Highly efficient g-C₃N₄/Cr-ZnO nanocomposites with superior photocatalytic and antibacterial activity

Currently, fabricating a narrow bandgap photocatalyst that can degrade pollutants in natural sunlight is critical but inspiring. In this study, a hybrid g-C₃N₄/Cr-ZnO nanocomposite was synthesized by a simple chemical co-precipitation method and its photocatalytic and antimicrobial properties were explored. In the first step, the photocatalytic efficiency of Cr-ZnO (1−9 wt. %) nanoparticles were carried out to find out the optimum doping of Cr into ZnO. The as-prepared 5% Cr-ZnO nanoparticles demonstrated the best optical absorption of sunlight and methylene blue degradation and in the second step; these were dispersed on g-C₃N₄ nanosheets as an active component to form ternary heterostructured photocatalyst. The nanoparticles and composite photocatalysts were characterized by X-ray diffraction spectroscopy, energy-disperse X-ray spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. The optimized composite (60 %g-C₃N₄/5%Cr-ZnO) performed enhanced harvesting of solar energy compared to ZnO, g-C₃N₄ and g-C₃N₄/ZnO composite, achieving 93 % methylene blue dye degradation in 90 min. The improved photocatalytic activity of composite can be attributed to the better absorption and electron-hole pair separation between g-C₃N₄ and Cr-ZnO. The photocatalytic stability of the composite was testified by cyclic tests. The antibacterial aptitude of the samples was investigated against Gram-negative (Escherichia coli) and Gram-positive (Bacillus subtilis, Staphylococcus aureus and Streptococcus salivarius) bacteria applying diffusion well method. The 60 %g-C₃N₄/5%Cr-ZnO nanocomposite exhibits higher antibacterial activity compared to other samples. The enriched photocatalytic and antimicrobial activities of the composite may be predominantly ascribed to the synergistic effect of the heterojunction developed between g-C₃N₄ and Cr-ZnO.