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

2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

Photoinduced reactivity of titanium dioxide

Titanium dioxide, TiO2, is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.

https://link.springer.com/content/pdf/10.1007%2Fs10853-010-5113-0.pdf

Review of the anatase to rutile phase transformation

UV-Visible ار راد ن .د TiO2 ( تیفرظ راون مان هب نورتکلا یاراد یژرنا زارت لماش VB و ) رگید زارت ی یژرنا اب ( ییاناسر راون مان هب نورتکلا زا یلاخ و رتلااب VB یم ) .دشاب ت ود نیا نیب یژرنا توافت یژرنا فاکش زار ، پگ دناب هدیمان یم .دوش هک ینامز زا نورتکلا لاقتنا VB هب VB یم ماجنا دریگ ، TiO2 اب ودح یژرنا بذج د ev 2 / 3 ، نورتکلا تفج کی دیلوت یم هرفح .دیامن و نورتکلا هرفح ی نا اب هدش دیلوت یم کرتشم حطس هب لاقت ثعاب دناوت شنکاو ماجنا اه یی ددرگ . TiO2 دربراک ،دراد یدایز یاه هلمج زا یم ناوت اوه یگدولآ هیفصت یارب (CO2) و بآ و ... نآ زا هدافتسا درک .

Advanced Nanoarchitectures for Solar Photocatalytic Applications

This paper presents a systematic study on the role of particle size in pure and doped nanocrystalline TiO2 photocatalysts, which was made possible by a versatile wet-chemical process capable of generating near-agglomeration-free TiO2 with well-controlled particle sizes and dopant dispersion. It is shown that particle size is a crucial factor in the dynamics of the electron/hole recombination process. For TiO2 particles with 6 or 11 nm diameter, Fe3+ dopants were added to inhibit the charge carrier surface recombination. The optimal Fe3+ dopant concentration for different particle sizes was identified, and this concentration was found to decrease with increasing particle size. To assist electron and hole separation in TiO2 with 21 nm diameter, Nb5+ dopants were introduced in combination with minor surface Pt dispersion. These carefully engineered nanocrystalline TiO2 catalysts showed higher reactivities than Degussa P25 TiO2 material in photocatalytic decomposition of chloroform.

Role of Particle Size in Nanocrystalline TiO2-Based Photocatalysts

We present here a detailed study of the electrical transport properties of single-crystal bismuth nanowire arrays embedded in a dielectric matrix. Measurements of the resistance of Bi nanowire arrays with different wire diameters (60\char21{}110 nm) have been carried out over a wide range of temperatures (2.0\char21{}300 K) and magnetic fields (0\char21{}5.4 T). The transport properties of a heavily Te-doped Bi nanowire array have also been studied. At low temperatures, we show that the wire boundary scattering is the dominant scattering process for carriers in the undoped single-crystal Bi nanowires, while boundary scattering is less important for a heavily Te-doped sample, consistent with general theoretical considerations. The temperature dependences of the zero-field resistivity and of the longitudinal magneto-coefficient of the Bi nanowires were also studied and were found to be sensitive to the wire diameter. The quantum confinement of carriers is believed to play an important role in determining the overall temperature dependence of the zero-field resistivity. Theoretical considerations of the quantum confinement effects on the electronic band structure and on the transport properties of Bi nanowires are discussed. Despite the evidence for localization effects and diffusive electron interactions at low temperatures $(Tl~4.0\mathrm{K}),$ localization effects are not the dominant mechanisms affecting the resistivity or the magnetoresistance in the temperature range of this study.

Electronic transport properties of single-crystal bismuth nanowire arrays

By pressure injecting Bi liquid melt into the nanochannels of an anodic alumina template, we have successfully fabricated Bi nanowire arrays with ultrafine wire diameters and extremely high wire packing densities. Free-standing Bi nanowires with controlled wire diameters and large aspect ratios (length/diameter) were also obtained by subsequent etching of the alumina template. Various techniques such as SEM, TEM, AFM, EFM, HREM, and XRD have been used to investigate the physical characteristics of these nanowires. The Bi nanowires were found to be dense and continuous and had a uniform diameter throughout the length of the wires. Individual Bi nanowires were shown to be single crystals, and all the wires in an array were highly oriented. An interesting metastable phase of Bi was also observed, which can be attributed to a lattice stress-induced high-pressure phase of Bi formed inside the porous anodic alumina template.

Processing and Characterization of Single-Crystalline Ultrafine Bismuth Nanowires

Ultrafine bismuth nanowire arrays were synthesized by injecting its liquid melt into nanochannels of a porous anodic alumina template. A large area (1 cm × 1.5 cm) of parallel wires with diameters as small as 13 nm, lengths of 30–50 μm, and packing density as high as 7.1 × 1010 cm−2 has been fabricated. X-ray diffraction patterns revealed these nanowires, embedded in the insulating matrix, to be essentially single crystalline and highly oriented. The optical absorption spectra of the nanowire arrays indicate that these bismuth nanowires undergo a semimetal-to-semiconductor transition due to two-dimensional quantum confinement effects.

/pdf/bismuth-quantum-wire-arrays-fabricated-by-a-vacuum-melting-1op2khva9k.pdf

Zhibo Zhang

Papers

Role of Particle Size in Nanocrystalline TiO2-Based Photocatalysts

Electronic transport properties of single-crystal bismuth nanowire arrays

Processing and Characterization of Single-Crystalline Ultrafine Bismuth Nanowires

Bismuth quantum-wire arrays fabricated by a vacuum melting and pressure injection process

Photocatalytic decomposition of halogenated organics over nanocrystalline titania