Synthesis of TiO 2-x visible-light photocatalyst using N 2 /Ar/He thermal plasma for low-concentration elemental mercury removal

Oxygen-vacant titanium dioxide (TiO 2-x ) nanoparticles possessing a narrower band gap were synthesized with a single-step process using N 2 /Ar/He thermal plasma as a heating source. Sample characterization showed that the formed TiO 2-x nanoparticles had a size within 5-40nm and were in a mixing form of anatase and rutile. An evident absorption red shift to 470nm wavelength was observed. The deconvolution results of XPS spectra supported the formation of TiO 2-x due to the presence of Ti 3+ 2p peaks. The Hg removal efficiency of TiO 2-x nanoparticles increased with increasing O 2 concentration and in the presence of light irradiation, suggesting an enhancement in Hg 0 oxidation. H 2 O molecules, however, greatly reduced the Hg removal of TiO 2-x under visible-light (VL) irradiation. The photoinduced hydrophilicity of TiO 2-x under VL irradiation was suspected to amplify the competitive adsorption of H 2 O that decreased Hg capture. Hg removal performances at 50°C were better than those at 25 and 100°C, suggesting that both adsorption and catalytic oxidation limit the Hg removal. These observations also implicate that the bonding between TiO 2-x and adsorbed Hg was weak and adsorption reaction may be reversible. © 2012 Elsevier B.V.