C-doped WO3 microtubes assembled by nanoparticles with ultrahigh sensitivity to toluene at low operating temperature

Novel C-doped WO3 microtubes (MTs) were successfully synthesized by a facile infiltration and calcination process using the cotton fibers as templates. The prepared MTs were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), N2 adsorption and desorption measurements and ultraviolet–visible spectroscopy. XPS spectra show the carbon was doped into the lattice of the WO3 phase, resulting in a decrease of the band gap of the C-doped WO3 MTs from 2.45 eV to 2.12 eV. Moreover, the WO3 MTs were assembled by nanoparticles in size of ca. 40 nm and had larger specific surface area (21.3 m2/g) due to existence of meso/macro-pores inside them. At low operating temperature of 90 °C, the gas sensor based on the C-doped WO3 MTs had a detected limit of 50 ppb to the toluene gas (response of 2.0). The enhancement of toluene sensing performance of C-doped WO3 MTs was attributed to a larger surface area and higher porosity, which arises from its unique MTs. Furthermore, the band gap reduction and a new intragap band formation for C-doped WO3 MTs were proposed as the reason for the decrease in optimal operating temperature.