D has been defined as the ratio of concentration of sample material before andafter the dispersion process has taken place [491:D=C°/Cwhere D is the dispersion coefficient, C is the original sample concentration and C is theconcentration after dispersion. This is shown on the right hand side axis of Figure 1.4.FIA ReadoutWhen recorded, the transient signal observed by a detector during the passage ofthe dispersed sample zone has the form of a peak. The height H, width W, or area A of apeak is related to the concentration of the analyte present (Figure 1.5) [461.4’U)C0(I)0Figure 1.5H: the peak heightA: the peak areatr: the residence timeA typical recorder outputW: the peak width at a selected leveltb: the peak width at the baselineS: injection of sample16Peak height, H, is the most frequently measured peak dimension in FIA since it iseasily identified and directly related to detector response, such as absorbance, potential,current, etc. Provided that the detector used responds linearly to the concentration of thesensed species, then peak height is a linear function of analyte concentration:H a + bCwhere a and b are intercept and slope constants. Peak height is most commonly measuredat peak maximum, but (especially for high concentrated samples) may also be measured atany other point along the response curve.Peak area, A, is similarly to peak height, directly related to the detector output. Itcan provide improved sensitivity over peak height since it involves integration over alarger number of data points. However, its use is somewhat restricted by the difficulty ineliminating baseline noise and determining accurately the beginning and end of the peak.Furthermore, it cannot be used as accurately for “log(C) detectors” such as ion selectiveelectrodes: It distorts the readouts, since that portion of response which is close to thebaseline disproportionally weighs much more than the portions of readout close to thepeak apex.Peak width, W, typically measured as full width at half maximum of the peak(FW.HM), is logarithmically dependent on analyte concentration. It has a wider dynamicrange than peak height and peak area measurement, but is less precise. Peak widthmeasurements have been used in specialized applications such as titrations.1.2.2 PROCESS MONITORING BY FL4FIA is finding increasing applications in chemical routine analysis and research,teaching of analytical chemistry and monitoring of chemical processes. Perhaps the fastestgrowing area of interest is in using FIA for process control. The main reason is that by17analyzing the chemical composition of process streams in near real-time the processoperation can be tuned to its optimal level [50]. Optimization is of great importance foreconomic reasons, since it allows better use of raw materials and energy. Otheradvantages of the results of optimization include corrosion prevention, environmentalprotection, prevention of the production of undesirable, toxic or otherwise hazardous byproducts, compliance with stringent statutory regulations; and ensuring high productquality and product quality reproducibility.Advantages of use ofFIA in process controlMost sensors developed for detection of chemical components cannot be installeddirectly in the process stream, since they can quickly suffer from erosion, occlusion,poisoning or other physical damage. Also, regular calibration of some in-situ on-lineprocess sensors is very difficult. In process control applications, flow injection analyzersautomatically take, pretreat, and analyze samples. Their control microprocessors then thedata and communicate results with the process environment. They offer many practicalbenefits which enhance the attractiveness and acceptance of on-line chemical analysis aspart of closed-loop control.(1) They facilitate near real-time continuous monitoring by regularly aspirating samplesolution (for example, from a batch-type chemical reactor) into a carrier solution, thedetector being operated in an impulse response mode. Thus a chemically modulatedsignal, continuously recorded as a series of peaks, offers a valuable measurement of boththe detector and process performance. Near real-time measurement is an importantobjective to be pursued in process analysis.(2) One important advantage of using a pulsed technique in process control is theconstant check on baseline drift (Figure 1.6) [51]. In continuous FIA, a nearly completereturn to the baseline can be achieved between two successive injections by a properselection of the injection frequency. In this way, it is easy to correct for slow fluctuations18of the background. Detector fouling can be prevented by means of a periodic washsequence, perhaps using dilute acid and/or a detergent. Occasional injections of standardsolutions allow further control of detector performance, thus ensuring that the magnitudeof the recorded peaks truly reflects the concentration of the monitored species (and notdeterioration of the response characteristics of the detector).IFigure 1.6 Analyzer response vs. time.(a) No concentration change; drift of baseline.(b) Concentration change; constant baseline.Key: (—) Flow injection device; (---) Continuous monitoring device.(3) The profile of the transient signal obtained with plug injection can provide atrained operator with valuable information about the correct functioning of any flowinjection system.(4) The operation costs of FIA are low because of low consumption of reagent andsample. The operation and maintenance ofFIA systems are generally simple.time - time —19FIA approachesfor process controlThere are three approaches for process control applications utilizing peak height asthe source of information. They are based on sample injection, standard injection andreagent injection.Sample injection (Figure 1.7) follows the scheme most frequently used inlaboratory applications of FIA: a solution from a reactor, or a stream to be monitored, is(after possible pretreatment) propelled by a pump (P1) into an injection valve, which,when turned, injects the analyte into the carrier stream, merging downstream with asuitable reagent. After passage through a reaction coil, within which the species to bemonitored is produced, the sample zone enters the detector, which continuously recordsthe composition of the stream. A sufficient amount of time is allowed to transpirebetween individual injections, so that baseline is re-established, indicating that the systemhas been thoroughly washed and that the detector is fhnctioning properly. Calibration canbe performed before, after, or even during the monitoring period by injecting standardsolutions. Computer control of the FIA system allows for precise timing of events(injection, start-go pumping sequences, data collection, and recalibration).Standard injection involves continuously pumping and monitoring analytesolution. An occasional injection of a standard allows periodical control of the responseof the system. The drawback of the standard injection approach is that the FIA channeland the detector are not periodically washed by a cleansing carrier solution and mighttherefore become contaminated.Reagent injection saves reagent(s) consumption by injection of small amount ofreagents only at the times when a readout is required, while the analyte solution is pumpedcontinuously through the FIA channel. Since detectable species are formed only in thepresence of the reagent(s), the readout still has the form of a peak. A series of peaks isobtained that reflects the change of analyte concentrations during the monitoring period.Calibration is achieved by aspirating standard solutions instead of sample solution.20ReagentFigure 1.7 Continuous monitoring based on sample injection(a) The sample, aspirated from a process reactor by pump P1 is intermittently injected by avalve into the carrier stream which is merged with reagent solution, propelled by pump P2.(b) Before monitoring the process, the system is calibrated by injecting a series ofstandards. This procedure is repeated after the monitoring period. The baseline is reachedbetween each injection, thereby allowing control of the performance of the analyzer itself.Pump P1Pump P2CarrierProcess©©ReactionCoil Detector> ToWaste111ivN iiiHCalibration Monitoring Calibration21Flow injection analyzers have been used for in-process surveillance of causticstreams [52], hydroperoxide [53, 54] and analysis of commercial bleach [54]. Chemicalproduction [55-59], biological waste water treatment [60], and biotechnological processes[61-65] have been reported to be controlled by FIA techniques. Ruzicka [66], Van derLinden [511 and Gisin et a! [67] summarized the advantages of using FIA for industrialon-line process control and detailed a number of FIA approaches and techniques forprocess monitoring.1.3 MONITORING DEGRADATION OF CHLORINATED ORGANICS BYFIAEnvironmental contaminants present in an aqueous suspension of titanium dioxidepowder (anatase) can be degraded with UV light [21, 22, 68-72]. According to Zeltner,this technology has not as yet been successfully commercialized [73]. Difficulties remainin separating the titama (anatase form) particles from the suspension after degradation hasoccurred and in finding a simple, low cost, low labor consuming method to monitor thedegradation process.One solution to the separation problem is to immobilize the titanium dioxidepowder on a support that is transparent to UV irradiation. This kind of photo-reactorwith immobilized Ti02 on an inner support surface is usually wrapped on or set parallel toUV lamps, and is compatible with flow based monitoring systems. Most of the glassphotoreactors studied employ Pyrex glass as the support [73]. Pyrex was chosen becauseit is much less expensive than quartz and much easier to fabricate. In addition, titaniacoatings adhere very well to Pyrex, but such coatings readily delaminate from hardenedsilica or quartz. However, Pyrex is only transparent to UV radiation down to awavelength of about 340 nm and absorbs most of the radiation of wavelength < 300 nm22[73]. Titanium dioxide is activated only by photons of wavelength 350 nm [16]. Quartzis transparent to all UV wavelengths [19].Use of such a reactor in the flow injection determination of organic solutes inwater was first reported by Low and Matthews [74]. The reactor was constructed by firstimmobilizing a thin film of titanium dioxide onto the inner surface of a length of Teflontubing then wrapping the treated tubing around a near-UV illuminating source - a “blacklight” tube. The advantage of attaching the titanium dioxide to a stationary support is thatthe solution for oxidation may be passed continuously over the illuminated photocatalysten route to some detector. Hence, the process can be monitored in real-time. The in-linereactor was installed after the injector port of the flow system. An organic compound(methanol) injected in the flow stream was oxidized photocatalytically to carbon dioxide,which was subsequently monitored by a conductivity detector.Another solution to the problem of separating the Ti02 catalyst is to filter out thetitania powder prior to the determination. Barbeni [21] reported off-line centrifligationand filtration through a 0.22 p.m Millipore filter to remove the suspended solids. Ollis [14,16, 18] designed a recirculating, differential conversion photoreactor in which “blacklights” (UV lamps) were oriented parallel to the reactor axis. An aqueous slurry oftitanium dioxide was recirculated with a pump, centrifI.iged and monitoredpotentiometrically by a chloride ion selective detector in the line. This required a largeamount of solution. The detector was easily contaminated, in which case, performancerapidly deteriorated.231.4 OBJECTWESThe main objectives of this thesis were to develop a photocatalytic degradationmethod for destroying chlorinated organics and to develop a automated FIAinstrumentation for the real-time monitoring of the degradation process.The specific goals were as follows:(1) To develop a photo-reactor within which photocatalytic degradation reactionscould occur. The photo-reactor would contain a vessel to hold the solution, UV lamps toilluminate UV irradiation, photo-catalysts and a sonicator to produced power ultrasoundwhen needed.(2) To develop an in-line sampling system within which the solution would be sampledand pretreated prior to the detectors.(3) To develop an in-line automated FIA instrument to monitor the degradationprocess in real-time. This would contain a pump to propel the carrier solution, a injectionvalve to inject the pretreated sample, and the proper flow-through detectors to monitorthe products and/or reactants.The developed system would be used to examine the priority pollutants such aschloroform (CHC13)using aqueous suspensions of titanium dioxide illuminated with UVlight in a batch reactor. The photodegradation process would be monitored by anautomated flow injection analysis system by regularly aspirating sample solutions from thephoto-reactor. The samples would be filtered prior to injection into the flow injectionsystem. A process monitoring curve would be produced.In this work, four different stcategies were evaluated: UV irradiation alone, UVirradiation with Ti02 catalyst (anatase), ultrasound irradiation alone, and theircombination. It was also considered important to investigate other solutions to theproblem associated with using Ti02 powder. One of our objectives was to explore the24catalytic ability of another form of Ti02-- a Ti02 glass. With this, there is no separationprocedure needed for the system because titania glasses are large pieces of glass and tendto reside at the base of the solution, unlike the titania powder which is suspendedthroughout the solution. No paper has yet reported use of titania glass as a catalyst tophotodecompose aqueous organic impurities.It was hoped that this work, automatically monitoring the degradation ofchlorinated organics using FIA, would lead to improved fundamental knowledge of thedegradation kinetics and mechanism for chloroform.25CHAPTER 2INSTRUMENTATION2.1 DEVELOPMENT OF PHOTO-REACTOR FOR PHOTODEGRADATIONOF AQUEOUS CHLORINATED ORGAMCS2.1.1 REAGENTSChloroform was analytical reagent grade (BDH Inc., Toronto, Ontario). Milli-Qwater, obtained from a Milli-Q purification system (Chemistry Department, UBC), wasused for all solutions and had a specific resistance greater than 18 MQ cm. Anatase Ti02was obtained from Tioxide, UK, with a surface area of 10.8 m2/g, as determined byBET’ * nitrogen adsorption. Glassy Ti02was obtained from Dr. H. D. Gesser, ChemistryDepartment, University of Manitoba, with a determined BET surface area of 91.6 m2/g.2.1.2 APPARATUSPreliminary StudiesA flow-through reactor similar to that of Low and Matthews [74] was initiallybuilt. They immobilized a thin film of titanium dioxide onto the inner surface of Teflontubing then wrapped it around a 20W “black light”. The “black light” emitted ultravioletlight of between 320 nm and 400 nm. In this work we used silicone or Teflon tubingwrapped around a 100W mercury UV lamp which gives its most intense light at 254 nm.1* BET (Bi-unauer, Emmett and Teller) nitrogen adsorption method is used for the determination ofsurface area of the solids. The method assumes that the volume of nitrogen gas adsorbed by the solid inthe frozen system is equal to the volume of nitrogen gas released when heated, for a given mass of solid.The theory is based on the ideal adsorption isotherms. It assumes: (1) a single molecular layer ofadsorbed species and that (2) the energy of adsorption is invariant.26Responses were observed from both the conductivity detector and chloride ion selectiveelectrode when Milli-Q water was passed through the tubing. As the time of UVirradiation increased, the signal from both detectors increased. The silicone and Teflontubing had been washed sequentially with 1% (w/w) nitric acid and purified water toremove any contamination. Any possibility of a temperature effect caused from the UVlamp was eliminated by insertion of a cooling bath prior to the detectors. The effect wasattributed to tubing etching resulting from the mercury lamp, which had higher energy andhigher power than the “black light” tube. Because of these difficulties this design was notpursued in our study, and a more conventional reactor design was employed.PhotoreactorFigure 2.1 shows the photo-reactor cell then designed for degrading chlorinatedorganic compounds. The reactor vessel was a 250 ml pyrex beaker situated in a waterbath which was maintained at room temperature. Anatase Ti02 photocatalyst (typically0.05 wt%), used in most of the experiments, was added to the reactor. Then aqueoussolutions (200.0 ml) containing various concentrations of chloroform [typically ppm (mgIl)level j were placed in the reactor. UV-light was provided by two mercury vapor lamps(Model 80-1 127-01, BHK Analamp, CA.) and a power supply (Model 90-0001-01, BHKAnalamp, CA.). The lamps were quartz-jacketed and rated as ozone free. They emittedlight at wavelengths from 185 nm to over 600 nm with the most intense wavelength at 254nm. Each lamp had a length of 12.7 cm and an outside diameter of 0.9 cm. They weredirectly immersed in the sample solution to a depth of 10 cm. The system provided themost efficient irradiation to organic pollutants in aqueous solution because no mediumwhich absorbed UV light existed between the solution and the UV source.27SonicatorHg lampTn-line 0.22 j.i m filterto FIA manifoldFigure 2.1 Reactor for sono/photolytic degradation of chlorinated organics in water.(The solution may contain Ti02 suspension.The entire reaction vessel is situated in a water bath.)Hg iampSolutioncontainingchlorinated organic(s)28The solubility of chloroform in water at room temperature and 1 atm total pressureis 8.2 x i03 mg/i. Chloroform, which has a specific gravity of 1.49 g/ml, is heavier thanwater. At concentrations above or close its solubility in water, chloroform is immisiblewith water and collects at the base of the reactor as a separate organic phase. Anoutwardly protruding dimple (1 cm deep, 1 cm in diameter) was made at the bottom of thebeaker to hold that drop of chloroform for experiments which used for a highconcentration of chloroform and power ultrasound. The dimple holds that drop ofchloroform so that power ultrasound can be effectively directed at it.The power ultrasound probe was immersed into the solution when it was needed.The reactor was open to expose the Ti02 mixture solution to the atmosphere so thatoxygen from air could be used for degradation. The suspended solution was stirred by amagnetic stirrer during the entire degradation process. To protect the operator from UVirradiation, the whole reactor was covered with aluminum foil (obtained locally).SonicatorIn our system ultrasound was generated by a sonicator probe (Microson ModelXL2005, Heat Systems - Ultrasonics Inc., Farmingdale, NY) which is a reliable 23 kHzsource designed to economically supply over 50 watts average output into very lowvolumes (250 p1 to 4Oml or more). The unit used a titanium microtip (3 mm dia.). Thetip was immersed directly into the solution until the end was about 2.5 cm from the baseof the vessel. This provided the most efficient radiation to the chloroform layer. Themost intense sound is produced at the tip of the probe and intensity