Development of HCl-treated titania nanotube photocatalysts for dye photodegradation and low-concentration elemental mercury removal.

TiO 2 nanotube (TNT) photocatalysts were synthesized through a facile one-step hydrothermal method using Degussa P-25 as precursor. The resulting TNTs were subsequently washed with deionized water and 0.1–1.0 M HCl to possess a variety of physicochemical properties. Anatase was the major crystalline phase for the resulting TNTs. The Brunauer-Emmett-Teller surface area of TNTs was 307–392 m 2 g −1 . Hydroxyl groups and oxygen vacancies were shown to be generated on the surface of all TNTs. Photocatalytic activity of TNTs for Congo red and crystal violet dye decomposition was strongly determined by their pre-adsorption abilities, which are greatly affected by solution pH. Hg 0 removal by the TNTs was enhanced with increased HCl concentration and the presence of O 2 in the test environment; however, the presence of water vapor reduced the Hg 0 capture due to competitive adsorption of H 2 O. The Cl functionality formed on the surface of TNTs due to HCl treatment appeared to act as one of the adsorption sites and enhance Hg 0 removal, as well as helping in against the competition from water molecules. Nevertheless, the unwashed HCl residues also obstructed other active sites on TNT surface, such as oxygenated groups that also play important role in Hg 0 oxidation and adsorption. [ABSTRACT FROM AUTHOR]