Surface Modification of Magnesium Ferrite Nanoparticles for Selective and Sustainable Remediation of Congo Red

Abstract

Surface modification of silica-coated magnesium ferrite nanoparticles (MgFe2O4@SiO2 NPs) by 3-aminopropyltriethoxysilane (APTES) shows enhanced selectivity for the removal of Congo Red (CR) from both single and binary aqueous dye solutions. Before coating the surfaces of amine-functionalized magnesium ferrite nanoparticles (MgFe2O4–NH2 NPs) with silica, control studies of the adsorption of cationic, neutral, and anionic dyes were performed using both single and binary dye systems. The studies found that the MgFe2O4–NH2 nanoadsorbent favors the adsorption of indigo carmine (IC) and CR in single dye solutions (>90% removal efficiencies). However, MgFe2O4–NH2 NPs preferentially adsorb CR in binary dye solutions. Interestingly, the selectivity of CR over IC depends on the initial concentration of IC/CR in the IC/CR binary systems. A further enhancement in the selective removal of CR in both single and binary dye solutions was achieved by coating the MgFe2O4–NH2 NPs with silica followed by modification with APTES (i.e., APTES-modified MgFe2O4@SiO2 NPs). The highly selective adsorption capacity for CR on the APTES-modified MgFe2O4@SiO2 nanoadsorbent was attributed to the mixture of polar functional groups (i.e., −OH and −NH2) on the surface of the nanoadsorbent, which facilitates adsorbent–adsorbate interactions such as electrostatic and hydrogen-bonding interactions, which are amplified for CR with its more numerous polar functional groups (i.e., amine, azo, and sulfonate groups). From the results, the APTES-modified MgFe2O4@SiO2 nanoadsorbent offers an effective, inexpensive, and reusable/sustainable system for the selective removal and remediation of Congo Red from wastewaters.