decreased withdistance from the tip.29Sampling SystemA peristaltic pump (Model C6V, Alitea USA, Medina, WA) was used to propel thecarrier stream (Milli-Q water). A microfilter, which consisted of two plastic shells (25 mmdia.) sandwiching a 0.22 jim pore-size membrane (MSI, Cat. No. 64534, Westboro, MA),was situated in the sampling line to filter out particulate Ti02 catalyst (anatase).Polytetrafluoroethylene tubing (Teflon®, 0.8 mm i.d.) was used throughout. The samplesolution undergoing liv irradiation (and possibly sonication) was aspirated by a samplingpump through the micro-filter and propelled to the injection ioop of the FIA system.Aluminum foil was wrapped around the tubing in the sampling line to keep UV fromilluminating the tubing: ions were found to be released from Teflon tubing under UVirradiation.2.2 DEVELOPMENT OF AUTOMATED FL4 MANIFOLD FORMONITORING THE DEGRADATION OF CHLOROFORMThe FIA manifold developed for monitoring the degradation of aqueouschloroform is shown in Figure 2.2. It was constructed from components available withinthis laboratory. Sample solutions and earner were propelled by two separate peristalticpumps. Samples were injected using a six-port, air-driven, solenoid-actuated injectionvalve (Type 5020P, Rheodyne Inc., Cotati, CA) and control circuitry designed in thislaboratory. The chloride ion selective electrode was a combination chloride electrode(Model 96-17B, Orion, MA). The conductivity detector was built in our laboratory. Allcomponents were controlled by a microcomputer via a data acquisition and controladapter (described later). Operating software, also written in this laboratory, wasavailable to control and/or monitor pumps, injection valve and detectors. It was written inMicrosoft Quickbasic version 4.00 and is discussed elsewhere [75, 76, 771.30In-Ime filterdetectorFigure 2.2 Monitoring the degradation of chloroform by flow injection analysisPump 1ReactorCamer streamDACAPump2 Injection Conducti CModevalve ion selective To wasteelectrode31Samples which had undergone UV irradiation (and/or sonication) were firstpropelled by a pump through an in-line microfilter to remove any catalyst powder. Theywere then injected by an injection valve into the carrier stream (Milli-Q water) which waspropelled by another pump so that they were transported through a chloride ion selectiveelectrode and a conductivity detector. The two pump speeds were set at 0.79 mI/mm andwere calibrated gravimetrically. The distance between the two detectors was 3.0 cm. Inthis way, free chloride ions and total free ions produced from the degradation weremonitored by both detectors simultaneously, rapidly and automatically. The wholeprocess which included sampling, filtration, sample injection, analyte detection and datacollection was automated with a microcomputer.The best performance of FIA systems is obtained when peak broadening effects arekept to a minimum. These arise from manifold geometry, flow velocity, the hold upvolume of the detector flow-through cell, the speed of detector response, and the timeconstant of the associated electronics. All these factors were considered in its design.This system provides real-time continuous monitoring capability by regularlyaspirating sample solution from the reactor into the carrier stream. Signals were recordedas a series of peaks. Calibration was performed before and after the monitoring period toobtain quantitative measurements of chloride ions produced. Peak heights reach a flatplateau, indicating the process has come to the end.2.3 COMPONENTS OF FIA SYSTEM2.3.1 COMPUTER FOR CONTROL AND DATA ACQUISITIONControl of the flow injection development and optimization system wasaccomplished with an IBM-PC compatible computer (Nora Systems, Vancouver, B.C.)which issued commands to and/or monitored responses from all hardware components.32The computer communicated with the FIA system via an IBM data acquisition and controladapter (DACA) board (Mendelson Electronics, Dayton, OH).The IBM DACA board has 16 digital input and output lines, four channels of12-bit analog-to-digital (A/D) conversion and two channels of 12-bit digital-to-analog(D/A) conversion. The first eight digital output lines (BO0-B07) are used to provide datato the external interface which is addressed with the next three lines (B08-BO 10). Thesethree address lines allow up to eight external independently addressable devices to beused. Digital outputs BOl 1-B014 are used to provide direction control for the two Aliteapumps. Digital inputs BlO to B116 are used to return status information from externaldevices.The four analog-to-digital converter (ADC) inputs can, in most cases withinstrumentation constructed in this laboratory, be connected directly to detector outputs.Differential inputs are used and the voltage range is usually set at -5V to +5V. Alternativeranges of OV to +1OV and -1OV to +1OV are switch selectable on the DACA board. Thetwo digital-to-analog converter (DAC) outputs are used to control the speed of the Aliteapumps and set to an output range of 0 to ±1OV.2.3.2 PUMPS AND TUBINGSolutions were propelled via two peristaltic pumps (Model C6V, Alitea USA,Medina, WA). They are capable, in principle, of maintaining a constant volumetric flowrate. The main drawback of peristaltic pumps is pulsation which causes poor baseline anddecreased precision. Pulsation in this system was largely reduced by regular replacementof the organic-resistant flexible tubing and insertion of a depulse coil between the pumpand injection valve. The depulse coil was made from 2 m of 0.8 mm internal diameter(i.d.) polytetrafluoroethylene (PTFE) tubing and acted as an hydraulic buffer. It made nocontribution to dispersion of the sample because it was placed prior to the injection valve.33Control of the Alitea peristaltic pumps was facilitated through two external digitalconnections for direction control and an analog connection (0-by) for speed control.This voltage was provided by the output of the first 12-bit DAC, and gave a speedresolution of one part in 4095. Alternatively, the speed could be adjusted manually on thefront panel of the pump.The most suitable tube material for our manifold is PTFE (Teflon®) which,besides being chemically resistant, adsorbs the least solutes onto its surface. Tubing of 0.5and 0.8 mm i.d. is commonly used in our laboratory. Larger diameter tubing causesincreased dispersion while smaller internal diameter tubing can become easily clogged.Other tube materials are polypropylene, polyethylene and trade-name polymer materialssuch as PEEK® which are highly resistant to organics and strong acids.2.3.3 INJECTION VALVEA six-port, air-driven, solenoid-actuated valve (Type 5020P, Rheodyne Inc.,Cotati, CA) was selected. This is one of the most commonly used sample injection valvesin FIA. Actuator control circuitry was designed by Wentzell et a! [75]. The operation ofsuch a valve is shown in Figure 2.3. While in the “fill” position, a sufficient amount ofsample solution is introduced into a fixed volume ioop such that it completely displaces itsprevious contents. While in this position, the carrier stream by-passes the fixed volumeloop and flows directly to the reaction manifold. On switching the valve to the “inject”position (a 600 rotation of the 3 internal channels), the carrier stream then sweeps out thecontents of the loop, transporting the sample plug downstream. The procedure isrepeated as required. Similar designs are used in High Performance LiquidChromatography (HPLC). The sample loop used in this work was of PTFE tubing of0.8 mm id., 15 cm in length and 75 .tl in volume.34to reaction manifoldcarrier-I,FILLfrom samplereservoirto reaction manifoldcarrier7/ ;‘sample loopFigure 2.3 Internal workings of a six-port injection valvesample ioopto wastefrom samplereservoirto wasteINJECT352.3.4 DETECTORSMany different types of detectors have been used with FIA systems. These includespectrophotometric (UV, visible and IR), electrochemical (potentiometric andamperometric), mass spectrometric and thermal detectors. The most common of these areUV-visible absorbance detectors, fluorimeters, ion selective electrodes, conductivitydetectors, and atomic absorptionJemission spectrometers. In addition to obvious criteriasuch as sensitivity, limit of detection, linearity of response, noise characteristics, peakbroadening effects and response time, long-term uninterrupted operation is an importantconsideration for FIA detectors.The detectors used in this FIA manifold were a chloride ion selective electrode anda conductivity detector. Free chloride ions are one of the main final products ofphotodegradation of chloroform. These were monitored quantitatively over a5.000 x iO-5 to 1.000 M concentration range. Calibration was via a series of standardsolutions. Degradation of organics also results in ions other than chloride ions, whichincrease the conductivity of the solution. Thus, the extent of degradation was monitoredby a conductivity detector as well.The output from one of the detectors was connected directly to the first ADCinput of the DACA board. The input voltage range was set at -5V to +5V for the chlorideion selective detector and to -by to +1OV for the conductivity detector. Limitations ofthe operating software prevented computerized data acquisition from both detectorssimultaneously. Therefore, for the experiments in which both detectors were required, theresponse from the conductivity detector was captured via a chart recorder.The chloride ion selective electrode (Model 96-17B, Orion, Boston, MA) and itsflow-through cell are shown in Figure 2.4. It was developed specifically for measuringchloride in very small samples with