Selective Intercalation Research Articles

Electrochemical Ion Separations By Recyclable Electrode Cell

Electrochemical separations using Faradaic electrodes are able to exceed the ion adsorption values as well as selectivity when compared to capacitive electrodes, which is due to the bulk reactions for the former vs. surface confined for the latter. However, the cyclability of battery/faradaic electrodes is constrained to hundreds or a few thousands of cycles. This work proposes an electrochemical ion pumping design with the unique feature of using injectable electrodes to overcome the ciclability issue and easily control the areal capacity. The idea consists on using injectable electrodes with the intention of recycling the active material once the end-of-life of the device is reached due to active material degradation. In this fashion, the active material is replaced in a straightforward deinjecting-injecting process allowing direct reuse of the inactive components of the device, thus contributing to reducing the replacement cost. This device is called Ion Pumping Injectable Cell (IPIC).Moreover, the IPIC system is a tremendously versatile technology due to the simple and easy methodology employed to replace the electrodes. In this fashion, the system was tested using different types of lithium intercalation materials (LFP and LMO), different ion capturing such as potassium (Prussian Blue Analogs, PBA´s), sodium (NMO) or more conventional activated carbon electrodes (capacitive non-selective electrode). In addition to this feature, it is important to remark that the IPIC could be used in a symmetric (e.g. LFP-LFP) or asymmetric configuration (e.g. LFP-LMO). The main difference is that the asymmetric system has the ability of storing energy while capturing ions and deliver that energy in the subsequent step. This is so due to the different electrode potential. The selectivity toward specific ions is achieved by using a chemical ion-selective separator such as an ion exchange membrane (LFP-LFP or LFP-LMO systems), or by using ion selective intercalation materials such as LFP and PBA´s without the need of selective membranes.In this work, the benefits of the injectable electrode cell architecture will be examined, the performance of different cell configurations will be discussed and the electrochemical ion separation mechanism will be analyzed for different applications. Acknowledgements : J.J. Lado and Alba Fombona-Pascual acknowledge Comunidad de Madrid for the fellowship (2020-T1/AMB-19799).

Electrochemical performances and Li+-storage mechanism of highly proportional 1T-MoS2/hierarchical porous activated carbon nanocomposites

The metallic phase of molybdenum disulfide (1T-MoS2) shows distinct advantages for lithium storage owing to its superior electronic conductivity, abundance of electroactive sites, and wider interplanar spacing compared to the semiconducting phase (2H-MoS2). However, investigating lithium storage in 1T-MoS2 encounters significant challenges attributed to its thermodynamic instability during synthesis and its transformation to an amorphous structure following the irreversible conversion reaction. This study addresses these challenges by utilizing hierarchical porous activated carbon (HPAC) to achieve the highest reported proportion (85 %) of 1T-MoS2 and by restricting the potential window to induce selective intercalation reaction. Impressively, 1T-MoS2/HPAC anodes exhibit a reversible capacity that surpasses the theoretical capacity (167 mAh/g) at various current densities from 0.1 to 2.0 A/g. This superior performance extends even after 100 cycles, retaining a capacity of 276 mAh/g at 0.1 A/g. The kinetic analysis indicates that the additional capacity originated from non-Faradic lithium storage, reaching 96 % at 5.0 mV/s. Further studies employing ex-situ XRD and in-situ EIS at various lithiation depths unveil the formation of a novel permanent phase after lithiation, characterized by expanded interlayer spacing and improved conductivity compared to the un-lithiated material. These findings open promising avenues for developing anode materials for lithium-ion batteries/capacitors applications.

