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Proceedings Paper

Characterization of siloxane adsorbates covalently attached to TiO2
Author(s): Nobuhito Iguchi; Clyde Cady; Robert C. Snoeberger III; Bryan M. Hunter; Eduardo M. Sproviero; Charles A. Schmuttenmaer; Robert H. Crabtree; Gary W. Brudvig; Victor S. Batista
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Paper Abstract

Siloxanes with the general formula R-(CH2)n-Si-(OR')3 form durable bonds with inorganic materials upon hydrolysis of labile -OR' groups, and serve as robust coupling agents between organic and inorganic materials. In the field of dye-sensitized solar cells, functionalization of TiO2 thin-films with siloxane adsorbates has been shown to be useful as a surface-passivation technique that hinders recombination processes and improves the overall efficiency of light-to-electricity conversion. However, the attachment of siloxane adsorbates on TiO2 surfaces still remains poorly understood at the molecular level. In this paper, we report the characterization of 3-(triethoxysilyl) propionitrile (TPS) adsorbates, covalently attached onto TiO2 surfaces. We combine synthetic methods based on chemical vapor deposition, Fourier transform (FT) infrared (IR) spectroscopy and electronic structure calculations based on density functional theory (DFT). We predict that trifunctional siloxanes form only 2 covalent bonds, in a 'bridge' mode with adjacent Ti4+ ions on the TiO2 surface, leaving 'dangling' alkoxy groups on the surface adsorbates. Our findings are supported by the observation of a prominent fingerprint band at 1000-1100 cm-1, assigned to Si-O-C stretching modes, and by calculations of binding enthalpies at the DFT B3LYP/(LACVP/6-31G**) level of theory indicating that the 'bridge' binding (ΔHb= -55 kcal mol-1) is more stable than 'tripod' motifs (ΔHb= -45 kcal mol-1) where siloxanes form 3 covalent bonds with the TiO2 surface. The alkoxysiloxane groups are robust under heat and water treatment and are expected to be particularly relevant for analytical methods since they could be exploited for immobilizing other functionalities onto the TiO2 surfaces.

Paper Details

Date Published: 21 August 2008
PDF: 8 pages
Proc. SPIE 7034, Physical Chemistry of Interfaces and Nanomaterials VII, 70340C (21 August 2008); doi: 10.1117/12.798938
Show Author Affiliations
Nobuhito Iguchi, Yale Univ. (United States)
Clyde Cady, Yale Univ. (United States)
Robert C. Snoeberger III, Yale Univ. (United States)
Bryan M. Hunter, Yale Univ. (United States)
Eduardo M. Sproviero, Yale Univ. (United States)
Charles A. Schmuttenmaer, Yale Univ. (United States)
Robert H. Crabtree, Yale Univ. (United States)
Gary W. Brudvig, Yale Univ. (United States)
Victor S. Batista, Yale Univ. (United States)

Published in SPIE Proceedings Vol. 7034:
Physical Chemistry of Interfaces and Nanomaterials VII
Garry Rumbles; Oliver L. A. Monti, Editor(s)

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