Optimization of hydrogen peroxide/NiO nanoparticle photocatalytic process by degrading cephalexin from aqueous solution using Taguchi method: mineralization, mechanism and pathway

The present work investigated the efficiency of nickel oxide nanoparticle (NiO) activated hydrogen peroxide (H2O2) in the presence of ultraviolet (UV) irradiation degrading cephalexin (CLX) from aqueous solutions. The effect of pH of the solution (3-9), NiO dosage (1.5-2 mg/L), hydrogen peroxide concentration (5-20 ml/L), contact time (10-60 min) and CLX initial concentration (20-80 mg/L) was studied and optimized using Taguchi design. The percentage contribution of each operational parameter on CLX degradation determined using the analysis of variance. The results showed that in the optimum conditions, an initial concentration of 20 mg/L at pH = 3, 1.5 mg/L of NiO, 10 ml/L hydrogen peroxide with UV irradiation limit after 60 min contact time, degrading of CLX was 99.3%, and the least effective parameter was CLX initial concentration (73.3%). Results for 10 ml/L H2O2 in deionized water included a reduction to below the chemical oxygen demand (COD) detection after 60 min with the addition of 20 g/L Na2CO3 concentrated solution. Under optimum operational conditions, the rates of CLX mineralization for COD and total organic carbon removal were 83% and 68% within 60 min contact time, respectively. In addition, the removal process of CLX could be described by the pseudo-first-order kinetic model. The liquid chromatography/mass spectrometry was used to selectively detect degradation products of CLX degradation. Also, a tentative pathway for degradation of CLX using the UV/H2O2/NiO process was proposed.