Preparation And Enhanced Photocatalytic Performance Of MOFs-derived TiO₂-based Composites

With the acceleration of modernization process in the world,the problem of environmental pollution has become more and more serious,semiconductor photocatalysis is considered as one of the ideal ways to solve environmental problem.Among many semiconductor materials,TiO₂ is widely used in the field of photocatalysis due to its good chemical stability,non-toxicity,low cost and easy preparation.However,the high photo-generated electron-hole recombination rate and the narrow photoresponse range limit the practical application of TiO₂.This paper aims at improving the photocatalytic activity of TiO₂by constructing heterojunctions with narrow band-gap semiconductor materials and introducing oxygen vacancy based on the MOFs-derived TiO₂.1.The morphology of TiO₂ was controlled by using Ti-MOFs（MIL-125）as self-sacrificing template,and then Zn In₂S₄/TiO₂ composites were fabricated by in-situ growth of Zn In₂S₄on MOFs derived TiO₂.The results showed that the construction of heterojunction increased the specific surface area,widened the visible response range,reduced the band gap,and inhibited the recombination of photo-generated electron-hole pairs of TiO₂.Photocatalytic experiments showed that the construction of the heterojunction could effectively improve the photocatalytic degradation activity of TiO₂ toward Rhodamine B（Rh B）and tetracycline（TC）.When the molar ratio of Zn In₂S₄ and TiO₂ was 0.4:1,Zn In₂S₄/TiO₂-II possessed the highest photocatalytic degradation efficiency（93%for Rh B and 90%for TC）within 60 min.Recycled photocatalytic experiments exhibited that Zn In₂S₄/TiO₂-II still remained good degradation activity after five reused tests.Therefore,efficient and stable TiO₂-based photocatalyst can be prepared by using MOFs as self-sacrificing template and constructing heterojunction with Zn In₂S₄.2.Cd S nanoparticles were further deposited on the surface of Zn In₂S₄/TiO₂ binary composites to form Cd S/Zn In₂S₄/TiO₂ ternary composite photocatalysts.The results showed the ternary composite possessed wider the visible response range and higher the separation and migration rate of photo-generated carrier pairs than that of Zn In₂S₄/TiO₂ composite.The photocatalytic degradation experiments of Rh B and TC showed that the ternary composite had higher photocatalytic activities than the binary composite.When the mass ratio of Cd S and Zn In₂S₄/TiO₂ was 0.5:1,Cd S/Zn In₂S₄/TiO₂-II exhibited the highest photocatalytic degradation performance（95.3%for Rh B and 91.8%for TC）within 40 min,the recycled photocatalytic experiments the degradation rates of Rh B and TC still remained at about 80%and 74%after five reused tests.Therefore,constructing Cd S/Zn In₂S₄/TiO₂ ternary composites based on MOFs-derived TiO₂ can significantly improve the photocatalytic activity of TiO₂.3.A novel Zn In₂S₄/TiO_2-X composite was constructed by introducing oxygen vacancy into the as-synthesized Zn In₂S₄/TiO₂binary composite,and the photocatalytic activity of the composite toward Rh B was studied.The results showed that the introducing of oxygen vacancy could further broaden the photoresponse range of TiO₂and improve the separation rate of photo-generated carrier pairs.Photocatalytic degradation experiments showed that the degradation rate of Zn In₂S₄/TiO_2-X was 94%within 40 min,which was 1.2 times higher than that of Zn In₂S₄/TiO₂composite.The recycled photocatalytic experiments proved that Zn In₂S₄/TiO_2-Xstill had good degradation efficiency（73%）after after five reused tests.Therefore,the study shows that the photocatalyst performance of TiO₂can be effectively improved by constructing Zn In₂S₄/TiO_2-X composites based on the MOFs-derived TiO₂.