Preparation Of Strontium Titanate Photocatalysts And Their Degradation Of Tetracycline Under Visible Light

Strontium titanate（SrTiO₃）has the advantages of low cost,simple preparation conditions,and photocorrosion resistance.It is a widely used material in the fields of photocatalytic degradation of organic pollutants,decomposition of water to produce hydrogen,and photochemical batteries.SrTiO ₃ has a band gap of about 3.2 e V.It can be modified by morphology control,co-catalyst addition,semiconductor compounding and other methods to enhance the photocatalytic performance of the material.In this paper,SrCO₃ was selected as a cocatalyst to modify SrTiO ₃.SrCO₃-SrTiO₃ and pure phase SrTiO₃ were synthesized by sol-gel and in-situ pyrolysis,and the effects of photocatalyst were compared and explored.In order to further enhance the photocatalytic performance,SrTiO ₃,SrCO₃-SrTiO₃ materials and Ag₃PO₄ were composite modified,and SrTiO ₃/Ag₃PO₄,SrCO₃-SrTiO₃/Ag₃PO₄ series composite heterojunction materials were synthesized.Through XRD,SEM,EDS,XPS,DRS,PL and Mott-Schottky systems to characterize the microstructure,morphology and optical properties of the material.In this paper,the degradation of tetracycline hydrochloride was used to evaluate the effect of photocatalytic materials,and the stability of the materials was studied.The main contents of this study include:（1）SrCO₃-SrTiO₃ and pure phase SrTiO₃ catalysts were synthesized with band gaps of 3.0 e V and 3.2 e V,respectively.SrTiO₃ has little activity under visible light.50 mg SrCO₃-SrTiO₃ was added to 200 m L of 20 mg/L tetracycline hydrochloride and irradiated under visible light for 60 min,the degradation efficiency was 62%.Cycle experiments show that SrCO₃-SrTiO₃ is very stable.（2）The band gap Eg of the Ag₃PO₄ photocatalyst is 2.25 e V.The Ag₃PO₄ catalyst degraded tetracycline hydrochloride with an efficiency of 60%under visible light irradiation for 30 min.After three cycles,the degradation efficiency of the Ag₃PO₄photocatalyst decreased by 28%,and the photocorrosion phenomenon was serious.（3）The SrTiO₃/Ag₃PO₄ heterojunction photocatalyst was prepared,and theⅡtype heterojunction photocatalytic reaction mechanism was proposed.The DRS pattern shows that the forbidden band width Eg of the prepared SrTiO₃/Ag₃PO₄ is 2.1e V.The XRD pattern shows that the prepared sample does not contain silver phase,and a small amount of silver was generated during the degradation process.·OH is the main active free radical and does not produce·O₂^-.The efficiency of SrTiO₃/Ag₃PO₄catalyst to degrade tetrahydrochloric acid under visible light irradiation for 30 min was 72.2%.After three cycles,the degradation efficiency of the SrTiO₃/Ag₃PO₄photocatalyst decreased by 14.2%.（4）SrCO₃-SrTiO₃/Ag₃PO₄ photocatalyst was synthesized,and the Z-type heterojunction photocatalytic reaction mechanism was proposed.The XRD pattern shows that the prepared sample did not contain silver phase,and a small amount of Ag⁰ generated as a redox medium at the beginning of the photoreaction,forming a stable Z-type heterojunction structure.The DRS graph shows that the photocatalyst has a band gap of 1.7 e V.Comparing the PL spectrum,it is found that the PL pe ak intensity of the SrCO₃-SrTiO₃/Ag₃PO₄ sample is the weakest,indicating that its photogenerated charge separation efficiency is the highest.During the photodegradation process,active radicals such as e^-,h⁺,·O₂^-and·OH were generated,and the abundant active species accelerate d the process of photocatalysis.The efficiency of SrCO₃-SrTiO₃/Ag₃PO₄ catalyst in the degradation of tetracycline hydrochloride under visible light irradiation for 30 min was 85.9%.After three cycles,the degradation efficiency of SrCO₃-SrTiO₃/Ag₃PO₄ photocatalyst decreased by 7.9%and remained basically stable.The series of photocatalysts with visible light activity synthesized in this thesis,especially the SrCO₃-SrTiO₃/Ag₃PO₄ catalysts have a stable Z-type heterojunction structure,and have a highly efficient photocatalytic degradation ability,which provides a new idea for the application and promotion of strontium titanate photocatalytic materials.