Kinetic and mechanism studies of tetracycline photodegradation using synthesized ZnAl2O4

In this study, we report the photodegradation of a pharmaceutical pollutant namely the tetracycline (TC) onto the spinel ZnAl2O4. The semiconductor ZnAl2O4 was synthesized by chemical route and characterized by X-ray diffraction, scanning electron microscopy and optical analysis. The capacitance potential (C−2–E) measurements showed that the oxide exhibit n-type conduction, supported by a negative thermo-power. The degradation of TC was performed by combined adsorption/photocatalysis processes. The result showed that 30 min of contact time was sufficient to reach 42% of the adsorption capacity; the photodegradation rate of TC was evaluated on ZnAl2O4 under optimal operating parameters pH ~ 4.4, catalyst dose (1 g/L), and initial TC concentration (20 mg/L). The kinetic shows that the TC disappears almost completely (92%) and follows a second order model with a half photocatalytic lifetime of 21 min for a TC concentration of 20 mg/L. The mechanism of the antibiotic tetracycline photodegradation on ZnAl2O4 indicated that the O2·-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{O}}_{2}^{ \cdot - }$$\end{document} radicals and the holes are mainly responsible for the oxidation of TC. The process can be qualified as clean remediation and is a part of a sustainable development perspective.