A one-step facile synthesis of ZnO@fly ash from refuse-derived waste for adsorption-photocatalytic degradation of methylene blue

The increasing water pollution caused by rapid urbanization and industrialization necessitates the development of cost-effective treatment strategies. Addressing this issue, the present research focuses on the development of thermal power plant waste-derived fly ash combined with zinc oxide nanoparticles (ZnO NPs) to produce a ZnO-fly ash composite (ZnO@FA) using a facile, single-step microwave (MW) process. Low-molecular-weight chitosan was utilized to facilitate the effective binding of ZnO onto fly ash (FA) particles, resulting in the formation of the ZnO@FA composite. The synthesis parameters were optimized by varying the FA dosage to ensure maximum FA utilization and enhance sequential adsorption-photocatalytic activity for effective degradation of methylene blue (MB) dye. The prepared composite was characterized using sophisticated analytical techniques, including UV-Vis, FT-IR, XRD, SEM-EDS, DLS, BET, and ESR analyses to study its physicochemical properties. The ZnO@FA containing 2 g of FA (ZnO@FA-2) exhibited the highest degradation efficiency of 96.05% at pH 7, a composite dosage of 5 g/L, an initial MB dye concentration of 20 ppm, and a reaction time of 4 h. Further, ZnO@FA-2 exhibited promising photocatalytic activity even after five regeneration cycles, proving its sustainability. The superoxide (O 2 • - ) and hydroxyl (•OH) radicals were responsible for the photocatalytic degradation process. The degradation of MB dye was further confirmed using HPLC-MS analysis. Thus, the present research paves the way for developing novel composite materials from low-cost byproducts, facilitating both effective solid waste management and reutilization.