The removal of methyl orange from aqueous solution by biochar and activated carbon under microwave irradiation and in the presence of hydrogen peroxide

The effects of microwave irradiation and hydrogen peroxide addition on the removal of methyl orange by porous carbons (biochar and activated carbon) were investigated. There was no removal of methyl orange from the solution by biochar under microwave irradiation regardless of the presence of H2O2. In contrast, activated carbon could completely remove the dye under the experimental conditions. To investigate whether the removal was attributed to adsorption or degradation, the extraction with N,N-dimethylformamide was utilized. This extraction method can recover methyl orange adsorbed on the activated carbon. The results here demonstrated that in the absence of H2O2, microwave irradiation could not degrade methyl orange over the activated carbon, as opposed to other studies. In the presence of H2O2, both adsorption and degradation by H2O2 contributed to the removal of methyl orange over the activated carbon. The removal efficiencies were similar in microwave oven and on a hot plate. The extraction with N,N-dimethylformamide after H2O2 treatment, provided the evidence that degradation of methyl orange by H2O2 can occur through the attack of dye molecules adsorbed on the activated carbon surface without their transfer to liquid phase.