Removal of metronidazole antibiotic pharmaceutical from aqueous solution using TiO2/Fe2O3/GO photocatalyst: Experimental study on the effects of mineral salts

A TiO2/Fe2O3/GO photocatalyst is synthesized via the sol-gel method and characterized by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), FT-IR, Brunauer-Emmett-Teller (BET), and Ultraviolet-Visible Diffuse Reflection Spectroscopy (UV-Vis DRS) analyses. Metronidazole (MET) concentration (10-20 mg/L), photocatalyst concentration (0.5-1.5 g/L), irradiation time (60-120 min), and initial pH (4-6) are investigated through response surface methodology (RSM), and the optimal process conditions are determined. The removal efficiency of MET with the TiO2/Fe2O3/GO photocatalyst is 97% under optimal conditions: a pollutant concentration of 10 mg/L, the irradiation time of 120 min, photocatalyst concentration of 1 g/L, and pH of 5. The influence of mineral salts concentrations (50-800 mg/L), including NaCl, Na2SO4, NaHCO3, KCl, MgSO4, and CaCl2, are examined at the initial pH of 5, photocatalyst concentration of 1 g/L, and pollutant concentration of 20 mg/L. According to the results, the reaction rate constant decreases with an increase in mineral salts concentrations up to 800 mg/L, especially with Na2SO4 (42.43% deactivation) and also with MgSO4 (38.08%) and NaHCO3 (37.73%), under the same operational conditions. The effects of mineral salts such as NaCl and KCl on the reaction rate constant for the contaminant removal efficiency have a downward trend until these salts reach a 200 mg/L concentration, and then they experience an upward trend.