Photocatalytic Hydrogen Evolution from Silica-Templated Polymeric Graphitic Carbon Nitride-Is the Surface Area Important?

Low-surface-area, mesoporous silica-templated polymeric graphitic carbon nitride (SBA-g-C3N4), when irradiated with visible light, exhibits a greatly improved photocatalytic hydrogen evolution rate as compared to that of conventional bulk g-C3N4 synthesized directly from the condensation of dicyandiamide. It also performs very similarly to high-surface-area mesoporous g-C3N4 on a per-unit mass basis. However, on the per-unit area basis it greatly outperforms the other materials. The intrinsically high surface activity of SBA-g-C3N4 was con-firmed by using two different co-catalysts, in situ photodeposited Pt and a structurally well-defined molecular cobaloxime. Instead of the magnitude of the surface area as the dominant feature that determines activity, it was established that the high activity of SBA-g-C3N4 results from a much higher number of delocalized electrons present and a suppressed recombination probability of photogenerated electron-hole pairs.