Nanocrystalline anatase-electrolyte solution interface: A surface structural interpretation with the MUSIC and CD Models

Moira K. Ridley, Michael L. Machesky

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

Abstract

Mineral surface reactivity and pH-dependent charging in aqueous media is related to oxide surface structure and variations in the coordination of surface functional groups at mineral surfaces. Relatively little is known about how interface reactions affect the chemical and physical properties of nanoparticles. To develop a fundamental understanding of the surface reactivity of nanosized particles controlled studies with monodispersed crystalline anatase (TiO2) particles were performed. Bulk surface titrations were completed with commercially available anatase particles ranging in size from 200 to 3 nm diameter. The titrations were performed in NaCl media at ionic strengths from 0.005 to 0.3 molality. The focus of this contribution will be our efforts to rationalize the bulk surface titration data utilizing surface complexation modeling (SCM) that incorporates all available molecular information (e.g., Ti-O bond lengths), with crystallographic information acquired from abberation corrected electron microscopy (ACEM). ACEM imaging revealed that the [100] face predominates on the 20 nm particles, and edges/facets include [010], [001], and [0-11]. A MUSIC model based description of surface protonation permitted rationalization of the experimentally observed decrease in pHznpc values with increasing particle size. The surface charging curves were fit with a charge distribution (CD) model and a three-plane description of the Stern layer. Moreover, the titration data suggested an innersphere species for the so-called “inert” Na electrolyte cations. From the SCM, a bidentate innersphere Na-surface species predominated, with the spatial charge distributed between the anatase surface (0- plane) and the 1-plane. Conversely, the best-fit for the Cl- ions was a monodentate outersphere complex. As conventional, the outersphere complex was treated as a point charge at the Stern layer (2-plane). The capacitance value of the Stern layer increased with increasing particle size, equating to a narrower compact layer; thus, reproducing the experimental data which showed an enhancement in positive surface charge for the larger nanoparticles (>20nm).
Original languageEnglish (US)
Title of host publication18th annual V. M. Goldschmidt Conference, Vancouver, BC, Canada, July 13-18, 2008
PagesA796
StatePublished - 2008

Keywords

  • ISWS

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