Efficient degradation of methyl orange by heterogeneous Fenton reaction using modified bentonite by a simple method

In this investigation, a low-cost catalyst was prepared using a natural Maghnia sodic bentonite submitted to a simple ion exchange process and calcination at 500 °C for 3 h. This material was used in the removal of methyl orange (MO) dye by heterogeneous Fenton oxidation. The chemical composition was quantified by XRF and EDX and showed a significant increase in the iron content indicating a successful insertion of the iron within the clay reaching 5.98 wt%. Furthermore, XRD and FTIR analysis showed that the clay preserved its crystalline structure with the presence of montmorillonite as the main phase with some loss of characteristic peaks related to hydroxyl groups due to the calcination. Moreover, the specific surface area increased from 56 to 86 m 2 /g after the ion exchange treatment. High catalytic activity was reached, achieving the complete decolorization of the dye solution after only 10 min at T = 65 °C, [H 2 O 2 ] = 9.8 mM and m catalyst = 1 g/L. The kinetic constant rates were calculated by adjusting the experimental data to the nonlinear first-order model. The positive value of enthalpy variation (∆H° = 23.70 kJ/mol) indicated the endothermic nature of the process. The reaction rate was also found to be controlled by diffusion with an activation energy smaller than 29 kJ/mol (E a = 26.35 kJ/mol). The reusability of the catalyst was also examined showing high degradation efficiency (90%) even after 8 cycles. The catalyst showed low iron leaching during reaction experiments even in an acidic medium at 65 °C.