Intercalation and separation of isomeric nitrophenols using the anionic clay, Mg2Al(OH)6(CO3)0.5·nH2O and the structurally related layered hydroxy salt, Ni3Zn2(OH)8(CH3COO)2·mH2O

Intercalative sorption of isomeric nitrophenolates (NP) was investigated in two different layered hydroxide materials - anionic clay, magnesium aluminium layered double hydroxide (MgAl-LDH) through reconstructive mechanism and the structurally related layered hydroxy salt, Ni3Zn2(OH)8(CH3COO)2·mH2O (NiZn-LHS) through ion-exchange. Intercalation of NP isomers was confirmed by powder X-ray diffraction and infrared spectroscopy. The NP uptake by the layered hydroxide materials was quantified by high performance liquid chromatography. Both the layered hydroxide materials exhibit selective intercalation from the nitrophenolate mixtures. The order of preference is 4-NP > > 2-NP > 3-NP in MgAl-LDH and 4-NP > 2-NP > > 3-NP in NiZn-LHS. The bias in intercalation could be attributed to (1) the concentration of the phenolate ions influenced by the pKa of the isomer and (2) extent of H-bonding of the nitro group of the isomer with the hydroxide slabs. The 4-isomer with lower pKa and better H-bonding with the adjacent hydroxide slabs is preferentially intercalated. The anionic clays can be used to sorb out nitrophenols as well as separate them from their mixtures.

Controlling the spacing of the linked graphene oxide system with dithiol linkers under confinement.

2D nanoscale confined systems exhibit behavior that is markedly different from that observed at the macroscale. Confinement can be tuned by controlling the interlayer spacing between confining layers using organic dithiol linkers. Adjusting spacing and selective intercalation have important impacts for catalysis, superconductivity, spin engineering, sodium ion batteries, 2D magnets, optoelectronics, and many other applications. In this study, we report how reaction conditions and organic linkers can be used to create variable, reproducible spacings between graphene oxide to provide confinement systems. We determined the conditions under which the spacing can be variably adjusted by the type of linker used, the concentration of the linker, and the reaction conditions. Employing dithiol linkers of different lengths, such as three (TPDT) and four (QPDT) aromatic rings, we can adjust the spacing between graphene oxide layers under varied reaction conditions. Here, we show that by varying dithiol linker length and using different reaction conditions, we can reproducibly control the spacing between graphene oxide layers from 0.37 nm to over 0.50 nm.

Cationic Vacancies in Anatase (TiO2): Synthesis, Defect Characterization, and Ion-Intercalation Properties.

As one of the most studied materials, research on titanium dioxide (TiO2) has flourished over the years owing to technological interest ranging from energy conversion and storage to medical implants and sensors, to name a few. Within this scope, the development of synthesis routes enabling the stabilization of reactive surface structure has been frequently investigated. Among these routes, solution-based synthesis has been utilized to tailor the material's properties spanning its atomic structural arrangement, or morphological aspects. One of the most investigated methods of stabilizing crystals with tailored facets relies on the use of fluoride-based precursors. Fluoride ions not only provide a driving force for the stabilization of metastable/reactive surface structures but also alter the reactivity of titanium molecular precursors and in turn the structural features of the stabilized crystals. Here, we review recent progress in the solution-based synthesis of anatase (one of the polymorphs of TiO2) employing a fluoride precursor, with an emphasis on how cationic vacancies are stabilized by a charge-compensating mechanism and the resulting structural features associated with these defects. Finally, we will discuss the ion-intercalation properties of these sites with respect to lithium and polyvalent ions such as Mg2+ and Al3+. We will discuss in more detail the relevant parameters of the synthesis that allow controlling the phase composition with the coexistence of oxide, fluoride, and hydroxide ions within the anatase framework. The mechanism of formation of defective anatase nanocrystals has highlighted a solid-state transformation mostly implying an oxolation reaction (the condensation of hydroxide ions) that results in a decrease in the vacancy content, which can be synthetically controlled. The investigation of local fluorine environments probed by solid-state 19F NMR revealed up to three coordination modes with different numbers of coordinated Ti4+ and vacancies. It further revealed the occurrence of single and adjacent pairs of vacancies. These different host sites including native interstitial (and single/paired vacancies) display different ion-intercalation properties. We notably discussed the influence of the local anionic environments of vacancies on the thermodynamics of intercalation properties. The selective intercalation of polyvalent cations such as Mg2+ and Al3+ further supports the beneficial uses of defect chemistry for developing post-lithium-ion batteries. It is expected that the ability to characterize the local structure of defects is key to the design of unique, tailored-made materials.

