Abstract
Antibiotics pose potential ecological risks in the water environment, necessitating their effective removal by reliable technologies. Adsorption is a conventional process to remove such chemicals from water without byproducts. However, finding cheap adsorbents with satisfactory performance is still a challenge. In this study, polystyrene microspheres (PSM) were enhanced to adsorb tetracycline by surface modification. Simple urea immersion was used to prepare urea-immersed PSM (UPSM), of which surface groups were characterized by instruments to confirm the effect of immersion. Tetracycline hydrochloride (TC) and doxycycline (DC) were used as typical adsorbates. The adsorptive isotherms were interpreted by Langmuir, Freundlich, and Tempkin models. After urea immersion, the maximum adsorption capacity of UPSM at 293 K and pH 6.8 increased about 30% and 60%, achieving 460 mg/g for TC and 430 mg/g for DC. The kinetic data were fitted by first-order and second-order kinetics and Weber–Morris models. The first-order rate constant for TC adsorption on UPSM was 0.41 /h, and for DC was 0.33 /h. The cyclic urea immersion enabled multilayer adsorption, which increased the adsorption capacities of TC on UPSM by two to three times. The adsorption mechanism was possibly determined by the molecular interaction including π–π forces, cation-π bonding, and hydrogen bonding. The simple surface modification was helpful in enhancing the removal of antibiotics from wastewater with similar structures.
Highlights
Antibiotics are a concern as contaminants in the water environment due to their potential ecological risks and ubiquitous distribution in the world [1]
The surface morphologies of polystyrene microspheres (PSM) and urea-immersed PSM (UPSM) were characterized by using a scanning electron microscope (SEM; HT 7700, Hitachi Corp., Tokyo, Japan)
60 mg of PSM or UPSM was dosed into tetracycline solutions at 5 levels of initial concentration (100–300 mg/L)
Summary
Antibiotics are a concern as contaminants in the water environment due to their potential ecological risks and ubiquitous distribution in the world [1]. With the merits of low cost, high porosity, large surface area, and adsorption capacity, have potential for commercial application [14,19,20,21,22]. One idea is to impregnate an amino group (–NH2 ) on the adsorbent surface as a neutral anion receptor to link an ester group (–COO–R) in antibiotic molecules, in order to form chelated complexes with hydrogen bond acceptors like ditopic carboxylates. Another choice is to use a carbonyl group as an electron donor to enhance the π–π interaction and cation-π bonding. The interaction between antibiotic molecules and UPSM surface is discussed
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