One-Step Calcination to Gain Exfoliated g-C 3 N 4 /MoO 2 Composites for High-Performance Photocatalytic Hydrogen Evolution.

The difficulty of exposing active sites and easy recombination of photogenerated carriers have always been two critical problems restricting the photocatalytic activity of g-C 3 N 4 . Herein, a simple (NH 4 ) 2 MoO 4 -induced one-step calcination method was successfully introduced to transform bulk g-C 3 N 4 into g-C 3 N 4 /MoO 2 composites with a large specific surface area. During the calcination, with the assistance of NH 3 and water vapor produced by ammonium molybdate, the pyrolytical oxidation and depolymerization of a g-C 3 N 4 interlayer were accelerated, finally realizing the exfoliation of the g-C 3 N 4 . Furthermore, another pyrolytical product of ammonium molybdate was transformed into MoO 2 under an NH 3 atmosphere, which was in situ loaded on the surface of a g-C 3 N 4 nanosheet. Additionally, the results of photocatalytic hydrogen evolution under visible light show that the optimal g-C 3 N 4 /MoO 2 composite has a high specific surface area and much improved performance, which is 4.1 times that of pure bulk g-C 3 N 4 . Such performance improvement can be attributed to the full exposure of active sites and the formation of abundant heterojunctions. However, with an increasing feed amount of ammonium molybdate, the oxidation degree of g-C 3 N 4 was enhanced, which would widen the band gap of g-C 3 N 4 , leading to a weaker response ability to visible light. The present strategy will provide a new idea for the simple realization of exfoliation and constructing a heterojunction for g-C 3 N 4 simultaneously.