Oxidation of Rhodamine B in aqueous medium in ambient conditions with raw and acid-activated MnO2, NiO, ZnO as catalysts

Various catalysts have been utilized for wet oxidation of organic compounds in water. Rhodamine B is a cationic xanthene dye, used in a large number of industries and is considered as an undesirable chemical in water. In the present work, commercially available metal oxides, MnO2, NiO and ZnO, and those activated by treating with 1.0 N H2SO4 were used to oxidize the dye in water to innocuous compounds. The catalysts were characterized with FTIR, XRD, SEM, cation exchange capacity and BET surface area, pore volume and pore size distribution measurements. Oxidation was carried out in a batch reactor at ambient temperature and pressure under different conditions of pH, reaction time, dye concentration, catalyst loading, and temperature. Acid-activated MnO2 was the best catalyst with almost 100% Rhodamine B oxidation (dye 1.0 mg/L, catalyst loading 2.5 g/L). The catalysts could be recovered and reused. Oxidation followed first order kinetics and a reaction mechanism was proposed based on analysis of the products. (C) 2014 Elsevier B.V. All rights reserved.