Biotemplate Fabrication Of SnO₂ And WO₃ Hierarchical Structures And Their Gas-sensing Properties

Formaldehyde (HCHO) and toluene gases in the indoor environment are intensively harmful to the human health even at ppb-levels, so it has attracted a great attention to synthesis metal-oxide semiconductor (MOS) materials with high sensing performance for detecting and monitoring them. In this paper, the mesoporous SnO₂ fibers assembled by ultrafine nanoparticles (3-5 nm) were obtained by a facile solvothermal process using cotton fibers as templates and glycol (EG) as solvent. The synthesized mesoporous SnO₂ fibers exhibited high sensing performance toward HCHO gas. The lowest detection concentration reached 50 ppb, which meets the needs for detecting HCHO gas in the indoor environment. And the sensor response of mesoporous SnO₂ fibers increased nearly linearly with the rising of HCHO gas concentration, which indicates that it can be used as a promising material for detecting the indoor HCHO gas. In addition, the lower operating temperature (190℃) is an advantage for enhancing the reliability and stability of the mesoporous SnO₂ fibers in the gas-sensing application.Through the investigation it was found that with the calcication temperature increased the size of nanoparticles and average mesopores were both gradually increased, but BET special surface area and mesoporous volume were both decreased. Interestingly, the higher the calcination temperature was, the larger the sensor response to HCHO gas. And this phenomenon was explained from the influence of mesoporous size on the gas diffusion in the porous films.Novel C-doped WO₃ microtubes were also successfully synthesized by a facile infiltration and calcinations process using cotton fibers as templates and WCl6 as tungsten source. The obtained C-doped WO₃ microtubes exhibited larger BET surface area (21.3 m2/g) due to its specific porous structure. And because of C doping the optical band gap of the C-doped WO₃ microtubes was decreased to 2.12 eV. The C-doped WO₃ microtubes exhibited high gas-sensing properties toward ppb-level toluene gas. The lowest detection limit reached 50 ppb, and the optimal operating temperature of it was 90℃, which could enhance the sensor's reliability and stability. In addition, the enhancement of toluene sensing performance of C-doped WO₃ microtubes was explained from its unique microtube structure, which results in a large surface area and high porosity. Furthermore, the band gap reduction and a new intragap band formation by C doping were proposed as the reason for the decrease in optimal operating temperature for C-doped WO₃ microtubes.