Surface-functionalized granular activated carbon with enhanced interfacial hydrophobicity and electrostatic capture for selective perchlorate removal.

Perchlorate (ClO4⁻) is a persistent and toxic oxyanion widely used in military and industrial activities, posing a crucial challenge in drinking water treatment due to its high solubility and chemical stability. To meet increasingly stringent regulatory limits, adsorbents suitable for full-scale treatment must reconcile high selectivity, rapid kinetics and material safety. Herein, we develop a modified granular activated carbon (GAC) using poly(diallyldimethylammonium chloride) (PDDA), a cationic polyelectrolyte widely used in water-treatment processes. The PDDA-GAC exhibits high ClO4⁻ selectivity against common competing anions and rapid adsorption kinetics, reaching saturation within 10 min. The remarkable performance is attributed to a unique surface-confined functionalization. The enhanced surface hydrophobicity (water contact angle: 71.2°) favors the enrichment of weakly hydrated ClO4⁻, which is then rapidly captured via strong electrostatic interaction (∼70 kcal mol-1) with readily accessible quaternary ammonium groups, minimizing intraparticle diffusion resistance. In fixed-bed treatment of source water containing 500 μg L-1 ClO4⁻, PDDA-GAC increases the treatable volume before breakthrough at 70 μg L-1 from 950 to 3250 bed volumes, compared to pristine GAC, and maintains excellent reusability. Overall, this work provides an efficient, rapid, and safe adsorbent platform with strong potential for full-scale ClO4⁻ removal.