WO3 nanorods

Wang J, Eugene Khoo E, Lee PS, Ma J (2008) Synthesis, assembly, and electrochromic properties of uniform crystalline WO3 nanorods. J Phys Chem C 112 14306-14312... 

This reaction with water at 38°C is very slow and increases with increasing temperatures and pressures. Reaction with water vapor between 20 and 500°C leads strictly to the formation of WO3—no other oxides are formed. The rate of this reaction has been found to be dependent on temperature and the ratio of the partial pressure of water to that of hydrogen. However, by adjusting these partial pressures properly, all known oxides can be formed. When both are low, WO2 is formed. As these pressures increase, the more oxidized forms are produced (WO2.72, WO2.9, and finally WO3). Additionally, higher temperatures favor the more oxidized forms. It also must be noted that hydrated oxides can be easily volatilized above about 900°C, with most volatile form being W02(0H)2. Such volatile compounds may play a crucial role in the formation of tungsten oxide nanorods. 

Vapor deposition techniques have been extensively studied for the fabrication of metal and metal oxide structures. Indeed, the first reported tungsten oxide nanorods were essentially grown by this method. This groundbreaking synthesis of W02.72 leaves room for improvement, however, as it requires a reaction temperature of 1600°C in an argon atmosphere. Additionally, the researchers found the reaction product to be commingling WO2.72 nanorods and WO3 platelets rather than pure nanorods. Later,... 

Though they utilized a novel hollow-sphere form of WO3 rather than WO2 72 nanorods, the work of Li s group in researching tungsten oxide as gas sensors can be applied to thenanorodform. Li sporous, hollow spheres were substituted for tungsten oxide polycrystalline films used in the previous studies by Galatsis et al. and Choi et Thus, they overcome the sensitivity and selectivity problems caused by the... 

Nanorods of oxide can also be made using a template. In this case, the morphology of the nanorods would depend on the shape of the template. For example, WO3 can grow in mesoporous silica MCM-41 which consists of an array of cylindrical pores without intercormections [119]. The growing orientation of the nanorods is variable. 

Maiyalagan et al. studied platinum supported on tungsten oxide nanorods that were synthesized using anodic alumnia membrane (Maiyalagan et al., 2008). Their catalyst showed good activity for the MOR, which was attributed to a synergistic effect between the platinum and WO3 and the ability of their catalyst to avoid poisoning that could have otherwise occurred from oxidation of methanol intermediates. 

Although other nanostmctured materials (NiO nanotubes," ZnO nanowires," WO3 nanoparticles," and SnOa nanorods ) have been intensively studied as promising candidates for use in CO sensors operable at room temperature, their sensitivity is also insufficient to allow their use in practical application, similar to the status of sensors incorporating CNTs. 

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