Biosynthesis of ZnO using Senna siamea leaf extract for photodegradation of tetracycline antibiotic and azo dye in wastewater

The green fabrication of photocatalyst is an interesting research topic owing to the beneficials of non-toxicity, simplicity, and environmentally friendly. In this research, we report the biosynthesis of ZnO by a hydrothermal/solvothermal method with addition of leaf extract of Senna siamea in either water or ethanol. The prepared ZnO was used for removal of tetracycline (TC) antibiotic and reactive red 141 (RR141) azo dye. The complete degradation of the pollutant was achieved under both UV light (120 min) and sunlight (40 min). The ZnO-SV400, solvothermally grown using ethanol extract and then calcined at 400 °C, showed promising photoactivity assigning to the increment of the photogenerated charge carrier separation capacity and high crystallinity of the sample after thermal treatment. The degradation reaction follows nicely with the first-order reaction with a rate constant of 0.081 min−1. The result shows that hydroxyl radicals are the key spices involved in the detoxification of the contaminants. The recycling ability of about five cycles was reported. The structural stability was also confirmed. The strategy presented here demonstrates that the green synthesis with addition of plant extracts is the main parameter governing the fabrication of sunlight-active ZnO photocatalyst for detoxification of the toxic contaminants including organic dyes and antibiotics in wastewater.