Competitive adsorption of heavy metals from aqueous solution onto sodium alginate gel beads

Abstract

In this study, a straightforward method was employed to synthesize HNTs@PDA/SA/ZIF-8 gel beads, which involved the in situ formation of ZIF-8 on halloysite nanotubes coated with polydopamine/sodium alginate (HNTs@PDA/SA). The resultant beads were analyzed using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The effects of pH, contact time, and initial concentration were investigated in binary adsorption systems for heavy metals. The adsorption kinetics were best described by the pseudo-second-order model, in contrast to the pseudo-first-order and intraparticle diffusion models. Furthermore, the adsorption isotherms were effectively modeled using the extended Langmuir (EL), extended Langmuir–Freundlich (ELF), and modified competitive Langmuir (MCL) isotherm models, which all provided reasonable fits to the experimental data. Notably, the HNTs@PDA/SA@ZIF-8 gel beads demonstrated excellent resistance to co-existing ion interference and exhibited robust regeneration capabilities over four adsorption–desorption cycles. Overall, the HNTs@PDA/SA@ZIF-8 gel beads proved to be highly effective for the adsorption of heavy metals in binary systems, making them promising candidates for wastewater treatment applications.