minimal flow and measures free chloride ions inaqueous solutions quickly, simply, and accurately. The cell was made in-house from a36block of Teflon®. An amplifier circuit was constructed to match the output range of theion selective electrode (ISE) to the input range of the ADC. Its very high input impedancealso served to avoid current loading of the ISE. It was usually set to provide a gain of 25.The circuit diagram is shown in Figure 2.5.Flow into DACAand PCFigure 2.4 Flow through cell with chloride ion selective electrode (C[-ISE)37POWER SUPPLY1k 1k__fmCIRCUITGAINLITINPUTPOTENTIOMETERCOARSE10k-12VPOTENTIOMETERFINEOUTPUTFigure 2.5 Circuit of amplifier for chloride ion selective electrode(The opamps are PMT OP-27E.)1kV (+)V(-)tz’JFUSE—,FUSE1OOOLF1OOOtF+12V-12V10050+150 k10 k-12V38The flow through conductivity detector was made in this laboratory. Its twoelectrodes are made of platinum. A small ball was made at the end of each electrode toincrease the surface area, thereby improving the sensitivity of the detector. It is shown inFigure 2.6. A conductivity-to-voltage converter circuit was also built in this laboratory tofacilitate interfacing with the DACA. The circuit diagram for this is shown in Figure 2.7.Resistance R* was set to 100 Mfl, to provide a gain of 10 for our study.Figure 2.6 Flow-through conductivity detectorFlow into DACAand PC________________p390.01 JFPOWER SUPPLYCIRCUITResistanceFigure 2.7 Circuit of conductivity-to-voltage converterV(+)0.5 Amp1klk2V(-)0.5 Ampp 1000.tF+12V-12V+5 1kR*1G CellInput 2k21 KHz ‘ITL(IBM DACA)Note: All opamps are PMT OP-27Eunless otherwise noted.DC OUT1 .FlOkfl402.3.5 SIGNAL RECORDINGHistorically, chart recorders were used as output devices for FIA. Nowmicrocomputers equipped with a data acquisition card act as an inexpensive digitalreadout system and are more cost effective and very common. Both are used in thissystem. The 12-bit analog-to-digital converter (ADC) sampled the detector output at arate of 5 Hz. These values were plotted versus time on the screen in real-time to displaythe peak obtained from each injection. The control software then calculated peak heightand area, and stored the entire peak data set to disk for later data processing.2.4 CHARACTERIZATION OF MONITORING SYSTEM2.4.1 CHARACTERIZATION OF FIA-CONDUCTIVITY DETECTOR ANDFIA-CHLORIDE ISE DETECTORFigures 2.8a and 2.8b show the relationship plots between the conductivityresponses and the concentrations of HC1 and KC1 for the FIA-conductivity detector. Thesensitivities (slopes of the curves) were 11590 ADC units per mmolIl of HC1 over thelinear dynamic range of 0.0012 to 0.07000 mmol/l for HCI solution and 1590 ADC unitsper mmol/l of KCI over the dynamic range of 0.05000 to 0.5000 mmolJl for KCI solution.Measurement precisions (relative standard deviations) were 0.59% (n = 5) at 0.06000mmol/l for HC1 solution and 0.26% (n = 5) at 0.5000 mmol/l. Error bars were too smallto be seen on the figures.411200 I1000800600k-. 400-4-.200-0 .• I I I0.00 0.02 0.04 0.06 0.08 0.10 0.12Concentration of HCI (mM)1200 IZ 1000-c_)-on’.’‘—, uvu -C0O 600-kU0.2 0.4 0.6 0.8 1.0Concentration of KC1 (mM)Figure 2.8 Calibration plots for FIA-conductivity detector42The conductivity detector demonstrated a much higher sensitivity for HCI thanKCI. Hydrogen ions, when hydrated, are larger than potassium ions and would beexpected to be less mobile. The higher mobility of the hydrogen ion is observed only inhydroxylic solvents such as water and the alcohols, in which it is strongly solvated, forexample, in water to the hydronium ion, H3O. Thus the H3O ion is able to transfer aproton to a neighboring water molecule. It is believed to be an example of a Grotthusstype of conductivity, superimposed on the normal transport process.H H H HH 0— H + H H + H 0— HThis process may be followed by the rotation of the donor molecule so that it is again in aposition to accept a proton. This is the common mechanism for protonic solvents.H H0— HThe high mobility of the hydroxyl ion in water is also believed to be caused by aproton transfer between hydroxyl ions and water molecules.z + 0H H0 + 0Figure 2.9 shows a calibration plot for the chloride ion selective electrode. Themeasurement precision was between 0.80% and 5.3% (n = 8) across the linear dynamicrange of 5.000 x io to 1.000 molll. The electrode had a manufacturer’s (Orion43Instruments) rated sensitivity of 56 mV per 10-fold change in concentration of chlorideion. The amplifier circuit used experimentally had a calculated gain of 25, and the outputread by the chart recorder was found to be 966 mV per decade. This corresponds to only39 mV per 10-fold change in concentration of standard solutions of chloride ion injected.The difference could be due to a combination of the following effects: the cross-channeldesign of the flow cell was such that only 16 % of the electrode surface saw the solution,the observed signals were transients (not steady state), and the electrode saw the peakmaximum for less than 5 seconds (a time interval similar to the electrode’s expectedresponse time). The peaks observed were skewed Gaussian, rather than flat-topped,indicating that limited dispersion had occurred. 1x10 1x103 1x102 1x10 lxlO° 101Chloride ion concentration (M)Figure 2.9 Calibration plot for FIA-chioride ISE detector.442.4.2 REPRODUCIBILITY OF PHOTODEGRADATION-FIA MONITORINGSYSTEMThe reactor vessel was loaded with 200.0 mls of solution containing 100.0 ppminitial concentration of chloroform and 0.05 wt% anatase Ti02 catalyst powder.Photodegradation was used, without sonication. Samples were withdrawn from thereactor by the sampling system and analyzed every 5.5 mm for 60 mm. Three separatereplicate experiments were carried out.Figure 2.10 shows the average FIA-C1 ISE monitoring curve for the threereplicates, and error bars which provide an estimate of its reproducibility. The variabilityof results seen is due to less than perfect reproducibility of each of the steps involved:i.e., the photodegradation reaction, sampling, filtration by the in-line microfilter, injectionof sample into a flow system, and detection.The calibration and operation the ISE detector was checked before and after eachrun using standard potassium chloride solutions of 5.000 x i0 M, 1.000 x io M,5.000 x104 M, 1.000 x i03 M and 3.000 x103 M. The detector was found to maintainits calibration throughout the process.45ICI)C.)CC.)C• —C—c-)10080604020040 50 60 70Time of UV irradiation (mm)Figure 2.10 Reproducibility of photodegradation-FIA monitoring system(Initial concentration of chloroform: 100.0 ppm; titanium dioxide: 0.05 wt%;error bars are for three replicate experiments)0 10 20 3046CHAPTER 3MONITORING PHOTODEGRADATION OF CHLOROFORMBY FLOW INJECTION ANALYSISPhotocatalytic degradation was examined by monitoring the product(s) formedusing FIA. Chloroform as a reactant was also monitored off-line by gas chromatography-mass spectrometry (GC-MS). The effects of different amounts of anatase Ti02 and twoforms of Ti02 were studied, as was the effect of power ultrasound. The kinetics andmechanism of photocatalytic degradation are proposed and discussed in this chapter.3.1 IN-LINE MONiTORING CHLORIDE ION FORMATION BY HATo determine the degree and the rate that chloroform is converted from toxicorganic chlorine into nontoxic free chloride ions, the formation of chloride ions during thedegradation process was monitored with the in-line FIA manifold described in Chapter 2.The photo-reactor vessel (Figure 2.1) was initially filled with 200.0 ml of140.0 ppm chloroform solution. A 0.1 gram sample of anatase titanium dioxide powder,corresponding to 0.05 % by weight of the solution, was used as catalyst. While beingirradiated with UV light, the degraded chloroform solution in the reactor was sampled intothe FIA system every 2.75 minutes. As noted in Section 2.3.4, chloride ions formed in thephotodegradation process were quantitatively monitored by using an in-line chloride ionselective electrode (CI-ISE) in the FIA manifold (Figure 2.4). Figure 3.1 shows a sampleof a series of recorded FIA peaks which reflect the change in chloride ion concentrationduring the degradation process. The amount of chloride ions liberated is seen to increase47with UV irradiation time over the initial 50 minute span. After that, the peak heightsremain at a maximum level, indicating that chloride ions are no longer being produced.100ITime of UV irradiation (mm)Figure 3.1 Chloride ion peaks recorded with an in-line FIA-chioride ISE detectorThe chloride ion concentration corresponding to each peak in Figure 3.1 can becalculated by using a calibration curve prepared prior to each monitoring period.Figure 3.2 shows a curve of chloride ion concentration vs. UV irradiation time. Forclarity, every other peak from Figure 3.1 is used in Figure 3.2. The maximum chloride ionconcentration in the figure is measured to be 122.0 ppm. As summarized in Table 3.1, the140.0 ppm of original chloroform solution corresponds to a chlorine (Cl) concentration of124.8 ppm. Therefore, the 122.0 ppm maximum chloride ion concentration obtainedcorresponds to 9776 % mineralization of chloroform, i.e., 97.76 % of the organic bondedchlorine has been converted into inorganic free chloride ion.8060402000 10 20 30 .40 50 60 70 8048E2O• 90(440g 60IC.?0030080Figure 3.2 Variation of chloride ion concentration with UV irradiation timeTable 3.1 Degree of mineralization of chloroformInitial concentration of chloroformInitial chlorine concentration aFinal concentration of chloride ions detectedDegree of mineralization b140.0 ppm124.8 ppmL22 ppm97.8%a Initial chlorine concentration = 140 ppm x 3 FWC1 / FWCHCI3=140.0 ppm x 3 x 35.51(3 