The Effects of Hofmeister Cations at Negatively Charged Hydrophilic Surfaces

Flores, Sarah C.; Kherb, Jaibir; Konelick, Nicole; Chen, Xin; Cremer, Paul S.

doi:10.1021/jp210791j

Cited by 131 publications

(162 citation statements)

References 58 publications

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“…It is well accepted that electrolytes bring interfacial disorder, as evidenced by the intensity shrink of the ice-like vibrational signatures, which in turn shows the disappearance of the strong H-bonds formed by interfacial water molecules. At the fused quartz/water interface, it has been shown that SFG intensities depend on the nature of both cations 13 and anions. 14 From the spectroscopic results, cations with higher surface charge densities induce the largest SFG intensity weakening: such large perturbation on interfacial water may thus indicate that, for instance, Na + comes closer to the surface than Cs + .…”

Section: ■ Introductionmentioning

confidence: 99%

Electrolytes at the Hydroxylated (0001) α-Quartz/Water Interface: Location and Structural Effects on Interfacial Silanols by DFT-Based MD

Pfeiffer-Laplaud

Gaigeot

2016

J. Phys. Chem. C

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Structural properties of NaCl, KCl, and NaI electrolytes forming an electrical double layer (EDL) at the fully hydroxylated (0001) α-quartz/liquid water interface have been investigated by means of first-principles molecular dynamics simulations (FPMD). Cations are found in inner-sphere conformations, directly bonded on two in-plane silanol groups that replace water molecules that would be present in the first solvation shell of the aqueous cations. Anions are located within the second/third water layer above the surface, fully solvated as in pure liquid water, and cation−anion adopt rather flexible solvent separated ion-pair (SSIP) geometries in the EDL. While the individual solvation shells of the aqua-ions are only slightly affected by ion-pairing at the interface, the silanols at the quartz surface are strongly perturbed. The presence of the electrolytes in the EDL affects more deeply the silanols' geometrical properties than single ions do (J. Phys. Chem. C 2016, 120, 4866−4880): the silanol−silanol intrasurface H-bonding that was observed at the neat interface is extremely weakened by the presence of the electrolytes. Further disordering of the surface silanols is characterized by large changes in their orientation and covalent bond-lengths, regardless of their in-plane (IP) or out-of-plane (OP) orientations. Such structural changes of the surface silanols are tentatively correlated here with an increase in the basicity of all surface sites. ■ INTRODUCTIONIons from electrolytic solutions play key roles in interfacial water/mineral properties. Their adsorption behaviors typically drive pollutant transport in groundwater, 1,2 mineral dissolution, 3 or clay swelling, 4 to name a few. Electrolytes can strongly affect the binding of organic molecules because of competitive adsorption. 5 Even non-adsorbed electrolyte ions can influence adsorption of biomolecules like peptides or DNA 6−9 through conformational changes or ion-pairing.Cations and/or anions from electrolytes get distributed at aqueous solid interfaces so as to form an electrical double layer (EDL). EDLs are known to control the chemical reactivity of the surface, and varying the ionic strength tunes the EDL depth or Debye length. Ionic strength effects can be probed at water/ mineral interfaces via sum frequency generation (SFG) spectroscopy through the indirect knowledge of the interfacial water structural response to the presence of the ions. 10−12 Of particular interest are the electrolyte-induced perturbations on the "ice-like" and "liquid-like" bands in the O−H stretching region. It is well accepted that electrolytes bring interfacial disorder, as evidenced by the intensity shrink of the ice-like vibrational signatures, which in turn shows the disappearance of the strong H-bonds formed by interfacial water molecules. At the fused quartz/water interface, it has been shown that SFG intensities depend on the nature of both cations 13 and anions. 14 From the spectroscopic results, cations with higher surface charge densities induce the largest SFG i...

