Tunable surface charge of Fe, Mn substituted polyoxometalates/hydrotalcites for efficient removal of multiple dyes

Mn, Fe substituted Keggin type polyoxometalate/hydrotalcites hybrids were synthesized by anion exchange method. The structures and morphologies of the samples were determined by XRD, FTIR, SEM, TG and BET. The samples were used as heterogeneous catalysts for the Fenton reaction process and displayed high activity for degradation organic dyes in aqueous solution. The experimental parameters such as pH value, H2O2 concentration and type of dyes were studied. Especially, the surface charges of the catalysts could be changed by inserting different amount of Mn, Fe substituted polyoxometalate in the interlamination of hydrotalcites. Considering electrostatic forces between dyes and catalysts, tunable surface charge of catalyst was beneficial to deal with different types of dyes. The results demonstrated that the synthesized material could be served for the removal of mixed dyes from water. The experimental results also showed that the presence of Fe3+/Fe2+, Mn3+/Mn2+ pair at the surface of the catalysts promoted the degradation reactions, and W element from polyoxometalate also played a key role in this reaction. The catalytic activity was maintained after fourth cycles of reaction, which proved reusability and stability of the catalysts.