Application of response surface methodology for optimization of azo dye removal by oxalate catalyzed photoelectro-Fenton process using carbon nanotube-PTFE cathode

Decolorization of C.I. Basic Red 46 (BR46) by the oxalate catalyzed photoelectro-Fenton (PEF) process based on carbon nanotube-polytetrafluoroethylene (CNT-PTFE) cathode under visible light was studied. A comparison of electro-Fenton (EF), photoelectro-Fenton (PEF) and PEF/oxalate processes for decolorization of BR46 solution has been performed. Results showed that color removal follows the decreasing order: PEF/oxalate>PEF>EF. Response surface methodology (RSM) was employed to assess individual and interactive effects of the four main independent parameters (initial dye, Fe³⁺ and oxalate concentrations and electrolysis time) on decolorization efficiency. Analysis of variance (ANOVA) showed a high coefficient of determination value (R²=0.959). The optimum initial dye concentration, the initial amount of Fe³⁺, the initial oxalate concentration and the electrolysis time were found to be 10mg/l, 0.3mM, 0.2mM and 27min, respectively. Effect of experimental parameters on the decolorization efficiency of BR46 was established by the response surface and contour plots. Results showed that decolorization efficiency increases with increasing electrolysis time and initial Fe³⁺ concentration and reminds nearly constant with increasing initial oxalate concentration. But, increasing initial dye concentration decreases decolorization efficiency. This study clearly showed that RSM was one of the suitable methods to optimize the operating conditions.