Enhanced adsorption of caprolactam on phenols-modified Amberlite XAD16

Abstract Phenol, catechol, and pyrogallol were employed as the hydrogen-bond donors to chemically modify the commercial adsorbent Amberlite XAD16 via Friedel-Crafts reaction, and three phenols-modified XAD16 were named as, XAD16-Ph(OH), XAD16-Ph(OH)2, and XAD16-Ph(OH)3 respectively. The resulting polymers had porous parameters including Brunauer-Emmett-Teller (BET) surface area (SBET) and total pore volume (Vtotal) similar to Amberlite XAD16, however the oxygen (O) content was remarkably increased after the Friedel-Crafts reaction in the presence of anhydrous FeCl3 as catalyst. The synthesized polymers had larger equilibrium adsorption capacities toward e-caprolactam (qmax = 69.2 mg/g) than Amberlite XAD16 due to the enhanced adsorption contributed by hydrogen bonding between the phenolic hydroxyl groups uploaded on the polymers and the carbonyl of e-caprolactam (CPL). Experimental data indicated that the removal percentage of CPL reached 93.2% at a concentration of 0.2840 g/25 mL for XAD16-Ph(OH)2 while the equilibrium data were fitted by the Freundlich and Langmuir models, and the kinetic data were described by the pseudo-second-order rate equation and characterized by the micropore diffusion model.