Removal of methylene blue and lead(ii) via PVA/SA double-cross-linked network gel beads loaded with Fe3O4@KHA nanoparticles

Abstract

Novel magnetic gel beads were successfully fabricated via a polyvinyl alcohol (PVA) and sodium alginate (SA) double-cross-linked network and loaded with ferroferric oxide@potassium humate (Fe₃O₄@KHA) nanoparticles. The PVA/SA/Fe₃O₄@KHA gel beads were found to exhibit an excellent removal efficiency for methylene blue (MB) dye and Pb(II). The physicochemical properties of these gel beads were systematically characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, zeta analysis, Brunauer–Emmett–Teller analysis and vibrating sample magnetometry. The adsorption process was found to follow a pseudo-second-order kinetic model and the experimental data were in good agreement with the Langmuir model, with maximum adsorption capacity values of 781.92 and 347.19 mg g⁻¹ for MB and Pb(II) at 298 K, respectively. The thermodynamic measurements demonstrate that adsorption onto these gel beads was spontaneous, endothermic, and driven by an increase in the system entropy. Furthermore, FT-IR and X-ray spectroscopy investigations demonstrate that the mechanism through which Pb(II) was removed mainly involved chelation by the carboxyl groups, whereas MB adsorption takes place via H-bonding and electrostatic interactions. Notably, PVA/SA/Fe₃O₄@KHA showed high selectivity for MB adsorption. Additionally, the prepared magnetic gel beads could be readily regenerated and efficiently reused for several cycles and their excellent magnetic properties can simplify the adsorbent separation process.