Polynuclear Speciation of Trivalent Cations near the Surface of an Electrolyte Solution

Bera, Mrinal K.; Antonio, Mark R.

doi:10.1021/acs.langmuir.5b01354

Cited by 11 publications

(7 citation statements)

References 60 publications

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“…For instance, water is layered and orientationally ordered at interfaces, 14,15 the dielectric constant is significantly lower (~ 5) than the bulk value (~ 80), 16,17 and the ionic species that are not present in the bulk can be stable at the interface. 18 All these differences make it difficult to predict how ions behave at interfaces based on the bulk solution properties. The difficulty increases when the ion cannot be treated as a zero-dimensional unit charge interacting with an ideal surface.…”

Section: Introductionmentioning

confidence: 99%

Chemical Potential Driven Reorganization of Anions between Stern and Diffuse Layers at the Air/Water Interface

Kumal

Nayak

et al. 2022

J. Phys. Chem. C

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Ion adsorption and transfer at charged interfaces play key roles in various industrial and environmental processes. Molecular scale details of ion-ion, ion-water, and ion-surface interactions and their dependence on the character of the ion (ion-specific effects) are still debated.Complex ions, such as SCNand SeCN -, are particularly interesting due to their unexpected adsorption trends which are ascribed to their permanent dipole moment and non-spherical shape.Here, we combine vibrational sum frequency generation (VSFG) spectroscopy and surface sensitive synchrotron X-ray studies to provide a detailed description of SeCNadsorption at a charged surfactant monolayer at the air/aqueous interface. Using multiple polarization combinations in VSFG to probe the -CN stretch, we show that the average orientation of SeCNanions with respect to the surface normal changes from 45° to 22° with the increasing KSeCN concentration. X-ray fluorescence experiments of Se K-edge and VSFG studies of -OH stretch show that SeCNinterfacial coverage (Stern layer + diffuse layer) saturates at very low bulk concentrations, but their orientational organization, distribution between Stern and diffuse layers, and effects on the hydrogen bonding network of the interfacial water continue to change with increasing bulk KSeCN concentration. X-ray reflectivity (XR) studies provide further evidence for increasing SeCNpopulation in Stern layer correlated with the orientational reorganization. These results show that the increasing chemical potential may lead to further reorganization of the adsorbed ions, even though the total interfacial ion population does not change. The reorganization of the interfacial ions and the water may be very important in chemical separations of heavy metals, where metal-anion complexes drive the selective ion transfer at aqueous interfaces.

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Section: Introductionmentioning

confidence: 99%

Chemical Potential Driven Reorganization of Anions between Stern and Diffuse Layers at the Air/Water Interface

Kumal

Nayak

et al. 2022

J. Phys. Chem. C

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“…The surface water structure is related to the identity of the surface-active species due to surface solvation effects; for multivalent cations, this is not well understood. Of the few published studies, Antonio and co-workers provide evidence of a bridging-polynuclear motif between two aqua lanthanide metal centers at the air/aqueous interface in both Er(III) and Eu(III) solutions; these surface motifs are unique from the mononuclear complexes observed in the bulk. , However, unlike the lanthanide cations, Fe(III) can also complex with its counterions forming multiple species dependent on concentration and pH. , It is thus difficult to predict precisely which of these Fe(III) complex species exist at the aqueous surface, if at all.…”

Section: Introductionmentioning

confidence: 99%

Iron(III) Speciation Observed at Aqueous and Glycerol Surfaces: Vibrational Sum Frequency and X-ray

Husek

Biswas

et al. 2019

J. Am. Chem. Soc.

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Aqueous solutions of FeCl3 have been widely studied to shed light on a number of processes from dissolution, mineralization, biology, electrocatalysis, corrosion, to microbial biomineralization. Yet there are little to no molecular level studies of the air–liquid FeCl3 interface. Here, both aqueous and glycerol FeCl3 solution surfaces are investigated with polarized vibrational sum frequency generation (SFG) spectroscopy. We also present the first ever extreme ultraviolet reflection–absorption (XUV-RA) spectroscopy measurements of solvated ions and complexes at a solution interface, and observe with both X-ray photoelectron spectroscopy (XPS) and XUV-RA the existence of Fe(III) at the surface and in the near surface regions of glycerol FeCl3 solutions, where glycerol is used as a high vacuum compatible proxy for water. XPS showed Cl– and Fe(III) species with significant Fe(III) interfacial enrichment. In aqueous solutions, an electrical double layer (EDL) of Cl– and Fe(III) species at 0.5 m FeCl3 concentration is observed as evidenced from an enhancement of molecular ordering of water dipoles, consistent with the observed behavior at the glycerol surface. At higher concentrations in water, the EDL appears to be substantially repressed, indicative of further Fe(III) complex enrichment and dominance of a centrosymmetric Fe(III) species that is surface active. In addition, a significant vibrational red-shift of the dangling OH from the water molecules that straddle the air–water interface reveals that the second solvation shell of the surface active Fe(III) complex permeates the topmost layer of the aqueous interface.

