Potentiometric titrations of rutile suspensions to 250°C

Michael L. Machesky, David J. Wesolowski, Donald A. Palmer, Ken Ichiro-Hayashi

Research output: Contribution to journalArticlepeer-review

Abstract

A stirred hydrogen electrode concentration cell was used to conduct potentiometric titrations of rutile suspensions from 25 to 250°C in NaCl and tetramethylammonium chloride media (0.03 to 1.1 m). Hydrothermal pretreatment of the rutile improved titration reproducibility, decreased titration hysteresis, and facilitated determination of the point of zero net proton charge (pHznpc). These pHznpc values are 5.4, 5.1, 4.7, 4.4, 4.3 (±0.2 pH units), and 4.2 (±0.3 pH units) at 25, 50, 100, 150, 200, and 250°C, respectively. The difference between these pHznpc values and 1/4 pK(w) (the neutral pH of water) is rather constant between 25 and 250°C (-1.45 ± 0.2). This constancy is useful for predictive purposes and, more fundamentally, may reflect similarities between the hydration behavior of surface hydroxyl groups and water. A three-layer, 1pKa surface complexation model with three adjustable parameters (two capacitance values and one counterion binding constant) adequately described all titration data. The most apparent trend in these data for pH values greater than the pHznpc was the increase in proton release (negative surface charge) with increasing temperature. This reflects more efficient screening by Na+ relative to Cl-. Replacing Na+ with the larger tetramethylammonium cation for some conditions resulted in decreased proton release due to the less efficient screening of negative surface charge by this larger cation.

Original languageEnglish (US)
Pages (from-to)298-309
Number of pages12
JournalJournal of Colloid And Interface Science
Volume200
Issue number2
DOIs
StatePublished - Apr 15 1998
Externally publishedYes

Keywords

  • Adsorption
  • Metal oxide
  • PZC
  • Potentiometric titration
  • Rutile
  • Surface

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Colloid and Surface Chemistry

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