UBC Theses and Dissertations
Carbon nitride photocatalysis : an investigation on the influence of morphology Mitchell, Emma Louise
The development of reliable renewable energy sources is imperative for a sustainable future. To address this issue, the development of suitable photocatalysts that can produce clean renewable energy at a sustainable cost has become a rapidly expanding research area. Carbon nitride (CNx), an organic semiconductor, is a promising candidate for this role due to its easy synthesis, high stability and tunability. The potential of CNx has been highlighted with reports of highly efficient photocatalytic hydrogen production (quantum yields >50%) under sacrificial conditions. However, the efficiency remains limited for sustainable overall water splitting. To improve the efficiencies, modification of the material’s morphology has been pursued. However, research on the relationship between CNx morphology and photocatalytic efficiency has been inconclusive. Positive correlations as well as variances between CNx photocatalytic activity and surface area have been previously identified. To build a clear relationship between structure-photophysics-activity, different morphologies were prepared and studied. These were mesoporous (meso), macroporous (macro), SBA, and hollow sphere CNx. Progress towards synthesizing hollow sphere CNx was achieved, however, a reproducible synthesis has yet to be accomplished. The trend in photocatalytic hydrogen production of the successfully synthesized materials was as follows meso CNx, < Bulk CNx < SBA CNx < macro CNx. There were differences in the structural and electronic characterization, however, the trends were not consistent with the observed photocatalytic activity. Using Transient Absorption Spectroscopy (TAS), the normalized decay kinetics were found to be similar between all morphologies, indicating that changes in trap state distribution or electronic structure likely do not greatly impact the photocatalytic hydrogen evolution. A direct positive correlation between surface area and photocatalytic activity was observed. The largest increase in surface area of a modified morphology compared to bulk CNx was in macro CNx which had a surface area 1.7-fold larger and an apparent quantum yield (AQY) of 3.6%. These smaller surface area changes observed herein could indicate the morphological modifications do not extend to the nanostructure of the material. Extending CNx modification to the nanostructure of the material could be the key to induce more significant electronic or structural changes which affect the photocatalytic activity.
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