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Tetracycline (TC), an antibiotic, is persistent in nature and frequently detected in water and sediments. Visible-light-driven photocatalyst for TC degradation is a promising environmental-friendly technology. Bi 2 Zr 2 O 7 , an effective photocatalyst, but no studies on its photodegradation of TC could be found in literature. In this study, Bi 2 Zr 2 O 7 was synthesized by three soft templated sol-gel methods. Three synthesized Bi 2 Zr 2 O 7 catalysts have different structures, morphologies and band gaps. The Bi 2 Zr 2 O 7 nanoparticles synthesized with citric acid as the template (BZO-3) had a larger specific surface area (30.7 m 2 /g) and a narrower band gap (2.39 eV), and exhibited a better performance for TC degradation under visible light with an efficiency of up to 81.3%. They also exhibited good stability and reusability in recycled experiments. A reaction mechanism of TC degradation by these photocatalyst was proposed. The enhanced photocatalytic performance was mainly due to photogenerated holes of reactive species and TC was mainly degraded on the surface of the photocatalyst. Pathways of TC photodegradation were derived from the result of analyses of the reaction intermediates. In conclusion, Bi 2 Zr 2 O 7 nanoparticles were found effective as photocatalyst for TC photodegradation by visible light., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Effect of manganese dioxide (MnO 2 ) on tetracycline (TC) removal/degradation in zero-valent iron (ZVI) based permeable reactive barrier (PRB) system was investigated. To analyze the role of MnO 2 , three different PRB columns packed with ZVI, ZVI and a layer of MnO 2 , and MnO 2 were set up to investigate the removal effect and reaction mechanism of ZVI coupling with MnO 2 on TC removal, respectively. The results show that the removal efficiencies of three PRB columns are 65%, 85%, and 50%, respectively. MnO 2 could accelerate the transformation of Fe 2+ into Fe 3+ and combine with Fe 3+ to degrade TC in different reaction sites in the ZVI-MnO 2 PRB system. Hydroxyl radicals (·OH) were produced in this process, which contributed to about 58.3% for the TC degradation. The UV-Vis spectrum demonstrated that A ring of TC was the main reaction site for interaction with Fe 3+ and the BCD rings were crucial for interactions with MnO 2 . On the basis of intermediates identified by LC-ESI-MS, the ring structure of TC was opened, and low-molecular-weight compounds were produced in ZVI-MnO 2 PRB system., (Copyright © 2017 Elsevier Ltd. All rights reserved.)