Fabrication of visible-light-active ZnCr mixed metal oxide/fly ash for photocatalytic activity toward pharmaceutical waste ciprofloxacin

Visible active photocatalysts have attracted interest as a potentially efficient and sustainable approach for pollutant degradation treatment. In this work, ZnCr mixed metal oxide/fly ash (ZnCr-MMO/FA) compos-ites were prepared using fly ash (FA) from China coal mining power plants to improve photocatalytic per-formance. The formation of the ZnCr-MMO/FA composites was proved by XRD results which showed the two-phases combination of FA and MMO. Also, the presence of FA in the ZnCr-MMO/FA composite pro-vided a good arrangement of small particles of ZnCr-MMO on the surface of FA and higher light absorp-tion ability with a lower energy bandgap compared with the pure ZnCr-MMO. The photocatalytic performance of the prepared ZnCr-MMO and ZnCr-MMO/FA composites in different FA contents was evaluated by degradation of ciprofloxacin (CIP), which is an antibiotic and often found in pharmaceutical wastes, under visible light irradiation. Clearly, the ZnCr-MMO/FA composites showed higher photocat-alytic decomposition of CIP than pristine ZnCr-MMO, and the highest degradation performance for CIP was obtained from the ZnCr-MMO/FA sample with 0.5 mg FA, which has a reaction rate constant approx-imately four times greater than that of pure ZnCr-MMO. The improved CIP degradation activity of the ZnCr-MMO/FA composite might not only be due to the good arrangement of ZnCr-MMO particles on the FA surface but also high separation and less recombination of photogenerated electrons-holes pairs, proven by the photoluminescence spectra, photocurrent density, and electrochemical impedance spec-troscopy results. The lower recombination of the charge carriers of the ZnCr-MMO/FA composite might be caused by the heterojunction between the ZnCr-MMO as a main photocatalyst and FA. Thus, the pro-posed ZnCr-MMO/FA composite can be used as an effective photocatalyst for wastewater treatment, including the decomposition of organic pollutants, such as discarded pharmaceuticals.(c) 2022 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Automated summary

In this study, zinc-chromium mixed metal oxide/fly ash (ZnCr-MMO/FA) composites were prepared using fly ash from Chinese coal mining power plants, showing improved photocatalytic performance for pollutant degradation. The composites exhibited higher degradation activity for ciprofloxacin compared to the pure ZnCr-MMO, attributed to the good arrangement of particles and reduced recombination of charge carriers. Therefore, the proposed composites can be used as effective photocatalysts for wastewater treatment, including the decomposition of organic pollutants.