Soluble carbon nitride nanosheets as an alternate precursor for hard-templated morphological control

Carbon nitride (CN) is an organic semiconductor with promising applications in solar energy conversion via photocatalytic water splitting. Current efforts are being devoted to improve the photocatalytic activity of CN as it is limited by charge recombination which may be exacerbated by its low surface area. Hard-templated synthesis of CN by filling mesoporous silica with small molecule precursors is one of the conventional approaches to improving the efficiency of CN. However the relationship between activity and surface area has yet to be fully established. Herein we develop a new approach using soluble acidified CN nanosheets as the precursor in an effort to decrease the potential for unintended chemical modifications and better understand the complex relationship between morphology and activity. Deprotonation of acidified CN occurs at moderate temperatures to restore the π-π interactions. We prepared three modified morphologies with this synthetic route and completed a thorough study of the structural, optical, and photocatalytic properties. Supported by charge carrier dynamics studies, we found that the silica-templated CN with modified morphologies suffered from higher trap state densities and resulted in lower photocatalytic activity compared to CN prepared without a template. Characterization techniques showed that the chemical structure of the templated CN obtained is not sensitive to changes in the silica template shape. Our observations highlight the complex relationship between structure, photophysics, and activity, and demonstrate that hard templating can modify more than the intended surface area.