Valency-regulated interfacial selectivity by metal-crosslinked chitosan cryogels for capturing trace-level...

Developing high-affinity adsorbents for the selective sequestration of trace perchlorate (ClO₄^-) is critical due to its low hydration energy and interference from competing anions. To address this, transition metals with varying valences [Cu (II), Fe (III), and Zr (IV)] were systematically incorporated into chitosan to regulate the interfacial electronic landscape. Adsorption performance followed a distinct valence-dependent trend: Cu (II) < Fe (III) < Zr (IV). Specifically, Zr (IV)-CTS exhibited a superior maximum adsorption capacity of 133.69 mg/g and achieved a removal efficiency exceeding 99% for 1.0 mg/L ClO₄^- in complex water matrices. Advanced characterizations and DFT simulations revealed that increasing the metal valence significantly enhanced surface electropositivity (from 24.46 to 1264.67 kcal·Å²/mol) and coordination potential. Microscopic analyses using the electron localization function (ELF) and independent gradient model (IGMH) confirmed a fundamental mechanistic shift: while low-valence systems rely on electrostatic trapping; the high-valence Zr (IV)-CTS triggers a synergistic transition to coordination anchoring with a high molar uptake ratio of ~3.0 mol/mol-Zr. This work provides a practical strategy for designing high-performance adsorbents by precisely modulating the metal valence state.