Tailor-made zeolite-based magnetic nanocomposites (MNCs): rational design for effective and recyclable adsorption of sulfanilamide and methylene blue

A tailor-made design strategy was adopted for the synthesis of three zeolite-based magnetic nanocomposites (MNCs). In this view, ferrierite (Fe-FERR), L-type (Fe-L), and USY (Fe-USY) zeolites functionalized with FeSO4 and thermally treated were used for the simultaneous removal of pollutants with contrasting physicochemical properties. Sulfanilamide (SA) and methylene blue (MB) were selected as model pollutants as they offer contrasting physicochemical properties, which makes their adsorption potentially governed by both hydrophobic and polar interactions. To address this, we synthesized amphiphilic MNCs, to establish interactions of both types for simultaneous SA and MB adsorption. Preliminary magnetic functionalization ensured easier separation and multiple reuse of the adsorbents, as well as reduced generation of wastes. The structural (XRD, FTIR, SEM) and magnetic characterization confirmed their rapid separability under an external magnetic field. The amphiphilic MNCs exhibited efficient adsorption of SA (pH 5–6, mainly due to electrostatic interactions) and MB (pH 4.0–5.0, mainly attributed to the hydrophobic interaction). The adsorption kinetics of SA and MB could be described adopting the intraparticle diffusion and the pseudo-second order models, respectively. To enhance the comprehension of SA and MB adsorption, advanced adsorption models were adopted, rooted in statistical physics principles. The maximum values of the adsorption capacities (6.00 × 105 μmol/kg with sulfanilamide, and 120,000 mg/kg with Methylene Blue) were satisfactory if compared to conventional adsorbents. A pH-triggered regeneration procedure was developed, allowing an almost complete recycle and reuse of the magnetic adsorbents.