Vanadium dioxide nanoparticles as a promising sorbent for controlled removal of waterborne fluoroquinolone ciprofloxacin

Abstract

As recognized by international agencies, the uncontrolled release of antibiotics into global water resources have raised serious water security concerns. Herein, the uptake of a known persistent fluoroquinolone agent (ciprofloxacin; CIP) was studied by characterization of the adsorption properties of a novel metal oxide in aqueous media. Belt-like nanostructured vanadium dioxide (VO2) with specific surface area of 27.6 m2/g was prepared via an hydrothermal process that revealed exceptional chemical and physical properties related to its use as an adsorbent for CIP. The efficiency of the adsorption process was established using the Box–Behnken design (BBD) to determine optimal operational parameters: pH (4–10), contact time (5–60 min), CIP level (25–100 mg/L), and VO2 dosage (0.1–0.5 g/L). The BBD model enabled determination of the optimum CIP removal efficiency by considering different variables such as the adsorbent dosage, mixing time, pH, and CIP concentration. According to the BBD model, the optimized parameters for the highest uptake of CIP (theoretically 100%) are listed: pH 7, mixing time ~ 58.3 min, CIP concentration (27.6 mg/L), and VO2 dosage (0.49 g/L). The maximum adsorption capacity of CIP was calculated as 102.2 mg/g by the Langmuir isotherm model. The pseudo-second order kinetic model revealed that chemisorption was a rate-limiting step for the kinetic uptake process, in agreement with an ion-exchange mechanism based on the role of ionic charge on the adsorbate and adsorbent at the optimized conditions. The separation factor (0.01–0.09) values revealed that the process of CIP removal by VO2 is favorable. Regeneration of the VO2 adsorbent was demonstrated by use of a diluted HCl solution, where a slight decrease (ca. 10%) in the adsorption performance was evidenced over several cycles of adsorption-desorption.