Selective Intercalation of Phenolphthalein Quinone Dianion in Layered Hosts against UV-Photodegradation of Bitumen

Phenolphthalein quinone dianion (PPNq²–) exhibits excellent UV–vis absorbing capacity; however, it has never been considered as UV-absorbing materials because of the pH-dependent proton dissociation equilibrium. Here, layered double hydroxides (LDHs) are served as stable alkaline hosts to capture and fix the PPNq²– into their interlayers selectively. The resultant composites display a broad and strong absorption of UV light. Moreover, the alkaline hosts protect the ionization state of PPNq²– in a wide pH range and a long-term irradiation condition so that the material can be used as a UV-absorber in practice. This hybrid material effectively suppresses the UV-photodegradation of bitumen in terms of the viscosity aging index, softening point increment, and morphology. This simple host–guest strategy opens a new platform for exploring LDHs based molecular recognition and material innovation.

Two-dimensional superfluidity in He4 clusters intercalated into graphite

Motivated by recent technical developments on selective intercalation of inert gases just beneath the surface graphene of graphite, we perform path-integral Monte Carlo calculations to study structural and superfluid properties of $^{4}\mathrm{He}$ clusters encapsulated between a bulged surface graphene layer and the graphite (0001) substrate. The intercalated $^{4}\mathrm{He}$ atoms initially decorate the inner surface of the bulged graphene to form a shell structure, leaving a void inside it. Then, the additional $^{4}\mathrm{He}$ atoms form a disk-shaped liquid platelet in the void, which shows finite superfluid response at temperatures below 1 K. The temperature-dependent superfluid fractions of the platelet follow modified Kosterlitz-Thouless recursion relations, indicating that two-dimensional superfluidity can be realized in an intercalated $^{4}\mathrm{He}$ system.

On Demand One-Pot Mild Preparation of Layered Double Hydroxides and Their Hybrid Forms: Advances through the Epoxide Route.

Epoxide ring opening driven alkalinization process was explored with the aim of preparing layered double hydroxide (LDH) phases on demand, at room temperature. Employing iodide as nucleophilic agent, the precipitation reaction can be driven under much lower halide concentrations. This scenario favors the selective intercalation of concomitant bulky oxo anions as nitrate or perchlorate in the LDH products, allowing for the one-pot synthesis of an LDH able to delaminate in formamide. Even large dicarboxylic acids, - O2 C-(CH2 )n -CO2 - , with n up to 8, can be quantitively intercalated within the growing LDH phase, providing a versatile one-pot route for hybrid LDHs as well. Under the mild conditions employed, governed by a continuous pH rise from a starting acid condition, a MII to M*III ratio of 2 prevails, independently from the overall cationic composition. However, after moderate hydrothermal aging LDH phases bearing a cationic ratio higher than 2 could result. The solubility of a given chloride-containing MII 2 M*III LDH can be approximated as a linear combination of the solubility of the pure hydroxylated phases of the constitutive cations, M(OH)2 and M* (OH)3 .

Electrochemical methods for sustainable recovery of lithium from natural brines and battery recycling

Abstract This short review covers the recent developments in electrochemical methods for the extraction of lithium from natural brines, seawater, and battery recycling electrolytes by ion-pumping mixing entropy cells and electrodialysis. Lithium extraction by ion pumping takes advantage of the selective intercalation in lithium battery cathode materials and the concentration difference between the lithium source and the recovery electrolyte. Electrodialysis has attracted much interest in particular for large Mg/Li ratios in some natural brines.

