In this work, we report synthesis of Cu, Pt and Pd doped SnO₂ powders and their comparative CO gas sensing studies. Dopants were incorporated into SnO₂ nanostructures using chemical and impregnation methods by using urea and ammonia as precipitation agents. The synthesized samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) and High resolution transmission electron microscopy (HR-TEM). The presence of dopants within the SnO₂ nanostructures was evidenced from HR-TEM. Doped powders utilizing chemical methods with urea as precipitation agent presented higher sensitivities compared to the remaining, which is due to the formation of uniform and homogeneous particles resulted from the temperature assisted synthesis. The particle sizes of doped SnO₂ nanostructures were in the range of 40-100 nm. An enhanced sensitivity around 1783 was achieved with Cu doped SnO₂ when compared with two other dopants i.e., Pt (1200) and Pd: SnO₂(502). The high sensitivity of Cu: SnO₂ is due to formation of CuO and its excellent association and dissociation in the presence of CO with adsorbed atmospheric oxygen at sensor operation temperatures resulted in high conductance. Cu: SnO₂ may be an alternative and cost effective sensor for industrial applications.

A comparative study of the photocatalytic decoloration of methylene blue (MB) dissolved in water was conducted, using three semiconductor oxides: zinc oxide (ZnO), tin oxide (SnO2) and titanium dioxide (TiO2) in the form of thin films and varying their thickness ~ 100, 200, and 300 nm for each film. All the films were deposited using the cost-effective dip-coating technique, at moderate temperature processing (400 °C) with sol-gel solutions on cheap glass substrates. The structural, morphological, and compositional properties of the films were analyzed by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy, respectively. The degradation of MB was studied by varying both thickness and type of semiconductor oxides through measurements of optical absorbance of decolorated liquid by photocatalytic process. Structural analysis shows that ZnO and SnO2 films were polycrystalline with preferential growth of (002) and (110) planes respectively, whereas, an amorphous structure was observed for TiO2 films. In addition, morphological properties confirms that the surfaces of all the films are conformed with nano grains in round and irregular shapes. Based on all results reported in this work, that authors believe that the degradation efficiency of MB depends on the thickness of the film and the type of semiconductor material used as a catalyst. The highest degradation efficiencies were recorded with an exposure time of 120 min and with an initial concentration of 10 mg/L for ZnO, SnO2, and TiO2 films were: 100, 88 %, and 76 %, respectively.