Interfacial structures and acidity of edge surfaces of ferruginous smectites

Xiandong Liu*, Jun Cheng, Michiel Sprik, Xiancai Lu, Rucheng Wang

*Corresponding author for this work

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

We report an FPMD (first-principles molecular dynamics) study of the interfacial structures and acidity constants of the edge surfaces of ferruginous smectites. To understand the effects of Fe oxidation states on the interfacial properties, we investigated both the oxidized and reduced states of the (010)-type edges of two clay models with different Fe contents. The coordination states of edge Fe atoms are determined from the free energy curves for the desorption of the H2O ligands. The results of both clay models show that for Fe(III), only the 6-coordinate states are stable, whereas for Fe(II), both the 6- and 5-coordinate states are stable. Using the FPMD-based vertical energy gap technique, the pKa values of the edge sites are evaluated for both oxidation states. The results indicate that for both clay models, both the octahedral and tetrahedral sites become much less acidic upon Fe reduction. Therefore, the comparison reveals that the interfacial structures and protonation states are strongly dependent on the Fe oxidation states. Using the calculated results, we have derived the pH-dependent surface complexing mechanisms of ferruginous smectites.

Original languageEnglish
Pages (from-to)293-301
Number of pages9
JournalGeochimica et Cosmochimica Acta
Volume168
Early online date16 Jul 2015
DOIs
Publication statusPublished - 1 Nov 2015

ASJC Scopus subject areas

  • Geochemistry and Petrology

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