Hydrothermal-precipitation preparation of CdS@(Er3+:Y3Al5O12/ZrO2) coated composite and sonocatalytic degradation of caffeine

Here, we reported a novel method to dispose caffeine by means of ultrasound irradiation combinated with CdS@(Er3+:Y3Al5O12/ZrO2) coated composite as sonocatalyst. The CdS@(Er3+:Y3Al5O12/ZrO2) was synthesized via hydrothermal-precipitation method and then characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and UV-vis diffuse reflectance spectra (DRS). After that, the sonocatalytic degradation of caffeine in aqueous solution was conducted adopting CdS@(Er3+:Y3Al5O12/ZrO2) and CdS@ZrO2 coated composites as sonocatalysts. In addition, some influencing factors such as CdS and ZrO2 molar proportion, caffeine concentration, ultrasonic irradiation time, sonocatalyst dosage and addition of several inorganic oxidants on sonocatalytic degradation of caffeine were investigated by using UV-vis spectra and gas chromatograph. The experimental results showed that the presence of Er3+:Y3Al5O12 could effectively improve the sonocatalytic degradation activity of CdS@ZrO2. To a certain extent some inorganic oxidants can also enhance sonocatalytic degradation of caffeine in the presence of CdS@(Er3+:Y3Al5O12/ZrO2). The best sonocatalytic degradation ratio (94.00%) of caffeine could be obtained when the conditions of 5.00 mg/L caffeine, 1.00 g/L prepared CdS@(Er3+:Y3Al5O12/ZrO2), 10.00 mmol/L K2S2O8, 180 min ultrasonic irradiation (40 kHz frequency and 50 W output power), 100 mL total volume and 25-28 °C temperature were adopted. It seems that the method of sonocatalytic degradation caused by CdS@(Er3+:Y3Al5O12/ZrO2) displays potential advantages in disposing caffeine.