Surface acidity of 2:1-type dioctahedral clay minerals from first principles molecular dynamics simulations

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

Research output: Contribution to journalArticle

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Abstract

We report a first principles molecular dynamics (FPMD) study of the acid chemistry of 2:1-type dioctahedral phyllosilicates. Using the FPMD based vertical energy gap method, we computed intrinsic acidity constants of phyllosilicate edge sites. The investigated models include both neutral and charged frameworks (i.e., Mg for Al replacement in octahedral sheets and Al for Si replacement in tetrahedral sheets) and the common edge surface types (i.e., (0 1 0) and (1 1 0)). The result of the neutral framework agrees with the experiment of pyrophyllite. For charged frameworks, it is found that triple bond; length of mdashAl(OH) sites in T-sheets (i.e., Al-sub) and triple bond; length of mdashMg(OH2) sites (i.e., Mg-sub) have extremely high pKas and thus they all keep protonated. Both types of substitutions increase pKas of the apical oxygen sites on (1 1 0) surfaces and Mg substitution also increases the pKas of neighboring silanol sites. With the calculated pKas, we explore the mechanism of heavy metal cations complexation on edge surfaces. As a quantitative basis, the results in this work can be used in future modeling and experimental studies for understanding acid reactivity of phyllosilicates.
Original languageEnglish
Pages (from-to)410 - 417
Number of pages8
JournalGeochimica et Cosmochimica Acta
Volume140
Early online date7 Jun 2014
DOIs
Publication statusPublished - 1 Sep 2014

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phyllosilicate
Clay minerals
Acidity
clay mineral
acidity
Molecular dynamics
Computer simulation
substitution
Substitution reactions
replacement
simulation
pyrophyllite
Acids
acid
Heavy Metals
Complexation
complexation
Cations
Energy gap
experimental study

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Surface acidity of 2:1-type dioctahedral clay minerals from first principles molecular dynamics simulations. / Liu, Xiandong; Cheng, Jun; Sprik, Michiel; Lu, Xiancai; Wang, Rucheng.

In: Geochimica et Cosmochimica Acta, Vol. 140, 01.09.2014, p. 410 - 417.

Research output: Contribution to journalArticle

Liu, Xiandong ; Cheng, Jun ; Sprik, Michiel ; Lu, Xiancai ; Wang, Rucheng. / Surface acidity of 2:1-type dioctahedral clay minerals from first principles molecular dynamics simulations. In: Geochimica et Cosmochimica Acta. 2014 ; Vol. 140. pp. 410 - 417.
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AU - Wang, Rucheng

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N2 - We report a first principles molecular dynamics (FPMD) study of the acid chemistry of 2:1-type dioctahedral phyllosilicates. Using the FPMD based vertical energy gap method, we computed intrinsic acidity constants of phyllosilicate edge sites. The investigated models include both neutral and charged frameworks (i.e., Mg for Al replacement in octahedral sheets and Al for Si replacement in tetrahedral sheets) and the common edge surface types (i.e., (0 1 0) and (1 1 0)). The result of the neutral framework agrees with the experiment of pyrophyllite. For charged frameworks, it is found that triple bond; length of mdashAl(OH) sites in T-sheets (i.e., Al-sub) and triple bond; length of mdashMg(OH2) sites (i.e., Mg-sub) have extremely high pKas and thus they all keep protonated. Both types of substitutions increase pKas of the apical oxygen sites on (1 1 0) surfaces and Mg substitution also increases the pKas of neighboring silanol sites. With the calculated pKas, we explore the mechanism of heavy metal cations complexation on edge surfaces. As a quantitative basis, the results in this work can be used in future modeling and experimental studies for understanding acid reactivity of phyllosilicates.

AB - We report a first principles molecular dynamics (FPMD) study of the acid chemistry of 2:1-type dioctahedral phyllosilicates. Using the FPMD based vertical energy gap method, we computed intrinsic acidity constants of phyllosilicate edge sites. The investigated models include both neutral and charged frameworks (i.e., Mg for Al replacement in octahedral sheets and Al for Si replacement in tetrahedral sheets) and the common edge surface types (i.e., (0 1 0) and (1 1 0)). The result of the neutral framework agrees with the experiment of pyrophyllite. For charged frameworks, it is found that triple bond; length of mdashAl(OH) sites in T-sheets (i.e., Al-sub) and triple bond; length of mdashMg(OH2) sites (i.e., Mg-sub) have extremely high pKas and thus they all keep protonated. Both types of substitutions increase pKas of the apical oxygen sites on (1 1 0) surfaces and Mg substitution also increases the pKas of neighboring silanol sites. With the calculated pKas, we explore the mechanism of heavy metal cations complexation on edge surfaces. As a quantitative basis, the results in this work can be used in future modeling and experimental studies for understanding acid reactivity of phyllosilicates.

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