x 35.5 + 13) = 124.8 ppm (FW: formula weight)b Degree of mineralization (%) = 100 * final concentration of chlorideinitial chlorine concentration0 20 40 60Time of UV irradiation (mm)493.2 EFFECT OF TITANIUM DIOXIDE CONCENTRATION ON RATE ANDEFFICIENCY OF DEGRADATIONAnatase Ti02 with a determined BET surface area of 10.8 m2/g was obtainedcommercially. In order to examine the effect of titanium dioxide concentration on the rateand the efficiency of photodegradation, five chloroform solutions of the sameconcentration (560 ppm) were prepared to contain 0.00, 0.01, 0.05, 0.20 and 0.40 weightpercentage of Ti02. UV irradiation was applied to each solution for 80 minutes duringwhich the degradation process was monitored by an in-line FIA-chloride ISE detector.Samples were injected every 2.5 minutes. Figure 3.3 shows how the amount and rate ofchloride ions produced are effected by the amount of catalyst used and the time of UVirradiation.Time of UV irradiation (mm)Figure 3.3 The effect of titanium dioxide concentrationon rate and efficiency of degradation.250200150I 1000 20 40 60 80 10050In the absence of photocatalyst, a slow photodegradation curve is observed.Homogeneous reactions occurred under this condition. The energy of UV, provided bythe two mercury lamps, might be strong enough to cause breakage of C-Cl bond, but thereaction is not sufficient, nor result in complete destruction of chloroform within areasonable time period.When photocatalyst is present, UV irradiation can cause the desired heterogeneousphotocatalytic degradation process in addition to homogeneous photolysis reactions. Asignificant increase in the rate and efficiency of reaction resulted from increasing theconcentration of Ti02 present from 0.0% to 0.05%. A Ti02 concentration at 0.05 wt%provided the fastest and most efficient destruction. A gradual decrease in rate andefficiency was observed for higher amounts of Ti02 tried.Matthews [17] has shown that a dichotomous effect will occur with increasingTi02 concentration. At low concentration, the degradation rate can be enhanced by usingmore catalyst material in order to increase the probability of reaction. The reaction rateincreases because more surface area is available for the reactants and because it is morelikely that photogenerated electrons and holes will reach the surface of the solid beforethey recombine. At high concentration, the high opacity and light-scattering properties ofthe semiconductor limit penetration of the UV light into the solution. Moreover,aggregation of catalyst particles may also reduce the available surface area.Tominaga et al [75] demonstrated that the oxidation rate of an organic solute on aphotocatalyst is proportional to the fraction of the surface of the semiconductor coveredby the solute molecules. At low solute concentrations, there is an overabundance ofadsorption sites available to the solute and any fi.irther increase in number of sites wouldnot significantly increase the rate of photocatalytic oxidation. In contrast, for solutions ofhigher concentration, sites are available for only a fraction of the total solute present andthis limits the photooxidation rate. An increase in the number of adsorption sites will51therefore increase the rate of oxidation for solutions of higher concentration (subject tothe limitations discussed above).3.3 STUDY ON TWO DIFFERENT TYPES OF T102 CATALYSTSThe anatase modification of Ti02 in the form of powder suspended in water showspromise as a photocatalyst for the photodegradation of organic contaminants in water.Since this powder is very fine and light, it must be filtered before analysis can beperformed with the FIA system. This inconvenience has prompted the author to make apreliminary investigation into the use of amorphous Ti02 in the form of a porous glass.The high surface area of porous glassy Ti02 makes it suitable for photocatalyticapplications. Glassy Ti02 exists in the form of small pieces of glass and does not needseparation prior to the detection. Porous glassy Ti02 has been used as a photocatalyst forhydrogen production from water [79]. No papers have reported its use inphotodegradation of aqueous organic impurities.The glassy Ti02 was provided by Dr. Gesser of the Chemistry Department,University of Manitoba. It was prepared by a slow low-temperature hydrolysis of TiCl4,followed by partial removal of HC1 and partial neutralization by the addition of KOH.Dialysis of the solution resulted in the formation of a gel which shrank as it dried to atransparent porous glass which was then annealed (79, 80). The glassy Ti02 is in theshape of flat wafers 0.5-1 mm thick and up to 3.5 mm in diameter. Its BET surface areawas determined to be 91.6 m2/g.In this experiment, three solutions with 700 ppm concentration of chloroform wereprepared, and run in series. 0.0, 0.2 g of glass and 0.2 g of anatase Ti02 powder wereadded to separate solutions. Samples were analyzed every 1.5 minutes. Photodegradationwas monitored for 45 mm. Conductivity responses were recorded on a chart recorder.52Figure 3.4 shows the recorded peaks for each set of experimental conditions. All thepeaks were plotted using the same scale.Reaction without catalyst is slow. It has a different reaction route. Themechanism of photodegradation solely by UV irradiation involves homogeneous reactionsor bond cleavage caused by the high energy of IJV light. When catalyst was added to thesolution, efficiency was enhanced. The reaction involves electrons, holes, and HOradicals as intermediates which have a much higher reactivity. With a same weightconcentration (0.1%), anatase Ti02 acts about four times more efficiently than glassyTi02. The first step of the reaction involves the movement of chloroform molecules toreach the Ti02 surface by diffi.ision. The size of glass is much larger than powder, thusonly a few pieces of glass were used in 200 ml solution while anatase Ti02 was suspendedthroughout the solution. Therefore, in glassy Ti02 catalyst solution chloroform moleculeshave to travel a longer distance on average to reach the catalyst. Further, most of thesurface area is already saturated by water molecules before the chloroform reaches thembecause water is much more concentrated and polar than chloroform. A greater numberof chloroform molecules are in the immediate vicinity of anatase Ti02 particles since theseparticles are suspended everywhere in the solution. Therefore the anatase Ti02 had alarger chance of reaction than glassy Ti02 even though the glassy Ti02 has a much largermeasured BET surface area.This study shows the potential of glassy T102 in photodegradation of aqueousorganic impurities. Increasing the amount of glass and decreasing its size may improve theefficiency of photodegradation significantly. This should be studied in the fi.iture. Usingglassy TiO2 is one way to solve the separation problem which exists when using theanatase form. The system could be simplified from “photodegradation-filtration-FIAmonitoring” to “photodegradation-FIA monitoring”.531000.1 wt% anaase hO2r r — — 1 r0.1 wt% glassy hO24’4th0Ut catalystJ± 45Time of UV irradiation (mm)Figure 3.4. Comparison of the efficiencies of two different forms ofTi02 catalyst.(1.5 minutes between sample injections)543.4 COMPARISONS OF EFFICIENCIES OF PHOTODEGRADATION BYUSING DIFFERENT CONDiTIONS IN THE REACTOR CELLAddition of power ultrasound did not affect the photodegradation of homogeneouschloroform solution. For the study of power ultrasound, a heterogeneous solution wasprepared by adding 1.00 ml of chloroform to deionized water and making up to 200.00 ml.The solution had two layers because the chloroform did not completely dissolve. Sixdifferent conditions of the reactor cell were examined. These were: (1) testing of theblank solution itself, (2) anatase Ti02 catalyst (0.1 wt %), (3) UV irradiation; (4) UVirradiation with anatase Ti02 catalyst (0.1 wt %); (5) power ultrasound; and (6) thecombination of UV irradiation, catalyst and power ultrasound. Replicate chloroformsolutions were prepared for the study of each of the different conditions. UV light andlorpower ultrasound were turned off at different times and the degraded chloroform solutionunder each condition was sampled and analyzed for three replicates. Signals obtainedwere recorded using chart recorders. Figure 3. 5a shows the conductivity response andfigure 3. 