The Control And Application Of Nanocomposite Structure Titanium Dioxide And Its Physical Mechanics Behavior

Titanium dioxide(TiO2)has excellent physical and chemical properties such as electricity,mechanics,optics and thermal.It has broad application prospects in photocatalysis,photovoltaic cells,sensors and bioengineering.After years of research and development,TiO2 nanomaterials with different crystal structures,morphologies,surface states and sizes have been developed and used for different purposes.However,no breakthrough has been made in the study of nanostructural TiO2 either in mechanics or in functional applications.Unlike bulk phase,nanostructured TiO2 has quantum effect,size effect,surface effect and coupling effect.Macro-mechanical theories are not suitable for nano-scale materials in most cases.In this paper,the low-dimensional nanostructural TiO2 was taken as the research object.Firstly,the preparation,regulation and characterization methods of TiO2 nanocomposites were introduced and its physicochemical properties were studied in detail.Secondly,the properties of nanocomposites for environmental purification,energy storage and energy conversion were studied,and the related mechanisms were discussed.Thirdly,based on the first principle of quantum mechanics,we studied the micro-nanomechanical properties of TiO2 nanobelt and their effects on energy band structure and optical properties.Then,based on the theory of plates and shells mechanics,the mechanical behavior of TiO2 nanobelt and nanotube was simulated by using the equivalent continuum model,and the rationality of the theoretical model was verified by the test results of atomic force microscopy.Finally,the interaction between single-walled TiO2 nanotube and water molecules was simulated by molecular dynamics.There are seven chapters in this thesis.The main contents are as follows:(1)Carbon-silicon layers with different thickness were uniformly coated on the surface of TiO2 nanobelts by the in-situ grafting-graphitization technique.In the aspect of photocatalytic degradation of organic pollutants,the prepared nanocomposites not only have 2.5 times higher photocatalytic degradation performance than the commercial TiO2(Degussa,P-25),but also can be applied to different kinds of organic dyes.As anode materials of lithium-ion batteries,the core-shell structure can buffer the volume expansion in the discharge-charge process,even after 100th cycles,its capacity can still be maintained at a higher level.In the aspect of solar energy conversion,we used a mechanochemical method to prepare a stable and efficient photocatalyst.Under irradiation of AM 1.5G simulated light(Power:one sunlight),the optimal TiO2/MgTiO3/C photocatalyst can show a super-high solar-driven hydrogen production rate(33.3 mmol·h-1·g-1),which is much greater than the best yields ever reported for gram-scale synthesized photocatalysts.The solar-to-hydrogen(STH)efficiency reaches 1%,indicating that the photocatalysts prepared by our method has an excellent performance in restraining the recombination of photoexcited electrons and holes.(2)Basing on first principle,we studied the mechanical properties of anatase-type TiO2 nanobelt and its effects on band structure and optical properties.The results show that although the bulk anatase TiO2 is isotropic in the direction of[100]and[010],the TiO2 nanobelt exhibits anisotropy,its crystal structures,Young's modulus,failure mechanism and Poisson's ratio show different results along the two directions.In addition,we found that uniaxial stretching in both directions can affect the optical absorption of TiO2 nanosheets,but their mechanism is different.Then,we systematically studied the geometric structure,formation energy,electronic structure and mechanical properties of TiO2 nanobelt with different oxygen defects(Vo).The results exhibit that due to the lower formation energy,the more internal oxygen atoms are,the easier it is to lose.The mechanical properties of TiO2 nanobelt with or without oxygen defect have some similarities,especially in the structural damage.However,due to the absence of oxygen atoms,some mechanical properties of TiO2 nanobelt with oxygen defects have variation,which should be attributed to the change of internal crystal structure under stress conditions;(3)Based on the theory of plates and shells mechanics,we abstracted the TiO2 nanobelt and nanotube into two-dimensional thin plate model and cylindrical shell model,respectively.We discussed their mechanical behavior under load in the corresponding working environment,established their corresponding continuum or equivalent continuum mechanics model,and calculated their mechanical behavior theoretically.In order to verify the rationality of the theoretical models and provide a theoretical basis for the study of nanobelts and nanotubes of TiO2,the theoretical and experimental results were compared with the measured results of atomic force microscopy.(4)The geometric and fluid models of single-walled TiO2 nanotube and water molecules were constructed by molecular dynamics.Lennard-Jones(LJ)potential field was used to simulate the interaction of solid-liquid force,and SPC/E potential field was used to simulate the interaction between water molecules.The interaction between single-walled TiO2 nanotube and water molecules was simulated and calculated.By changing the hydrophilicity and hydrophobicity of the surface of TiO2 nanotube to simulate the illumination and non-illumination environment,the velocity distribution,density distribution and slip length of water molecules in TiO2 nanotube under different environments were compared.The mechanical behavior of water molecules in the interior of TiO2 nanotube,such as movement,adsorption and flow,was studied,which provides a bridge for the cross-study of mechanics and photocatalysis.