Fabrication of CaWO4 microspheres with enhanced sonocatalytic performance for ciprofloxacin removal in aqueous solution

Abstract The calcium tungstate (CaWO4) microspheres were prepared with citric acid as an adjuvant by a hydrothermal process and characterized. The removal ratio of ciprofloxacin (CIP) was 15.43% ± 3.31% under ultrasonic irradiation alone at 120 min. In the presence of CaWO4, the sonocatalytic removal ratio of CIP was 27.35% ± 2.81%. When the molar ratio of calcium ions to citric acid was 4 : 1 in the synthesis process, the prepared CaWO4-4 exhibited superior sonocatalytic performance, and the removal ratio of CIP was up to 74.75% ± 1.32%. The reaction rate constant k of the sonocatalytic removal of CIP in the presence of CaWO4-4 was 7.15 and 4.73 times than that of ultrasound alone and in the presence of CaWO4, respectively. The results indicated that citric acid had a great influence on the microstructure of CaWO4 microspheres during the synthesis process, thus enhanced the sonocatalytic performance of the samples. The results of sonocatalytic mechanism suggested that the sonocatalytic decomposition of CIP was mainly due to the production of hydroxyl radicals and holes. In addition, CaWO4-4 had good stability and reusability within four recycles. These results suggested that CaWO4 microspheres had the potential applied in the sonocatalytic removal organic pollutants in aqueous solution as a sonocatalyst.