A novel approach for green synthesis of WO3 nanomaterials and their highly selective chemical sensing properties

Sensing devices have become a necessary part of our daily lives with a wide range of applications including in healthcare and environmental safety. Metal oxide nanomaterials are very promising candidates for the fabrication of next-generation sensing systems due to their attractive physical, chemical and electronic properties. However, the improvement of their performances to satisfy the modern requirements in sensing technologies remains a challenging issue. Inspired by natural processes, we report a novel green synthesis approach for the preparation of WO3 nanomaterials. We developed a hydrothermal synthesis method and performed the thermal treatment of tungsten thin films using sodium chloride and distilled water. Meanwhile, we studied the effect of water, sodium chloride and water vapor on the formation of nanomaterials. The morphological, compositional and structural investigations of samples demonstrate that it is possible to prepare porous materials composed of polycrystalline WO3 nanoparticles in an aqueous solution of sodium chloride and upon exposure to water vapor. Both materials show a good selective response to acetone compared to different interfering gases. The limits of detection of the samples prepared in sodium chloride-containing water and upon exposure to water vapor are 170 and 220 ppb, respectively. We propose that the effect of environmental humidity is more evident on the functional stability of WO3 nanostructures fabricated upon exposure to water vapor due to the presence of relatively big porous regions on their surface. However the crystal structure of WO3 nanoparticles has a significant effect on their sensing response and selectivity. The monoclinic gamma-WO3 structure is more reactive and selective to acetone compared to orthorhombic beta-WO3. We attribute this feature to the catalytic activity and large dipole moment of monoclinic gamma-WO3. Thus, this work provides a new strategy based on green chemistry for the preparation of WO3 nanomaterials and their application in health and environmental monitoring.