title: Influence of Aqueous Inorganic Anions on the Reactivity of Nanoparticles in TiO2Photocatalysis.
abstract: The influence of inorganic anions on the photoreactivity and aggregation of titanium dioxide nanoparticles (NPs) was assessed by dosing carbonate, chloride, nitrate, phosphate, and sulfate as potassium salts at multiple concentrations. NP stability was monitored in terms of aggregate morphology and electrophoretic mobility (EPM). Aggregate size and fractal dimension were measured over time by laser diffraction, and the isoelectric point (IEP) as a function of anion and concentration was obtained by measuring EPM versus pH. Phosphate, carbonate, and to a lesser extent, sulfate decreased the IEP of TiO2and stabilized NP suspensions owing to specific surface interactions, whereas this was not observed for nitrate and chloride. TiO2NPs were exposed to UV-A radiation, and the photoreactivity was assessed by monitoring the production of reactive species over time both at the NP surface (photogenerated holes) and in the bulk solution (hydroxyl radicals) by observing their reactions with the selective probe compounds iodide and terephthalic acid, respectively. The generation of photogenerated holes and hydroxyl radicals was influenced by each inorganic anion to varying degrees. Carbonate and phosphate inhibited the oxidation of iodide, and this interaction was successfully described by a Langmuir-Hinshelwood mechanism and related to the characteristics of TiO2aggregates. Chloride and nitrate do not specifically interact with TiO2, and sulfate creates relatively weak interactions with the TiO2surface such that no decrease in photogenerated hole reactivity was observed. A decrease in hydroxyl radical generation was observed for all inorganic anions. Quenching rate constants for the reaction of hydroxyl radicals with each inorganic anion do not provide a comprehensive explanation for the magnitude of this decrease, which arises from the interplay of several physicochemical phenomena. This work shows that the reactivity of NPs will be strongly influenced by the makeup of the waters they are released into. The impact of anion species on hydroxyl radical inhibition was as follows: carbonate > chloride > phosphate > nitrate > sulfate.
authors.affiliation: Department of Civil and Environmental Engineering, Pratt School of Engineering, Duke University , 27708 Durham, North Carolina, United States.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Farner Budarz
authors.affiliation: DICA-Environmental Section, Politecnico di Milano , Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Turolla
authors.affiliation: Department of Civil and Environmental Engineering, Pratt School of Engineering, Duke University , 27708 Durham, North Carolina, United States.
authors.forename: Aleksander F
authors.initials: AF
authors.lastname: Piasecki
authors.affiliation: CEREGE, CNRS and Aix-Marseille University , Europole Méditerranéen de l'Arbois, BP80, 13545 Aix en Provence Cedex 04, France.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Bottero
authors.affiliation: DICA-Environmental Section, Politecnico di Milano , Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
authors.forename: Manuela
authors.initials: M
authors.lastname: Antonelli
authors.affiliation: Department of Civil and Environmental Engineering, Pratt School of Engineering, Duke University , 27708 Durham, North Carolina, United States.
authors.forename: Mark R
authors.identifier: 0000-0001-7152-7852
authors.initials: MR
authors.lastname: Wiesner
mesh_terms: D000838:Anions / Q000737:chemistry*; D002384:Catalysis; D007526:Isoelectric Point; D053758:Nanoparticles / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
chemical_list: D000838:Anions; C009495:titanium dioxide; D014025:Titanium