Study On Preparation And Photocatalytic Properties Of TiO₂-based Heterojunction

Human demand for fossil fuels is improving,also brings environmental pollution and energy shortage problems,for which photocatalysis is an effective solution.Titanium dioxide（TiO₂）is one of the most mature semiconductor photocatalysts,which has been widely used in photocatalytic degradation and solar cells due to its cheap price,non-toxicity and high catalytic activity.However,it has some inherent defects,a large forbidden band width and rapid compounding of photogenerated carriers,which reduce its photocatalytic activity.Constructing heterojunctions using metal sulfides（Sn S₂,Mo S₂）and metal organic skeletons（ZIFs）can effectively improve the photocatalytic activity and photoelectrochemical performance of TiO₂,and the main work in this paper is as follows.（1）Z-type heterojunction TiO₂/Sn S₂/Mo S₂（TOSSMS）nanorod arrays were successfully prepared by sequentially compounding Sn S₂ nanoparticles and Mo S₂nanosheets on rutile TiO₂ nanorod arrays by a two-step hydrothermal method.The morphological characteristics,compositional composition,energy band structure and optical properties of the samples were also investigated.The results showed that Sn S₂and Mo S₂ could effectively broaden the TiO₂ light absorption range and provide more reactive sites,thus improving the photocatalytic and photoelectrochemical properties of TiO₂.Under visible light irradiation,the TOSSMS sample had the best photocatalytic performance for the organic pollutant methylene blue（MB,5 mg/L）with a degradation efficiency of 81.8%at 90 min,which was 3.4 times higher than that of the TiO₂ sample.the photocurrent density of the TOSSMS sample was 0.92 m A/cm² at a bias voltage of0 V,which was 8.4 times higher than that of the TiO₂ sample.Therefore,the construction of Z-type heterojunction can effectively suppress the compounding of photogenerated carriers and improve the TiO₂ photocatalytic and photoelectrochemical performance.（2）Ternary heterojunction TiO₂/ZIF-67/ZIF-8（TiO₂/ZIF-67-8）nanospheres were successfully prepared by preparing anatase TiO₂ nanospheres by hydrothermal method,and then ZIF-67 and ZIF-8 were co-modified on the surface of the spheres by sol-gel method.The morphological structure,composition and optical properties of the samples were investigated separately by characterization,and the results showed that the TiO₂/ZIF-67-8 samples co-modified with ZIF-67 and ZIF-8 had an expanded absorption range for visible light and a large specific surface area.The photocatalytic degradation efficiency of TiO₂/ZIF-67-8 sample for MB（10 mg/L）was 81.1%in 90min under simulated sunlight,which was 4.9 times higher than that of TiO₂ sample,and the TiO₂/ZIF-67-8 sample showed the best photocatalytic activity（～100%）in alkaline（ph=12）solution.TiO₂/ZIF-67-8-67-8 sample had a photocurrent density of 36.69μA/cm²,which was 15.7 times higher than that of the TiO₂ sample.The experimental results indicate that the synergistic interaction between ZIF-67 and ZIF-8 facilitates the interfacial charge transport,accelerates the electron-hole separation rate,and effectively improves the TiO₂ photocatalytic activity and photoelectrochemical performance.