The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

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

TiO2 photocatalysis and related surface phenomena

Nano-sized TiO 2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production

Low-Temperature Fabrication of Light-Emitting Zinc Oxide Micropatterns Using Self-Assembled Monolayers

Visible-light-driven photocatalysis on fluorine-doped TiO2 powders by the creation of surface oxygen vacancies

N−F−codoped TiO2 (NFT) powders, prepared by spray pyrolysis (SP), were further characterized by ultraviolet−visible (UV−Vis) absorption spectroscopy and photoluminescence (PL) spectra. The UV−Vis spectra indicated that the NFT powders could absorb not only ultraviolet light like pure TiO2 powder but also part of the visible-light spectrum (λ < 550 nm). The PL spectra provided confirmation that four electronic energy states exist between the valence band and conduction band of N−F−codoped TiO2 that were attributed to F center, F+ center, an origin-unidentified energy state, and an impurity energy state formed by doped N atoms. Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalytic properties of these NFT powders. As a result, we found that the photocatalytic activity of the NFT powder prepared at the SP temperature of 1173 K was superior to that of commercial P25 under both UV and Vis irradiation. Moreover, trichloroethylene and toluene were selected as the other two target ...

Visible-Light-Driven N−F−Codoped TiO2 Photocatalysts. 2. Optical Characterization, Photocatalysis, and Potential Application to Air Purification

Origin of visible-light-driven photocatalysis: A comparative study on N/F-doped and N–F-codoped TiO2 powders by means of experimental characterizations and theoretical calculations

Novel photocatalytic materials, yellow-colored N−F-codoped TiO2 (NFT) powders, were synthesized from a mixed aqueous solution containing TiCl4 and NH4F by spray pyrolysis (SP). The resulting powders were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), NH3-temperature-programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and N2 adsorption. FE-SEM images and N2 adsorption confirm that the NFT powders possessed spherical particles with a highly porous surface morphology. The doped N and F concentrations in the NFT powders depended significantly on the SP temperature and ranged from 0.10 to 0.26 and from 0.11 to 0.40 atomic % (at. %), respectively. NH3-TPD measurement indicates that the surface of the NFT powder was strongly acidic. Moreover, by investigating the characteristics of the TiO2 precursor hydrolysis and the thermal decomposition behaviors of the other components in the starti...

Naoki Ohashi

Papers

Low-Temperature Fabrication of Light-Emitting Zinc Oxide Micropatterns Using Self-Assembled Monolayers

Visible-light-driven photocatalysis on fluorine-doped TiO2 powders by the creation of surface oxygen vacancies

Visible-Light-Driven N−F−Codoped TiO2 Photocatalysts. 2. Optical Characterization, Photocatalysis, and Potential Application to Air Purification

Origin of visible-light-driven photocatalysis: A comparative study on N/F-doped and N–F-codoped TiO2 powders by means of experimental characterizations and theoretical calculations

Visible-Light-Driven N−F−Codoped TiO2 Photocatalysts. 1. Synthesis by Spray Pyrolysis and Surface Characterization