The amorphous silica–liquid water interface studied by<i>ab initio</i>molecular dynamics (AIMD): local organization in global disorder

Cimas, Álvaro; Tielens, Frederik; Sulpizi, Marialore; Gaigeot, Marie‐Pierre; Costa, Dominique

doi:10.1088/0953-8984/26/24/244106

Cited by 75 publications

(101 citation statements)

References 49 publications

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“…We also note that recent ab initio experiments of a fully hydroxylated amorphous silica/water interface determined that there were three different silanols that donate hydrogen bonds to water molecules. 35 These sites were isolated silanols, geminal and vicinal disilanols ( Figure 6B). It is possible that these three sites correspond to the three sites observed although the authors did not determine their corresponding pK a values from the simulations.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Bimodal or Trimodal? The Influence of Starting pH on Site Identity and Distribution at the Low Salt Aqueous/Silica Interface

2015

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Second harmonic generation (SHG) is commonly employed to monitor processes at mineral oxide/liquid interfaces. Using SHG, we determine how the starting pH affects the acid−base chemistry of the silica/aqueous interface. We observe three different sites with pK a values of approximately 3.8, 5.2, and ∼9 (pK a -I, pK a -II, pK a -III, respectively), but the presence and relative abundance of these sites is very sensitive to the starting pH. For titrations initiated at pH 12, all three sites are observed, whereas only two sites are observed for titrations initiated at pH 2 or pH 7. Moreover, exposure to pH 2 facilitates the formation of pK a -II and pK a -III sites, while exposure to pH 7 results in pK a -I and pK a -III sites. Based on previous computational work, we assign these sites to three different hydrogen bonding environments at the interface including a hydrophobic site for the most acidic silanol corresponding to pK a -I. ■ INTRODUCTIONThe silica/water interface is one of the most environmentally and technologically relevant interfaces. The charged nature of this interface above pH 2, results in most processes at this interface involving electrostatic interactions. 1 These electrostatic interactions, which largely depend on the acid−base chemistry of silica, are critical to many geochemical, environmental and industrial processes. Consequently, to accurately predict both pollutant adsorption and transport 2,3 and interactions between analytes and glass substrates in biodiagnostics, 4 a complete picture of the silica interface is required. Furthermore, numerous geochemical studies on silicates have found that a layer of amorphous silica forms at the quartz/water 5 and silicate/water 6 interfaces, indicating that the reactivity of amorphous silica is relevant to a variety of geochemical systems. 5−7 Despite its importance, measuring the interfacial acid−base chemistry of silica over a wide pH range is challenging. Because silica is an insulator, techniques that measure the surface charge density through the conductivity of the material cannot be used. Potentiometric methods are amenable to silica, and consequently, there have been many studies that have looked at how the acid−base chemistry of silica colloids is perturbed by the addition of aqueous electrolytes. 8,9 More recently, X-ray photoelectron spectroscopy measurements have yielded the interfacial potential of colloidal silica. 10 However, one of the many difficulties in measuring colloidal silica is that it is unstable over a large pH range. 8 An alternative strategy involves utilizing planar silica and directly determining its acid−base chemistry with surface specific methods. Nonlinear optical techniques like second harmonic generation (SHG) and sum frequency generation (SFG) present unique advantages that include the ability to identify interfacial molecules based on their spectroscopic signatures, differentiate between molecules ordered at the interface versus those in the bulk solution, and study interfaces for a variety of materials including ...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Bimodal or Trimodal? The Influence of Starting pH on Site Identity and Distribution at the Low Salt Aqueous/Silica Interface

2015

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“…[52] Chemical shifts are a good proxy for the strength of hydrogen bonding, and entirely non-hydrogen-bonded water exhibits a strong upfield shift. [53][54][55] Hydrogen bonding at the amorphous silica interface was also studied in detail in a recent publication by Cimas et al [56]…”

Section: Hydrogen-bond Coordinationmentioning

confidence: 99%

Ab Initio H₂O in Realistic Hydrophilic Confinement

et al. 2014

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A protocol for the ab initio construction of a realistic cylindrical pore in amorphous silica, serving as a geometric nanoscale confinement for liquids and solutions, is presented. Upon filling the pore with liquid water at different densities, the structure and dynamics of the liquid inside the confinement can be characterized. At high density, the pore introduces long-range oscillations into the water density profile, which makes the water structure unlike that of the bulk across the entire pore. The tetrahedral structure of water is also affected up to the second solvation shell of the pore wall. Furthermore, the effects of the confinement on hydrogen bonding and diffusion, resulting in a weakening and distortion of the water structure at the pore walls and a slowdown in diffusion, are characterized.

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“…Molecular dynamics simulations of these systems 22,[26][27][28][29][30][31][32] provide molecularly detailed insight into the system and have been used extensively in conjunction with nonlinear optical experiments to fully elucidate interfacial organization and orientation.…”

Section: Introductionmentioning

confidence: 99%

Mechanism and Dynamics of Molecular Exchange at the Silica/Binary Solvent Mixtures Interface

Karnes

2015

J. Phys. Chem. A

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Abstract:Non-equilibrium molecular dynamics simulations of acetonitrile/methanol mixtures in contact with a hydroxylated silica surface are used to elucidate the mechanism of molecular exchange at a hydrophilic liquid/solid interface. The different hydrogen-bonding ability of the two solvents provides a driving force for the adsorption/desorption process, which is followed by examining several structural and energetic properties of the system. Two different reaction coordinates for the hydrogen bonding exchange are defined and are used to identify transition states in which the methanol attains a well-defined orientation. The reaction coordinates are used to examine the mechanism and dynamics of the exchange. We find that the exchange process involves multiple recrossing of the transition state and can progress via two different mechanisms, depending whether the methanol first acts as a hydrogen bond donor or acceptor at the silica surface.

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The amorphous silica–liquid water interface studied byab initiomolecular dynamics (AIMD): local organization in global disorder

Cited by 75 publications

References 49 publications

Bimodal or Trimodal? The Influence of Starting pH on Site Identity and Distribution at the Low Salt Aqueous/Silica Interface

Bimodal or Trimodal? The Influence of Starting pH on Site Identity and Distribution at the Low Salt Aqueous/Silica Interface

Ab Initio H₂O in Realistic Hydrophilic Confinement

Mechanism and Dynamics of Molecular Exchange at the Silica/Binary Solvent Mixtures Interface

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The amorphous silica–liquid water interface studied byab initiomolecular dynamics (AIMD): local organization in global disorder

Cited by 75 publications

References 49 publications

Bimodal or Trimodal? The Influence of Starting pH on Site Identity and Distribution at the Low Salt Aqueous/Silica Interface

Bimodal or Trimodal? The Influence of Starting pH on Site Identity and Distribution at the Low Salt Aqueous/Silica Interface

Ab Initio H2O in Realistic Hydrophilic Confinement

Mechanism and Dynamics of Molecular Exchange at the Silica/Binary Solvent Mixtures Interface

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Ab Initio H₂O in Realistic Hydrophilic Confinement