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

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.