Adsorptive removal of Fe(III) using gallic acid anchored iron magnetic nano-adsorbents synthesized via two different routes under microwave irradiation

Abstract

Under microwave solvent free conditions, bare iron magnetic nanoparticles (Fe₃O₄-MNPs) have been silica coated, amine functionalized and gallic acid grafted, in presence and absence of tetraethylorthosilicate (TEOS). The synthesized adsorbents in both cases have been followed up by Fourier transform infrared, scan electron microscopy and transmission electron microscopy analyses to verify and compare the progress of surface modification. The effects of various parameters on the adsorption efficiency of Fe(III) such as pH of solution, amount of adsorbent and contact time have been studied and optimized. The adsorbents Fe₃O₄-MNPs-SiO₂-CPTMS-1,2-EDA-GA and MNPs-CPTMS-1,2-EDA-GA exhibit higher Fe(III) capacities (4.980 and 4.700 mmol/g) than their analogous Fe₃O₄-MNPs-SiO₂-APTMS-GA and Fe₃O₄-MNPs-APTMS-GA (4.324 and 4.230 mmol/g). The studies of sorption kinetics showed rapid sorption dynamics by a second-order kinetic model, suggesting chemisorption mechanism. Fe(III) adsorption equilibrium data have been fitted well to the Langmuir isotherm. The results of medium stability as criteria for potential coating and values of metal uptake capacity support the possibility of the direct use of alkoxysilanes as an alternative to TEOS not only for coating but also for amine functionalization. This is strengthened by almost equal capability of gallic acid anchored adsorbents for extraction of trace concentrations of Fe(III) spiked natural water samples.