Magnetic amino-functionalized hyper-crosslinked resin as a reusable adsorbent for methylene blue

Contamination of water resources by organic dyes is a major environmental issue associated with industrial activities. Methylene blue (MB), a widely used cationic aromatic dye, is particularly problematic due to its high chemical stability and toxicity, highlighting the need for efficient and cost-effective treatment strategies. In this study, a magnetic amino-functionalized hyper-crosslinked resin (Fe3O4@XDV-NH2) was synthesized and evaluated as an efficient adsorbent for MB removal from aqueous solutions. The material was prepared via post-synthetic amino functionalization of a hyper-crosslinked polymer followed by in situ deposition of Fe3O4 nanoparticles, combining high surface area, permanent porosity, and chemical stability with easy magnetic separation. Structural and magnetic characterizations confirmed the uniform incorporation of Fe3O4 without significant loss of porosity. Amino functionalization enhanced hydrophilicity and introduced polar active sites, promoting strong interactions with MB. Batch adsorption experiments revealed a maximum adsorption capacity of 79.60 mg/g at 298 K and pH 9 and 0.06 g L-1 adsorbent dosage. Adsorption kinetics followed the pseudo-second-order model (R-2 = 0.976). Equilibrium data were best fitted by the Langmuir isotherm model (R-2 = 0.996), indicating monolayer adsorption with a maximum theoretical capacity of 183.48 mg/g. Thermodynamic analysis showed that MB adsorption was spontaneous and exothermic. High removal efficiencies were maintained in complex matrices such as tap water (94.11%) and synthetic wastewater (78.41%). Moreover, the adsorbent retained approximately 89% of its initial capacity after six adsorption-desorption cycles, demonstrating good reusability. These results indicate that Fe3O4@XDV-NH2 is a promising and sustainable adsorbent for dye-contaminated wastewater treatment.