Anion-Cation Co-Doped g-C3N4 Porous Nanotubes with Efficient Photocatalytic H2 Evolution Performance

Graphitic C3N4-based materials are promising for photocatalytic H-2 evolution applications, but they still suffer from low photocatalytic activity due to the insufficient light absorption, unfavorable structure and fast recombination of photogenerated charge. Herein, a novel anion-cation co-doped g-C3N4 porous nanotube is successfully synthesized using a self-assembly impregnation-assisted polymerization method. Ni ions on the surface of the self-assembly nanorod precursor can not only cooperate with H3P gas from the thermal cracking of NaH2PO2 as an anion-cation co-doping source, but, more importantly, suppress the shape-collapsing effect of the etching of H3P gas due to the strong coordinate bonding of Ni-P, which leads to a Ni and P co-doped g-C3N4 porous nanotube (PNCNT). Ni and P co-doping can build a new intermediate state near the conduction band in the bandgap of the PNCNT, and the porous nanotube structure gives it a higher BET surface area and light reflection path, showing a synergistic ability to broaden the visible-light absorption, facilitate photogenerated charge separation and the light-electron excitation rate of g-C3N4 and provide more reaction sites for photocatalytic H-2 evolution reaction. Therefore, as expected, the PNCNT exhibits an excellent photocatalytic H-2 evolution rate of 240.91 mu mol center dot g(-1)center dot h(-1), which is 30.5, 3.8 and 27.8 times as that of the pure g-C3N4 nanotube (CNT), single Ni-doped g-C3N4 nanotube (NCNT) and single P-doped g-C3N4 nanotube (PCNT), respectively. Moreover, the PNCNT shows good stability and long-term photocatalytic H-2 production activity, which makes it a promising candidate for practical applications.