It is significant to selectively remove Ni(II) ions from wastewater. A novel sulfonic acid-based magnetic rattle-type ion-imprinted polymer (Fe₃O₄@void@IIP-Ni(II)) was designed by taking advantage of the strong interaction between Ni(II) and sulfonic acid groups. Green polymerization was used to synthesize Fe₃O₄@void@IIP-Ni(II), which was then investigated using SEM, TEM, FT-IR, VSM, TGA, EDS, and XPS. The adsorption results indicated that the prepared imprinted material had a short adsorption equilibrium time (10 min), good magnetic responsiveness (about 5 seconds) and high adsorption capacity (44.64 mg g⁻¹) for Ni(II) at the optimal pH of 6.0. The removal rate of Ni(II) was up to 99.97%, and the adsorption process was spontaneous and endothermic, following the pseudo-secondary kinetic model and Langmuir model. The selectivity coefficients of the imprinted material were 4.67, 4.62, 8.94 and 9.69 for Ni(II)/Co(II), Ni(II)/Cu(II), Ni(II)/Pb(II) and Ni(II)/Zn(II), respectively. The regeneration and application of the imprinted material in actual water samples have been verified. Moreover, the mechanism of selective adsorption for Ni(II) was investigated by FTIR, XPS and density functional theory (DFT) calculation. The results showed that the imprinted sorbent has a strong binding ability with Ni(II), and the adsorption of Ni(II) on Fe₃O₄@void@IIP-Ni(II) was the result of the co-coordination of O atoms of the sulfonic acid groups and N atoms of –N–CO groups in AMPS with Ni(II).

A novel recoverable magnetic Cd(II) ion-imprinted polymer was synthesized on the surface of silica-coated Fe₃O₄ particles via the surface imprinting technique and chemical grafting method. The resulting polymer was used as a highly efficient adsorbent for the removal of Cd(II) ions from aqueous solutions. The adsorption experiments revealed that Fe₃O₄@SiO₂@IIP had a maximum adsorption capacity of up to 29.82 mg·g⁻¹ for Cd(II) at an optimal pH of 6, with the adsorption equilibrium achieved within 20 min. The adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model. Thermodynamic studies showed that the adsorption of Cd(II) on the imprinted polymer was spontaneous and entropy-increasing. Furthermore, the Fe₃O₄@SiO₂@IIP could rapidly achieve solid–liquid separation in the presence of an external magnetic field. More importantly, despite the poor affinity of the functional groups constructed on the polymer surface for Cd(II), we improved the specific selectivity of the imprinted adsorbent for Cd(II) through surface imprinting technology. The selective adsorption mechanism was verified by XPS and DFT theoretical calculations.

With the increase of hexavalent Cr(VI) wastewater discharged from industrial production, it seriously pollutes water bodies and poses a risk to human health. Adsorption is used as an effective means to treat Cr(VI), but its effectiveness is affected by pH, and the adsorption performance decreases when acidity is strong. Furthermore, research on the mechanism of Cr(VI) adsorption using DFT calculations needs to be developed. This study focuses on the development of magnetically responsive core–shell nano-ion imprinted materials (Fe₃O₄@GO@IIP) through magnetic separation and surface imprinting techniques. Characterization techniques including FT-IR, XRD, and EDS confirmed the core–shell nanostructure of Fe₃O₄@GO@IIP. Batch adsorption experiments and model simulations demonstrated the exceptional adsorption capacity of Fe₃O₄@GO@IIP for Cr(VI) in strongly acidic solutions (pH = 1), reaching a maximum of 89.18 mg/g. The adsorption mechanism was elucidated through XPS and DFT calculations, revealing that Fe₃O₄@GO@IIP operates through electrostatic interactions and chemical adsorption, with charge transfer dynamics quantified during the process. This research provides new insights for addressing Cr(VI) treatment in highly acidic environments.

The recovery of precious metals from secondary resources is significant economically and environmentally. However, their separation is still challenging because they often occur in complex metal ion mixtures. The poor selectivity of adsorbents for gold in complicated solutions prevents further application of adsorption technology. In this study, a Zr-based MOF adsorbent, MIL-161, was synthesized using s-tetrazine dicarboxylic acid (H₂STz) as an organic ligand. MIL-161 demonstrated a high adsorption capacity of up to 446.49 mg/g and outstanding selectivity for gold(III) in a simulated electronic waste solution as a result of the presence of sulfur- and nitrogen-containing groups. In addition, the MIL-161 adsorbents were characterized using Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TG), Brunner–Emment–Teller (BET), and X-ray photoelectron spectroscopy (XPS). Additionally, the adsorption kinetics, isotherms, and thermodynamics of the MOF adsorbents were also thoroughly examined. More importantly, the experimental results and DFT calculations indicate that chelation and electrostatic interactions are the main adsorption mechanisms.