Synthesis of Tungsten-Doped Titania Nanopowders Prepared by Pulsed-Laser Decomposition in Liquid Precursor Bath

Tungsten-doped TiO₂(W-TiO₂) nanostructure is successfully synthesized by pulsed-laser ablation of a tungsten foil immersed in liquid titanium tetra-isopropoxide (TTIP). Interaction between the focused laser beam and the W substrate generates a submerged plasma, where vaporization of the W substrate and decomposition of the liquid precursor combine to produce W-doped TiO₂ nanoparticles upon quenching by the surrounding unreacted liquid precursor. The as-synthesized nanoparticles display various morphologies, including nano-spheres and nano-fibers, and occur in discrete, agglomerated and aggregated forms. Whatever their morphologies, all nanoparticles have non-crystalline or amorphous structures, primarily because of rapid condensation and quenching of vaporized species from the plasma-reaction zone. Interestingly, after heat treatment in air or oxygen, starting at ~400 C, transformation to the more stable anatase-TiO₂ phase occurs, but doped with tungsten. The phase transformation from anatase to rutile TiO₂ in the doped sample is shifted to higher temperatures 950 C compared to non-doped TiO₂ 800 C. In addition, the average crystallite size of TiO₂ (about 13 nm) is slightly reduced by doping with W (10 nm) as the ionic radius of W⁶⁺ (0.60 Å) is quite similar to Ti⁴⁺ (0.68 Å). Ultraviolet-visible spectroscopic characterization shows that W-doped anatase TiO₂ exhibits a higher UV and visible photochemical activity than un-doped anatase-TiO₂, where the band gap is reduced from 3.08 to 2.92 eV, compared to the un-doped TiO₂nanostructures.