New insight into highly efficient removal of tetracycline by calcined hydroxyapatite activated peroxymonosulfate: The role of calcium carbonate and phosphate group

Abstract

Tetracycline (TC) is an important antibiotic extensively used in livestock breeding and aquaculture, and so an effective removal strategy is urgently needed. This study explores the use of a series of hydroxyapatite calcinated at different temperatures (300, 400, 500, 600, and 700 °C) to activate peroxymonosulfate (PMS) for the removal of TC. The optimal conditions for the removal of 10 mg/L TC using hydroxyapatite calcinated at 600 °C (CHAP600) as a catalyst were determined to be: pH of 6.0, a catalyst dosage of 0.2 g/L and a PMS concentration of 0.3 mM. Under these conditions, the removal efficiency of TC reached 94 %. The potential degradation pathway of TC was proposed by identifying the intermediates using High Performance Liquid Chromatography/Triple Quad mass spectrometry. The characterization analysis revealed that the presence of calcium carbonate on the surface of CHAP600 promoted the generation of singlet oxygen (1O2). Additionally, the phosphate group in CHAP600 served as a catalyst for the production of sulfate radicals (SO4·−) from PMS, which subsequently react with hydroxyl or surface hydroxyl group to generate hydroxyl radicals (·OH). And the active species 1O2 is the most significant contributor to the catalytic degradation process of TC by CHAP600 activated PMS, followed by ·OH, and then SO4·−. This study provides new insight for the mechanism of removing organic contaminants using PMS activated with calcined hydroxyapatite.