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.
We report herein the synthesis of monodisperse cobalt ferrite (CoFeO) nanoparticles (NPs) via a surfactant-assisted high temperature thermal decomposition method and then their assembly on reduced graphene oxide (rGO) to yield CoFeO-rGO nanocomposites, which displayed outstanding sonocatalytic activity for the removal of organic dyes from aqueous solutions under ultrasonic irradiation. As-prepared CoFeO-rGO nanocomposites were characterized by using transmission electron microscopy (TEM), high-resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Micro-Raman spectroscopy, Vibrating sample magnetometer (VSM) and inductively couple plasma mass spectrometer (ICP-MS). To evaluate the sonocatalytic activity of the CoFeO-rGO nanocomposites, the sonocatalytic removal of several organic dyes (AO7, AR17, BR46 and BY28) was studied. The reaction conditions were optimized by studying the effects of various key operating parameters such as pH, catalyst dosage, HO initial concentration, initial dye concentration, ultrasonic power and reaction time on the removal of AO7 dye. The maximum removal efficiency of 90.5% was achieved at pH 3 using 0.08gL catalyst, 3mM HO and 10mgL AO7 dye under 350W ultrasonic power in 120min of reaction time span. Experimental results revealed that the kinetic of the removal process could be described using Langmuir-Hinshelwood (L-H) kinetic model. The trapping experiments showed that O radicals constitute the major reactive oxygen species (ROS) in the AO7 dye removal process. The reusability of the nanocomposites revealed about 22% drop in the removal efficiency within five consecutive runs. A possible sonocatalytic mechanism for the removal of organic dyes was also proposed. The intermediate by-products of the dye formed in the removal process were characterized by using the GC-MS technique.
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