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Section: ■ Introductionmentioning

confidence: 99%

Electrolytes at the Hydroxylated (0001) α-Quartz/Water Interface: Location and Structural Effects on Interfacial Silanols by DFT-Based MD

Pfeiffer-Laplaud

Gaigeot

2016

J. Phys. Chem. C

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“…The surface structure of these particles has been previously studied by in-situ 29 Si NMR and no evidence of surface bound polymeric brushes were seen, 36 5 frequency generation study on the effects of cations at the water-silica and water-titania (TiO 2 ) interfaces. 28 Potentiometric Titrations. Surface charge densities (SCDs) are determined by potentiometric titration using a Mettler-Toledo G20 Compact Titrator equipped with a Mettler-Toledo Expert electrode and an electronic controlled rod stirrer (70% polypropylene and 30% fiberglass).…”

Section: Introductionmentioning

confidence: 99%

Quantifying Specific Ion Effects on the Surface Potential and Charge Density at Silica Nanoparticle–Aqueous Electrolyte Interfaces

2016

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The surface charge density and surface potential of oxide surfaces are to a large extent regulated by the co-and counterion distributions in the electrical double layer. Here we study the effect of different anions (Cl − , Br − , I − , HCOO − and NO 3 − ) in sodium electrolytes and different cations (Li + , Na + , K + and Cs + ) in chloride electrolytes on the surface charge density and relative surface potential of colloidal nanometer sized silica (SiO 2 ) as a function of electrolyte concentration and bulk pH using potentiometric titrations, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) from a liquid microjet. Our results reveal that the identity of the anion has no significant effect on the nanoparticles surface charge density and relative surface potential at bulk pH where silica is negatively charged, consistent with textbook arguments of electrostatics and their exclusion from the region of the electrical double layer that regulates these properties. By contrast, the identity of the cation in solution is significant on both the surface charge density and surface potential. Specific cation effects are rationalized by their respective distance of closest approach to the nanoparticles surface-the hydrated cation diameter sets the outer Helmholtz plane and in turn the capacitance of the Stern layer.

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“…7 Depending on the molecular context, the hydration properties of ammonium can vary somewhat, but in general it behaves similar to larger alkali cations. 8 In contrast, the guanidinium functionality can be found on either of the extreme sides of the Hofmeister series depending on the particular process under investigation.…”

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confidence: 99%

Surface Behavior of Hydrated Guanidinium and Ammonium Ions: A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics

et al. 2014

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Through the combination of surface sensitive photoelectron spectroscopy and molecular dynamics simulation, the relative surface propensities of guanidinium and ammonium ions in aqueous solution are characterized. The fact that the N1s binding energies di↵er between these two species was exploited to monitor their relative surface concentration through their respective photoemission intensities. Aqueous solutions of ammonium and guanidinium chloride, and mixtures of these salts, have been studied in a wide concentration range and it is found that the guanidinium ion has a greater propensity to reside at the aqueous surface than the ammonium ion. A large portion of the relative excess of guanidinium ions in the surface region of the mixed solutions can be explained by replacement of ammonium ions by guanidinium ions in the surface region in combination with a strong salting out e↵ect of guanidinium by ammonium ions at increased concentrations. This interpretation is supported by molecular dynamics simulations, which reproduce the experimental trends very well.The simulations suggest that the relatively higher surface propensity of guanidinium compared to ammonium ions is due to the ease of dehydration of the faces of the almost planar guanidinium ion, which allows it to approach the water-vapor interface oriented parallel to it.

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The Effects of Hofmeister Cations at Negatively Charged Hydrophilic Surfaces

Cited by 131 publications

References 58 publications

Electrolytes at the Hydroxylated (0001) α-Quartz/Water Interface: Location and Structural Effects on Interfacial Silanols by DFT-Based MD

Electrolytes at the Hydroxylated (0001) α-Quartz/Water Interface: Location and Structural Effects on Interfacial Silanols by DFT-Based MD

Quantifying Specific Ion Effects on the Surface Potential and Charge Density at Silica Nanoparticle–Aqueous Electrolyte Interfaces

Surface Behavior of Hydrated Guanidinium and Ammonium Ions: A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics

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