Study On Preparation Of NaTaO₃ Photocatalysts And Their Performance For Degradation Of Tetracycline In Water

Antibiotics have been used widely in agriculture,livestock and human health since their discovery due to their features of promoting the growth and inhibiting diseases.The unreasonable using of antibiotics may threaten human beings and the ecosystem.Therefore,the efficient removal of antibiotics has been a research hotspot of scholars.Photocatalytic oxidation technology provides a new way to solve the problem of antibiotic pollution in the environment due to its advantages of lower cost,simpler operation and greener environmental protection compared with traditional technology.Among many photocatalysts,NaTaO₃ has great advantages in photocatalytic decomposition of water for hydrogen production due to its unique perovskite structure of ABO₃.The conduction band（hybridized of O 2p antomic orbits）of NaTaO₃ is more negative than the hydrogen reduction potential,which makes its electrons have a strong reduction ability.However,its wide band gap and difficult separation of electron holes limit its photocatalytic research in visible light.At the same time,it has a large degree of structural tolerance and can be combined with a variety of materials to form new type of high-activity photocatalysts.In this paper,three composite photocatalyst materials,Sr-NaTaO₃,MoS₂/NaTaO₃ and Bi₄Ti₃O₁₂/NaTaO₃,were synthesized by modifying pure NaTaO₃ through metal ion doping,p-n heterojunction and Type II heterojunction construction.At the same time,various characterization methods（SEM,XRD,XPS,FT-IR and UV-vis）were used to analyze the microstructure,size,crystal,chemical elements and composition of the materials.Under the condition of xenon lamp simulating sunlight,the degradation of tetracycline solution with different composite ratios photocatalysts was studied,and the possible mechanism of photocatalytic degradation on tetracycline was discussed.The main research contents of this paper are as follows:1.Sr-NaTaO₃ was synthesized by adding strontium nitrate as Sr source in the synthesis of NaTaO₃.According to the calculation of UV-vis map and Tauc formula,the band gap of the sample was decreased and the optical response range widened after doping.The photocatalytic performance test showed that when the content of Sr reached 50%,the efficiency of the catalyst was the strongest,which was 2.1 times higher than that of pure NaTaO3.The reason for this phenomenon is that the introduction of metal ions broadens the absorption range of light and reduces the gap width.2.The p-n type MoS₂/NaTaO₃ composite photocatalyst was prepared by hydrothermal method.It was found that the flower spherical MoS₂ surrounded the cubic NaTaO₃,and there was a heterojunction interaction between MoS₂ and NaTaO₃.Moreover,the composite material had a strong light absorption intensity and was responsive to visible light.Photocatalytic experiments showed that the MoS₂/NaTaO₃ composites had strong adsorption and photodegradation abilities,and the best performance was achieved when the MoS₂ content was90%.The reason for the improvement of its photocatalytic performance was that the built-in electric field generated by the formation of p-n type heterojunction caused the separation efficiency of photogenrated carriers.3.A Type II heterojunction Bi₄Ti₃O₁₂/NaTaO₃ composite photocatalyst was prepared by solvothermal method with bismuth nitrate（Bi（NO₃）₃·5H₂O）and butyl titanate(C₁₆H₃₆O₄Ti)as bismuth source and titanium source respectively.XRD and XPS analysis showed that both substances existed in the composite and formed heterogeneous structures.The introduction of the narrow band gap Bi₄Ti₃O₁₂ extended the light response range of NaTaO₃ to the visible light and enhanced the absorption intensity of light.Further photocatalytic performance test showed that the best performance（87.8%）was obtained when the content of Bi₄Ti₃O₁₂2 was 50%in the composite.The improvement of photocatalytic performance was due to the formation of Type II heterojunction structure between the two phases,which was more effective in reducing the composite probability of photogenerated electrons and holes,and·O₂-and·OH generated under light excitation can decompose tetracycline.