Study On The Preparation And Properties Of TiO₂-based Heterostructures

In this thesis,based on the morphological synthesis of TiO₂ materials,the preparation and properties of heterojunctions,which composed of TiO₂ as the modification materials and the matrix materials,were studied.The thesis attends to synthesize different morphologies of TiO₂ materials and study the effects of microstructure,phase composition and defects on their properties.TiO₂ as the modification materials are used to form composites with Ag nanowires and rGO,as well as their properties are researched.TiO₂ as the matrix material,we introduce SnO₂ to vary the morphologies of heterojunctions,and study their applications in photocatalysis,lithium-ion batteries,and sensing.The specific research contents are as follows:1.The morphological synthesis of TiO₂ materials and their properties study.?1?TiO₂ hollow structure makes full use of incident lights to enhance its own photocatalytic properties.Monodispersed mesoporous anatase TiO₂ hollow microspheres with controllable morphology and size are prepared via thioglycolic acid?TGA?chemically induced self-assembly.We study the preparation process on the morphologies,and discuss the formation mechanism of TiO₂ hollow spheres.Among them,the self-assembly of Ti-oxo clusters formed by hydrolysis of tetrabutyl titanate?TBT?played a key role in the formation of spherical structure,then with the synergistic effects of thermodynamics?Ostwald ripening process?and kinetics?gas release?,various morphologies are controlled to prepare.In the photocatalytic degradation of organic pollutants and photocatalytic hydrogen production,hollow spheres exhibit superior performance compared to solid sphere structures.?2?Anatase and rutile mixed-phase hollow TiO₂ hierarchical boxes were prepared by a Topotactic synthetic method.The CaTiO₃ microcubes were used as sacrificial templates to make the phases distribute uniformly in the hollow boxes.When the phase composition of the sample is similar with that of P25?⁸0%anatase and 20%rutile?,it exhibits an excellent photocatalytic properties.Anatase and rutile are closely contacted in the hierarchical boxes,which improve the separation efficiency of photo-generated carriers,and the hollow structure can make full use of incident light.As a result,the experimental results show that in the photocatalytic degradation of methylene blue organic pollutants,the degradation rate of the TiO₂ hierarchical hollow structure is 2.7times higher than that of P25 nanoparticles.?3?TiO₂-B samples self-doped by Ti³⁺were prepared using a mixed solvent of ethylene glycol and water.In the preparation process,ethylene glycol was oriented adsorbd on the surface of TiO₂ to form a layered structure.The viscosity of the solvent and reductivity induce the material to form Ti³⁺.The number of lamellae and the thickness of the TiO₂-B spheres can be easily adjusted.The layered structure of TiO₂ has a large specific surface area and shows excellent photocatalytic performance due to the presence of Ti³⁺in the TiO₂-B material.After H₂O₂ oxidation treatment with the sample,the number of surface defects in the TiO₂-B sample decreases,which reduces the photocatalytic activity of the samples.It indicates that the defect plays an important role in the photocatalytic performance.2.Different morphologies of silver nanowire/titanium dioxide?Ag NW@TiO₂?composite photocatalyst.AgNW@TiO₂ necklace-like heterostructures were prepared for the first time.They were prepared by a two-step synthesis method.Firstly,uniform silver nanowires were prepared and then TiO₂ was deposited on the surface.The use of thioglycolic acid?TGA?molecules as linkers solves the problem of lattice mismatch between the Ag NW core and TiO₂.The addition amount of water and the dielectric constant of the solvent are important factors in the formation of necklace-like heterostructures.By changing the amount of tetrabutyl titanate?TBT?,the diameter of the TiO₂ beads can be changed.The photocatalytic activity of necklace-like Ag NW@TiO₂was evaluated by degradation of methyl orange?MO?under ultraviolet?UV?light.The results show that the molar ratio of TiO₂ to Ag and the diameter of TiO₂ beads have a synergistic effect on