Isolation of cyclic penta(ethylene oxide) from mixtures with its linear analog by combining selective intercalation into graphite oxide and solvent approaches

Cyclic oligomers of poly(ethylene oxide)s intercalate slower into graphite oxide (GO) than their linear analogs from the melt. In present study these kinetic differences are exploited to isolate 15-crown-5 (15C5) from mixtures with linear penta(ethylene glycol) (5EG) by using two approaches: a) melt intercalation and solvent extraction and b) intercalation from solution and filtration. In both cases we found that fractions highly enriched in the cyclic component are obtained by using an appropriate selection of the solvent. Solvents that do not penetrate the interlayer space of GO (such as CCl4 and toluene) lead to an increase of the cyclic fraction from 50 wt% in the initial mixture to values as high as 99 wt%. On the contrary, solvents that penetrate the interlayer space of GO produce fractions with low content of 15C5. The ability of non-penetrating solvents to achieve an effective isolation of 15C5 demonstrates that separation is driven by a faster intercalation of 5EG into unswollen GO, without solvent assistance, and the permanence of 15C5 in solution. These results are discussed in the light of data collected by X-ray diffraction, differential scanning calorimetry and gel permeation chromatography. This study provides substantial evidence of a very promising separation method for a topological purification of cyclic poly(ethylene oxide)s with GO.

Selective Calixarene-Directed Synthesis of MXene Plates, Crumpled Sheets, Spheres, and Scrolls.

Fully exploiting the electronic and mechanical properties of 2D laminar materials not only requires efficient and effective means of their exfoliation into low dimensional layers, but also necessitates a means of changing their morphology so as to explore any enhancement that this may offer. MXenes are a rapidly emerging new class of such laminar materials with unique properties. However, access to other morphologies of MXenes has not yet been fully realised. To this end we have developed the synthesis of MXenes (Ti2 C) as plates, crumpled sheets, spheres and scrolls, which involves selective intercalation of p-phosphonic calix[n]arenes, with control in morphology arising from the choice of the size of the macrocycle, n=4, 5, 6, or 8. This opens up wider avenues of discovery/design for new morphologies from the wider family of MXenes beyond Ti2 C, along with opportunities to exploit any new physico-chemical properties proffered.

Synergistic local toughening of high performance epoxy-matrix composites using blended block copolymer-thermoplastic thin films

A new block copolymer-thermoplastic dual toughening concept for high performance RTM6 epoxy matrix composites is elaborated through a comprehensive microstructural study of well-defined model systems. A blend of phenoxy and MAM (copolymer of poly(methyl methacrylate) and poly(butyl acrylate)) increases the toughness of the corresponding carbon fiber reinforced composite by 125%, a five-fold synergistic improvement over the situation where the tougheners are used alone at the same total concentration. Selective intercalation of blended toughener thin films in the preform gives rise to a diffusion-induced composition gradient during the RTM process, which generates a morphology gradient upon curing. The observed microstructures results from MAM self-assembly in the miscible mixture of phenoxy and the epoxy resin precursor, followed by reaction induced phase separation, forming wormlike micelles, interconnected micelles and co-continuous morphologies. The resulting microstructures activate different toughening mechanisms responsible for the observed synergy.

Electrochemical Lithium Recovery from Aqueous Sources

Lithium shortage is inevitable, given the massive growth in its demand for use in transportation industry and various technologies. Consequently, recovery of lithium from seawater and brine is gaining attention to potentially alleviate the impending crisis. Two widely investigated methods for lithium recovery from seawater and brine deposits are adsorption using inorganic lithium ion sieves (LIS) and electrochemical processes. But the former has a drawback due to the use of toxic solvents which negatively affects the environment. Herein, an efficient type of lithium recovery approach is proposed by systematically designing an electrochemical system to sequester Li+ from aqueous sources. An electrochemical cell was designed to selectively intercalate Li+ into the anode during charging phase. A microcell reactor was prepared and investigated for its feasibility to capture lithium ions (Li+). The reactor consists of a three-electrode assembly with an Li+-selective intercalating electrode, a chloride-capturing silver electrode, and Ag/AgCl reference electrode. Repetitive cyclic voltammetry and galvanostatic cycling showed highly selective and stable electrode system for aqueous Li+ uptake and release. The energy efficiency of the process was also investigated and compared with other electrochemical Li+ recovery methods. Overall, the results demonstrate the ability of the electrochemical system to selectively recover Li+ from aqueous sources. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2009-0093816) and Ministry of Science, ICT and future Planning (2015R1A2A1A15055407).

