Combination of nanophotocatalysis with electro-Fenton-like process in the removal of phenol from aqueous solution: GC analysis and response surface approach

Background: This study focuses on the application of photoelectro-Fenton (PEF) with Mn²⁺ as catalyst combined with a photocatalytic process using supported TiO₂ nanoparticles for the removal of phenol from aqueous solutions. TiO₂ nanoparticles (Degussa P-25) immobilized on glass plates were used as photocatalyst, and carbon nanotube-polytetrafluoroethylene electrode was employed as cathode. Response surface methodology (RSM) was performed to evaluate the effects of the four key factors (initial amount of Mn²⁺, initial concentration of phenol, reaction time, and applied current) on the PEF/TiO₂ process. Results: The application of RSM after analysis of variance showed a high coefficient of determination value (R² = 0.918) and thus indicated a high correlation between the observed and predicted values. The optimum operation conditions were located by graphical response surface and contour plots. The optimum initial amount of Mn²⁺, initial phenol concentration, applied current, and reaction time were found to be 0.3 mM, 15 mg/L, 300 mA, and 150 min, respectively. The observed experimental response for removal efficiency was 69.36 in optimum conditions of variables. The total organic carbon measurements showed 95% mineralization of 20 mg/L phenol at 15 h using the PEF/TiO₂ process. The degradation product evolution was verified by gas chromatography analysis. Conclusions: An empirical relationship between the response and independent variables was attained and expressed by the second-order polynomial equation. Effect of experimental parameters on the removal efficiency of phenol was established by the response surface and contour plots of the model-predicted responses.