First principles studies of the interactions between alkali metal elements and oxygen-passivated nanopores in graphene

Heath, Jonathan; Kuroda, Marcelo A.

doi:10.1039/c8cp04958k

Cited by 15 publications

(8 citation statements)

References 60 publications

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“…However, while critical to molecular dynamics (MD) simulations, the charge distribution and response of this pore is unknown. Previous simulations on this and related systems assume oxygen partial charges that span between q O = −0.21e and q O = −0.74e (10)(11)(12)(13)(14)(15), over which transport properties will vary markedly. To provide a more comprehensive approach, we reexamine this assignment using density functional theory (DFT) (see Methods and the Supplementary Materials for details).…”

Section: Partial Charge Distributionmentioning

confidence: 99%

Optimal transport and colossal ionic mechano-conductance in graphene crown ethers

et al. 2019

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Biological ion channels balance electrostatic and dehydration effects to yield large ion selectivity alongside high transport rates. These macromolecular systems are often interrogated through point mutations of their pore domain, limiting the scope of mechanistic studies. In contrast, we demonstrate that graphene crown ether pores afford a simple platform to directly investigate optimal ion transport conditions, i.e., maximum current densities and selectivity. Crown ethers are known for selective ion adsorption. When embedded in graphene, however, transport rates lie below the drift-diffusion limit. We show that small pore strains (1%) give rise to a colossal (100%) change in conductance. This process is electromechanically tunable, with optimal transport in a primarily diffusive regime, tending toward barrierless transport, as opposed to a knock-on mechanism. These observations suggest a novel setup for nanofluidic devices while giving insight into the physical foundation of evolutionarily optimized ion transport in biological pores.

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Section: Partial Charge Distributionmentioning

confidence: 99%

Optimal transport and colossal ionic mechano-conductance in graphene crown ethers

et al. 2019

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“…The landscape also depended on the pore charge, which is, however, not known. For the crown ether pore in graphene, the charge per oxygen atom (q O ) could be between −0.2 e and −0.7 e [27,[51][52][53]. We thus used two representative test charges, −0.24 e and −0.54 e. In the former, there was an energy barrier, and in the latter, there was a potential well at the center of the unstrained pore.…”

Section: Methodsmentioning

confidence: 99%

Diffusion Limitations and Translocation Barriers in Atomically Thin Biomimetic Pores

Sahu

Zwolak

2020

Entropy

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Ionic transport in nano- to sub-nano-scale pores is highly dependent on translocation barriers and potential wells. These features in the free-energy landscape are primarily the result of ion dehydration and electrostatic interactions. For pores in atomically thin membranes, such as graphene, other factors come into play. Ion dynamics both inside and outside the geometric volume of the pore can be critical in determining the transport properties of the channel due to several commensurate length scales, such as the effective membrane thickness, radii of the first and the second hydration layers, pore radius, and Debye length. In particular, for biomimetic pores, such as the graphene crown ether we examine here, there are regimes where transport is highly sensitive to the pore size due to the interplay of dehydration and interaction with pore charge. Picometer changes in the size, e.g., due to a minute strain, can lead to a large change in conductance. Outside of these regimes, the small pore size itself gives a large resistance, even when electrostatic factors and dehydration compensate each other to give a relatively flat—e.g., near barrierless—free energy landscape. The permeability, though, can still be large and ions will translocate rapidly after they arrive within the capture radius of the pore. This, in turn, leads to diffusion and drift effects dominating the conductance. The current thus plateaus and becomes effectively independent of pore-free energy characteristics. Measurement of this effect will give an estimate of the magnitude of kinetically limiting features, and experimentally constrain the local electromechanical conditions.

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“…The transport and interactions of alkali metals at mineral surfaces are important for various natural processes and industrial applications ranging from biological − and environmental chemistry to energy storage − and electrochemistry . Despite this general importance and relevance, the quantification of interfacial structure and electrostatics for the alkali halides has been hampered by the fact that there are only a few label-free and surface-selective experimental probes that are ion-specific. − Among them are X-ray spectroscopies, which can track the exchange of alkali cations on various mineral substrates such as muscovite mica but require a synchrotron source .…”

Section: Introductionmentioning

confidence: 99%

Quantification of Stern Layer Water Molecules, Total Potentials, and Energy Densities at Fused Silica:Water Interfaces for Adsorbed Alkali Chlorides, CTAB, PFOA, and PFAS

Chang,

Lozier,

et al. 2023

J. Phys. Chem. A

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We have employed amplitude- and phase-resolved second-harmonic generation spectroscopy to investigate ion-specific effects of monovalent cations at the fused silica:water interface maintained under acidic, neutral, and alkaline conditions. We find a negligible dependence of the total potential (as negative as −400 mV at pH 14), the second-order nonlinear susceptibility (as large as 1.5 × 10–21 m2 V–1 at pH 14), the number of Stern layer water molecules (1 × 1015 cm–2 at pH 5.8), and the energy associated with water alignment upon going from neutral to high pH (ca. −24 kJ mol–1 to −48 kJ mol–1 at pH 13 and 14, close to the cohesive energy of liquid water but smaller than that of ice) on chlorides of the alkali series (M+ = Li+, Na+, K+, Rb+, and Cs+). Attempts are presented to provide estimates for the molecular hyperpolarizability of the cations and anions in the Stern layer at high pH, which arrive at ca. 20-fold larger values for α total ions (2) = α M + (2) + α OH – (2) + α Cl – (2) when compared to water’s molecular hyperpolarizability estimate from theory and point to a sizable contribution of deprotonated silanol groups at high pH. In contrast to the alkali series, a pronounced dependence of the total potential and the second-order nonlinear susceptibility on monovalent cationic (cetrimonium bromide, CTAB) and anionic (perfluorooctanoic and perfluorooctanesulfonic acid, PFOA and PFOS) surfactants was quantifiable. Our findings are consistent with a low surface coverage of the alkali cations and a high surface coverage of the surfactants. Moreover, they underscore the important contribution of Stern layer water molecules to the total potential and second-order nonlinear susceptibility. Finally, they demonstrate the applicability of heterodyne-detected second-harmonic generation spectroscopy for identifying perfluorinated acids at mineral:water interfaces.

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First principles studies of the interactions between alkali metal elements and oxygen-passivated nanopores in graphene

Abstract: We characterize the structure–property relationship of alkali metal elements in oxygen-passivated graphene pores using the density functional theory. We identify common trends in these systems based on their structural and electronic properties.

Cited by 15 publications

References 60 publications

Optimal transport and colossal ionic mechano-conductance in graphene crown ethers

Optimal transport and colossal ionic mechano-conductance in graphene crown ethers

Diffusion Limitations and Translocation Barriers in Atomically Thin Biomimetic Pores

Quantification of Stern Layer Water Molecules, Total Potentials, and Energy Densities at Fused Silica:Water Interfaces for Adsorbed Alkali Chlorides, CTAB, PFOA, and PFAS

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