5b shows the chloride ion selective electrode response obtained after degradingfor 20 minutes.To establish that chloroform solution does not degrade on its own in water, achloroform solution which did not contain any catalyst, and was subjected to neitherultrasonic nor UV irradiation, was also studied. Samples were propelled without passingthrough the micro filter. It was found that no ions were produced during the first 20minutes.Chloroform solution containing Ti02 catalyst gave tiny signals at both detectors.The signals did not increase with time. Therefore, chloroform did not degrade in thepresence of catalyst only. The small signals detected resulted from a very small amount ofions from impurities contained in Ti02 powder or the 0.22 j.im microfilter.55Figure 3.5 Recorded FIA peaks after 20 minute degradation with each differentconditions. (a) FIA-conductivity responses, (b) FIA-chioride ISE responses.L) Ex(9+50+ +C-)xQ Q+- 0C0+xcCCC-) .2 zZr RE0 Ox>C4 f4...ox>C.9=el+5::.56UV illumination of aqueous solutions of chloroform in the presence of suspendedtitanium dioxide caused a rapid degradation. UV irradiation causes homolytic cleavage ofthe C-Cl bond of chloroform. Hydroxyl radicals, HO, produced from Ti02 catalystirradiated with UV light cause rapid destruction of chloroform. In the presence of UVillumination without Ti02, or in the presence of ultrasound only, very slow degradationwas observed. Combined sonolysis and catalyzed photolysis provided the most efficientdegradation of chloroform and the yield was improved by about 41% based on thedetection of chloride ions.The effects of power ultrasound on the degradation of chloroform are discussedbelow.Direct sonolysis ofchloroform:Chloroform may be directly decomposed by irradiation with power ultrasound.When an aqueous medium containing organic halogen compounds (e.g., CH21 CHC13or CC14) is irradiated with ultrasound, the extreme energy of power ultrasound can causecleavage of the carbon-halogen bond [311.A very detailed study has been made of the decomposition of chloroform by theirradiation of power ultrasound [81]. Homolysis occurs yielding a large number ofproducts among which are HC1, CC14 and C214. One of the products of sonolysis ofchloroform, HC1, can be detected by both a conductivity detector and a Cl-ISE detector.The precise mechanism involved in the decomposition is complex but almost certainlyinvolves the homolytic fission of chloroform to radicals and the formation of carbenoidintermediates as shown in scheme 3.1 [82].CHC13 —* •CHC12 + •Cl—* •CC13 + H•—* :CCI2 + HC1— :CHCI + Cl2Scheme 3.1 Decomposition reactions of chloroform57Evidence for the generation of these reactive intermediates was obtained from astudy of the effect of added cyclohexene (1) on the sonication of chloroform [82]. Thepresence of free radicals in the system was confirmed by the appearance ofchlorocyclohexane as a product and by the increase rate of decomposition of chloroformin the presence of cyclohexene. Carbene intermediates are implicated by the formation ofthree member ring compounds such as (2) via dichiorocarbene addition to cyclohexene.+ :CCl(1) (2)A second important factor is the generation of active intermediates — HO radicalsfrom water. When water is sonicated, extreme conditions are generated by collapse of thecavitation bubbles. These are sufficient enough to cause the rupture of the 0-H bonditself with formation of highly reactive radical species and subsequent production ofoxygen gas and hydrogen peroxide (Scheme 3.2) [34]. The ultrasonically produced HOradicals are very important in the photodegradation of organic impurities. Any speciesdissolved in the water are clearly going to be subject to chemical reactions with theseultrasonically produced HO radicals and/or hydrogen peroxide H02. Organiccompounds can be degraded in this environment, and inorganic compounds can beoxidized or reduced.58H20 -* HO• + H•H- + 02 —* H02•HO2- + HO2- -* H20 + 02HO• + HO• -* H20Scheme 3.2. The decomposition of water by power ultrasoundSonochemicalphotodegradation ofchloroform:When power ultrasound irradiation was combined with catalytic UV irradiation, anenhanced degradation efficiency was obtained. Some factors which may contribute to thiseffect are as follows:(1) Reaction was promoted by improving the activity of the catalyst powder.Solid catalysts suffer from surface deactivation through chemical contamination(poisoning) and passivation during continuous usage. The cleaning effect of ultrasoundand its surface activation are important in the enhancement of catalytic reactions.Ultrasound also increases movement of fresh solution to the catalyst surface. When thecatalyst is in the form of a powder like anatase Ti02, power ultrasound can also be used toincrease its dispersion in solvents and reduce the particle size, thereby increasing theavailable surface area for reaction. Thus, the activity of Ti02 powder as catalyst in thephotodegradation study was improved by sonication.(2) Sonication generated an extremely fine emulsion, resulting in very large interfacialcontact areas between the two layers. More chloroform molecules contacted the aqueoussolution where photodegradation occurred. The vigorous mechanical vibration fromultrasound enhanced the transfer of chloroform molecules from organic to aqueous layer,thus increasing the reactivity.59(3) Photodegradation reaction was further facilitated by the localized hightemperatures and pressures associated with cavity implosion near the catalyst surface.3.5 OFF-LINE QUANTITATIVE ANALYSIS OF RESIDUAL CHLOROFORMThe decrease in chloroform concentration during the degradation process wasmonitored by using gas chromatography-mass spectrometry (GCIMS). Samples ofchloroform solutions were taken from the photo-reactor (Figure 2.1) at different UVirradiation times and stored in glass vials without headspace at 4°C in a refrigerator forseveral days until GC-MS instrument time was available. Each of these degradationsamples was introduced into the GC column via a purge and trap procedure. To minimizethe effects of run-to-run changes in instrument performance or execution of the purge andtrap technique, C6D was added into each sample as an internal standard and detectedtogether with chloroform.To dilute the sample solution, 1.0 p.1 C6D (20 ppb) internal standard and 100.0 p.1of chloroform sample solution were added to deionized water and made up to 5.00 ml.This aqueous sample was then purged by Helium gas and the resultant effluent wasallowed to pass through a gel column which adsorbed the purged organics. The trappedorganics were then desorbed into the GC column where chloroform and the internalstandard were separated. The GC effluents were finally analyzed by a mass spectrometerequipped with an electron impact ionization source.Figure 3.6a shows a sample total ion current (TIC) chromatography detected byGC/MS. The small TIC peak corresponds to C6D, as verified by the mass spectrumextracted from the peak. Figure 3.6b shows the mass spectrum extracted from the largeTIC peak; it matches the standard mass spectrum of chloroform. Therefore, the large TICpeak in Figure 3.6a corresponds to chloroform, the only major component that waspurged from the sample solution.60Intensity TIC0.0 5.0 10.0 16.02.5e+007 I 2.5e+0072.Oe+007 2.Oe+0071.5e+007 1.5e+0071.Oe+007 l.Oe+007(a) Se+006 5e+006Oe+000-. ........-0e+0”0.0 5.0 10.0 16.0Time (s)Intensity Scan45 60 80 90 100. 110 125100% I I 100%83(b) 50% 50%0%- . -I45 60 70 80 90 100 110 125m/ zFigure 3.6 (a) Total ion current chromatogram of partially degraded sample.(b) Mass spectrum of chloroform.61In order to determine the concentration of chloroform in each degradation sample,a series of calibration solutions were prepared in a similar way in which the samplesolutions were prepared. Internal standard was added to both the calibration solutions andto the degradation samples. Any changes in the instrument conditions affect the responseof analyte and internal standard in the same way. Therefore, the ratio of chloroformresponse (peak area) to that of the internal standard will not be affected by measurementfluctuations in the GC/MS system. The relative response factor (R) is used to build therelationship between internal standard and standards or analytes in samples and is definedas:R= (Cstd Alstd) / (Cjstd Astd)where Cstd is the concentration of the sample standard (CHCI3), Clstd is theconcentration of the internal standard (C6D),Astd is the peak area of the sample standardand Alstd is the peak area of the internal standard. The relative response factor is aconstant. In this experiment, all the calibration solutions prepared had the sameconcentration ofC6D and therefore the ratio of peak area of standard to that of internalstandard was proportional to the concentration of standard. In the mass spectrum ofbenzene-d6,the molecular ion C6D (m/z 84) gives the base peak. As noted in Figure3 .6b, CHCl2 (m/z 83) is the most abundant ion in the mass spectrum of chloroform. Inthis study, the ratio between the peak area of CHC12’ and that of C6D for eachcalibration sample was used to prepare the calibration curve shown in Figure 3.7. TheCHCl2-to-6Dratio was then calculated for each degradation sample to determine theconcentration of chloroform.621.5Concentration of chloroform (ppm)Figure 3.7 Calibration curve of chloroformThe concentration of chloroform for each degradation sample taken at a differentUV irradiation time was measured. The disappearance curve of chloroform withirradiation time is shown in Figure 3.8. Chloroform was rapidly degraded and thepercentage converted at 44 minutes was about 94%, which is compatible with the valueobtained by monitoring the formation of chloride ions (Figure 3.2).0.3 0.6 0.9 1.263150 I I I IE120-2 90-CC)o 60C10 20 30 40 50 60Time of UV irradiation (mm)Figure 3.8 Disappearance of chloroform643.6 MECHANISM AND KINETICS OF PHOTOCATALYTICDEGRADATIONFigure 3.9 shows the disappearance curve of chloroform and the appearance curveof chloride ions plotted using the data from sections 3.1 and 3.5. Chloroform disappearsexponentially with UV irradiation time, which indicates a first-order decomposition.Assuming that the first-order decomposition of chloroform directly yields chlorideions, i.e., the reaction follows an A -4 B’ kinetic model (A is a reactant, B’ is a product),the appearance of C1 would follow the dotted curve indicated in Figure 3.9. Instead, theformation rate of CP at shorter times is slow and then increases significantly until theconcentration of C1 reaches the maximum level. This formation pattern resembles anA -4 B —> C consecutive first-order reaction (A is a reactant, B is an intermediateproduct, C is a final product), with Cl- being the final product. Accordingly, this authorproposes the following mechanism for catalyst-assisted photodegradation of chloroform.k1CHC13. [CHC13 - Ti02 - H20J(A) Adsorption (B)k2 k3Products . Products which can be detectedDecomposition Desorption (C)Scheme 3.3 Three steps of photocatalytic degradation of chloroform.65150I‘S 12090C60030Cr-)080Figure 3.9 Variations of the concentrations of CHC13 and C1 vs. UV irradiation time.The dotted curve is manipulated by assuming an A—> B’ reaction mechanism from CHC13to Cl-.The whole degradation process is believed to involve three major steps:(Step 1) adsorption of chloroform on the surface of T102, (Step 2) decomposition ofchloroform on the surface of Ti02 and, (Step 3) desorption ofproducts from the surfaceof TiO-,. Steps 1 and 2 are slow and determine the rate of the overall reaction, i.e. theformation rate of chloride ions. Therefore, the reactions correspond to the A —* B —> Cseries reactions, which is consistent with the appearance curve of chloride ions indicated inFigure 3.9 by filled circles.0 20 40 60Time of UV irradiation (mm)66Assuming that the process corresponds to the simplest first-order consecutivereactions: A undergoes a first-order reaction to give B, which in turn undergoes afirst-order reaction to give C, back reactions are neglected. The system can berepresented as:A ki> k2>Cin our case, k1 is the rate constant of the adsorption reaction, k2 is the overall rateconstant of the decomposition reaction. The rate of disappearance of A is given by-d[A]/dt =k1[A]. (1)The rate of appearance of B is given byd[B]/dt =k1[A] -k2[B]. (2)and that of C byd[C]/dt = Rk2[B] (3)where [A], [B] and [C] are concentrations in ppm units, R is the ratio of chlorine inchloroform.It is to be noted thatd[A}/dt + d[B]/dt + d[C]/(Rdt) = 0; (4)this is necessary since the sum of the concentrations of A, B, and C must remain constantthroughout the degradation process.Equation (1) may be integrated at once to give[A]=[A0] e -kit (5)where [A0] is the initial concentration of reactant which is 140 ppm.Equation (2) can be integrated by inserting equation (5) to give[13]=[A0] {k1 / (k2- ki)}{ e1t - e2t}. (6)The rate of change of C is readily found using the fact that[C] = R([A0]- [A]-[B]), (7)67which leads to[C] = R [A0] (1- (k2eklt - k1 e2t) / (k2-k1)} (8)or [C] = [Cf] { 1- (k2eklt - k1 et) / (k2-k1)} (9)where the final concentration of chloride ion, Cf is 125 ppm.According to the equation (5), the variation of [A] with time inFigure 3.8 is shown schematically in Figure 3.10 (fitted curve). It was obtained from thecurve fitting program (Jandel Sigma Plot for Window, Version 1.0), using k1 as a fittedparameter. The k1 value was calculated as 0.0488 min1. The mean value of the sum ofsquare errors (MS SE = (X-X)2/N, Xe experimental value; X, calculated value; andN, number of points) of the fitted curve was 26.13 ppm2.150-______________________________120 \\\\\90-\\o• 60- \ fitted curve30-expenmental curve0- I I I0 10 20 30 40 50 60Time of UV irradiation (mm)Figure 3.10 The variations of chloroform concentration with UV irradiation time:(_) experimental curve; and (--) fitted curve.68EL)CC.)CL)According to equation (9), the variations of [C[] with the time used inFigure 3.2 are shown schematically in Figure 3.11. Fitted curve 1 was obtained by usingk2 as the only fitted parameter. k1 was known as 0.05 min1,which was calculated fromthe fitted curve in Figure 3.10. The k2 value was given as 0.16 min1. The MSSE valueof the fitted curve 1 was 64.96 ppm2. Ifk1 was allowed to vary, the better curve fit (fittedcurve 2) with the MSSE value of 36. 80 ppm2was obtained. The values ofk1 and k2 wereboth calculated as 0.08 min1.150120906030020 40 60 80Time of UV irradiation (mm)Figure 3.11 Variations of chloride ion concentration with UV irradiation time:(1) experimental curve, (2) fitted curve 1- k1 as the only fitted parameter,and (3) fitted curve 2- k1 and k2 as fitted parameters.069The mechanisms of individual step are proposed as follows:Step 1, adsorption of chloroform molecules on the surface of the Ti02 catalyst.Chloroform molecules in the solution move and reach the surface of Ti02 In the originalsolution, the concentration of chloroform is much lower than that of water. Chloroformmolecules are also less polarized than water molecules. It is believed that the surface ofthe Ti02 catalyst is mainly covered by water molecules. In addition to the adsorptionproperties of catalyst and the bonding ability of reactant, the rate of this step mainlydepends on the concentration of chloroform and the distance between Ti02 catalysts andchloroform molecules.The rate of adsorption, R5, can be expected to be proportional to the fraction ofcoverage (Os) by an adsorbed reactant, S on the illuminated catalyst surface:Rs = k1 Owhere k1 is the rate constant which is proportional to the available surface area of thecatalyst and Os is given by a Langmuirian isotherm. Thus the rate of adsorption is givenby:R5kK[A]/(1 +K[A])where K is the adsorption equilibrium constant which is related to the adsorptionproperties of the catalyst and the bonding ability of the reactant, [A] is the concentrationof the reactant.Step 2, decomposition of chloroform on the surface of the Ti02 catalyst. Asnoted in Section 1.1.1, under UV irradiation, holes and electrons are created on the Ti02surface and then H0 radicals are formed. As schematically shown below, hydroxylradicals would be expected to have the highest concentration on the surface of Ti02.Once a chloroform molecule is absorbed on the surface of Ti02, it will undergo a series ofreactions (discussed below) with the hydroxyl radicals to form chloride ions as one final70product. These reactions affect the overall formation rate of chloride ions. The proposedmechanism is as follows:hv -Ti02 TiO * (h + e ) (1)H20 + h HO+H (2)02+e O (3)02 + H HO 1/2 02 + HO (4)Sub-total reaction (1 )+2x(2)+(3)+(4):2H0 + 2h + e + 1/202 3H0 + H (5)Cl ClH0Cl—C——H Cl—C-—- H + ci (6)ci OHCl OHH0Cl—C-—-H Cl—C——H + ci (7)OH OHOH 0 0-H20 H2OCl—c--— H H—C——Cl‘ H—C——OH + + cr (8)OH710 0HC OHH0HO C OH + H (9)0HO C— OH CO2 + H20 (10)H + h H (11)2Cl + 2e 2C1 (12)Sub-total reaction (6)+(7)+(8)+(9)+( 1 0)+( 11 )+( 12):CHCI3 + 3H& + h + 2e CO2 + 2H + H20 + 3Cl (13)Total reaction (5)+(13):CHCI3 + H20 + 1/202 CO2 + 3H + 3C1 (14)Scheme 3.4 Proposed mechanism of decomposition of chloroformStep 3, desorption of chloride ions from the surface of Ti02. Chloride ionsformed will desorb from the surface of TiO2 and diffuse to the bulk solution where theyare detected. The catalyst contained jn solution was stirred by using a magnetic stirrerduring the reaction time and the rate of transfer of Cl to bulk solution was dramaticallyimproved. Therefore, the rate of this step was relatively fast and do not affect the overallreaction rate.72CHAPTER 4FURTHER WORKDevelopment of an in-line automated flow injection analysis (FIA) system forcontinuous real-time monitoring of photodegradation has been completed. A photo-reactor has been developed which efficiently degrades chloroform in water. The in-linemicrofilter has provided fast, unpressurized filtration. However, there are still many waysin which the whole system can be improved to increase its efficiency, capability andflexibility. Some advancement strategies and suggestions are detailed below.4.1 OPTIMIZATION OF THE PHOTOREACTORIn addition to concentration of titanium dioxide (anatase) in aqueous organicsolution, some other important facts should be considered.pH valueIn general, addition of acid into suspended solution can significantly inhibit the rateof reaction. Many compounds show this effect [16, 74]. The photoreactor should beoptimized by chosing the best pH value of the degradation for each organic compound.OxygenThe oxygen concentration is an important parameter in determining the rate ofreaction since oxygen is necessary for the photooxidation [16]. Oxygenated and aeratedsuspensions should be investigated in the future.73Ti02glass as catalystGlassy Ti02 has shown the potential as a photocatalyst in photodegradation in thisstudy. Increasing its amount and decreasing its size to improve its surface area should beinvestigated in the fi.iture. Its photocatalytical efficiency may exceed that of anatase Ti02powder while eliminating the separation problem.4.2 APPLICATION TO MORE COMPOUNDSThe application of this photochemical process should be extended to otherchlorinated compounds such as chiorophenols, and even nonchiorinated compounds.Chlorophenols represent an important class of environmental pollutants. They are presentin untreated waste water from many pulp and paper mills.4.3 iMPROVEMENTS TO OPERATING SOFTWAREThe present version of operating software can only obtain data and compute peakquantities such as peak height, peak area from one of four ADC channels. The FIAsystem uses more than one detector in series to obtain different information from morethan one channel. For example, a photodetector and chloride ion selective electrode canbe used in series to monitor the concentration change of reactant and product. Presently,the information from other present detectors has to be sent to another computer or to achart recorder. The capability of the FIA system will be greatly improved if the operatingsoftware allows more than one ADC channel (more than one detector) to worksimultaneously.744.4 IMPROVEMENTS TO TilE FL4 MANIFOLDThe present FIA manifold could be improved to monitor the change inconcentration of reactant andlor intermediates. Use of a single wavelength flow throughphotodetector or diode-array spectrophotometry would both be possible. Fornonchiorinated compounds such as hydrocarbons, alcohols, etc. which give H20 and CO2as final products, a conductivity detector can be used to monitor CO2 quantitatively.Calibration could use standard CO2. Detectors can be set in series or in parallel so thatone sample injection gives all the