Preparation Of Titanium Dioxide Hollow Composites And Their Photocatalytic Properties

Environmental pollution and energy shortage have been the major issue and must be resolved in the 21 century.Semiconductor photocatalytic technology has broad application prospects in the use of solar energy and environmental pollution.TiO2 semiconductor photocatalyst has been widely used in pollution treatment,air purification,antibacterial,self cleaning materials,hydrogen production and so on,owing to its non-toxic,cheap,low environmental impact,high stability and relatively high photocatalytic activity.However,broader application in real life of pure TiO2 is still limited due to its relatively wide band gap that can hardly absorb the visible light and rapid recombination of photogenerated electron-hole pairs making the low quantum efficiency.In view of the above problems,in this dissertation,TiO2 hollow spheres were selected as based materiai,and then modified with noble metal nanoparticels,coupling with graphene and semiconductor,doping with non-metal to improve the light absorption range and reduce the recombination of electron hole pairs to enhance the photocatalytic activity.The main points could be summarized as follows:1.r-GO/Au/TiO2 Sandwich-like Nanostructure Hybrid Shellsr-GO/Au/TiO2 hollow hybrids with high surface area and visible light response were synthesized using SiO2-NH2 spheres as templates,followed by graphene oxide and Au nanoparticle deposition and TiO2 coating through electrostatic interaction and sol method,and then post-treatments of template removal and calcination.The r-GO/Au/TiO2 hollow hybrids were characterized by TEM,XRD,STEM,EDS mapping and N2 adsorption-desorption.The photocatalytic performance of as-prepared r-GO/Au/TiO2 hollow hybrids was investigated by degradation of Rhodamine B,Methylene blue(MB)and Methyl orange(MO)under the irradiation of UV,visible light,and simulated daylight.The results show that the rate constant of r-GO/Au/TiO2 catalyst under visible light and simulated sunlight degradation of Rhodamine B are 0.012 and 0.029 min-1 respectively,and increased by 4.3 and 0.75 times while compared with the r-GO/TiO2 catalyst(k=0.0023 and 0.017 min-1).The prepared r-GO/Au/TiO2 hybrids also exhibited enhanced photocatalytic activity on degradation of MB and MO under visible light and simulated daylight.Mesoporous r-GO/Au/TiO2 hollow hybrid is a kind of photocatalytic material with excellent performance and application prospect.2.Au@r-GO/TiO2 Yolk@Shell Nanostructure HybridsOn the basis of the previous study,by structure optimization and reducing the amount of Au nanoparticles,yolk@shell nanostructures of Au@r-GO/TiO2 with mesoporous shells were prepared by a sol coating process sequentially with GO and TiO2 on Au/SiO2 core/shell spheres,followed by calcination and template removal,where the silica interlayer acts as a template not only to produce the void space but also to promote the coating of the r-GO and TiO2 layer.The yolk@shell Au@r-GO/TiO2 hybrids were characterized by TEM,XRD,HRTEM,EDS mapping,N2 adsorption-desorption and UV-Vis.The results showed that the yolk@shell Au@r-GO/TiO2 hybrids exhibited excellent photocatalytic activity on degradation of organic pollution Rhodamine B and hydrogen production while compared with TiO2,r-GO/TiO2 and Au@TiO2.The photoluminescence and impedance performance test results show that the addition of graphene effectively improve the transferring of photogenerated electrons.The prepared Au@r-GO/TiO2 yolk-shell hybrids are expected to be widely used in the field of environmental treatment and.hydrogen production.3.TiO2/NiO Hollow Hybrid ShellsNoble metals are hardly for large-scale applications in real life due to their high price,how to reduce cost becomes an important research topic.In this part,coupling TiO2 with noble metal-free semiconductor to improve the photocatalytic performance of TiO2.Mesoporous hybrid shells of TiO2/NiO with high surface area,excellent adsorption capability and visible light response were prepared by sequential coating of TiO2 and NiO on SiO2 nanospheres through a combined sol and hydrothermal process followed by calcination and template removal.The TiO2/NiO hollow hybrids were characterized by TEM,XRD,HRTEM,UV-Vis and N2 adsorption-desorption.Characterization results found the surface area of hollow hybrids was significantly increrased with the introduction of NiO,the surface area of pure TiO2 hollow spheres with 90.3 m2 g-1 was increased to 114-180 m2 g-1.The prepared TiO2/NiO hollow hybrids shells exhibited higher photocatalytic activity while compared with TiO2 hollow spheres.The TiO2/NiO hollow hybrids catalyst showed the best photocatalytic performance on degradation of organic pollution and photocatalytic hydrogen production with the NiO content is 3.4 wt%.4.Ni0/TiO2/C Hollow Hybrid ShellsOwing to the inherent poor conductivity of metal oxide semiconductors hinders the efficient transfer of excitons,leaving room for further improvement of the photocatalytic activity of NiO/TiO2 p-n heterojunctions.In this part,Carbon-incorporated mesoporous NiO/TiO2(NiO/TiO2/C)hybrid shells as low-cost and highly efficient visible light photocatalysts have been developed.The NiO/TiO2/C hybrid shells were synthesized by choosing polystyrene nanospheres as templates,followed by TiO2 and NiO coating,and finally the calcination post-treatment to carbonize PS with the aid of metal oxides.Polystyrene nanospheres serve dual purposes as both a template to ensure the hollow structure and the electrically conductive graphite carbon source.The NiO/TiO2/C hollow hybrids were characterized by TEM,XRD,HRTEM,UV-Vis and N2 adsorption-desorption isotherms.The results of photocatalytic degradation of organic pollution and photocatalytic hydrogen production showed that NiO/TiO2/C(800 ℃)exhibited the best visible light photocatalytic activity.Compared with TiO2/NiO,the photocatalytic performance was further improved with the introduction of graphitized carbon,the photocatalytic hydrogen production rate(356 μmol h-1 g-1)increased nearly doubled(180 μmol h-1 g-1).5.C,N-Codoped TiO2 Hollow Hybrid ShellsDoping TiO2 by nonmetal is the effective way to improve the photocatalytic activity.Mesoporous C/N-TiO2 hollow hybrids have been successfully fabricated using polyaniline(PANI)as the source of C/N,and PS/PANI hybrids as template.The C/N-TiO2 hollow hybrids were characterized by TEM,XRD,HRTEM,UV-Vis and N2 adsorption-desorption isotherms.The incorporation of C/N into the TiO2 lattice leads to the formation of a new mid-gap energy state,in detail,the C/N 2p band above the O 2p valence band,which eventually decreases the band gap of TiO2.Results of photocatalytic degradation of organic pollution and hydrogen production under visible light showed that C/N codoping can remarkably enhance the photocatalytic performance of TiO2,while compared with TiO2(600)hollow spheres and C-TiO2(600)hollow hybrids.C/N-TiO2(600)hollow hybrids exhibited the best photocatalytic netivity,the apparent reaction rate of C/N-TiO2(600)for degradation of RhB pheool are 0.022 and 0.012 min-1,respectively.The highest H2 production activity,as observed for C/N-TiO2(600)hollow hybrids,is about 291 μmol h-1 g-1 with 0.9%apparent quantum efficiency.The excellent photocatalytic performance of C/N-TiO2 hollow hybrids indicated that they can be used as potential as low-cost but powerful visible light photocatalysts.