Characterization and photocatalytic activity of Ag/Mn₃O₄/graphene composites under visible light irradiation for organic dyes degradation

Ag/Mn₃O₄ composites were synthesized with various concentrations of graphene using a sol-gel method followed by hydrothermal synthesis. The as-synthesized Ag/Mn₃O₄/graphene composites were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (DRS), Raman spectroscopy, and nitrogen adsorption/desorption isotherm measurements. The photocatalytic performance of the Ag/Mn₃O₄/graphene composites was tested in organic dye pollutants in pure water as well as in complex mixtures of organic compounds. Therefore, the degradation of organic dyes was also evaluated in the presence of organic acid as common substances in natural water. The characterization results revealed that the Mn₃O₄ nanoparticles exhibited an excellent stability and crystalline structure and were successfully connected with Ag nanoparticles and graphene. In the presence of organic acid, the degradation of organic dye increases in comparison with the dye degradation in the absence of organic acid. The strength of the synergic effect between photocatalysis and the presence of organic acids was not significantly related to the structure of the organic acid. The effectiveness in increasing the photocatalytic degradation of the organic dyes was as follows: ascorbic acid > oxalic acid > citric acid > formic acid > ethylenediaminetetraacetic acid > acetic acid > no acid > EDTA + ascorbic acid. The leached Mn and Ag species were found to be indirectly proportional to the photocatalytic performance trend. The highest concentrations of leached species were observed when ascorbic acid was present in the solution.