Enhancing electron density of bulk g-C3N4 through phosphorus doping for promoting photocatalytic hydrogen evolution reaction

Abstract

Graphite-phase carbon nitride (g-C3N4) has attracted extensive attention due the ubiquity of the raw materials, low price, and excellent visible light photocatalytic hydrogen evolution reaction (HER) activity. Bulk g-C3N4 is more advantageous for industrial production and application compared with g-C3N4 nanostructures such as nanosheets. Polyphosphate cyanogen was used herein as a phosphorus source to prepare phosphorus-doped bulk g-C3N4 with a coral-like hierarchical structure. This structure affords more extensive contact between the photocatalyst and reaction medium, and is thus beneficial for the photocatalytic hydrogen evolution reaction (HER). Density functional theory calculations showed that phosphorus-doping in bulk g-C3N4 can increase the electron density, thereby enhancing the separation and transfer of photon-generated carriers. The rate of the photocatalytic HER is thus promoted due to the faster separation and transfer of photoexcited electron-hole pairs. Bulk g-C3N4 doped with 20% phosphorous afforded a photocatalytic hydrogen production rate of 2.96 mmol g−1h−1, which is ∼ 3 times higher than that of the original bulk g-C3N4 sample with 1% Pt loading (1.01 mmol g−1h−1) under visible light. This study may inspire the further development of phosphorus-doped g-C3N4 for harvesting and converting solar energy to hydrogen energy.