Effect of selectively intercalated polyiodide on the electric transports of metallic- and semiconducting-enriched single-wall carbon nanotube networks

We report the selective intercalation of polyiodide chains (I5−) inside the interstitial sites of single-wall carbon nanotube (SWCNT) bundles of which internal sites are pre-encapsulated with monatomic sulfur chains. By using metallic- and semiconducting-enriched SWCNTs with diameter of ∼1 nm, our direct-current electric transport measurements reveal that the I5− intercalation on the metallic- and semiconducting-enriched SWCNT networks exhibits an opposite trend on the temperature dependence of the electric resistance at cryogenic temperature. Based on our analysis using the fluctuation-induced tunneling conduction model, the intercalation of I5− chains into the semiconducting-SWCNTs leads to the increase in energy barriers required for tunneling processes. Since the charge transfer is negligible between I5− chains and the semiconducting-SWCNTs, the main effect of the intercalated I5− on the semiconducting-SWCNTs is to behave as a scattering center below 50 K. In contrast to the semiconducting-SWCNTs, the intercalation of I5− chains into the metallic-SWCNTs results in the suppression of tunneling barriers due to the charge transfer interaction. The energy barrier is further reduced by the encapsulation of I5− chains inside the metallic-SWCNT, implying that the doping effect could be more effectively enhanced by the interaction through the inner spaces of SWCNTs.

Electrochemical study on the intercalation properties of hydroxyl anion for the reversible conversion of graphene quantum dots into carbon dots

Abstract The intercalating property of hydroxyl anion for reversible conversion of graphene quantum dots (GQDs) into carbon dots (CDs) by electrochemical techniques such as cyclic voltammetry (CV) was studied in detail. For this purpose, the three-electrode system was a Pt disk as counter, Ag/AgCl as reference and GQDs-modified Pt disk as working electrodes. Based on the results, among various anions such as Cl−, Br−, PO43 −, PO33 −, NO2−, OH−, and NO3− as well as different cations like Na+, K+ and Li+, only OH− can selectively intercalate nanocarbons during reversible conversion of GQDs to CDs. According to the cyclic voltammograms at potential the same as − 0.2 V (vs, Ag/AgCl) GQDs were converted into CDs. However reverse conversion of CDs into GQDs was simply occurred by continuous scanning the potential from + 0.1 to − 0.8 V (vs. Ag/AgCl). Effective role of OH− as selective intercalating agent was further approved using some surface analytical methods such as scanning electron microscopy (SEM), BET, BJH as well as some spectroscopic techniques such as Fourier transform-infrared (FT-IR). This study was applicable from several aspects such as i) in the intelligent controlling the morphology as well as the active surface area of nanocarbons during fabrication of carbon-based sensors ii) selective separation of OH− through the electro-filtration process, iii) selective exchange between OH− and other anionic species in the separation analyses and iv) controlling the bandgap (Fermi levels) between the inter-layers of graphene-based nanostructures through the intercalation process.

Terpy(Pt-salphen)2 switchable luminescent molecular tweezers.

The design and synthesis of switchable molecular tweezers based on a luminescent terpy(Pt-salphen)2 (1; terpy=terpyridine) complex is reported. Upon metal coordination, the tweezers can switch from an open "W"-shaped conformation to a closed "U"-shaped form that is adapted for selective recognition of cations. Closing of the tweezers by metal coordination (M=Zn(2+), Cu(2+), Pb(2+), Fe(2+), Hg(2+)) was monitored by (1)H NMR and/or UV/Vis titrations. During the titration, exclusive formation of the 1:1 complex [M(1)] was observed, without appearance of an intermediate 1:2 complex [M(1)2]. The crystallographic structure of the 1:1 complex was obtained with Pb(2+) and showed a distorted helical structure. Selective intercalation of Hg(2+) cations by the closed "U" form was observed. The tweezers were reopened by selective metal decoordination of the terpyridine ligand by using tris(2-aminoethyl)amine (tren) as a competitive ligand without modification of the Pt-salphen complex. Detailed photophysical studies were performed on the open and closed tweezers. Structured emission was observed in the open form from the Pt-salphen moieties, with a high quantum yield and a long lifetime. The emission is slightly modified upon closing with 1 equivalent of Zn(2+) or Hg(2+), whereas a dramatic quenching was obtained upon intercalation of additional Hg(2+).

