Nano-MnOx on activated carbon prepared by hydrothermal process for fast and highly efficient degradation of azo dyes

Abstract

Azo dyes are recalcitrant and refractory pollutants that pose a threat to environmental safety. Therefore, it is of significance to develop fast, cheap and highly effective materials for removal of azo dyes in water. Herein, fast oxidative removal of azo dyes by highly active nano-MnOx on activated carbon prepared via hydrothermal process was explored. Active manganese oxide was supported on coconut shell activated carbon (CSAC) via hydrothermal method and was characterized. The hydrothermal treatment changed the morphology of the MnOx@CSAC and led to the in situ synthesis of nano-MnOx onto CSAC surfaces with the incorporation of the multi-valence oxidation states (Mn4+ and Mn3+) of manganese. The decolorization reactions by MnOx@CSAC were fast and the dye removal was most pronounced at pH 3 (99.1%). Through GC-MS analyses, the most detectable degradation products were identified and possible degradation pathway was proposed. Additionally, the MnOx@CSAC also could effectively degrade other anionic dyes. The oxidative degradation of C. I. Acid Red 73 was still strong after 20 usage cycles, with a maximum removal rate of 99.1% and a minimum removal rate of 89.7% from the same sample. Overall, these results indicate that highly active nano-MnOx@CSAC prepared via a hydrothermal method is very attractive, implying that this material has potential practical applications for treating azo dyeing effluent.