Using chitosan-based heterogeneous catalyst for degradation of Acid Blue 25 in the effective electro-Fenton process with rotating cathodes

Abstract

Herein, the capability of glutaraldehyde cross-linked magnetic chitosan nanoparticles (Fe3O4/CS/GA NPs) was investigated as a heterogeneous electro-Fenton catalyst for the degradation of Acid Blue 25. A cylindrical reactor with rotating cathodes was used for performing the electro-Fenton process. Fe3O4/CS/GA NPs were characterized by Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray Powder Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray (EDX), and Vibrating Sample Magnetometer (VSM). According to the results, the dye removal efficiency reached 94.83% after 90 min under the optimal conditions of Fe3O4/CS/GA NPs with the iron content of 15 mmol Fe/g chitosan and concentration of 0.3 g/L, natural pH of dye (6.8), initial dye concentration of 150 mg/L, the current intensity of 0.7 A, and rotational speed of 100 rpm. Also, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal reached 74.19% and 61.53% after 120 min, respectively. Average oxidation state (AOS) and carbon oxidation state (COS) values were increased after treatment, indicating that wastewater's biodegradability was improved. Moreover, the heterogeneous electro-Fenton process using optimal Fe3O4/CS/GA NPs resulted in about 16% improvement in the removal efficiency compared to the homogeneous process. The catalyst showed good reusability up to 5 cycles. The amounts of leached iron into the solution were much less than allowable amounts of the Iranian wastewater discharge standard, thus no need for secondary treatment. Furthermore, scavengers studies under the optimum conditions showed the dye degradation occurred mainly by surface-bonded hydroxyl radicals. In short, this study proved, Fe3O4/CS/GA NPs are a promising heterogeneous electro-Fenton catalyst due to their low cost, excellent stability and reusability, negligible iron leaching, environmental compatibility, and superior catalytic activity in a wide range of pH.