information about reactant and product, even any stableintermediates.To help us identif,’ and characterize the products or intermediates formed, HPLCcapability would be added to our present system, as in Figure 4.1. This would be used tomonitor degradation of chlorinated or nonchiorinated organics. Two mercury lampsand/or one sonicator horn are immersed in solution. An in-line filter removes the catalystpowder from suspended sample solution. The filtered sample solution is injected by aninjection valve into the carrier stream and goes to detectors sequentially. More uninjectedsample solution periodically goes into HPLC system via its own injection valve.The conductivity detector detects the total free ions, or CO2 itself quantitatively ifCO2 is the only conducting compound in the reaction. The chloride ion selectiveelectrode detects the free chloride ions. The pH electrode monitors the hydrogen ions.The diode array is able to monitor the original organic reactant (at 220 nm in the UVregion). It also has the benefits of rapid scanning the solution over the entire UV-visrange, and simultaneous detecting several species at different wavelengths.In the HPLC system, a sample is injected by the HPLC injection valve into itscarrier. It is transported downstream to the column where components in solution areseparated and then carried into a UV detector in which the analytes are detected. Stable75intermediates and some products can be separately identified and quantitativelydetermined.76PowerupptylotHgLampsControllines(toIfromComputer)Centralcompartmentofreactorcontainsorganic,water,andFigure4.1(a)FIAsamplingsystemwithproposedinterfacetoHPLC.SequentialFIAdetectorsusedare:In-LineFilterStirrerControl lines(toIfromComputer)ToThermostatedReactor, withSonicator HornandTwoHgLampsAliteaPeristalticPumpToSequentialDetectorsCphotocatalystmaterial.1conductivity, C1-ISE,pHandUVabsorbance(spectra).-J 0OtmpFromFIAInjectionValveConductivityDetectorLDiodeArraySpectrophotometerChlorideIonSelectiveElectrodepHElectrodeToWasteorSelectiveChemicalDetectors(DispersionPermitting)Figure4.1(b)Sequential detectorspresentlyavailable.APPENDIXPRELIMINARY WORKChlorinated phenolic compounds have often been singled out as being aparticularly toxic group of compounds of industrial origin. Many pulp mills in Canada usechlorine in the bleaching process to remove the brown lignin, a natural product present inall wood puips. Typically, bleaching is done in 5 or 6 sequential steps, which aredesignated as chlorination, alkaline extraction, hypochiorite, and chlorine dioxide stage.Effluents are produced by washing the pulp after each stages. During this process,chlorinated phenolics are formed as byproducts by electrophilic aromatic substitution,electrophilic displacement, and dealkylation/demethylation reactions occurring on lignin.The major phenolics found in pulp and paper effluents can be classified into thefollowing 5 groups of compounds: chiorophenols, chloroguaiacols, chiorocatechols,chlorosyringols and chlorovanillins. The chemical structures of the above compounds aregiven in Figure Al [3].4-chiorophenol was the compound initially studied in this research. Due to theinitial unsuccessful development of photo-reactor and filtration system, the reaction wasnot efficient and the monitoring system was insufficiently precise. Two experiments werecarried out: (1) photodegradation of 4-chiorophenol, and (2) chemical degradation of4-chiorophenol with Fenton’s reagent (Fe2 + H20). In the following sections, we willdescribe these preliminary experiments, the corresponding results, the reasons that workhad been discontinued and the potential to have 4-chiorophenol experiment continued ifthe new system is used.79C-C-C-ClxOHLignin UnitOCH3OCH3 OHChiorophenols Chloroguaiacols ChiorocatecholsClxCH3OOCH3ChiorosyringolsCHOLC1xOCH3ChiorovanillinsFigure Al Chemical structures of chlorinated phenolics (from ref. [3])ORClx -ClxOH OH80A.1 EXPERIMENTAL- DECOMPOSITION OF 4-CHLOROPHENOLAll the chemicals used in the experiments were analytical reagent grade quality.All the solutions were prepared using distilled water.Photodegradation of4-chiorophenolThe reaction was carried out in a 100 ml glass beaker. An aqueous slurrycontaining 0.1 wt % titanium dioxide (anatase) and 3.0 x io M 4-chiorophenol wasstirred by a magnetic stirrer. Two UV lamps were located outside of the beaker and theUV irradiation illuminated the solution through the wall of the beaker. Each of 5.00 ml ofsample solution was collected at different time of UV irradiation: 5, 10, 20, 30, 40, 50 and60 minutes. Solutions were filtrated manually through celite layers and made ready forchloride ion determination using a FIA system with chloride ion selective electrodedetector (Figure 2.2).Chemical degradation of4-chiorophenol with Fenton’s reagent (Fe2 +H20)In this experiment, an 80 ml aqueous solution of 4-chlorophenol and perchioricacid in the selected quantities (10.00 ml of 0.03 M of 4-chlorophenol and 5.00 ml of 0.5 Mof HC1O4) was thermostated at 23°C and maintained under vigorous stirring.Subsequently, two 5.00 ml aliquots of a FeSO4 (0.01 M) and H20 (0.5 M) respectively,were added simultaneously to the reaction mixture. The concentration of the chloride ionsproduced at different reaction times was monitored by an in-line automated FIA systemwith chloride ion selective electrode (Figure 2.2).81A.2 RESULTS AND DISCUSSIONPhotodegradation of4-chiorophenolFigure A2 shows the preliminary results for the photodegradation of4-chlorophenol. The reaction was not efficient. It is evident that there are at least twodistinct stages to the detectable reactions. The first occurs within the first 10 minutes ofdegradation. The second proceeds rapidly after 40 minutes of reaction. There was 47 %chlorine recovered after 60 minutes of reaction.I 10 20 30 40 50 60 70Time of UV irradiation (mm)Figure A2 Photodegradation of 4-chiorophenol82The main reasons for discontinuing this work at that time were:(1) An effective in-line filtration system to remove catalyst powder had not beenfound. A celite layer was used to filter out vely fine Ti02 powder manually and it madeprocedure complicated, tedious, unprecise and inaccurate.(2) The photo-reactor had not been fully developed. Two mercury lamps were locatedoutside of the photo-reactor. UV irradiation had been attenuated when it reached thesolution because air and the glass of the beaker could absorb UV.Chemical degradation of4-chiorophenol with Fenton’s reagent (Fe2 +H20)Photodegradation is based on reaction of organics with hydroxyl radical reaction,Fenton’s reagent is another source which generates hydroxyl radicals. To gain insight intothe photodegradation reaction without having a complete solution for the above problems,it was decided to make a preliminary study of the chemical degradation of 4-chlorophenolwith Fenton’s reagent.Figure A3 depicts the increase in concentration of chloride ion as a function ofreaction time. The result demonstrates that the 4-chlorophenol is rapidly degraded in thepresence of the Fenton’s reagent and an equal (quantitative) amount of free chloride ionsin solution was detected.The presence ofFe3 alone (without any Fe2)with H20 had no degrading effecton 4-chiorophenol. The presence ofH20alone (without any Fe2jhad very little effect.The results reported may be interpreted on the basis of the followingconsiderations. The interaction of iron (II) ions with hydrogen peroxide yields HOradicals and iron (III) [38J.Fe2 + H20 —+ Fe + HO + 0HThe HO formed can easily interact with an aromatic compound inasmuch as HO radicalsare good electrophiles and reactive species. They attack chiorophenol, following which83ring opening occurs to form aldehydes, ketones, acids and the ultimate degradation ensuesto CO2 and HC1 (Figure A4) [23].0.0040.0030.0020.0010.000Time of reaction (mm)Figure A3 Degradation of 4-chiorophenol with Fenton’s reagentIC.)C0 10 20 30 40 5084OH+ H0OH+cI.OH+ H0 — + H20O.H0 H0a — — — aII.. a — e e •II Q2+ e+ H20Figure A4 Mechanism of decomposition of chiorophenol (from ref. [23])Cl. Cl-85To be able to monitor the disappearance of 4-chiorophenol (280 nm) using aspectrophotometric detector, ideally the reactant should be separated from intermediatessuch as resorcinol before detection. Intermediates interfered with the spectrophotometricdetection of reactant since their absorption peaks overlapped with these of the reactant(Figure. AS). Therefore, use of an HPLC technique equipped with a spectrophotometricdetector would be best suitable for this purpose. The calibration curve of 4-chiorophenolwhose absorbance was detected at 280 nm is shown in Figure. A6.Power ultrasound provided little effect to this reaction since amount of HOradicals generated from water by ultrasound is ignorable compared to the amount of HOproduced from Fentons reagent.3518AS01anCep1268Figure AS UV spectra of 4-chlorophenol and a photodegaded sample862.0EC00C)1Cdi•i:: 0.50.00 2 4 6 8 10 12 14Concentration of 4-chiorophenol (xl05M)Figure A6 Calibration curve of 4-chiorophenol(The calculated molar absorptivity coefficient: e calculated = 13352 1 cmmo1)A.3 POTENTIAL TO CONTINUE THE STUDY OF 4-CHLOROPHENOLWITH NEW DEGRADATION AND MONiTORiNG SYSTEMWith the degradation and monitoring system we successfully developed(Figure 2.1 and Figure 2.2), 4-chiorophenol should be photodegraded efficiently and theprocess could be easily monitored in-line. The new system has eliminated the catalystseparation problem by inserting a micro-filter in the sampling line and an efficient photo-reactor was obtained by directly immersing UV lamps in the sample solution. 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