Heterogeneous Fenton-like discoloration of Rhodamine B using natural schorl as catalyst: optimization by response surface methodology

A cationic dye, Rhodamine B (RhB), could be efficiently discolored by heterogeneous Fenton-like reaction catalyzed by natural schorl. In this work, with the main goal of the optimization for RhB discoloration, central composite design under the response surface methodology (RSM) was employed for the experiment design and process optimization. The significance of a second-order polynomial model for predicting the optimal values of RhB discoloration was evaluated by the analysis of variance and 3D response surface and counter plots for the interactions between two variables were constructed. The Pareto graphic analysis of the discoloration process indicated that, among all the variables, solution pH (X ₃, 47.95 %) and H₂O₂ concentration (X ₁, 24.39 %) had the largest influences on the heterogeneous Fenton-like discoloration of RhB. Based on the model prediction, the optimum conditions for RhB discoloration were determined to be 45 mM H₂O₂ concentration, 2.5 g/L schorl dosage, solution pH 2, and 110 min reaction time, with the maximum RhB discoloration ratio of 98.86 %. The corresponding experimental value of RhB discoloration ratio under the optimum conditions was determined as 99.31 %, which is very close to the optimized one, implying that RSM is a powerful and satisfactory strategy for the process optimization.