Electrochemically anodized solid and stable ZnO nanorods as an adsorbent/ nanophotocatalyst: ROS mediated degradation of azo dyes congo red and methyl orange

The fast industrial growth and discharge of industrial effluents into water bodies necessitate investigations of biocompatible and economically viable strategies to combat water pollution. This work presents the successful use of solid and stable ZnO nanorods fabricated by anodization as an adsorbent and photocatalyst for water treatment, circumventing the requirement of any post treatments currently needed with powder catalyst. The ZnO nanorods well- characterized structurally, morphologically and compositionally by a variety of methods manifest superior photocatalytic property than adsorption ability. Scavenger tests indicate that the photocatalytic action is controlled predominantly by superoxide (*O2−) radicals. Kinetic studies reveal that adsorption of MO as well as CR follow pseudo second order model favouring chemisorption, while adsorption isotherms correlate well with the Freundlich model suggesting heterogenous mode of dye adsorption. The photocatalyst manifests good cyclic stability with reduction in dye degradation efficiency by only 4–8 % in the fourth cycle of operation.