Selective intercalation of ionic liquid in montmorillonite and influence of water molecules

The influence of water molecules on ionic liquid (IL; 1-butyl-3-methylimidazolium tetrafluoroborate) intercalated montmorillonite (MIL) and the selectivity of IL have been studied. The intercalation behavior of IL into an IL-intercalation compound containing various amounts of water (MILW) was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and a selected area electron diffraction pattern (SAED). The structural change of MIL influenced by the water was also confirmed by a TEM study. Based on the amount of interlayer exchangeable cations as measured by inductively coupled plasma (ICP), the extent of the intercalation and arrangement of cations in the interlayers of MIL treated by different amounts of water was studied. In addition, the Raman spectroscopy results showed that the water molecules do not interact with both the IL and the montmorillonite. These results suggest that the IL-intercalation compound can maintain its property in water due to its high water resistance. Moreover, this technique would be useful for the adsorption reaction and fabrication of montmorillonite composite materials using non-polar organic molecules.

Counter-ion Dependent, Longitudinal Unzipping of Multi-Walled Carbon Nanotubes to Highly Conductive and Transparent Graphene Nanoribbons

Here we report for the first time, a simple hydrothermal approach for the bulk production of highly conductive and transparent graphene nanoribbons (GNRs) using several counter ions from K2SO4, KNO3, KOH and H2SO4 in aqueous media, where, selective intercalation followed by exfoliation gives highly conducting GNRs with over 80% yield. In these experiments, sulfate and nitrate ions act as a co-intercalant along with potassium ions resulting into exfoliation of multi-walled carbon nanotubes (MWCNTs) in an effective manner. The striking similarity of experimental results in KOH and H2SO4 that demonstrates partially damaged MWCNTs, implies that no individual K+, SO42− ion plays a key role in unwrapping of MWCNTs, rather this process is largely effective in the presence of both cations and anions working in a cooperative manner. The GNRs can be used for preparing conductive 16 kΩsq−1, transparent (82%) and flexible thin films using low cost fabrication method.

Intercalation‐Controlled Cyclodehydration of Sorbitol in Water over Layered‐Niobium‐Molybdate Solid Acid

Layered niobium molybdate (HNbMoO6 ) was used in the aqueous-phase dehydration of sorbitol and was found to exhibit remarkable selectivity toward its monomolecular-dehydrated intermediate 1,4-sorbitan. This was attributed to the selective intercalation of sorbitol within the interlayers with strong Brønsted acid sites.

Selective Intercalation of Graphite Oxide by Methanol in Water/Methanol Mixtures

Graphite oxide is selectively intercalated by methanol when exposed to liquid water/methanol mixtures with methanol fraction in the range 20–100%. Insertion of water into the GO structure occurs only when the content of water in the mixture with methanol is increased up to 90%. This conclusion is confirmed by both ambient temperature XRD data and specific temperature variations of the GO structure due to insertion/deinsertion of an additional methanol monolayer observed upon cooling/heating. The composition of GO–methanol solvate phases was determined for both low temperature and ambient temperature phases. Understanding of graphite oxide structural properties in binary water/methanol mixtures is important for understanding the unusual permeation properties of graphene oxide membranes for water and alcohols. It is suggested that graphite oxide prepared by Brodie’s method can be used for purification of water using selective extraction of methanol from water/alcohol mixtures.