Biogenic synthesis of gold-anchored ZnO nanorods as photocatalyst for sunlight-induced degradation of dye effluent and its toxicity assessment

Abstract A new biogenic method was used for fabricating gold-anchored ZnO nanorods (Au@ZnO) as photocatalyst using leaf extract of Ziziphus Jujuba as a reducing and stabilizing agent. The green method did not involve any toxic chemicals (such as organic solvents and surfactants) and additional reducing agents. UV–Vis spectra of Au@ZnO showed an absorbance band around 547 nm due to the biogenic formation of gold nanoparticles (AuNPs) on the ZnO nanorods (NRs). In addition, the deposition of AuNPs alleviated the photoluminescence emission from the ZnO NRs, indicative of enhanced separation and transfer of photo−generated charge carriers. Transmission electron microscopy (TEM) image of Au@ZnO showed the distinct deposition of multiple AuNPs on the ZnO surface. In the photodegradation of methyl orange and industrial textile effluent, the Au@ZnO exhibited significantly enhanced photocatalytic activity (up to 3–4 times) compared to Au-free analogue (i.e., ZnO NRs), due to its extended absorbance and effective Schottky barrier between the AuNPs and ZnO NRs. A scavenger study revealed that ˙OH and ˙O2− were the main active species playing vital roles in the photodegradation process. Most importantly, toxicity assessment on the tissue histopathology of Oreochromis niloticus gills revealed that the degraded products from the textile effluent (TE) had negligible toxicity, indicating the excellent photocatalytic activity of biogenic Au@ZnO in the treatment of industrial TE.