Magnetically recyclable adsorption of anionic pollutants from wastewater using 3,5-diaminobenzoic acid-functionalized magnetic iron oxide nanoparticles

Abstract

Surface-active magnetic materials having suitable anchoring moieties have gained great interest in the field of environmental pollution management. Herein, 3,5-diaminobenzoic acid (DABA)-functionalized Fe₃O₄ (Fe₃O₄@DABA) nanoparticles were synthesized for adsorbing anionic pollutants from wastewater. First, Fe₃O₄ nanoparticles were fabricated via aqueous coprecipitation of Fe³⁺ and Fe²⁺ ions, and then, the bare-surface of Fe₃O₄ was functionalized concomitantly with DABA. The production of Fe₃O₄ particles and their surface functionalization with DABA, and the thermal stability of Fe₃O₄@DABA were confirmed using Fourier transform infrared spectroscopy and gravimetry. Core-Fe₃O₄ particles had a spinel structure, and their concurrent surface functionalization did not alter the initial phase purity of Fe₃O₄, as revealed by an X-ray diffraction study. Fe₃O₄@DABA particles showed nano-sized, spherical-shaped, improved surface morphology, surface area, surface porosity, and pH-dependent surface activities. Fe₃O₄@DABA nanoparticles exhibited a higher hydrodynamic average diameter and better aqueous dispersity than those of bare-Fe₃O₄. The saturation magnetization of Fe₃O₄@DABA was found to be 47 emu g⁻¹ under ambient conditions. Our designed magnetic Fe₃O₄@DABA nanoadsorbent showed very high affinity towards the uptake of azo dye molecules: maximum adsorption of 259 mg g⁻¹ for Congo red (CR) and 282 mg g⁻¹ for Eosin yellow (EY) was reached at pH 3 and 25 °C by using an adsorbent dose of 0.02 g. Adsorption isotherm and kinetic study suggested both CR and EY adsorption followed the Freundlich adsorption model and pseudo-first-order kinetics. The adsorbed azo dye was eluted effectively from the surface of the investigated nanoadsorbent by aqueous alkali (0.1 M NaOH) treatment. In addition, Fe₃O₄@DABA showed excellent magnetic recyclability without considerable loss of adsorption capacity. After recycling five times, the adsorption efficiency of Fe₃O₄@DABA slightly declined (90.16% for CR, and 95.52% for EY) compared to that of the initial adsorption.