Gas sensors were fabricated from Cr2WO6 nanoparticles for NO2 detection. Low dimensional materials Cr2WO6 were prepared by a wet chemistry method followed by hydrothermal treatment. The morphology of the nanoparticles and their sensing properties to NO2 were investigated in both dry and humid conditions. Additionally, the sensing response was also characterized in a non-oxygen condition. It was concluded that the sensor responses in N2 conditions were higher than that in air conditions at 200°C. Moreover, the sensing characteristics were inhibited by water vapor at 200°C. The oxygen adsorption behavior was also investigated to verify the basic sensing mechanism of Cr2WO6 in the absence and presence of NO2 and water vapor separately. Based on the power law response, it was indicated that both NO2 and water vapor have a strong adsorption ability than oxygen ions of Cr2WO6 sensors.
Tian Chen,Zhou Min,Hua Zhongqiu,Yuan Wenjing,Wu Yi,Tian Xuemin,Song Tao
In the present work, gas sensors based on Cr 2 WO 6 nanoparticles were fabricated by a screen-printing technique, and the sensing properties were characterized with acetone and other typical reducing gases under both dry and humid air backgrounds. Interestingly, it was found that Cr 2 WO 6 sensors showed a p-type conduction characteristic with a highly sensitive response to acetone vapor in a relatively low concentration. In the presence of humidity, resistances of Cr 2 WO 6 sensors were significantly increased; nevertheless, sensor responses were obviously inhibited. In addition, the basic sensing mechanism of Cr 2 WO 6 sensor was also investigated based on oxygen adsorption behavior and catalytic properties of Cr 2 WO 6 surface. According to experimental results, it is proposed that the resistive responses of Cr 2 WO 6 sensor to reducing gases were highly oxygen-dependent, indicating that the surface oxygen adsorption and reaction also played the basic role in the sensing process as that observed in typical n-type MOS sensors. Additionally, sensors also suffered from a high cross-sensitivity to water vapor due to the competition of chemisorption of water and oxygen on the surface of Cr 2 WO 6 .
The oxidative desulfurization (ODS) of fuel oils is of great significance for environmental protection, and the development of efficient ODS heterogeneous catalysts is highly desired. Herein, we have designed and synthesized a novel material of amorphous Cr2WO6-modified WO3 (a-Cr2WO6/WO3) nanowires (3–6 nm) with a large specific surface area of 289.5 m2·g–1 and rich Lewis acid sites. The formation of such a unique nanowire is attributed to the adsorption of Cr3+ cations on non-(001) planes of WO3. In the ODS process, the a-Cr2WO6/WO3 nanowires can efficiently oxidize benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to their corresponding sulfones in a quasi-microemulsion reaction system and possess the highest activity (Ea = 55.4 kJ/mol) for DBT: 99.0% of 15,000 ppm DBT with 2600 ppm S can be removed (70 °C, H2O2 as the oxidant). The improvement in ODS activity from most of WO3 catalysts is owing to the sufficient active sites and enhanced adsorption of DBT on the basis of structural features of a-Cr2WO6/WO3 nanowires. Combined with free radical capture experiments, a possible ODS mechanism of W(O2) peroxotungstate route based on surface −OH groups is reasonably proposed. Moreover, the a-Cr2WO6/WO3 nanowires have good stability and can be synthesized on a large scale, suggesting its potential applications as an efficient heterogeneous catalyst.
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