Purification of water contaminated with traces of Rhodamine B dye by microwave-assisted, oxidant-induced and zinc oxide catalysed advanced oxidation process

Microwave (MW)-activated H2O2 and persulfate (PS)-induced ZnO-catalyzed purification of water contaminated with the cationic dye Rhodamine B (RhB) is investigated. The degradation is much faster compared with that under identical conventional heating (CH) conditions thus suggesting that the MW effect is not just thermal. PS is more efficient for the oxidation and eventual mineralization of RhB compared with H2O2. Combination of H2O2 and PS does not have either synergic effect or even additive effect thereby demonstrating the mutual destruction of the oxidants in the presence of one another at least to a limited extent. The enhanced MW degradation in the presence of oxidants is attributed to increased formation of reactive free radicals and their interaction with the dye. ZnO, which enhances the degradation of many organic chemical pollutants under advanced oxidation process (AOP) conditions, inhibits the degradation in the presence of MW/PS and CH/PS. The activation energy of the degradation is reduced by MW in comparison with CH under identical reaction conditions. The effect of different reaction parameters, namely, oxidant dosage, concentration of the dye, pH, MW power, dosage of catalyst, temperature, and reaction volume on the degradation/mineralization rate is evaluated and optimum conditions are determined. The identity of many of the intermediates formed during the degradation is confirmed by LC/MS.