Facile and Scalable Fabrication of Porous g-C3N4 Nanosheets with Nitrogen Defects and Oxygen-Doping for Synergistically Promoted Visible Light Photocatalytic H2 Evolution

A facile and scalable approach is firstly presented to fabricate novel O-doped nitrogen defective porous g-C3N4 nanosheets (PNV-CN) through thermal polymerization of a guanylurea nitrate (GLUN) precursor that forms by a nitric acid assisted heating reaction process of dicyandiamide (DCDA), in which nitrate ions act as the intensified gas template function for producing pores and carbon nitride nanosheet structures and the oxidant for forming nitrogen defects. PNV-CN demonstrates a high visible light photocatalytic activity of 62.4molh(-1) and an apparent quantum efficiency of 4.0% at 420nm with 17.3 and 5.5 times higher hydrogen evolution rate (HER) than bulk g-C3N4 (B-CN) prepared by thermal polymerization of DCDA and the loose g-C3N4 (LB-CN), prepared via thermal polymerization of a mixture (DMDN) consisting of dicyandiamide nitrate (DN), GLUN, and their hydrogen-bonding macromolecular compounds by drying the physical mixture of DCDA and nitric acid, respectively. The outstanding photocatalytic properties of PNV-CN for visible light-driven hydrogen evolution originate from the enhanced charge separation and migration, extending visible light absorption tails, promoting recombination of charge carriers, increased active sites, and strengthened mass transfer process that results from the synergistically promoting effect of hierarchical porous morphology, as-formed nitrogen defects, O-doping and the unique nanosheet structure.