Reduction of hexavalent chromium and degradation of tetracycline using a novel indium-doped Mn2O3 nanorod photocatalyst.

Abstract This study investigates the photocatalytic reduction of hexavalent chromium (Cr(VI)) and degradation of tetracycline (TC) via visible-light-active In-doped Mn2O3 photocatalysis. Mn2O3 photocatalysts loaded with different In doses are prepared using a simple hydrothermal method, and the results indicate the formation of Mn2O3 nanorod-like structures with good crystallinity. The most significant photocatalytic parameters, namely the catalyst and substrate concentrations, pH, and co-existing ions for the Cr(VI) reduction and TC degradation reactions are systematically examined. Result demonstrates that the Cr(VI) reduction and TC mineralization efficiencies of 52% and 40%, respectively are achieved at the optimum pH of 7, undoped Mn2O3 (10 mg/L), and Cr(VI) or TC concentration of 50 mg/L. However, these efficiencies are remarkably increased to 95% and 93%, respectively, when 10 mg/L of 5% In-doped Mn2O3 is used as the photocatalyst under the same reaction conditions. Moreover, the co-existing HCO3− anions and Ca2+ and Mg2+ divalent cations considerably deteriorate the performance of the In-doped photocatalysts compared with the SO42− and Cl− anions and Na+ and K+ monovalent cations. Liquid chromatography–mass spectrometry analysis reveals that the photodegradation of TC is mainly driven by the elimination of the –CH3 group followed by the subsequent cleavage of the primary –NHCH3 group.