Imine‐Linked Covalent Organic Frameworks Tuned by Quaternary‐Ammonium‐Alkyl for Highly Effective and Selective Adsorption of Perchlorate from Water

Abstract Perchlorate (ClO 4 − ) contamination in surface water is an escalating issue for drinking water safety. Herein, an imine‐linked covalent organic framework (COF) tuned by quaternary ammonium alkyls (R 4 N + ) is developed for ClO 4 − adsorption. The hydrophobic and cationic COF adsorbent achieves a record‐breaking adsorption capacity of ClO 4 − at 912.7 mg g −1 , demonstrating remarkable selectivity for ClO 4 − over other environmentally relevant anions and exhibiting rapid adsorption kinetics. Furthermore, the adsorbent maintains excellent recycling performance (removal efficiency ≥ 80% after 10 cycles) using tetrachloroferrate for regeneration. In dynamic flow‐through experiments with real water samples, the adsorbent effectively treats ≈3200‐bed volumes of feed streams (≈500 µg L −1 ), with an enrichment factor of 15.2. The hydrophobicity of the COF adsorbent is identified as a premise for its interaction with ClO 4 − . Molecular dynamic simulations and density functional theory calculations reveal that R 4 N + anchored in COF cores enriches ClO 4 − via electrostatic attraction and bonds with ClO 4 − via unconventional hydrogen bonds (C─H─O). These key insights pave the way for future design and optimization of adsorbents for removing oxo‐anion from water, especially for ClO 4 − .