Enhanced photocatalytic activity of ZnO/g-C3N4 nanofibers constituting carbonaceous species under simulated sunlight for organic dye removal

Semiconductor-based photocatalysis is an efficient approach for degradation of organic pollutants. In this context, ZnO/g-C3N4 composite nanofibers containing carbonaceous species with different concentrations of gC3N4 nanosheets (x = 0.25, 0.5, 1, 2, 10 wt%) noted as ZnO/carbon/(x wt%) g-C3N4 are prepared by electrospinning technique. For preparation of the composite nanofibers, bulk g-C3N4 is exfoliated to nanosheets, and then it is mixed with polyvinyl alcohol and appropriate zinc acetate content followed by electrospinning process. Thermal annealing of the as spun zinc acetate/poly(vinyl alcohol)/g-C3N4 nanosheets sample under N2 atmosphere leads to the formation of carbonaceous species (Zn-O-C) on the hexagonal wurtzite structured ZnO nanofibers. Moreover, the oxygen vacancy formed in the ZnO structure is verified by X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) techniques. The prepared ZnO/carbon/(0.25 wt%) g-C3N4 nanofibers demonstrated the highest photocatalytic degradation rate towards methylene blue (MB) at about 2.5 times (with degradation efficiency of 91.8% after 2 h) higher than the ZnO/carbon under similar conditions. To understand the reason behind the improved photocatalytic activity of ZnO/carbon/g-C3N4 composite nanofibers a mechanism of electron-hole generation, separation and transformation are suggested and a Z-scheme charge transfer approach is proposed.