Peroxymonosulfate-based catalytic degradation of reactive dyes in real wastewater by Fe/N-codoped carbocatalysts loaded on carbon cloth

Abstract

This study simulated actual dyeing wastewater in dyeing factories with three types of dyeing wastewaters from laboratory cotton fabric dyeing to investigate the effects of catalyst and oxidant peroxymonosulfate (PMS) concentrations, pH level, and temperature on dye degradation in wastewater and determine the optimal conditions for dyeing wastewater treatment accordingly. The results demonstrated that the optimal conditions varied with the reactive dyes. Specifically, the optimal oxidant PMS concentration for degrading Reactive Yellow and Reactive Blue was 0.6 g/L, and that for degrading Reactive Red was 0.4 g/L. The optimal pH level for degrading Reactive Red and Reactive Blue was around 7.0, and that for degrading Reactive Yellow was about 5.0. The activation energy of the degradation and the mineralization degree of the three dyes were also discussed. Reactive Blue showed greater activation energy (47.0 kJ/mol) and a higher mineralization degree (81% chemical oxygen demand removal) than the other two dyes under optimal disposal conditions. The Fe/N-codoped carbocatalyst loaded on carbon cloth exhibited desirable reusability and good stability for the degradation of the three dyes. Mechanisms involved in their degradation were analyzed through X-ray photoelectron spectroscopy, focusing on N species, Fe-N binding, and C=C and C–N active components in the Fe/N-codoped carbocatalyst. Electron paramagnetic resonance experiments demonstrated that both the radical and non-radical pathways were accountable for the degradation of the three dyes, primarily the non-radical pathway. This study may contribute to the application of activated PMS for practical dyeing wastewater treatment.