Anions Enhance Rare Earth Adsorption at Negatively Charged Surfaces

Nayak, Srikanth; Lovering, Kaitlin; Bu, Wei; Uysal, Ahmet

doi:10.1021/acs.jpclett.0c01091

“…[51][52][53] Ion-specific effects in bulk phase 54 and at the interfaces 50,55 can play a significant role in SX. 14,56,57 TOMA-NO3 system stands out in all known lanthanide SX systems, as it preferentially extracts light lanthanides over heavy lanthanides (DLa/DLu ~ 500) (Figure 1c, dataset D). Some plausible sources of this preference are differences in aqueous phase speciation, interfacial phenomena, and organic phase speciation and aggregation.…”

Section: Methodsmentioning

confidence: 99%

Ion-specific clustering of metal–amphiphile complexes in rare earth separations

Nayak

¹

,

Lovering

²

,

Uysal

³

2020

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“…Surface sensitive experimental techniques like vibrational sum-frequency generation (VSFG) 11,12 and X-ray diffraction 13 can provide an ensemble average depiction of molecular orientation and species distributions, however these do not characterize dynamic phenomena. 14–16 The instantaneous water/oil interface is often interpreted in terms of capillary waves that derive from thermal fluctuations and interfacial anisotropy, 13,17 yet on top of this rough and dynamically evolving surface other architectures have been predicted that are modulated by the presence of surfactants. These include protrusions that extend from the aqueous to organic phase, “islands” of surfactant bilayers, and budding micellar-like structures.…”

Section: Introductionmentioning

confidence: 99%

Unexpected inverse correlations and cooperativity in ion-pair phase transfer

Kumar

¹

,

Clark

²

2021

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“…[51][52][53] Ion-specific effects in bulk phase 54 and at the interfaces 50,55 can play a significant role in SX. 14,56,57 TOMA-NO3 system stands out in all known lanthanide SX systems, as it preferentially extracts light lanthanides over heavy lanthanides (DLa/DLu ~ 500) (Figure 1c, dataset D). Some plausible sources of this preference are differences in aqueous phase speciation, interfacial phenomena, and organic phase speciation and aggregation.…”

Section: Resultsmentioning

confidence: 99%

Ion-Specific Clustering of Metal-Amphiphile Complexes in Rare Earth Separations

Nayak¹,

Lovering²,

Uysal³

2020

Preprint

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0

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<p>The nanoscale structure of a complex fluid can play a major role in the selective adsorption of ions at the nanometric interfaces, which are crucial in industrial and technological applications. Here we study the effect of anions and lanthanide ions on the nanoscale structure of a complex fluid formed by metal-amphiphile complexes, using small angle X-ray scattering. The nano- and mesoscale structures we observe can be directly connected to preferential transfer of light (La, Nd) or heavy (Er, Lu) lanthanides into the complex fluid from an aqueous solution. While the toluene-based complex fluids containing trioctylmethylammonium-nitrate (TOMA-nitrate) always show the same mesoscale hierarchical structure regardless of lanthanide loading and prefer light lanthanides, those containing TOMA-thiocyanate show an evolution of mesoscale structure as a function of the lanthanide loading and prefer heavy lanthanides. The hierarchical structuring indicates the presence of attractive interactions between ion-amphiphile aggregates, causing them to form clusters. A clustering model, that accounts for the hard sphere repulsions and short-range attractions between the aggregates, has been adapted to model the X-ray scattering results. The new model successfully describes the nanoscale structure and helps in understanding the mechanisms responsible for amphiphile assisted ion transport between immiscible liquids. Accordingly, our results imply different mechanisms of lanthanide transport depending on the anion present in the complex fluid and correspond with anion-dependent trends in rare-earth separations. </p>

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Anions Enhance Rare Earth Adsorption at Negatively Charged Surfaces

Abstract: Anions are expected to be repelled from negatively charged surfaces. At aqueous interfaces, however, ion-specific effects can dominate over direct electrostatic interactions. Using multiple in situ surface sensitive

Cited by 37 publications

References 53 publications

Ion-specific clustering of metal–amphiphile complexes in rare earth separations

Ion-specific clustering of metal–amphiphile complexes in rare earth separations

Unexpected inverse correlations and cooperativity in ion-pair phase transfer

Ion-Specific Clustering of Metal-Amphiphile Complexes in Rare Earth Separations

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