Fabrication of magnetic biochar-MIL-68(Fe)-supported cobalt composite material toward the catalytic reduction performance of crystal violet

Abstract

A magnetic biochar-MIL-68(Fe)-supported cobalt composite material (Co@MIL-68(Fe)@Fe3O4@CM-BC) was synthesized and used as a novel and effective catalyst for the catalytic reduction of crystal violet (CV) in aqueous environments. The prepared material was thoroughly characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and vibrating-sample magnetometer (VSM) techniques. Four operating parameters, including the CV dye concentration, time, catalyst dosage, and NaBH4 amount, were evaluated by employing central composite design (CCD) based on response surface methodology (RSM) for the catalytic reduction of CV. In the catalytic reduction of CV dye, the optimum conditions were determined as 15.67 mg/L CV dye concentration, 80.24 s time, 0.341 mg/mL catalyst dosage, and 14.56 mM NaBH4 amount with CV reduction efficiency of 99.98 %. The catalytic reduction kinetic of CV was studied by applying the pseudo-first-order model, and the apparent rate constant (kapp) values were obtained under different temperature (293–323 K). It was observed that kapp values increased upon increment of temperature. From kinetic studies, the activation energy was measured as 37.18 kJ/mol. Moreover, thermodynamic results showed that the activation entropy (ΔS#) and enthalpy (ΔH#) were obtained as −179.49 J/mol K and 34.62 kJ/mol, respectively. The thermodynamic parameters suggest that the catalytic reduction of CV was favorable and endothermic in nature. Regeneration tests indicated that the activity of Co@MIL-68(Fe)@Fe3O4@CM-BC was retained after five uses. Based on all of the results, the prepared material is a good candidate for the treatment of wastewater containing dyes like CV.