Electrochromics for smart windows: Oxide-based thin films and devices

In this review, for a variety of metals and semiconductors, an attempt is made to generalize observations in the literature on the effect of process conditions applied during photodeposition on (i) particle size distributions, (ii) oxidation states of the metals obtained, and (iii) consequences for photocatalytic activities. Process parameters include presence or absence of (organic) sacrificial agents, applied pH, presence or absence of an air/inert atmosphere, metal precursor type and concentration, and temperature. Most intensively reviewed are studies concerning (i) TiO2; (ii) ZnO, focusing on Ag deposition; (iii) WO3, with a strong emphasis on the photodeposition of Pt; and (iv) CdS, again with a focus on deposition of Pt. Furthermore, a detailed overview is given of achievements in structure-directed photodeposition, which could ultimately be employed to obtain highly effective photocatalytic materials. Finally, we provide suggestions for improvements in description of the photodeposition methods applied when included in scientific papers.

Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review.

Inorganic semiconductor nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating the size and dimensionality dependence of their properties for potential applications. The use of such nanostructures with tailored geometries as building blocks is also expected to play crucial roles in future nanodevices. Since the discovery of carbon nanotubes much attention has been paid to exploring the usage of inorganic semiconductor nanostructures as field-emitters due to their low work functions, high aspect ratios and mechanical stabilities, and high electrical and thermal conductivities. This article provides a comprehensive review of the state-of-the-art research activities in the field. It mainly focuses on the most widely studied inorganic nanostructures, such as ZnO, ZnS, Si, WO3, AlN, SiC, and their field-emission properties. We begin with a survey of inorganic semiconductor nanostructures and the field-emission principle, and then discuss the recent progresses on several kinds of important nanostructures and their field-emission characteristics in detail and overview some additional inorganic semiconducting nanomaterials in short. Finally, we conclude this review with some perspectives and outlook on the future developments in this area.

Inorganic semiconductor nanostructures and their field-emission applications

Environmental pollution and global energy demand require advanced photocatalytic materials such as visible-light-driven semiconductor photocatalysts. In particular, Tungsten oxide (WO3) appears promising candidate because of high absorption of visible light (up to 480 nm), its tunable bandgap, and outstanding optical properties. Fascinatingly, WO3 also hold advantages like nontoxic nature, economic cost, and stability in oxidative and acidic conditions. It is well-known that various synthetic procedures can be utilized for fabrication of a photocatalyst with different morphologies, sizes and structures which are dynamic on its catalytic performance to distinctive degrees. This review comprises several synthesis ways which are low-cost and environmentally friendly and detail analysis of the relationship between morphology control and photocatalytic performance of WO3. Additionally, some top strategies for enhancing the photocatalytic performance of semiconductor WO3, like as elemental doping, hybridization with co-catalyst, heterojunction formation etc. are also summarized. Moreover, photocatalytic enhancement aspects and photocatalytic mechanisms of WO3/semiconductor photocatalyst were elaborated. Lastly, the conclusion and main future prospects of WO3-based semiconductor photocatalysts were deliberated.

An overview on WO3 based photocatalyst for environmental remediation

Tungsten oxide (WO3) nanostructures such as nanowires, nanorod bundles and nanotube bundles are synthesized by a facile hydrothermal method. The ultraviolet (UV) photoresponse characteristics of devices containing these WO3 nanostructures are investigated for the first time and new photosensitive mechanisms involving both photo-generated electron–hole pairs and reversible electrochemical reactions are proposed. We find that h-WO3 nanowires with large specific surface areas and fewer defects exhibit excellent UV photoresponse properties with switch ratios (defined as Iphoto/Idark) as high as 60, which is due to the existing large tunnels serving as channels and intercalation sites for mobile ions and active electrochemical reactions, and our findings provide a new family and more selectivity for UV photosensitive nanomaterials in the future.

Synthesis of WO3 nanostructures and their ultraviolet photoresponse properties

Crystals of hexagonal tungsten oxides (hex-WO3) have been synthesized using hydrothermal method at 150 degrees C, assisted by the capping reagent of ammonium tartrate (AT). The XRD and EDX results reveal that the lattice distortion exists in all the samples, possibly due to the defects and the intercalation of the residual sodium ions. Different crystal shapes including plate-like, urchin-like, and particle structures were obtained by varying concentration of AT and pH values in the precursor solution. Beside the absorption action of the NH4+ and Na+ ions, the capping effect can be reinforced by the hydrogen bonding from the tartrate groups in the crystallization process. The bandgap energies were modulated by the size of the nanostructured hex-WO3 crystals due to quantum confinement effect, which increases from 2.74 to 3.04 eV. Based on the analysis of the photoluminescence and X-ray photoelectron spectroscopy, the enhancement of the blue emission of the nanocrystals is assigned as a result of a complex of the local intercalation of the residual sodium ions and the oxygen vacancies or defects. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Xia Xiang

Papers

Hydrothermal synthesis and optical properties of hexagonal tungsten oxide nanocrystals assisted by ammonium tartrate