Contribution of H-bond in adsorptive removal of pharmaceutical and personal care products from water using oxidized activated carbon

Adsorption of four pharmaceuticals and personal care products (PPCPs) by activated carbon (AC) before and after oxidative modification with ammonium persulfate (APS) at different concentrations was studied. The PPCPs were selected to exhibit a wide range of acid-base characteristics, i.e., basic atenolol, neutral N,N-diethyl-meta-toluamide, weakly acidic triclosan, and acidic naproxen. The oxidized ACs (OACs) showed highly improved adsorption of the PPCPs compared with that of the pristine AC, irrespective of the acid-base properties of the PPCPs. For example, the best OAC adsorbed 93, 55, 89, 80 mg/g of atenolol, N,N-diethyl-meta-toluamide, triclosan, and naproxen, respectively, from water in 12 h; however, pristine AC adsorbed only 33, 39, 60, 39 mg/g, respectively. The adsorption mechanism was explained in terms of H-bonding and a partial contribution by electrostatic and π-π interactions through analyses of the adsorptive performances and surface charges of the OACs over a wide range of pH conditions. Especially, the direction of H-bond could be clearly explained (H-acceptor: PPCPs; H-donor: OACs). OACs are a promising adsorbent for PPCPs over a wide acidity/basicity range owing to their high adsorption capacity and facile reusability.