One-Step Calcination to Gain Exfoliated g-C3N4/MoO2 Composites for High-Performance Photocatalytic Hydrogen Evolution

Abstract

The difficulty of exposing active sites and easy recombination of photogenerated carriers have always been two critical problems restricting the photocatalytic activity of g-C3N4. Herein, a simple (NH4)2MoO4-induced one-step calcination method was successfully introduced to transform bulk g-C3N4 into g-C3N4/MoO2 composites with a large specific surface area. During the calcination, with the assistance of NH3 and water vapor produced by ammonium molybdate, the pyrolytical oxidation and depolymerization of a g-C3N4 interlayer were accelerated, finally realizing the exfoliation of the g-C3N4. Furthermore, another pyrolytical product of ammonium molybdate was transformed into MoO2 under an NH3 atmosphere, which was in situ loaded on the surface of a g-C3N4 nanosheet. Additionally, the results of photocatalytic hydrogen evolution under visible light show that the optimal g-C3N4/MoO2 composite has a high specific surface area and much improved performance, which is 4.1 times that of pure bulk g-C3N4. 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-C3N4 was enhanced, which would widen the band gap of g-C3N4, 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-C3N4 simultaneously.

Rational Design of Monolithic g-C3N4 with Floating Network Porous-like Sponge Monolithic Structure for Boosting Photocatalytic Degradation of Tetracycline under Simulated and Natural Sunlight Illumination

“…It can be seen from the figure that the characteristic diffraction peaks of FSCN (37.5°, 43.9°, 64.3°, and 77.3°) [ 39 ] were similar to those of the MS, and the peak intensities had some subtle changes, which may have been due to the evolution of the morphology of melamine after calcination at high temperature. In accordance with g-C 3 N 4 powders (JCPDS 87-1526) [ 40 , 41 ], the XRD pattern for FSCN showed a characteristic diffraction peak at 26.7° (002), attributed to the layer stacking of the in-planar repeating units of the continuous heptazine skeleton and the conjugated aromatic structure with a spacing of 0.32 nm [ 42 , 43 ]. The diffraction peak of FSCN was weaker, indicating that the interlayer period relevance length of the tri-s-triazine building block was reduced [ 44 , 45 ].…”