Interface Engineering And Study On The Visible Light Photocatalytic Activity Of MoS₂ And TiO₂ Heterojunction

Semiconductor photocatalytic technology is one of the important ways to solve the two serious problems facing human beings,namely environmental pollution and energy crisis.The use of semiconductor photocatalytic technology to degrade pollutants and decompose water into hydrogen is one of the research hotspots in the energy field.However,currently most of the photocatalytic materials show low efficiency.The key factors affecting the improvement of photocatalytic efficiency include:full absorption and utilization of sunlight;effective separation and transport of carriers;and chemical reaction of redox on the surface.In recent years,domestic and foreign researchers have achieved excellent photocatalytic efficiency by constructing semiconductor heterojunction photocatalytic composite materials to regulate photogenerated electron-hole separation,migration and transport.In this paper,heterojunction is constructed by two kinds of semiconductor materials,molybdenum disulfide and titanium dioxide with matching band gaps and electronic structures.The interfacial structure of the heterojunction is adjusted:effective transfer of interface charges;effective utilization of large interface specific surface area;strong interfacial charge binding improves the photocatalytic efficiency of the composite.The main research content is as follows:First,in the second chapter,hydrothermal method was used to synthesize titanium dioxide nanowire array film on titanium substrate.By changing the molar ratio of molybdenum source?molybdenum disulfide?and sulfur source?thioacetamide?,different loadings of molybdenum disulfide-titanium dioxide?MoS₂-TiO₂?composite materials were synthesized.The XRD,Raman,SEM,TEM,UV-vis and other characterization methods have proved that MoS₂ nanosheets with the hexagonal phase are wrapped in TiO₂nanowires of the anatase phase,forming heterojunction.And the absorption of the composite material extended to the visible light region with the increase of MoS₂ loading.Then the fluorescence and photocurrent of the composites were tested and analyzed.The results showed that the fluorescence intensity gradually decreased with the increase of MoS₂ loading,and the photocurrent gradually increased,indicating that the separation efficiency of photogenerated electrons and holes was enhanced.The degradation of organic pollutants for a series of composite materials were further studied under visible light.The results showed that the RhB degradation rate of 6%-MoS₂-TiO₂ as photocatalyst composite film was about 90%under visible light within 1 h.The photocatalytic efficiency of composites is higher than that of TiO₂nanowire array film,because the formation of heterojunction promotes the effective separation and transport of interface photogenerated electrons and holes.In the third chapter,PS/TiO₂/MoS₂ composites were synthesized by PS spheres?polystyrene microspheres?as a template by two-step hydrothermal method,and then annealed under a nitrogen atmosphere to form hollow structure of C/TiO₂/MoS₂ composites material.The morphologies and crystal structure of the materials were characterized by SEM,TEM,XRD,and Raman.The results show that PS/TiO₂/MoS₂ is spherical,and C/TiO₂/MoS₂ formed after annealing is hollow structure.TiO₂ and MoS₂belong to the anatase phase and the hexagonal phase,respectively,and Raman results show the presence of graphite carbon.UV-vis indicates that the absorption of C/TiO₂/MoS₂ in the visible light region is significantly enhanced.The results of fluorescence spectroscopy and photocurrent analysis show that the fluorescence intensity of C/TiO₂/MoS₂ is the lowest,and the photocurrent is significantly higher than that of hollow spheres of TiO₂.This is due to the formation of heterojunction and the increase of specific surface area promoting the separation and transport of photogenerated electrons and holes.Lastly,the photocatalytic efficiency is significantly improved.Then the photodegradation dyes under visible light were evaluated for the composites and hydrogen generation under full spectrum was performed.The results showed that RhB degraded about 92%within 2 h under visible light with C/TiO₂/MoS₂ as photocatalyst and that he rate of hydrogen production under full-spectrum irradiation was 37.08?mol/?g·h?.The photocatalytic efficiency significantly improved than TiO₂ hollow spheres.The improvement of the catalytic efficiency of C/TiO₂/MoS₂ is due to the change of the specific surface area of the material,the presence of graphite carbon and the formation of heterojunction between TiO₂ and MoS₂,which together promote the separation and transport of photogenerated electrons and holes.Because of the strong restrained interface between the two materials,it facilitates the effective transfer of interface charges.In the fourth chapter,we used acetic acid to adjust the pH value to regulate the surface charge of MoS₂ and TiO₂.Then the surface of the two materials is oppositely charged and can increase the interface contact area of MoS₂ and TiO₂?the material used in Chapter 4 is synthesized in the previous two chapters?to synthesize MoS₂-TiO₂ composites.A series of analytical tests were performed with the pH-adjusted composite material?P-TiO₂-MoS₂?and the mechanically-composite material?M-TiO₂-MoS₂?.The results of light absorption spectroscopy showed that the absorption of both P-TiO₂-MoS₂ and M-TiO₂-MoS₂ extends to the visible region.But the fluorescence intensity of P-TiO₂-MoS₂ is significantly lower,indicating that the probability of electron and hole recombination decreased.After that,the photodegradation dyes under visible light were evaluated for the composites and hydrogen generation under full spectrum was performed.The results showed that P-TiO₂-MoS₂ as photocatalyst degraded about80%of RhB within 2 h,while the rate of hydrogen production under full spectral irradiation was 28.8?mol/?g·h?.The photocatalytic performance of two kinds of composite materials is lower.It may be due to the defects of the prepared composite material that acted as the electron-hole recombination center.