Catalytic reduction of methylene blue by magnetite - silica composite

Abstract

Iron oxide nanoparticle-based nanomaterials have well-known catalytic activity for the degradation of organic dyes in the water remediation process. The objective of this research was to synthesize iron oxide silica composite by sol-gel method and assess their applicability in wastewater treatment as a catalyst. Synthesized catalysts were characterized by FT-IR spectroscopy, X-ray diffractometry (XRD), and scanning electron microscopy (SEM). Vibration modes in FT-IR spectra show the presence of SiO2 and Fe-O bonds. The formation of Fe3O4 is shown by the XRD patterns. SEM images indicate that iron oxide particles and flakes are distributed in the silica matrix. The effects of catalyst dosage, temperature, the initial concentration of methylene blue (MB), NaBH4 concentration, foreign salts and ionic strength on MB degradation were studied. Maximum degradation of MB (99.89%) was obtained with an initial MB concentration of 20 mg dm-3, catalyst dose of 1.0 g dm-3, NaBH4 concentration of 6.25 mmol dm-3 and at a temperature of 50 °C. Common salts found in industrial wastewater such as NaCl, KCl, CaCl2, and MgCl2 inhibit the degradation of MB, while Na2SO4 enhances the degradation rate. Iron oxide helps in electron relay from BH4- to MB and silica tends to adsorb MB molecules and provide the proximity required for the catalytic reaction.