The motivation of using metal oxides is mainly due to its charge storage capabilities, and electrocatalytic, electrochromic and photoelectrochemical properties. But comparing with bulk, nanostructured materials present several advantages related with the spatial conﬁnement, large fraction of surface atoms, high surface energy, strong surface adsorption and increased surface to volume ratio, which greatly improves the performances of these materials. The deposition of this materials can be accomplished by a variety of physical and chemical techniques but nowadays, electrodeposited metal oxides are generally used in both laboratories and industries due to the flexibility to control structure and morphology of the oxide electrodes combined with a reduced cost. Tungsten oxide (WO3) is a well-studied semiconductor and is used for several applications as chromogenic material, sensor and catalyst. The major important features is its low cost and availability, improved stability, easy morphologic and structural control of the nanostructures, reversible change of conductivity, high sensitivity, selectivity and biocompatibility. For the electrodeposition of WO3, more than one method can be adopted: electrodeposition from a precursor solution, anodic oxidation, and electrodeposition of already produced nanoparticles; however, in this case the mechanism of the electrodeposition is not fully understood. In this chapter, a review of the latest published work of electrodeposited nanostructured metal oxides is provided to the reader, with a more detailed explanation of WO3 material applied in sensing devices.
Part of the book: Electroplating of Nanostructures
The use of metal-oxide-semiconductor nanostructures as photocatalytic materials has been an area of intense research over the last decade, and in this field, titanium dioxide (TiO2) receives much attention. TiO2 is an attractive material since it is stable, insoluble, non-toxic, resistant to corrosion and relatively inexpensive. In this chapter, we will demonstrate the influence of different solvents on the synthesis of TiO2 nanostructures considering a solvothermal method assisted by microwave radiation and their photocatalytic behaviour. The TiO2 nanostructured arrays were synthesized on seeded polyethylene naphthalate (PEN) substrates with different solvents: water, 2 – propanol, ethanol and methanol. TiO2 thin films deposited by spin-coating were used as seed layer for the nanostructures growth. Structural characterization of the microwave synthesized materials has been carried out by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The optical properties have also been investigated. The TiO2 nanostructures arrays were tested as photocatalytic agents in the degradation of pollutant dyes like methylene blue (MB) in the presence of UV radiation. Expressive differences between the different solvents were detected, in which methanol demonstrated higher MB degradation for the conditions tested.
Part of the book: Semiconductor Photocatalysis