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

Perchlorate (ClO4-) 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 (R4N+) is developed for ClO4- adsorption. The hydrophobic and cationic COF adsorbent achieves a record-breaking adsorption capacity of ClO4- at 912.7 mg g-1, demonstrating remarkable selectivity for ClO4- 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 approximate to 3200-bed volumes of feed streams (approximate to 500 mu g L-1), with an enrichment factor of 15.2. The hydrophobicity of the COF adsorbent is identified as a premise for its interaction with ClO4-. Molecular dynamic simulations and density functional theory calculations reveal that R4N+ anchored in COF cores enriches ClO4- via electrostatic attraction and bonds with ClO4- via unconventional hydrogen bonds (C & horbar;H & horbar;O). These key insights pave the way for future design and optimization of adsorbents for removing oxo-anion from water, especially for ClO4-.