The electron transfer and free radical generated in the degradation of tetracycline on goethite

Abstract

Goethite can adsorb and degrade tetracycline (TC). In this study, the mechanisms of TC degradation and the influences of common inorganic ions were investigated through batch experiments, thermogravimetric analysis, microscale characterization and chemical probe method. The results indicated that TC degradation rate constant on goethite in the fast stage was one order of magnitude higher than that in the slow stage. More than 50% of TC degradation occurred in the fast stage. There was electron transfer between TC and goethite, in which ^•OH was generated and the amount was positively related to the specific surface area of goethite. The more surface hydroxyl groups on goethite, the stronger the redox reaction in the system. Cl^- and SO₄^2- promoted TC degradation on goethite, but HCO₃^-, Ca²⁺and Mg²⁺had an inhibitory effect. The effect of anions on TC degradation was related to the presence of ^•OH in the system. The complexation of Ca²⁺ with TC reduced the conversion of ≡Fe(III)/≡Fe(II) and the amount of surface hydroxyl groups involved in TC degradation. These findings can provide a basis for a deeper understanding of the interaction between antibiotics and minerals.