Supramolecular suppression of aggregation enabling monomeric QAC loading on powdered activated carbon towards efficient perchlorate removal from water

Aggregation of long-chain quaternary ammonium compounds (LC-QACs) into aggregates (e.g., micelles) during material modification often limits their grafting efficiency in porous adsorbents like powdered activated carbon (PAC), thereby constraining performance in anionic pollutant removal. Herein, we report a supramolecular strategy that employs β-cyclodextrin (β-CD) to suppress CTAB aggregation, enabling monomeric diffusion and enhanced CTAB loading within PAC micropores. The resulting β-CD/CTAB–PAC composite achieves a high perchlorate (ClO 4 − ) adsorption capacity of 211 mg g −1 , significantly surpassing the conventional CTAB-modified PAC (87 mg g −1 ), along with remarkable selectivity (distribution coefficient > 10× higher than competing anions), stability (<8% leaching in 10-day immersion), and regenerability (>91% capacity retention over 6 cycles). Fixed-bed column tests validated its practical efficacy, treating >5400 bed volumes of contaminated water (500 μg L −1 ) to below the drinking standard of 70 μg L −1 . Furthermore, density functional theory calculations attribute the high selectivity to the low hydration energy of ClO 4 − . Its sparse hydration shell results in a lower energy penalty for desolvation, enabling a more direct and stronger electrostatic interaction with the quaternary ammonium sites compared to the heavily hydrated competing anions. Overall, this aggregation-suppression approach provides a generalizable route for optimizing LC-QAC-based functionalization of porous materials.