Elucidating Trivalent Ion Adsorption at Floating Carboxylic Acid Monolayers: Charge Reversal or Water Reorganization?

Nayak, Srikanth; Kumal, Raju R.; Lee, Seung Eun; Uysal, Ahmet

doi:10.26434/chemrxiv-2023-n278x

Cited by 9 publications

(25 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is in contrast to the strong ion specific trends observed at the silica interface but agrees well with the indistinguishable behavior of these salts at AA monolayers [18]. In recent years, many studies demonstrated that the surface characteristics play an important role in ion-specific effects, and it is not trivial to generalize the observations in one specific system to others [32,49].…”

Section: Identifying Water Populations With Different Hydrogen Bondin...supporting

confidence: 83%

Monovalent Ion - Graphene Oxide Interactions are Controlled by Carboxylic Acid Groups: Sum Frequency Generation Spectroscopy Studies

Lee

Carr

Kumal

et al. 2023

Preprint

View full text Add to dashboard Cite

Graphene oxide has been extensively researched for use in separating rare earth elements. The presence of monovalent ions during separation processes is inevitable and can impact the adsorption of target ions. To better understand how monovalent ions behave near graphene oxide surfaces, we conducted a systematic investigation using vibrational sum frequency generation spectroscopy to study the effects of alkali metal ions on water organization near graphene oxide thin films at the air/water interface. We used an arachidic acid Langmuir monolayer as a benchmark for a pure carboxylic acid surface. The sum frequency signal showed a nonmonotonic trend with increasing salt concentration, reaching a maximum at 100 µM and 1 mM salt concentrations for graphene oxide and arachidic acid, respectively. Theoretical modeling of the concentration-dependent sum frequency signal from graphene oxide and arachidic acid surfaces revealed that the adsorption of monovalent ions is mainly controlled by the carboxylic acid groups on graphene oxide. An in-depth analysis of sum frequency spectra revealed at least three distinct water populations with different hydrogen bonding strengths. Interestingly, interfacial water structure seemed mostly insensitive to the character of the alkali cation, in contrast to similar studies conducted at the silica/water interface. However, an ion-specific effect was observed with lithium, whose strong hydration prevented direct interactions with the graphene oxide film. Overall, our study provides molecular-scale insights into water structures near interfacial graphene oxide in the presence of monovalent ions, which can aid in the development of graphene oxide-based separations.

show abstract

Section: Identifying Water Populations With Different Hydrogen Bondin...supporting

confidence: 83%

Monovalent Ion - Graphene Oxide Interactions are Controlled by Carboxylic Acid Groups: Sum Frequency Generation Spectroscopy Studies

Lee

Carr

Kumal

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

“…demonstrated with another light lanthanide, neodymium. 39 The intensity of this SFG peak, which is associated with dehydration, increases as the subphase concentration increases likely because there are more partially dehydrated La 3+ ions present. We speculate the carboxylic acid groups of AA can facilitate ion dehydration thus encouraging adsorption.…”

Section: La 3+ and Lu 3+ Hydration Structure During Adsorption To Gra...mentioning

confidence: 98%

“…38 X-ray scattering and molecular dynamics simulations 35 have shown a gradual transition from ~9 to ~8 waters in the first coordination shell from La 3+ to Lu 3+ . The hydration structure of ions at the air/water interface is directly relevant to separation efforts, as ions may undergo partial or total dehydration during adsorption 32,[39][40][41] . Recently, our group studied Nd 3+ adsorption to arachidic acid (AA) films using vibrational sum frequency generation spectroscopy (SFG) and observed a red-shifted signal within the water region, which was attributed to the partial dehydration of adsorbed Nd 3+ ions.…”

mentioning

confidence: 99%

“…Recently, our group studied Nd 3+ adsorption to arachidic acid (AA) films using vibrational sum frequency generation spectroscopy (SFG) and observed a red-shifted signal within the water region, which was attributed to the partial dehydration of adsorbed Nd 3+ ions. 39 SFG is an inherently surface-specific technique that is well-suited to understand local water structures near the air/water interface, as signal is only generated when centrosymmetry is broken (Figure 1). [40][41][42][43][44] In this work, we consider both light lanthanide La 3+ and heavy lanthanide Lu 3+ adsorption to a GO thin film and an ideal AA monolayer at the air/water interface to understand the effects of ion size on adsorption and local water structure.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Heavy versus Light Lanthanide Selectivity for Graphene Oxide Films is Concentration Dependent

