Heterogeneous photo-Fenton oxidation of methylene blue solution using Fe(II)-montmorillonite calcinated clay catalyst

The textile dyes such as methylene blue are used with high frequency in the dying and printing of natural, synthetic, man-made and mixed textile materials such as wool, silk, nylon among others. These textile dyes are very dangerous if released into the environment due to the dark colors, and because their recalcitrant nature, which makes them very hard to degrade. Thus, chemical methods such as advanced oxidation processes (AOPs) can be applied. Among the AOPs, Fenton based processes are suitable methods to degrade these contaminants, with the generation of hydroxyl radicals. However, considering the drawbacks associated with homogeneous Fenton processes, the aim of this work was to develop a catalyst using a montmorillonite clay as based material. After the application of an impregnation method, the Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction analysis showed the successful impregnation of iron into the montmorillonite clay. The catalyst Fe(II)-Mt was tested under different AOPs and results showed that under the best operational conditions (pH = 3.0, [Fe(II)-Mt 0.5M] = 1.0 g/L, [H₂O₂] = 4 mM, [MB] = 0.16 mM, radiation = UV-C (254 nm), time = 25 min) it was achieved 99.7% MB removal. The catalyst showed great stability and was reused for 3 consecutive cycles. It is concluded that the catalyst Fe(II)-Mt is efficient for MB removal from aqueous solution.