Macroporous Polystyrene Resins as Adsorbents for the Removal of Tetracycline Antibiotics from an Aquatic Environment

Six macroporous polystyrene resins (strong-acid resins D001, D061, D072, and NKC-9, strong-base resin D201, and alkalescent resin D370) were selected as adsorbents for removing tetracycline (TC) and doxycycline hydrochloride (DC) from aqueous solutions. The solution pH and ionic strength had significant effects on the sorption of TC and DC. The basic resins D201 and D370 exhibited strong sorption capabilities (70.08-105.60 mg/g) at pH 4-9, but strong-acid resins showed good sorption abilities only under acidic conditions of pH 2-3 (83.30-95.78 mg/g). The inhibitory effect of the ionic strength was much weaker for D370 than for D201. The adsorption ratio of TC and DC on D201 and D370 were all above 90% when the amount of adsorbent exceeded 50 mg. By performing kinetic experiments, we determined that the pseudo-second-order model fit the data best for DC sorption on the six resins and TC sorption on D201 and D370, but the pseudo-first-order model fit the data of TC sorption on the four strong-acid resins better at pH 7.0. Intraparticle diffusion was not the only rate-controlling step, and an initial external mass transfer or chemical reaction might have existed in the sorption process. The Langmuir equation was the best isotherm equation to describe the sorption with a monolayer sorption maximum larger than 98.04 mg/g under all temperatures. Thermodynamic studies showed that the sorption of TC and DC on the resins was thermodynamically feasible and spontaneous. (c) 2014 Wiley Periodicals, Inc.