P-doped tubular g-C3N4 with surface carbon defects: Universal synthesis and enhanced visible-light photocatalytic hydrogen production

Hetero-element doping or vacancy defects of g-C3N4 framework were found significantly to control its electronic structure and enhance photocatalytic activity under visible light. Herein, we fabricated P-doped tubular g-C3N4 (P-TCN) with surface carbon defects wherein the P-doping and carbon defects were conveniently introduced during thermal polymerization of a supramolecular precursor. The supramolecular precursor of rod-like morphology was obtained only from melamine molecules under a sodium pyrophosphate-assisted hydrothermal process. As contrast, similar P-doped g-C3N4 tubes were obtained using other phosphates, such as ammonium phosphate, sodium hypophosphite and sodium phosphite, thus highlighting the versatility of this method to tune the morphology and C/N ratio for g-C3N4 tubes. The photocatalytic activities of P-TCNs were evaluated using hydrogen evolution from water under visible light. Among these, P-TCN obtained by sodium pyrophosphate-assisted hydrothermal reaction showed the highest photocatalytic activity due to high P element doping, enhanced visible light absorption and improved charge separation. The novel synthetic method described here thus represents an effective way of non-metal doping and C/N ratio tuning of g-C3N4 with excellent photocatalytic performance.