Electronic Structure Of Nanostructured Titanium Dioxide And Its Applications As Bioimplant And Battery Electrode

Titanium dioxide(TiO2)nanomaterials has been widely applied in the fields of bioimplant,photocatalyst and electrochemical battery due to its high biocompatibility,good photostability and high energy storage property,but the understanding about the mechanism of their structural variations during application is not so clear.In this thesis,X-ray absorption spectroscopy(XAS)have been applied to study the electronic structure of TiO2 nanomaterials.The main research content includes the following three parts:(1)The effect of crystal structure on the formation of calcium phosphate(CaP)coatings during biomimetic deposition,and how the formation of CaP coatings is affected by tuning the experimental parameters.TiO2 nanotubes were prepared by electrochemical anodization method.Such method produces a nanotube-on-foil structure,which serves as an ideal substrate for calcium phosphate crystallization.Calcium phosphate was deposited on TiO2 nanotubes by pre-treating the substrate using an alternating immersion method,followed by biomimetic deposition.The compositions of CaP coatings were studied using X-ray absorption near-edge structures(XANES)at the Ca K-edge in combination with other conventional laboratory characterization methods.CaP species,such as hydroxyapatite(HAp),octacalcium phosphate(OCP),calcium phosphate dihydrate(brushite,DCPD)and amorphous calcium phosphate(ACP),are found in the CaP coatings.TiO2 nanotubes of amorphous and anatase phases are comparatively studied to determine their effect on the efficiency of CaP formation and the phase transformation among CaP species in prolonged deposition time.It is found the composition of CaP coating has a strong dependency on the crystal structure of TiO2 substrate and the kinetics(deposition time).On the other hand,anatase TiO2 nanotubes is used to study how the formation of CaP coatings is affected by varying experimental parameters,and it is found the composition of CaP coating has a strong dependency on the immersion cycles.These findings provide important guide for the preparation of biological implant with higher biocompatibility.(2)Electronic structure analysis of TiO2 nanowires during phase transformation.TiO2 nanowires was prepared by hydrothermal method.Nanowires transform from HZTi3O7 to B-phase TiO2(TiO2(B)),and eventually to anatase as annealing temperature increases.XAS and X-ray emission spectroscopy(XES)were employed to study the band gap of the TiO2 nanowires at different transformation stage.We find TiO2 nanowires of a mixed phase has a lower band gap than pure-phase TiO2 nanowires.(3)Investigation of sodium-induced structural variation in TiO2 nanowires when they are used as anode materials in sodium ion battery.TiO2(B)nanowires and anatase nanowires were prepared by hydrothermal method,and used as an anode materials for sodium ion batteries.It is found that TiO2(B)nano wires are a better anode material than anatase nanowires.X-ray absorption spectroscopy is employed to investigate the difference in electronic structure which leads to the discrepancy in battery performance of these two systems.It is found that sodium insertion in TiO2(B)causes a strong lattice distortion,while little structure distortion is seen in anatase,making TiO2(B)nanowire a better anode material than the anatase counterpart.