A central composite statistical experiment design was used to evaluate the effects of four independent variables (initial solution pH (A), initial TC concentration (B), initial S2O8−2 concentration (C) and reaction time (D)) on the TC degradation. The application of RSM provides a mathematical relationship between variables and experimental data can be fitted to an empirical second-order polynomial model as the following Eq. (8). [55–57].8 Y=β0+β1A+β2B+β3C+β4D+β12AB+β13AC+β14AD+β23BC+β24BD+β34CD+β11A2+β22B2+β33C2+β44D2