Flow-based multiadsorbate ellipsometric porosimetry for the characterization of mesoporous Pt-TiO 2 and Au-TiO 2 nanocomposites

R. Alan May, Mehul N. Patel, Keith P. Johnston, Keith J. Stevenson

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27 Citations (Scopus)

Abstract

Au and Pt nanoparticle distributions within hierarchically ordered mesoporous TiO 2 were explored using a combination of techniques including ellipsometric porosimetry (EP) and X-ray photoelectron spectroscopy (XPS). EP studies were used to examine adsorbate-TiO 2 interactions and the influence of adsórbate polarity upon adsorption isotherms for mesoporous TiO 2 films with and without Pt and Au nanoparticles. In particular, methods are described for modeling EP data to estimate the surface area and porosity of mesoporous TiO 2 films and for estimating the pore size distribution (PSD) directly from the ellipsometry parameters Ψ and △ when fitting parameters alone are unable to extract reliable optical constants from the ellipsometry data. This approach reveals that mesoporous TiO 2 films of ∼200 nm thickness and ∼10 nm pore diameter can be loaded with 1.7 nm diameter Pt and 3.9 nm diameter Au nanoparticles up to 26 and 21 wt %, respectively. The BET surface area of a representative mesoporous TiO 2 sample using toluene as the adsorbate was found to be 44 m 2/g with a mean pore diameter of 8.8 nm. EP and XPS depth profiling experiments indicate that 1.7 nm diameter Pt nanoparticles are well dispersed through the mesoporous TiO 2 film, while 3.9 nm diameter Au nanoparticles are concentrated at the top of the film, blocking a significant portion of the available TiO 2 pore volume. UV irradiation of the TiO 2 films indicates that adsorbate-TiO 2 interactions and surface wetting effects can play a critical role in the resulting isotherm and in evaluation of PSD.

Original languageEnglish
Pages (from-to)4498-4509
Number of pages12
JournalLangmuir
Volume25
Issue number8
DOIs
Publication statusPublished - 21 Apr 2009
Externally publishedYes

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