Synergistically Catalytic Degradation of Azo Dyes by Ag/MgO

Transition metal supported catalysts were prepared by impregnation method with nano MgO as support. Among several supported transition metals, Ag/MgO showed the best performance in degradation of azo dyes and the structure and micro morphology of selected Ag/MgO catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), extended X-ray absorption fine structure spectroscopy (EXAFS) and X-ray absorption near edge structure (XANES). The results show that Ag was evenly dispersed on the surface of MgO in the form of nano clusters, and the formation of bimetallic sites between Ag and Mg and the high electron density of Ag in the catalysts give it high catalytic activity. In formaldehyde solution, azo dye AR1 could be efficiently degraded at room temperature without illuminating or heating treatment. Temperature and formaldehyde concentration are the main factors affecting the degradation efficiency. The degradation efficiency increased with temperature and the optimal formaldehyde concentration was 1 mol.L-1. Two kinds of free radicals were detected by electron paramagnetic resonance (EPR) trapping experiment to play significant roles in azo dyes degradation process. The reductive hydrogen radical and oxidizing superoxide radical synergistic effect could easily break the chromogenic group (-N=N-) in dye molecules. This reduction-oxidation synergistic mechanism improves the reaction efficiency. Moreover, as one of the common pollutants, using aldehyde promoter achieves the dual treatment of pollutants.

Automated summary

Transition metal supported catalysts, especially Ag/MgO, showed high catalytic activity in degradation of azo dyes. The synergistic effect of reductive hydrogen radical and oxidizing superoxide radical assists in breaking down chromogenic group in dye molecules, enhancing the reaction efficiency. Using aldehyde promoter achieves the dual treatment of pollutants, demonstrating a potential method for pollutant degradation.