Biosynthesized monodispersed spherical Se co-catalyst nanoparticles impregnated over ZnO for 4-chloroguaiacol degradation under solar irradiations

Abstract The present study outlines the importance of biosynthesized selenium (Se) nanoparticles as co-catalyst for enhanced photoactivity of Se@ZnO nanocomposites under solar irradiations. The selenium-rich Bacillus sp. bacteria were isolated and used to synthesize extracellular Se nanoparticles (Se NPs), and structural characterization was carried out using various techniques. Different amounts (0.5-2 wt%) of Se NPs were loaded over ZnO followed by calcination at 200 oC for 120 min to form Se@ZnO nanocomposites. The optical absorption of Se@ZnO showed a slight red shift as compared to bare ZnO and a new broadband in 500-700 nm range appeared with increasing the amount of Se. HR-TEM analysis showed spherical shaped, highly monodispersed Se NPs with size less than 100 nm. Further, 1 wt% Se@ZnO nanocomposites exhibited the highest degradation efficiency (93%) of 4-chloroguaiacol (4-CG) as compared to bare ZnO (8%) under natural sunlight. The reaction followed first-order kinetics with an apparent rate constant k = 0.16 min-1. Moreover, the environmental applicability of the synthesized Se@ZnO was also tested for real pharmaceutical industrial effluent degradation. It was observed that the chemical oxygen demand (COD) level decreased from 1140 mgL-1 to 500 mgL-1 after 240 min of sunlight exposure.