Comparison of the morphology and structure of W03 nanomaterials synthesized by a sol-gel method followed by calcination^or hydrothermal treatment

Tungsten （VI） oxide （WO3） nanomaterials were synthesized by a sol-gel method using WC16 and C2HsOH as precursors followed by calcination or hydrothermal treatment. X-Ray diffraction （XRD）, scanning electron microscopy （SEM） and high resolution transmission electron microscopy （HRTEM） equipped with energy dispersive X-ray spectroscopy （EDX） were used to characterize the structure and morphology of the materials. There were significant differences between the WO3 materials that were calcinated and those that were subjected to a hydrothermal process. The XRD results revealed that calcination temperatures of 300℃and 400℃ gave hexagonal structures and temperatures of 500℃ and 600℃ gave monoclinic structures. The SEM images showed that an increase in calcination temperature led to a decrease in the WO3 powder particle size. The TEM analysis showed that several nanoparticles agglomerated to form bigger clusters. The hydrothermal process produced hexagonal structures for holding times of 12, 16, and 20 h and monoclinic structures for a holding time of 24 h. The SEM results showed transparent rectangular panicles which according to the TEM results originated from the aggregation of several nanotubes.

WO3 nanomaterials synthesized via a sol-gel method and calcination for use as a CO gas sensor

Carbon monoxide is a poisonous and hazardous gas and sensitive sensor devices are needed to prevent humans from being poisoned by this gas. A CO gas sensor has been prepared from WO3 synthesized by a sol-gel method. The sensor chip was prepared by a spin-coating technique which deposited a thin film of WO3 on an alumina substrate. The chip samples were then calcined at 300, 400, 500 or 600 ℃ for 1 h. The sensitivities of the different sensor chips for CO gas were determined by comparing the changes in electrical resistance in the absence and presence of 50 ppm of CO gas at 200 ℃. The WO3 calcined at 500 ℃ had the highest sensitivity. The sensitivity of this sensor was also measured at CO concentrations of 100 ppm and 200 ppm and at operating temperatures of 30 and 100℃. Thermogravimetric analysis of the WO3 calcined at 500 ℃ indicated that this sample had the highest gas adsorption capacity. This preliminary research has shown that WO3 can serve as a CO gas sensor and that is should be further explored and developed.

The effect of calcination temperature on the capacitive properties of WO3-based electrochemical capacitors synthesized via a sol-gel method

Electrochemical capacitor （EC） is a promising energy storage device which can be hybridized with other energy conversion or energy storage devices. One type of ECs is pseudocapacitor made of metal oxides. WO3 is an inexpensive semiconductor metal oxide which has many applications. However the application of WO3 as an EC material was rarely reported. Therefore in this research EC was prepared from WO3 nanomaterial synthesized by a sol-gel process. The WO3 gel was spin-coated on graphite substrates and calcined at various temperatures of 300~C, 400℃, 500℃ and 600℃ for 1 h. Cyclic voltammetry （CV） measurements were used to observe the capacitive property of the WO3 samples. SEM, XRD, FTIR and Brunauer-Emmett-Teller （BET） analyses were used to characterize the material structures. WO3 calcined at 400~C was proved to have the highest capacitance of 233.63 Fo g^-1 （1869 mFo cm-2） at a scan rate of 2 mVo s-1 in 1 mol/L H2SO4 between potentials -0.4 and 0.4 V vs. SCE. Moreover it also showed the most symmetric CV curves as the indication of a good EC. Hence WO3 calcined at 400℃ is a potential candidate for EC material of pseudocapacitor type.