Adsorption of pharmaceuticals by novel carbonaceous materials from the leaves of Ailanthus altissima (Mill.) Swingle - Case study on the adsorption of tetracycline

Abstract

In the last two decades, there has been a growing awareness of the presence of pharmaceuticals in the aquatic environment. Antibiotics are particularly alarming because their occurrence may result in increased antibiotic resistance. Difficulties in sample preparation and removal of low concentrations of pharmaceuticals from environmental water could be overcome by their adsorption onto novel, non-polluting, and inexpensive materials. In this study, biochar prepared by pirolysis of biomass at 500°C (BC500) and 800°C (BC800) and activated carbon prepared upon treatment with ZnCl2 at 800°C (AC800) were evaluated as potential adsorbents. Ailanthus altissima was selected as a source of raw material, leaf, because it is a widespread invasive tree that negatively affects biodiversity. Tetracycline hydrochloride was selected as a model substance, since it is an antibiotic widely present in environmental water. Central composite design was employed to simultaneously investigate the effects of adsorbate solution pH, ionic strength (KCl concentration), and adsorbent mass on removal efficiency of all three adsorbents, and to find optimal conditions for studying adsorption kinetics and equilibrium on the most promising adsorbent. The removal efficiency and adsorbed mass were calculated from the HPLCUV determined concentration of tetracycline post-adsorption. Under optimal conditions (10.18 mg of adsorbent, pH 4.42, and ionic strength 165mM), AC800 showed the highest affinity for tetracycline, i.e. 38.22% removal and adsorbed mass of 56.32 mg g-1 compared to 14.57% and 21.48 mg g-1 (BC500) and 18.82% and 27.73 mg g-1 (BC800). Removal efficiency of AC800 was strongly influenced by the adsorbent mass and solution pH. The kinetics study showed a rapid adsorption process (equilibrium attained in 120 minutes), while equilibrium studies revealed a high adsorption capacity for tetracycline (131.55 mg g-1). AC800 has been shown to be a promising novel drug adsorbent and should be further tested for its suitability in water treatment and sample preparation.