Optimized synthesis of carbon-doped nano-MgO and its performance study in catalyzed ozonation of humic acid in aqueous solutions: Modeling based on response surface methodology

Abstract

This research study focused on the optimization of the synthesis of carbon-doped nano-MgO (C-MgO) and the investigation of its catalytic capacity in a catalytic ozonation process (COP) for the removal of humic acid (HA). Characterization analyses, including SEM, EDX, XRD, BET, and photoluminescence test showed that the C-MgO was successfully synthesized. L8 orthogonal arrays according to the Taguchi methodology optimized the synthesis of the C-MgO as follows: sucrose to MgO ratio = 0.5, sonication time = 15 min, calcination temperature = 400 °C and pH = 10.5. A central composite design based on response surface methodology was employed to optimize and model the COP in the removal of HA. A quadratic polynomial model with p-value < 0.0001 and R² = 0.9988 showed a better fit to experimental responses. The optimum levels of the studied parameters in the COP based on the predictive model were obtained as follows: pH = 9.5, reaction time = 12 min, catalyst dose = 1 g/L, and HA concentration = 5 mg/L. The HA mineralization was determined to be 86.8% at the 100 min reaction time. Additionally, the COP exhibited 34% synergistic effect and the kinetic rate constant of 0.1898 min^-1 in the HA removal. The presence of tert-butanol, methanol, salicylic acid, and some anions did not significantly affect the removal of the HA in the COP. From a practical view, this report indicated that the C-MgO catalyst could be potentially applied in the COP for the treatment of the water having high concentrations of HA substances.

Keywords: C-MgO; Catalytic ozonation process; Humic acid; Mineralization; Response surface methodology; Water treatment.