Synthesis of novel magnetic carboxyl-functionalized crosslinked copolymer microspheres for methylene blue removal from water

Magnetic carboxyl-functionalized crosslinked copolymer microspheres of α-methyl styrene and maleic anhydride (MCPMs) with a uniform particle size were synthesized based on self-stabilized precipitation polymerization. Magnetic crosslinked copolymer microspheres (MPMs) were prepared by <i>in situ</i> polymerization using oleic acid-modified Fe₃O₄ as the magnetic source, α-methyl styrene and maleic anhydride as monomers and divinylbenzene as the crosslinking agent, and MCPMs were then obtained by hydrolyzing the anhydride groups of MPMs into carboxyl groups. The as-prepared MCPMs were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, vibrating sample magnetometry and the Brunauer–Emmett–Teller method. The adsorption behavior, adsorption kinetics and adsorption isotherms of MCPMs for methylene blue (MB) removal from water were systematically investigated. It was found that MCPMs manifested good MB removal ability from water with a maximum MB adsorption capacity of 315 mg/g. The kinetic and isothermal data of MCPMs for MB removal followed the pseudo-second-order model and the Langmuir isothermal model, respectively. In addition, MB-loaded MCPMs could be separated easily by magnets, and the MB removal rate of MCPMs still reached more than 90.0% after five cycles. These results indicate that MCPMs have great potential in cationic dye wastewater treatments.