Carbon and phosphorus co-doped carbon nitride hollow tube for improved photocatalytic hydrogen evolution

Graphitic carbon nitride, regarded as a charming conjugated polymer, has been a visible light photocatalyst. Bulk carbon nitride endures the limited light absorption ability, few surface active sites and slow separation of photoinduced charge carriers, leading to the poor catalytic activity. Herein, a new carbon (C) and phosphorus (P) co-doped carbon nitride hollow tube with adjustable optical property (CPCN) was developed by applying melamine and polyacrylic amide as the precursors and phosphoric acid as the P source via a hydrothermal-thermal copolymerization way. The effects of polyacrylic amide content on the morphology and photocatalytic performance were intensively investigated. The special hollow tube favors the improvement of active sites and visible light harvesting ability. Meantime, C and P co-doping results in the narrow band gap and rapid charge transfer, thus enabling an enhanced catalytic activity under visible light irradiation. Particularly, CPCN-50 exhibits a remarkable H₂ generation rate of 4485.7 μmol h^-1 g^-1 under λ > 400 nm, which is higher than pure carbon nitride CN (902.3 μmol h^-1 g^-1), C doped sample CCN-50 (3741.1 μmol h^-1 g^-1) and P doped sample CNP (2280.0 μmol h^-1 g^-1). It implies that C, P co-doping exhibits a synergistic effect on boosting photoinduced charge transfer and hindering the recombination. Moreover, CPCN-50 illustrates a higher H₂ generation rate (3024.5 μmol h^-1 g^-1) than CN (400.8 μmol h^-1 g^-1) under λ > 420 nm irradiation. This way developed in this work might exhibit utility for synthesizing highly effective photocatalysts for the CO₂ reduction, H₂ evolution and so on.