A novel mechanism for protonating bridging O atoms (O br) and dissolving silica is proposed that is consistent with experimental data and quantum mechanical simulations of the α-quartz (101)/water interface. The new hypothesis is that H +-transfer occurs through internal surface H-bonds (i.e., SiOH-O br) rather than surface water H-bonds and that increasing ionic strength, I, favors formation of these internal H-bonds, leading to a larger pre-exponential factor, A, in the Arrhenius equation, k = A exp(-ΔE a/RT), and higher rates of dissolution. Projector-augmented planewave density functional theory (DFT) molecular dynamics (MD) simulations and static energy minimizations were performed on the α-quartz (101) surface and with pure water, with Cl-, Na +, and Mg 2+. Classical molecular dynamics were performed on α-quartz (101) surface and pure water only. The nature of the H-bonding of the surface silanol (SiOH) groups with the solution and with other surface atoms is examined as a test of the above hypothesis. Statistically significant increases in the percentages of internal SiOH-O br H-bonds, as well as the possibility of Obr protonation with H-bond linkage to silanol group, are predicted by these simulations, which is consistent with the new hypothesis. This new hypothesis is discussed in relation to experimental data on silicate dissolution.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films