Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

TiO2 photocatalysis and related surface phenomena

Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Understanding TiO2 photocatalysis: mechanisms and materials.

[Yang, Hua Gui; Sun, Cheng Hua; Qiao, Shi Zhang; Liu, Gang; Smith, Sean Campbell; Lu, Gao Qing] Univ Queensland, ARC Ctr Excellence Funct Nanomat, Sch Engn, Brisbane, Qld 4072, Australia. [Yang, Hua Gui; Sun, Cheng Hua; Qiao, Shi Zhang; Liu, Gang; Smith, Sean Campbell; Lu, Gao Qing] Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Computat Mol Sci, Brisbane, Qld 4072, Australia. [Zou, Jin] Univ Queensland, Ctr Microscopy & Microanal, Brisbane, Qld 4072, Australia. [Zou, Jin] Univ Queensland, Sch Engn, Brisbane, Qld 4072, Australia. [Liu, Gang; Cheng, Hui Ming] Chinese Acad Sci, Met Res Inst, Shenyang Natl Lab Mat sci, Shenyang 110016, Peoples R China.;Lu, GQ (reprint author), Univ Queensland, ARC Ctr Excellence Funct Nanomat, Sch Engn, Brisbane, Qld 4072, Australia;s.qiao@uq.edu.au maxlu@uq.edu.au

/pdf/anatase-tio-2-single-crystals-with-a-large-percentage-of-2scpj9a9n2.pdf

Anatase TiO(2) single crystals with a large percentage of reactive facets

TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

TiO2 nanotubes: synthesis and applications.

Electrical and optical spectroscopic studies of TiO2 anatase thin filmsdeposited by sputtering show that the metastable phase anatase differs in electronic properties from the well‐known, stable phase rutile. Resistivity and Hall‐effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self‐trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.

Electrical and optical properties of TiO2 anatase thin films

Photoemission spectromicroscopy was used to investigate the electronic structure of TiO2 anatase single crystals and polycrystalline thin films The stoichiometry and the degree of oxidation of as-grown crystals, as-deposited films, as well as of thermally annealed samples in different atmospheres, were analyzed, based on the Ti 2p and O 1s core levels, with an energy resolution of 04 eV The experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals In reduced samples, the experimental DOS is characterized by intense emission in the region of O 2p bonding orbitals, and does not exhibit an appreciable density of states in the band gap As-grown crystals exhibit small band gap emission (a few percent of the valence band VB signal) at about 08 eV, which is attributed to Ti3+ (3d) defect states Annealing the crystals at high temperatures in O2 or subsequent thermal reduction in an Ar-H2 Mixture (95%-5%) produces nearly stoichiometric surfaces with smaller or undetectable density of Ti3+ States In addition, some redistribution of the spectral weight is observed in the VB spectra

Electronic-Structure of Anatase Tio2 Oxide

The anatase modification of TiO2 shows properties quite different from those of the extensively studied and used rutile phase. We have investigated the chemi-resistive behavior of anatase TiO2 thin films exposed to oxidizing and reducing gases (O2, H2 and ethanol) in the temperature range between 300 and 400 °C. The undoped anatase films demonstrate significant and rapid response to ethanol as well as an appreciable response to hydrogen. The high electron mobility and the low density of trapping or compensating centers are considered to have contributed to this good response. Doping the anatase thin films with Sr, Ce, Y and Tb makes then insensitive to hydrogen, but still sensitive to ethanol. The modification of the sensitivity and its dynamics by dopants have been measured and analyzed.

TiO2 anatase thin films as gas sensors

In recent years, the material preparation technology has ushered into a stage of rapid development, increasingly more carbon materials are found to display superior properties, making them suitable for designing nano-scale devices. Within the applications of electronic devices, a considerable amount of consumed energy has to be converted into heat; thus the efficiency of heat transport inside these devices can largely determine their overall performance. Decent elucidations of the heat transport mechanisms within low-dimensional materials will be helpful to achieve thermal management control of the related devices and furthermore, to improve their conversion efficiency. It is well understood that the heat transport within these kinds of materials is largely associated with their structural features. In this study, we focused on a novel material, body centered cubic carbon (C14), which is composed of sp3 hybridized carbon atoms. Such a novel material displays superior electronic properties; however, its thermal properties remain to be investigated. In order to systematically evaluate the practical applicability of this novel material, first-principles calculations were employed to systematically solve its structure; furthermore, its thermal conductivity, phonon dispersion spectrum, phonon properties, Grüneisen parameters, scattering phase space and mechanical properties were all described in detail. We found that C14 performs well in heat transport; and via systematical comparison with another allotrope, diamond, its transport mechanism was further summarized. We hope the physical insights provided by this study could serve as theoretical support for nano-scale device design.

Lower thermal conductivity of body centered cubic carbon (C14): a comparative study with diamond.

With the rapid development of material preparation and quantum computation technologies, the discovery of superior electronic devices in the nanoscale has been widely facilitated. For materials for application in thermoelectric and thermal conductivity devices, their overall performance can be demonstrated by their inner heat transport efficiency. Thus, fundamental elucidation of the heat transport mechanism within low-dimensional materials with physical insight, is of great significance for novel electric device development. In addition, theoretical clarification can also help with the efficient control of the developed thermal devices, and furthermore, provide strategies to improve the efficiency of heat conversion. In this study, we focus on a novel carbon monolayer (net-Y) that is composed of sp2 hybridized C atoms, we systematically assess its practical applicability in electronic device design by conducting first-principles calculations. Furthermore, to obtain in-depth understanding of the factors that determine its heat transport efficiency, its mechanical and phonon spectrum related properties were also investigated. Through a comparative study with graphene, the heat transport mechanism of net-Y was successfully summarized; the methodology and theoretical findings presented in this study could provide an instructive reference for future experimental work.

H. Tang

Papers

Electrical and optical properties of TiO2 anatase thin films

Electronic-Structure of Anatase Tio2 Oxide

TiO2 anatase thin films as gas sensors

Lower thermal conductivity of body centered cubic carbon (C14): a comparative study with diamond.

Heat transport properties of novel carbon monolayer (net-Y): a comparative study with graphene.