Flame synthesis of tungsten-doped titanium-dioxide nanoparticles using novel precursor combination of liquid titanium tetra-isopropoxide and solid tungsten mesh

Tungsten-doped titanium-dioxide (W-TiO₂) nanoparticles are successfully synthesized using a multiple-diffusion-flame burner with a separate center tube. Vaporized titanium tetra-isopropoxide (TTIP) precursor issues from a center tube to produce TiO₂ nanoparticles, while a tungsten mesh, suspended above the surrounding multiple over-ventilated hydrogen diffusion flames, serves as the solid-phase metal doping source. At a lower tungsten loading rate, W-TiO₂ nanoparticles are generated, as indicated by an obvious angle shift of 0.15° for the entire x-ray diffraction spectrum. However, at a higher tungsten loading rate, homogenous nucleation of WO_x occurs before or concurrently with TiO₂ nucleation, producing mixed nanopowders, permitting fewer tungsten ions to be doped into TiO₂. Ultraviolet–visible spectroscopic characterization reveals that the as-synthesized W-TiO₂ nanoparticles possess augmented absorbing ability in the visible-light wavelength range, where the band gap is reduced from 3.20 to 3.05 eV, compared with that for the nondoped TiO₂ nanoparticles.