title: Towards a better understanding on agglomeration mechanisms and thermodynamic properties of TiO₂ nanoparticles interacting with natural organic matter.
abstract: Interaction between engineered nanoparticles and natural organic matter is investigated by measuring the exchanged heat during binding process with isothermal titration calorimetry. TiO2 anatase nanoparticles and alginate are used as engineered nanoparticles and natural organic matter to get an insight into the thermodynamic association properties and mechanisms of adsorption and agglomeration. Changes of enthalpy, entropy and total free energy, reaction stoichiometry and affinity binding constant are determined or calculated at a pH value where the TiO2 nanoparticles surface charge is positive and the alginate exhibits a negative structural charge. Our results indicate that strong TiO2-alginate interactions are essentially entropy driven and enthalpically favorable with exothermic binding reactions. The reaction stoichiometry and entropy gain are also found dependent on the mixing order. Finally correlation is established between the binding enthalpy, the reaction stoichiometry and the zeta potential values determined by electrophoretic mobility measurements. From these results two types of agglomeration mechanisms are proposed depending on the mixing order. Addition of alginate in TiO2 dispersions is found to form agglomerates due to polymer bridging whereas addition of TiO2 in alginate promotes a more individually coating of the nanoparticles.
authors.affiliation: Group of Environmental Physical Chemistry, University of Geneva, F.-A. Forel Institute Section des Sciences de la Terre et de l'Environnement, 10 route de Suisse, 1290 Versoix, Switzerland.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Loosli
authors.affiliation: Laboratoire Matière et Systèmes Complexes, UMR 7057 Université Paris-Diderot/CNRS, Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, F-75205 Paris Cedex 13, France.
authors.forename: Letícia
authors.initials: L
authors.lastname: Vitorazi
authors.affiliation: Laboratoire Matière et Systèmes Complexes, UMR 7057 Université Paris-Diderot/CNRS, Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, F-75205 Paris Cedex 13, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Berret
authors.affiliation: Group of Environmental Physical Chemistry, University of Geneva, F.-A. Forel Institute Section des Sciences de la Terre et de l'Environnement, 10 route de Suisse, 1290 Versoix, Switzerland. Electronic address: serge.stoll@unige.ch.
authors.forename: Serge
authors.initials: S
authors.lastname: Stoll
mesh_terms: D000327:Adsorption; D000464:Alginates / Q000737:chemistry*; D000465:Algorithms; D002151:Calorimetry / Q000379:methods; D019277:Entropy; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D053768:Metal Nanoparticles / Q000737:chemistry*; D008956:Models, Chemical; D010316:Particle Size; D013816:Thermodynamics; D014025:Titanium / Q000737:chemistry*
chemical_list: D000464:Alginates; D006603:Hexuronic Acids; C009495:titanium dioxide; D020723:Glucuronic Acid; D014025:Titanium
keywords: Alginate; Aquatic systems; Isothermal titration calorimetry; Metal oxide stability; Natural organic matter; TiO(2) nanoparticles