Highly stable, reusable, and MW-assisted prepared ZnO nanorods for wastewater decontamination: Precursors ratios effect and insights on matrix and pollutants mineralization

Abstract

In this work, the impact of microwave (MW) irradiation time and precursors molar ratios on the yield, size, shape, and photodegradation activity of ZnO nanorods (ZNs) has been studied. The as-prepared ZNs photocatalyst (PC) are employed for the degradation of dyes mixture and antibiotic pharmaceuticals under simulated sunlight (SL). The results have shown MW irradiation time has the foremost influence on improving crystallinity, light absorption, and decreasing band gap, as well as enhancing degradation efficiency. It is found that the precursor's molar ratio has minor effects on the crystallinity and bandgap. ZN5 PC has the highest crystallinity and light absorption with the lowest bandgap, and the highest performance in methylene blue (MB) mineralization as well. It is recorded that after 45 min the increase in the initial MB concentration reduces the photodegradation efficiency from 98 % to 35 %. Complete mineralization of dyes and pharmaceuticals is achieved with 100 % COD removal using ZN5 within 150 min. Conclusively, the ZN5/solar simulator system is not a selective technology for the decontamination of dyes and pharmaceutical wastewater. In addition, the matrix effect using humic acid (HA) has been investigated, the degradation rate constant of dye decreased from 4 × 10−2 min-1 to 2.3 × 10−2 min-1, 1.1 × 10−2 min-1, and 1 × 10 min-1 for 1, 5, and 10 mg.L-1 HA, respectively. The influence of salinity on the photodegradation efficiency is also studied. The application of ZN5 in wastewater degradation is found to have great stability and reusability with a reduction of the treatment cost and the environmental impact by 90 %.