Characterization of siloxane adsorbates covalently attached to TiO 2

Nobuhito Iguchi, Clyde Cady, Robert C. Snoeberger, Bryan M. Hunter, Eduardo M. Sproviero, Charles A. Schmuttenmaer, Robert H. Crabtree, Gary W. Brudvig, Victor S. Batista

Research output: Chapter in Book/Report/Conference proceedingConference contribution

15 Citations (Scopus)

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.

Original languageEnglish
Title of host publicationPhysical Chemistry of Interfaces and Nanomaterials VII
DOIs
Publication statusPublished - Nov 21 2008
EventPhysical Chemistry of Interfaces and Nanomaterials VII - San Diego, CA, United States
Duration: Aug 11 2008Aug 12 2008

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume7034
ISSN (Print)0277-786X

Other

OtherPhysical Chemistry of Interfaces and Nanomaterials VII
CountryUnited States
CitySan Diego, CA
Period8/11/088/12/08

Keywords

  • Binding enthalpy
  • DFT
  • IR vibrational spectroscopy
  • Linkers
  • Silanes
  • Siloxanes
  • Solar cells
  • TiO

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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  • Cite this

    Iguchi, N., Cady, C., Snoeberger, R. C., Hunter, B. M., Sproviero, E. M., Schmuttenmaer, C. A., Crabtree, R. H., Brudvig, G. W., & Batista, V. S. (2008). Characterization of siloxane adsorbates covalently attached to TiO 2. In Physical Chemistry of Interfaces and Nanomaterials VII [70340C] (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 7034). https://doi.org/10.1117/12.798938