photocatalytic activity.The highest photocatalytic activity was found when the molar ratio of Ti to Ag in the TiO₂ heterostructure was 2.8.In order to improve the photocatalytic activity of AgNW@TiO₂ material,three kinds of Ag NW@TiO₂heterostructures with core shell,necklace-like,and particle deposited were prepared.The existence of TGA and the solvents polarity to regulate the coating state of TiO₂ on the Ag NW surface.The molar ratio of TiO₂ to Ag is critical to the photocatalytic activity.The close contact between Ag NW@TiO₂ samples with core-shell structure shows superior performance compared to the other two samples.3.Fabrication rGO and TiO₂ heterostructures to enhance their photocatalysis.Full spectrum Z-scheme rGO/TiO₂-Bronze?TiO₂-B?/W₁₈O₄₉ photocatalyst is fabricated by a two-step solvothermal method.The ternary heterostructure has ability to absorb sunlight ranging from UV to near infrared?NIR?regions,which makes full use of solar energy for efficient photocatalytic degrading organic pollutants.TiO₂-B nanosheets tightly attached on the rGO firstly,and then W₁₈O₄₉ nanowires grew on rGO/TiO₂-B.The light absorption intensity increased with the addition of rGO in the composite,as well as the localized surface plasmon resonance effect arising from the nonstoichiometric ratio of W₁₈O₄₉,which are in favour of the absorption range of the rGO/TiO₂-B/W₁₈O₄₉composite material broadening to NIR range.Z-scheme photocatalytic mechanism of rGO/TiO₂-B/W₁₈O₄₉ is verified by electron spin resonance test.The conduction band of TiO₂-B and the valence band of W₁₈O₄₉ are used in the photocatalytic degradation of rhodamine B,facilitating the efficient separation of photogenerated carriers.As a result,the rGO/TiO₂-B/W₁₈O₄₉ heterostructure exhibits an excellent photocatalytic performance under full spectrum irradiation.4.The morphology and phase composition of TiO₂ are regulated by SnO₂ as well as studied in photocatalysis,Li-ion batteries,and gas sensing areas.The CaTiO₃ precursor was prepared by a Topotactic synthetic method and converted into TiO₂ by ion exchange.The waxberry-like anatase/rutile mixed-phased TiO₂ hollow structure was successfully prepared,and an appropriate amount of SnCl₄ was added in the initial stage of the reaction,the TiO₂@SnO₂ hierarchical structure can also be successfully prepared.The structural characteristics of the samples are that rutile TiO₂ nanorods nearly radial alignment growth on the external surface of the hollow sphere composed of anatase TiO₂and SnO₂ nanoparticles.The addition of SnO₂ not only adjusts the morphology of the product,but also changes the ratio of anatase and rutile phases in the composite.?1?In the study of photocatalytic properties,methylene blue was degraded using low-power UV light to evaluate its photocatalytic performance.The hollow structure enhances light-harvesting ability,and the appropriate proportion of phase composition improves the charge separation.SnO₂ nanomaterials were added into the TiO₂ matrix material,making that the waxberry-like TiO₂@SnO₂-5%sample exhibits an excellent photocatalytic performance and good cycle stability.?2?The synthesized TiO₂ and TiO₂@SnO₂ hierarchical structures were used as anode materials for lithium ion batteries.Compared with TiO₂ samples,the TiO₂@SnO₂-5%shows the improved lithium storage capacity,cycling performance and rate properties.After adding a small amount of SnO₂,the impedance of the TiO₂ electrode significantly decreased.The hollow hierarchical structure with different compositions provide much more active sites,and well connect interface among anatase,rutile,and SnO₂,facilitating the electron and ion transport quickly and efficiently.?3?TiO₂ hierarchical structure uniformly decorated with SnO₂ nanoparticles gives an excellent performance in the detection of triethylamine?TEA?gas.As a novel sensing material,TiO₂@SnO₂ shows a higher response in low concentration of TEA and a rapid responding speed in comparison with individual TiO₂ components.At the case of 5 ppm TEA gas under the operation temperature of 240?,the response value of TiO₂@SnO₂sample is up to 21.6,which is three times higher than that of TiO₂ sample.The responding speed of TiO₂@SnO₂ sensors elevates 28%in comparison with TiO₂.