title: A Close Look at the Structure of the TiO2-APTES Interface in Hybrid Nanomaterials and Its Degradation Pathway: An Experimental and Theoretical Study.
abstract: The surface functionalization of TiO2-based materials with alkylsilanes is attractive in several cutting-edge applications, such as photovoltaics, sensors, and nanocarriers for the controlled release of bioactive molecules. (3-Aminopropyl)triethoxysilane (APTES) is able to self-assemble to form monolayers on TiO2surfaces, but its adsorption geometry and solar-induced photodegradation pathways are not well understood. We here employ advanced experimental (XPS, NEXAFS, AFM, HR-TEM, and FT-IR) and theoretical (plane-wave DFT) tools to investigate the preferential interaction mode of APTES on anatase TiO2. We demonstrate that monomeric APTES chemisorption should proceed through covalent Si-O-Ti bonds. Although dimerization of the silane through Si-O-Si bonds is possible, further polymerization on the surface is scarcely probable. Terminal amino groups are expected to be partially involved in strong charge-assisted hydrogen bonds with surface hydroxyl groups of TiO2, resulting in a reduced propensity to react with other species. Solar-induced mineralization proceeds through preferential cleavage of the alkyl groups, leading to the rapid loss of the terminal NH2moieties, whereas the Si-bearing head of APTES undergoes slower oxidation and remains bound to the surface. The suitability of employing the silane as a linker with other chemical species is discussed in the context of controlled degradation of APTES monolayers for drug release and surface patterning.
authors.affiliation: Department of Chemistry, Università degli Studi di Milano, Via Golgi 19, 20133 Milano, Italy; Consorzio INSTM, Via Giusti 9, 50121 Firenze, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Meroni
authors.affiliation: Department of Chemistry, Università degli Studi di Milano, Via Golgi 19, 20133 Milano, Italy; Center for Materials Crystallography, Aarhus University, Langelandsgade 140, DK-8000 Aarhus, Denmark.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Lo Presti
authors.affiliation: Department of Chemistry, Università degli Studi di Milano , Via Golgi 19, 20133 Milano, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Di Liberto
authors.affiliation: Department of Chemistry, Università degli Studi di Milano, Via Golgi 19, 20133 Milano, Italy; Consorzio INSTM, Via Giusti 9, 50121 Firenze, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Ceotto
authors.affiliation: Imaging and Medical Beamline, Australian Synchrotron, Clayton, Victoria, Australia 3168.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Acres
authors.affiliation: Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy; Molecular Model Discovery Laboratory, Department of Chemistry and Biotechnology, Swinburne University of Technology, Melbourne 3122, Australia; Istituto Officina dei Materiali, Consiglio Nazionale delle Ricerche, 34149 Basovizza, Italy.
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Prince
authors.affiliation: Department of Chemistry, Università degli Studi di Milano , Via Golgi 19, 20133 Milano, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bellani
authors.affiliation: Department of Engineering Physics, Polytechnique Montréal , H3T 1J4 Montreal, Canada.
authors.forename: Guido
authors.initials: G
authors.lastname: Soliveri
authors.affiliation: Department of Chemistry, Università degli Studi di Milano, Via Golgi 19, 20133 Milano, Italy; Consorzio INSTM, Via Giusti 9, 50121 Firenze, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Ardizzone