Polycondensation of ammonium thiocyanate into novel porous g-C3N4 nanosheets as photocatalysts for enhanced hydrogen evolution under visible light irradiation

Porous graphitic carbon nitride (pg-C3N4) nanosheets have been prepared through a one-step ammonia thermopolymerization method. The effects of synthetic temperature on the structural, optical and photocatalytic properties of the samples have been investigated. Characterization results show that the heptazine-based conjugate heterocyclic structure was formed over 500 degrees C, which is attributed to the inhibitory effect of ammonia from the decomposition of NH4SCN. Precise nanosheet morphology and an increased pore distribution with an enlarged surface area are observed for the samples obtained under high temperatures. Optical analysis results show that the bandgap of the samples widens and photoluminescene intensity is gradually quenched as the treating temperature is increased. The results demonstrate that a higher polymerization temperature improves the nanolayer structure, porosity and migration rate of the photo-induced carriers of the samples. The pg-C3N4 nanosheets prepared at 600 degrees C presents the highest photocatalytic activity for hydrogen evolution from water under visible-light irradiation. This study demonstrates a novel strategy for the synthesis and optimization of polymer semiconductor nanosheets with gratifying photocatalytic performance. (C) 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.