Rapid and facile synthesis of Z-scheme ZnO/g-C3N4 heterostructure as efficient visible light-driven photocatalysts for dye degradation and hydrogen evolution reaction

The coupling of two-different semiconductors which are photocatalytically active is gaining popularity in recent years because the heterojunction can decrease the rate of recombination of photoexcited electron-hole pairs and enhance the photocatalytic activity. In the current work, ZnO/g-C3N4 heterojunction hybrids have been generated by simple solution mixing of the dispersed ZnO and graphitic carbon nitride (g-C3N4) nanoparticles. The ZnO/g-C3N4 composite under visible light exhibits 91.5% degradation of the methylene blue (MB) dye in 120 min and also demonstrated excellent cyclic stability. Mechanistic studies and dye degradation experiments carried out in the presence of scavengers (ascorbic acid, potassium dichromate and ammonium oxalate) revealed that the generated superoxide radical (O2•‒) and hydroxyl radicals play a crucial role in MB dye degradation using ZnO/g-C3N4 as a photocatalyst. Further, the ZnO/g-C3N4 composite exhibits improved hydrogen evolution reaction (HER) activity (1358 μmol g-1 h-1) compared to the pristine ZnO nanoparticles (545 μmol g-1 h-1) and g-C3N4 (238 μmol g-1 h-1). The superior HER activity of the hybrid is ascribed to the increased charge-transfer rate owing to the better interfacial contact between the heterocomponents. Secondly, the nanoparticle nature of ZnO and g-C3N4 heterocomponents provides more exposed edge sites and thereby gives significant photocatalytic activity.