aThis paper reports on a new ozone gas sensor based on a-Ag 2 WO 4 nanorod-like structures. Electrical resistance measurements proved the efficiency of a-Ag 2 WO 4 nanorods, which rendered good sensitivity even for a low ozone concentration (80 ppb), a fast response and a short recovery time at 300 C, demonstrating great potential for a variety of applications.Metal semiconducting oxides have drawn the interest of many researchers due to their wide range of applications, especially as gas sensing materials. 1-5 Among them, one-dimensional (1-D) semiconductor nanostructures have been proposed as very interesting materials, especially as gas sensor devices.6-12 It is well known that several technological applications of nanostructured materials are directly related to the morphology, particle size, crystalline phase and activity of specic crystalline planes strictly dependent on synthesis methods. 4,[13][14][15] In particular, the relationship between morphology and gas sensing properties has been well established. 4,16,17Tungsten-based oxides are an important class of materials that display wide potential functional properties, 18-20 speci-cally the silver tungstate (Ag 2 WO 4 ) compound, which can exhibit three different structures: a-orthorhombic, b-hexagonal, and g-cubic.21-25 Recently, our research group reported a detailed study of the synthesis, structural and optical properties of hexagonal nanorod-like elongated a-Ag 2 WO 4 nanocrystals obtained by different methods. 26-28Ozone (O 3 ) is an oxidizing gas used in many technological applications in different areas, such as the food industry, drinking-water treatment, medicine, microelectronic cleaning processes, and others.29,34-39 For example, ozone has been employed as a powerful drinking-water disinfectant and oxidant. 34,35,40 On the other hand, when the ozone level in an atmosphere exceeds a certain threshold value, the exposure to this gas becomes hazardous to human health and can cause serious health problems (e.g. headache, burning eyes, respiratory irritation and lung damage).34,41 The European Guidelines (2002/3/EG) recommend avoiding exposure to ozone levels above 120 ppb.41 Such arguments support the requirement for the determination and continuous monitoring of ozone levels. 3,29,41Gas sensing properties are evaluated in terms of operating temperature, sensitivity, response time, recovery time and stability.29-33 SnO 2 , In 2 O 3 and WO 3 compounds have been considered the most promising ozone gas sensors. 29-33To the best of our knowledge, to date the gas sensing properties of a-Ag 2 WO 4 nanocrystals have never been evaluated.Here, we report the sensing properties of 1-D a-Ag 2 WO 4 nanorod-like structures obtained by the microwave-assisted hydrothermal (MAH) method.42-46 Because of such properties, nanorods are potential candidates for practical applications as ozone gas sensors.The crystalline phase of the as-obtained a-Ag 2 WO 4 sample was analyzed by X-ray diffraction measurement and all reec-tions were indexed to an orthorhombic struc...

International audienceno abstrac

A detailed study of the structural, surface, and gas-sensing properties of nanostructured CoZnO films is presented. X-ray diffraction (XRD) analysis revealed a decrease in the crystallization degree with increasing Co content. The X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopies (XPS) revealed that the Co ions preferentially occupied the Zn sites and that the oxygen vacancy concentration increased as the amount of cobalt increased. Electrical measurements showed that the Co dopants not only enhanced the sensor response at low ozone levels (ca. 42 ppb) but also led to a decrease in the operating temperature and improved selectivity. The enhancement in the gas-sensing properties was attributed to the presence of oxygen vacancies, which facilitated ozone adsorption.

The sensitivity of ZnO-SnO 2 heterojunctions to ozone gas was investigated in this work, the two-phase materials of which were prepared via a hydrothermal route, resulting in nanocomposites in which the formation of heterojunctions was confirmed by microscopy analyses. While the sensing effectiveness of these materials is currently verified for application above 150 • C, these temperatures are here drastically reduced to room temperature by considering sensing activity under continuous UV irradiation, even for ozone concentrations as low as 20 ppb. This approach resulted in a fast sensing response, a short recovery time and a good selectivity compared to other gases, demonstrating a great potential of such heterojunctions for applications in environmental monitoring devices.