Catalytic ozonation assisted by rGO/C-MgO in the degradation of humic acid from aqueous solution: modeling and optimization by response surface methodology, kinetic study

The present study investigated the performance of catalytic ozonation with C-MgO-doped reduced graphene oxide support (rGO/C-MgO) in humic acid (HA) removal from aqueous solution in a labscale batch reactor. The analyses of scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction, UV-Vis, and Brunauer-Emmett-Teller showed that the rGO/C-MgO has been synthesized successfully. Photoluminescence analysis confirmed that the number of oxygen vacancy defect in C-MgO structure increased strongly rather than MgO because of the presence of carbon in the structure of MgO. Response surface methodology-central composite design (RSM-CCD) suggested a quadratic polynomial model (F-value = 363.38 and R-2 = 0.9971) for describing the effects of independent variables on the response (removal efficiency). The optimum values of the independent parameters based on the maximum removal efficiency were obtained at pH = 8.46, contact time = 12 min, catalyst dose = 1 g/L and NaCl = 10 mg/L. The salicylic acid and chloroform application as radical scavengers in the reaction solution demonstrated that non-hydroxyl radical mechanisms are the main reactions involved in HA degradation. Synergetic effect exhibits a noticeable enhancement in the hybrid catalytic ozonation process in comparison with the separate processes. The behavior of HA degradation under the process was described as well by pseudo-first-order kinetic model with a rate constant of 0.2092 min(-1). The efficiency of total organic carbon removal was determined to be 86.8% and 25.3% at 100 and 10 min reaction times. In conclusion, the rGO/C-MgO composite can be suggested as a promising catalyst in catalytic ozonation process for treating water polluted with organic compounds such as HA.