Fabrication Of CdS Based Photocatalysts And The Photocatalytic Degradation Performance On Ibuprofen

Pharmaceuticals and personal care products（PPCPs）have been widely detected in environment with the abuse use of PPCPs.PPCPs are toxic to aquatic organisms,and pose potential risks to human health through the food chain.Photocatalytic oxidation,which is a kind advanced oxidation processes（AOPs）,is favored by researchers because its mild reaction conditions is and only requires sunlight as energy input.The key to photocatalytic technology application in large-scale is developing a safe,highly efficient,and stable photocatalyst.Cd S is one of the narrow bandgap（2.4 e V）semiconductors,which has excellent absorption performance for visible-light.However,the photochemical properties of Cd S are unstable,and photocorrosion occurs by holes in the valence band under light irradiation.Ti O₂ semiconductor is a relatively inexpensive,non-toxic,and stable photocatalyst,while it can only be excited by ultraviolet light（4%of solar spectrum）due to its 3.2 e V bandgap.Constructing heterojunctions between two kinds of semiconductors to form the composite photocatalysts is an effective way to improve the photocatalytic performance.Therefore,in this study,a photocatalyst was synthesized with rational design and exhibited high photocatalytic activity and stability.The main conclusions are as follows:Firstly,Cd S/Ti O₂composite photocatalyst was prepared via a simple hydrothermal method.Cd S/Ti O₂ formed a Type-Ⅱheterostructure,which promoted the electron transfer at the interface of the semiconductors and thereby enhanced photocatalytic efficiency.73.61%of ibuprofen was decomposed after visible-light irradiation for 180 min in the presence of Cd S/Ti O₂（molar ratio of Cd S and Ti O₂was 1:2）.The dominant reactive species accounting for ibuprofen degradation are hole（h⁺）,superoxide radical（·O₂^-）,and hydroxyl radicals（·OH）.The enhanced absorption properties in the region of 400～520 nm and the rapid electron transfer at the interface of Type-Ⅱheterostructure are the main reasons for the enhanced photocatalytic activity of Cd S/Ti O₂.To futher improve the photocatalytic activity and magnetic separation ability of the photocatalyst,Cd S/Fe₃O₄/Ti O₂composite was prepared by using the two-steps method including coprecipitation and hydrothermal.The composite photocatalyst has excellent long-wavelength light absorption ability,rapid electron separation transfer.The introduced Fe₃O₄ particles enabled the photocatalyst to be easily separated by an external magnetic field,and promoted the construction of the Z-scheme photocatalytic system as an electronic mediator,which can effectively separate the electron-hole pairs in the process of photocatalytic reaction and hold their redox potential.94.16%of ibuprofen was decomposed after visible-light irradiation for 180 min in the presence of Cd S/Fe₃O₄/Ti O₂（molar ratio of Cd S and Ti O₂was 1:2,1 g/L photocatalyst,10 mg/L ibuprofen）,and the reaction rate was significantly higher than that in the presence of Cd S or Cd S/Ti O₂.The dominant reactive species accounting for ibuprofen degradation are h⁺and·OH.The Z-scheme heterostructure contributes to the holes transfer in Cd S valence band,thus weaken photocorrosion process,and makes the composite photocatalyst has favorable stability.The degradation rate could still reach 65.5%after reused for five recycles.To sum up,this study provides an easy method to synthesize a novel Cd S-based Z-scheme magnetic composite photocatalyst,which can be efficiently used to degrade PPCPs under visible-light irradiation.