Ultra-high Cr(VI) removal by novel super-hydrophilic spherical hyper-crosslinked polyethyleneimine adsorbents: Performance and synergistic mechanisms.

Hexavalent chromium (Cr(VI)) poses a significant threat to both ecosystems and human health. In this study, a novel series of adsorbents were constructed via free-radical polymerization followed by hyper-crosslinking with polyethyleneimine (PEI). These adsorbents were characterized by its distinctive spherical morphology and exceptional super-hydrophilicity. Remarkably, they demonstrated ultra-high Cr(VI) adsorption capacities, the maximum of 1028 mg g-1 was achieved by DBP25000@1.5 under highly acidic conditions (pH = 1.0). The adsorption process conformed to the pseudo-second-order kinetic model and the Freundlich isotherm, suggesting a chemisorption-driven multilayer adsorption mechanism. Thermodynamic evaluations indicated that the adsorption process is both spontaneous and endothermic. Through combined characterization techniques and density functional theory (DFT) calculations, the adsorption mechanism was elucidated, revealing that it involves electrostatic interactions between protonated amines and Cr(VI) anions, reduction of Cr(VI) to Cr(III), and subsequent chelation of Cr(III) species. Furthermore, DBP25000@1.5 exhibited excellent selectivity, remarkable recyclability, and a robust resistance to interference from coexisting ions. In this work, super-hydrophilic functionalized microspheres were constructed to effectively remove and transform the valence state of Cr(VI) in aqueous environments. From the perspectives of material structural design and fundamental action mechanisms, this study introduces an innovative paradigm for the practical application of super-hydrophilic adsorptive microspheres in wastewater treatment.