Iron-doped zinc oxide for photocatalyzed degradation of humic acid from municipal wastewater

Abstract Degradation of natural organic matter especially Humic acid is a big challenge, while its byproducts are carcinogenic, which is a threat to life. Here, Fe3+:ZnO has been deployed on ceramic plats (CP) using SILAR method for solar photocatalytic mineralization of HA in municipal wastewater. Structural results show that ZnO and Fe3+:ZnO deployed over CP have an average crystallite size of 47.43 nm and 29.54 nm, respectively. Further, Fe3+ doping increased the conductivity of ZnO due to enhanced photon capturing ability and effective surface area. Almost 90% HA photodegradation was achieved at the reaction parameters optimized by response surface methodology. Owing to the strong interaction between negatively charged HA and positive zeta potential of ZnO@CP (24 mV) and Fe3+:ZnO@CP (26 mV). Moreover, a significant reduction in BOD (~73%), COD (~76%) and TOC (~63%) have been observed after solar photocatalytic treatment of municipal wastewater. In comparison, ZnO@CP hybrid removed HA (400 mgL−1) at the rate of 3.3 kgm−3d−1 with a lower reduction in BOD (~57%), COD (~45%) and TOC (~57%) than Fe3+:ZnO@CP, confirming that the Fe doping has tuned the bandgap and manipulated the active sites onto the surface of ZnO. Moreover, direct coating of photocatalyst over CP provided exceptional stability and reusability as a photocatalyst which maintained ~80% of its activity even after 14 cycles of wastewater treatment and only lose 29% of its activity after 22 cycles. Hence, by designing a photocatalyst adhered directly onto the ceramic (substrate) present the novel sustainable photocatalyst supported wastewater treatment systems at a large scale.