Propensity of Hydrated Excess Protons and Hydroxide Anions for the Air–Water Interface

Tse, Y.-L. S.; Chen, Chen; Lindberg, Gerrick E.; Kumar, Revati; Voth, Gregory A.

doi:10.1021/jacs.5b07232

Cited by 116 publications

(157 citation statements)

References 53 publications

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“…However, as will be shown in the next section, the behavior of OH − is completely different al low pH values. On the other hand, the slight decrease of the surface tension of acids with increasing acid concentration suggests that the interaction between H + and the surface is attractive and of the order of 0.5-1 kT, again in agreement with many experimental and computational results [22].…”

Section: Determination Of Short-range Potentials From the Surface Tensupporting

confidence: 88%

On the surface tension and Zeta potential of electrolyte solutions

Manciu

Ruckenstein

2017

Advances in Colloid and Interface Science

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Section: Determination Of Short-range Potentials From the Surface Tensupporting

confidence: 88%

On the surface tension and Zeta potential of electrolyte solutions

Manciu

Ruckenstein

2017

Advances in Colloid and Interface Science

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“…The electrokinetic experiments of both air and oil droplets paint a very similar picture despite having rather disparate chemistries namely, that the zeta potential (ζ) vanishes under acidic conditions and that with increasing pH, it becomes increasingly negative showing that these interfaces retain a negative charge at neutral pH. 3 If waters constituent ions, the proton and hydroxide are the only sources of charging in water, these experiments suggest that the negatively charged OH − ions stick to the surfaces with binding energies on the order of [10][11][12][13][14][15][16][17][18][19][20] times larger than thermal energy 5,6 ! This interpretation has been heavily contested from both experimental and theoretical fronts.…”

Section: Introductionmentioning

confidence: 92%

Charge transfer as a ubiquitous mechanism in determining the negative charge at hydrophobic interfaces

2020

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The origin of the apparent negative charge at hydrophobic-water interfaces has fueled one of the biggest debates in physical chemistry for several decades. The most common interpretation given to explain this observation is that negatively charged hydroxide ions (OH-) bind strongly to the interfaces. Here, using first principles calculations of the air-water and oil-water interfaces consisting of thousands of atoms, we unravel a mechanism that does not require the presence of OH-. We show that small amounts of charge transfer along hydrogen bonds and asymmetries in the hydrogen bond network, associated with local topological defects can lead to the accumulation of negative surface charge at both interfaces. For water near oil, we show that there is also some spillage of electron density into the oil leaving it negatively charged. The surface charge densities at both interfaces is computed to be approximately −0.015 e/nm 2 in agreement with electrophoretic experiments. We also show, using an energy decomposition analysis, that the electronic origin of this phenomena is rooted in a collective polarization and charge transfer effect.

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“…It is found that (H O ) versus [HX] is consistent for distinct halide species within our measurement uncertainty, even if the corresponding /| | appears with different One could convert the deduced K to the partitioning coefficient defined as the ratio of the volume ion density in the surface region to that in the bulk, denoted by KV, if the depth profile of ion distributions can be known. Because such information is not experimentally available, we follow the theoretical reports(4,8,36) to consider the adsorbed hydronium ions to distribute in a surface layer with an effective thickness L that ranges from a H-bonding length (1.97 Å) to an intermolecular distance (~3.1 Å). This approximation yields KV ≈ K/L = 3.61 ~ 5.68, corresponding to a pH difference of the surface with respect to the bulk region,pH, by -0.66 (±0.10), and the adsorption free energy for hydronium ions G = -3.74 (±0.56) kJ/mol.…”

mentioning

confidence: 99%

Affinity of Hydrated Protons at Intrinsic Water/Vapor Interface Revealed by Ion-Induced Water Alignment

Chiang

Dalstein

Wen

2020

J. Phys. Chem. Lett.

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ABTRACT:Protons at the water/vapor interface are relevant for atmospheric and environmental processes, yet to characterize their surface affinity on the quantitative level is still challenging.Here we utilize phase-sensitive sum-frequency vibrational spectroscopy to quantify the surface density of protons (or their hydronium form) at the intrinsic water/vapor interface, through inspecting the surface-field-induced alignment of water molecules in the electrical double layer of ions. With hydrogen halides in water, the surface adsorption of protons is found to be independent of specific proton-halide anion interactions and to follow a constant adsorption free energy, G ~ -3.74 (±0.56) kJ/mol, corresponding to a reduction of the surface pH with respect to the bulk value by 0.66 (±0.10), for bulk ion concentrations up to 0.3 M. Our spectroscopic study is not only of importance in atmospheric chemistry, but also offers a microscopic-level basis to develop advanced quantum-mechanical models for molecular simulations. MAIN TEXT:Protons at water/vapor interfaces play a key role in atmospheric chemistry and environmental science (1, 2). They have been the topics of extensive theoretical and experimental studies for decades (3-18), but good understanding of the surface affinity of protons on the microscopic and quantitative level is still lacking. Molecular dynamics (MD) simulations generally predicted that protons (H + ) could appear at the interface in the form of hydronium (H3O + ), while the quantitative details, such as the adsorption free energy and the depth profile of ion concentrations, depend very much on the molecular model and interaction potentials assumed (3-8). Several experimental approaches have been used to verify the qualitative conclusion from the simulations (9-18), but extension of these efforts to quantitative characterizations of the proton adsorption remains challenging (17). This largely limits our knowledge on the underlying mechanisms and the role of proton in many relevant interfacial processes. Technically, it is generally difficult to adopt macroscopic observables from surface tension, electrokinetic, and Kelvin probe measurements to yield molecular-level interfacial properties without crucial model assumption (17)(18)(19). For molecular-scale measurements, X-ray spectroscopies can examine the proton effect at water interfaces indirectly through probing relative concentration changes of the counterions (9, 10), but, yet, the surface affinity of protons has not been quantified from the results. Surface-specific optical sum frequency generation (SFG) and second harmonic generation (SHG) were widely employed to explore this issue (11)(12)(13)(14)(15)(16). But, in many reports, the proton propensity were only studied comparatively with respect to other ions without quantitative details (13)(14)(15). In the other, the surface concentration of protons was estimated by inspecting their reaction with extrinsic interfacial label molecules (16), whereas how the result is affected by the proton-label m...

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Propensity of Hydrated Excess Protons and Hydroxide Anions for the Air–Water Interface

Cited by 116 publications

References 53 publications

On the surface tension and Zeta potential of electrolyte solutions

On the surface tension and Zeta potential of electrolyte solutions

Charge transfer as a ubiquitous mechanism in determining the negative charge at hydrophobic interfaces

Affinity of Hydrated Protons at Intrinsic Water/Vapor Interface Revealed by Ion-Induced Water Alignment

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