Aqueous and alcoholic syntheses of tungsten trioxide powders for NO2 detection

Different synthetical routes involving several solvents for obtaining WO3 powders, suitable for gas sensing have been studied. Aqueous and alcoholic solvents proved to be the most promising media to grow nanometric particles. Among these, a modified sol–gel route that involves ethanol and a di-chetone, highlighted a more homogeneous grain-size distribution. The structure and morphology evolution of pure WO3 powders with time and annealing temperature have been studied. The study of the energy barrier and conductance versus temperature allows to understand the reason for the high response of WO3 to oxidising gases and its lack of sensitivity to reducing agents. Films of WO3 responded to NO2, sensing as low a gas concentration as 200 ppb.