Sonocatalytic removal of methylene blue from water solution by cobalt ferrite/mesoporous graphitic carbon nitride (CoFe2O4/mpg-C3N4) nanocomposites: response surface methodology approach

Abstract

In this study, cobalt ferrite/mesoporous graphitic carbon nitride (CoFe2O4/mpg-C3N4) nanocomposites were successfully synthesized by using a two-step protocol. Firstly, monodispersed CoFe2O4 nanoparticles (NPs) were synthesized via thermal decomposition of metal precursors in a hot surfactant solution and then they were assembled on mpg-C3N4 via a liquid phase self-assembly method. The sonocatalytic performance of as-synthesized CoFe2O4/mpg-C3N4 nanocomposites was evaluated on the methylene blue (MB) removal from water under ultrasonic irradiation. For this purpose, response surface methodology (RSM) based on central composite design (CCD) model was successfully utilized to optimize the MB removal over CoFe2O4/ mpg-C3N4 nanocomposites. Analysis of variance (ANOVA) was applied to investigate the significance of the model. The results predicted by the model were obtained to be in reasonable agreement with the experimental data (R2 = 0.969, adjusted R2 = 0.942). Pareto analysis demonstrated that pH of the solution was the most effective parameter on the sonocatalytic removal of MB by CoFe2O4/mpg-C3N4 nanocomposites. The optimum catalyst dose, initial dye concentration, pH, and sonication time were set as 0.25 g L−1 , 8 mg L−1 , 8, and 45 min, respectively. The high removal efficiency of MB dye (92.81%) was obtained under optimal conditions. The trapping experiments were done by using edetate disodium, tert-butyl alcohol, and benzoquinone. Among the reactive radicals, • OH played a more important role than h+ and O−• 2 in the MB dye removal process. Moreover, a proposed mechanism was also presented for the removal of MB in the presence of CoFe2O4/mpg-C3N4 nanocomposites under the optimized sonocatalytic conditions. Finally, a reusability test of the nanocomposites revealed a just 9.6% decrease in their removal efficiency after five consecutive runs.