Surface modification of Magnesium Ferrite nanoparticles for selective adsorption of dyes and catalytic reduction of Nitroaromatics

Abstract

In this study, magnesium ferrite nanoparticles were developed for use as nanoadsorbents and nanocatalysts in the remediation of organic dyes and nitroaromatics. The primary focus was modifying the surfaces of magnesium ferrite nanoparticles with suitable active sites to achieve nanoadsorbents possessing high selectivity for specific dye adsorption and effective nanocatalysts for reduction of nitroaromatics. Amine-functionalized magnesium ferrite nanoparticles (MgFe2O4 NPs) synthesized via a one-pot coprecipitation method were evaluated for their adsorption behaviors towards cationic, anionic, and neutral dyes in single-component and binary dye solutions. The study revealed that the MgFe2O4 NPs efficiently removed anionic dyes, specifically indigo carmine (IC) and Congo Red (CR), from both single-component and binary dye solutions. However, the MgFe2O4 NPs preferably adsorbed CR rather than IC from binary IC/CR solutions, suggesting low selectivity for adsorption of CR. To improve the selectivity, the MgFe2O4 NPs were encapsulated within a silica shell and functionalized with 3-aminopropyltriethoxysilane to obtain APTES-modified MgFe2O4@SiO2 NPs (designated as MgFe2O4@SiO2 NPs). Combination of XRD, FTIR, XPS, SEM, and zeta potential analyses indicated the successful surface modification of MgFe2O4 NPs. The adsorption study demonstrated that the MgFe2O4@SiO2 NPs exhibited high selectivity for the adsorption of CR, attributed to the presence of appropriate functional groups on nanoadsorbents and chemical structure of CR molecules. To synthesize MgFe2O4-based nanocatalysts, the surfaces of MgFe2O4 and MgFe2O4@SiO2 NPs were modified by depositing bimetallic gold/silver nanoparticles (Ag/Au) via a seed-mediated growth method. The synthesized nanocatalysts, i.e., MgFe2O4/Au/Ag and MgFe2O4@SiO2/Au/Ag NPs, were used in the reduction of 4-nitrophenol (4-NP) using sodium borohydride as a reducing agent. Several characterization techniques, such as XRD, XPS, TEM, SEM, EDS, and VSM were employed to confirm the depositing Au/Ag metals on the surfaces of MgFe2O4 and MgFe2O4@SiO2 NPs. The catalytic test revealed that the catalytic activity of the MgFe2O4/Au/Ag NPs was slightly higher than that of the MgFe2O4@SiO2/Au/Ag NPs. However, both nanoparticles exhibited rapid catalytic reduction for 4-NP within 1.5 minutes, due to the presence of bimetallic Au/Ag nanoparticles onto the nanocatalyst surfaces. The reusability test revealed that MgFe2O4@SiO2/Au/Ag NPs maintained ~85% 4-NP removal after consecutive uses for 10 cycles, while the MgFe2O4/Au/Ag NPs provided 7 cycles with ~85% removal. Furthermore, both nanocatalysts efficiently catalyzed the reduction of other representative nitroaromatics, such as 4-nitroaniline and 4-nitrobenzaldehyde.