Interactions between ZnO nanoparticles and amorphous g-C3N4 nanosheets in thermal formation of g-C3N4/ZnO composite materials: The annealing temperature effect

Abstract

In this study, C3N4/ZnO composite materials were prepared at various annealing temperatures and systematically characterized to investigate the role of ZnO in the thermal formation of graphitic C3N4 (g-C3N4), and to understand effect of annealing temperatures on the interaction between g-C3N4 and ZnO in the composite materials. ZnO nanoparticles in the composite materials facilitated the thermal formation of the g-C3N4 structure due to the strong interaction between g-C3N4 and ZnO nanoparticles, resulting in a decrease in thermal polymeric condensation temperatures. Moreover, the morphological structure of g-C3N4 was significantly influenced by the presence of ZnO nanoparticles with an amorphous g-C3N4 nanosheet structure in the composite materials and a crystalline interlayered g-C3N4 structure in g-C3N4 only. The higher annealing temperatures for composite materials induced the stronger interaction between ZnO nanoparticles and g-C3N4 nanosheets. The strong interaction in a core-shell g-C3N4/ZnO structure not only gradually decreased the electronic density of ZnO nanoparticles but also proportionally inhibited the recombination of photo-generated electron-hole pairs in the composite materials, with increasing the annealing temperature. The g-C3N4/ZnO composite material prepared at 500 °C exhibited the highest photocatalytic reaction rate constant for photocatalytic degradation of methylene blue, which might be caused by the slowest recombination rate.