Preparation And Photocatalytic Performance Of N-doped TiO₂/MoS₂ Composites

As a new development technology,photocatalysis has been widely used in the research of water pollution treatment,hydrogen production from photolysis water and dye-sensitized solar cells.Titanium dioxide（TiO₂）is an oxide semiconductor material,which has the advantages of non-toxicity,harmlessness,low price,stable chemical properties,and has attracted much attention in this field.However,the photocatalytic activity of TiO₂ is limited by its wide band gap（anatase,～3.2 e V）,fast photogenerated electron-hole recombination,which seriously affect its application process.In this paper,non-metallic elements N and MoS₂ are used to modify TiO₂ to improve its photocatalytic activity.MoS₂/TiO₂ nanocomposite,N-doped TiO₂ sphere and N-doped TiO₂/MoS₂ composite are synthesized by sol-gel method combined with hydrothermal method.Scanning electron microscope（SEM）and transmission electron microscope（TEM）and other characterization methods were used to study its crystal form,structure and morphology,and methylene blue was used as a degradation substrate to evaluate sample photocatalytic activity.The main contents are as follows:（1）MoS₂/TiO₂ nanocomposites were synthesized by sol-gel method combined with hydrothermal method.The preparation process of the powder was optimized,and the structure,morphology and photocatalytic activity of the powder were studied.The results show that the prepared MoS₂/TiO₂ nanocomposite TiO₂ is an anatase phase with a particle size of about 10 nm,and MoS₂ exists on the surface of TiO₂ particles in the form of 2 nm quantum dots.When the Mo/Ti molar ratio is 1:7,MoS₂/TiO₂nanocomposites have the highest adsorption capacity for methylene blue,with a maximum adsorption capacity of 32.299 mg/g.When exposed to light for 60 min,the degradation rate of methylene blue by MoS₂/TiO₂ nanocomposites was 28.2%,and its pseudo-first-order rate constant k value was 1.25 times that of TiO₂.（2）N-doped TiO₂ spheres were synthesized by sol-gel method combined with hydrothermal method,and the process conditions were improved by changing single variables:reaction temperature,reaction time,calcination temperature,and N/Ti molar ratio.The results show that the diameter of the N-doped TiO₂ sphere is about 3μm,and the sphere is composed of nanoparticles with a size of about 10 nm.Compared with TiO₂,the sphere is a mesoporous material with a larger specific surface area and pore size,and a wider pore size distribution.3N-TiO₂ has the best photocatalytic performance.Under simulated sunlight,the degradation rate of methylene blue can reach 45.1%in 100 min.（3）MoS₂ was grown in situ on the surface of 3N-TiO₂ spheres by hydrothermal method to synthesize 3N-TiO₂@MoS₂ composite,and the crystal form,structure,morphology and photocatalytic activity are studied.The results show that MoS₂ grows vertically on the surface of 3N-TiO₂ spheres with a diameter of about 150 nm,good dispersion and irregular shape.When exposed to simulated sunlight for 160 min,the degradation rate of methylene blue by 3N-TiO₂@MoS₂ can reach 96.7%,and its pseudo-first-order rate constant k value is 0.02251 min^-1,which is 5.9 times that of3N-TiO₂.（4）MoS₂ was grown in situ on the surface of the 3N-TiO₂ sphere prepared by hydrothermal method to synthesize a 3N-TiO₂/MoS₂ composite material with controlled morphology.The optimal Mo/Ti molar ratio of 3N-TiO₂/MoS₂ composite material was explored,and its structure,morphology,light absorption,photocatalytic activity and stability were studied.The results show that MoS₂ successfully grows on the surface of 3N-TiO₂ spheres with a diameter of about 500 nm and good dispersion.The introduction of MoS₂ makes the 3N-TiO₂/MoS₂ composite material have a good absorption capacity for visible light.When Mo/Ti is 1:6,the band gap value is reduced to 2.05 e V.Under this condition,the photocatalytic activity of the prepared3N-TiO₂/MoS₂ composite material was significantly improved,and the degradation rate of methylene blue was as high as 97.9%after 100 min of light exposure.In addition,the 3N-TiO₂/MoS₂ composite material still has high activity after multiple degradations.