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 (CoFeO/mpg-CN) nanocomposites were successfully synthesized by using a two-step protocol. Firstly, monodispersed CoFeO nanoparticles (NPs) were synthesized via thermal decomposition of metal precursors in a hot surfactant solution and then they were assembled on mpg-CN via a liquid phase self-assembly method. The sonocatalytic performance of as-synthesized CoFeO/mpg-CN 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 CoFeO/mpg-CN 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 (R = 0.969, adjusted R = 0.942). Pareto analysis demonstrated that pH of the solution was the most effective parameter on the sonocatalytic removal of MB by CoFeO/mpg-CN nanocomposites. The optimum catalyst dose, initial dye concentration, pH, and sonication time were set as 0.25 g L, 8 mg L, 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 [Formula: see text] in the MB dye removal process. Moreover, a proposed mechanism was also presented for the removal of MB in the presence of CoFeO/mpg-CN 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.

Ultrasonically Induced Sulfur-Doped Carbon Nitride/Cobalt Ferrite Nanocomposite for Efficient Sonocatalytic Removal of Organic Dyes

“…The increase in catalyst dosage from 0 to 0.5 g/L led to an increase in the degradation efficiency by 26%. This suggests that the higher amount of dosage favors the MB degradation due to the excess availability of the active sites which help in the generation of surplus hydroxyl radicals (OH•) for the degradation of MB [7]. However, as indicated by the drop in the degradation efficiency from 63 to 55% at the catalyst dosage of 1 and 1.5 g/L, respectively, an excess amount of catalyst dosage (in excess of 1 g/L) tends to decrease the selectivity and yield of H 2 O 2 to form undesired water [56].…”

“…However, an increase in the amount of H 2 O 2 from 4 to 6 vol % decreased the degradation efficiency to 57%. This is because surplus H 2 O 2 serves as a scavenger of hydroxyl radical to lower the oxidation potential by the generation of perhydroxyl radical (HOO•) [7,10,42].…”

“…The degradation efficiencies of RhB, CR and MB were 20%, 58%, and 83%, respectively. The significant difference can be attributed to the difference in dye sizes, structural compositions and electric charges [6][7][8]. Degradation of mixed organic dyes is therefore a challenging study worth investigating further.…”

“…Hence, the reduction of the recombination rate due to the migration of sonogenerated electrons and holes in the opposite direction leads to the enhancement of sonocatalytic degradation. Further, the highly reactive ·OH is produced by the reaction of electrons in the CB with H2O2, which facilitate the degradation process [7]. The adsorbed OH − anions or H2O2 onto the surface of the SCN react with the sonogenerated holes to form ·OH.…”

“…Recently, great attention has been given to sonodegradation as an advanced oxidation process (AOP) for wastewater treatments. The abrupt growth, as well as the collapse of bubbles in solution under the ultrasound irradiation during the process, leads to extreme pressure and temperature around the bubbles [6,7]. The generation of a potent oxidizing agent like hydroxyl radicals (OH˙) increases because of the high temperature around the bubbles, which is useful for the non-selective oxidation of organic dyes.…”