Carr

Lee

Uysal

2023

Preprint

View full text Add to dashboard Cite

Rare earths are important materials in various technologies such as catalysis and optoelectronics. Graphene oxide (GO) is a promising material for separation applications, including the isolation of lanthanides from complex mixtures. Previous works using fatty acid monolayers have demonstrated preferential heavy versus light lanthanide adsorption, which has been attributed to differences in lanthanide ion size. In this work, we used interfacial X-ray fluorescence measurements to reveal that GO thin films at the air/water interface have no lanthanide selectivity for dilute subphases. However, at high subphase concentrations ~8x more Lu3+ adsorb than La3+. By comparing GO results with an ideal monolayer with a carboxylic acid headgroup, arachidic acid (AA), we demonstrate that the number of Lu3+ adsorbed at GO is significantly higher than the number needed to compensate the surface charge. Vibrational sum frequency generation (SFG) spectroscopy results on both GO thin films and AA monolayers reveal a red-shifted SFG signal in the OH region, which we attribute to partial dehydration of the adsorbed ions. Liquid surface X-ray reflectivity data show that the GO thin film structure does not significantly change between the very dilute and concentrated subphases. We speculate that the functional groups of both GO and AA facilitate cation dehydration, which is essential for ion adsorption. Heavy lanthanide Lu3+ has stronger ion-ion correlations that can overcome electrostatic repulsion between cations at higher concentrations compared to light lanthanide La3+, meaning GO and AA can overcharge with Lu3+. Lastly, the layered structure of the GO films and reactive chemical nature of GO itself can accommodate ion adsorption.

show abstract

“…32,39,40 Recently, our group studied Nd adsorption to arachidic acid (AA) films using vibrational sum frequency generation spectroscopy (SFG) and observed a red-shifted signal within the water region, which was attributed to the partial dehydration of adsorbed Nd ions. 41 SFG is an inherently surface-specific technique that is well suited to understand local water structures near the air/ water interface as the signal is only generated when centrosymmetry is broken (Figure 1). 39,40,42−44 In this work, we consider both light lanthanide La and heavy lanthanide Lu adsorption to a GO thin film and an ideal AA monolayer at the air/water interface to understand the effects of ion size on adsorption and local water structure.…”

Section: ■ Introductionmentioning

confidence: 99%

Heavy versus Light Lanthanide Selectivity for Graphene Oxide Films Is Concentration-Dependent

2023

Self Cite

View full text Add to dashboard Cite

Rare earths are important materials in various technologies such as catalysis and optoelectronics. Graphene oxide (GO) is a promising material for separation applications, including the isolation of lanthanides from complex mixtures. Previous works using fatty acid monolayers have demonstrated preferential heavy versus light lanthanide adsorption, which has been attributed to differences in lanthanide ion size. In this work, we used interfacial X-ray fluorescence measurements to reveal that GO thin films at the air/water interface have no lanthanide selectivity for dilute subphases. However, at high subphase concentrations, ∼8 times more Lu is adsorbed than La. By comparing the GO results with an ideal monolayer with a carboxylic acid headgroup, arachidic acid (AA), we demonstrate that the number of Lu ions adsorbed to GO is significantly higher than the number expected to compensate for the surface charge. Vibrational sum frequency generation (SFG) spectroscopy results on both GO thin films and AA monolayers reveal a red-shifted SFG signal in the OH region, which we attribute to partial dehydration of the adsorbed ions and carboxylic acid headgroups. Liquid surface X-ray reflectivity data show that the GO thin film structure does not significantly change between the very dilute and concentrated subphases. We speculate that the functional groups of both GO and AA facilitate cation dehydration, which is essential for ion adsorption. Heavy lanthanide Lu has stronger ion−ion correlations that can overcome the electrostatic repulsion between cations at higher concentrations compared to light lanthanide La, meaning GO and AA can exhibit apparent overcharge with Lu. Lastly, the layered structure of the GO films and reactive chemical nature of GO itself can accommodate ion adsorption.

show abstract

Elucidating Trivalent Ion Adsorption at Floating Carboxylic Acid Monolayers: Charge Reversal or Water Reorganization?

Cited by 9 publications

References 35 publications

Monovalent Ion - Graphene Oxide Interactions are Controlled by Carboxylic Acid Groups: Sum Frequency Generation Spectroscopy Studies

Monovalent Ion - Graphene Oxide Interactions are Controlled by Carboxylic Acid Groups: Sum Frequency Generation Spectroscopy Studies

Heavy versus Light Lanthanide Selectivity for Graphene Oxide Films is Concentration Dependent

Heavy versus Light Lanthanide Selectivity for Graphene Oxide Films Is Concentration-Dependent

Contact Info

Product

Resources

About