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“…In this paper, we study the adsorption of PtCl 6 2– anions at 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP) monolayers at the air/water interface (Figure ). Having a quaternary amine headgroup, DPTAP is a good model for most common extractants used in PGM extraction. , Also, its interactions with lighter anions are well-documented. , The air/water interface is a good model system to study the aqueous side of the oil/water interface, since air has a similar dielectric constant (ε = 1) to oil (ε ∼ 2) and allows us to tune the relevant parameters more easily. − Our aqueous subphase contains 0.5 M LiCl to simulate the process conditions, and the [PtCl 6 2– ]/[Cl – ] ranges from 10 –5 to 10 –1 . Anomalous X-ray reflectivity (a-XR) and X-ray fluorescence near total reflection (XFNTR) measurements directly determine the amount of PtCl 6 2– complexes adsorbed in the diffuse and Stern layers, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…Extractant-ion complexes at the oil/water interface have been investigated with in situ scattering and spectroscopy experiments. [9][10][11] Also, experiments designed to model certain aspects of ion speciation [26][27][28] and extractant-ion interactions at the air/water [29][30] and solid/water 22 interfaces have been reported.…”

mentioning

confidence: 99%

“…[33][34] The air/water interface is a good model system to study the aqueous side of the oil/water interface, since air has a similar dielectric constant ( = 1) to oil ( ~ 2), and allows us to tune the relevant parameters more easily. [26][27][28][29][30] Our aqueous subphase contains 0.5 M LiCl to simulate the process conditions, and the [PtCl6 2-]/[Cl -] ranges from 10 -5 to 10 -1 . Anomalous x-ray reflectivity (a-XR) and x-ray fluorescence near total reflection (XFNTR) measurements directly determine the amount of PtCl6 2complexes adsorbed in the diffuse and Stern layers, respectively.…”

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confidence: 99%

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Two-Step Adsorption of PtCl₆^2– Complexes at a Charged Langmuir Monolayer: Role of Hydration and Ion Correlations

et al. 2017

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Anion exchange at positively charged interfaces plays an important role in a variety of physical and chemical processes. However, the molecular scale details of these processes, especially with heavy and large anionic complexes, are not well-understood. We studied the adsorption of PtCl6 2anionic complexes to floating DPTAP monolayers in the presence of excess Clas a function of the bulk chlorometalate concentration. In situ x-ray scattering and fluorescence measurements, which are element and depth sensitive, show that the chlorometalate ions only adsorb in the diffuse layer at lower concentrations, while they adsorb predominantly in the Stern layer at higher concentrations. The response of DPTAP molecules to the adsorbed ions is determined independently by grazing incidence x-ray diffraction, and supports this picture. Molecular dynamics simulations further elucidate the nanoscale structure of the interfacial complexes. The results suggest that ion hydration and ion-ion correlations play a key role in the competitive adsorption process. TOC GRAPHICSKEYWORDS Air/water interface, anion recognition, Hofmeister effects, specific ion effects, solvent extraction.

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Polynuclear Speciation of Trivalent Cations near the Surface of an Electrolyte Solution

Cited by 11 publications

References 60 publications

Chemical Potential Driven Reorganization of Anions between Stern and Diffuse Layers at the Air/Water Interface

Chemical Potential Driven Reorganization of Anions between Stern and Diffuse Layers at the Air/Water Interface

Iron(III) Speciation Observed at Aqueous and Glycerol Surfaces: Vibrational Sum Frequency and X-ray

Two-Step Adsorption of PtCl₆^2– Complexes at a Charged Langmuir Monolayer: Role of Hydration and Ion Correlations

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Polynuclear Speciation of Trivalent Cations near the Surface of an Electrolyte Solution

Cited by 11 publications

References 60 publications

Chemical Potential Driven Reorganization of Anions between Stern and Diffuse Layers at the Air/Water Interface

Chemical Potential Driven Reorganization of Anions between Stern and Diffuse Layers at the Air/Water Interface

Iron(III) Speciation Observed at Aqueous and Glycerol Surfaces: Vibrational Sum Frequency and X-ray

Two-Step Adsorption of PtCl62– Complexes at a Charged Langmuir Monolayer: Role of Hydration and Ion Correlations

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Two-Step Adsorption of PtCl₆^2– Complexes at a Charged Langmuir Monolayer: Role of Hydration and Ion Correlations