Cationic Layers Research Articles

Cation exchange route to a Eu(II)-containing tantalum oxide

Traditional synthetic efforts to prepare Eu(II)-containing oxides have principally involved the use of high temperature reactions starting from EuO or a controlled, highly-reducing, atmosphere. Conversely, chimie douce approaches that are more amenable to the targeted syntheses of new, and potentially metastable, Eu(II)-oxides have yet to be explored. Herein, a cation-exchange route to new Eu(II)-containing oxides, e.g., EuTa4-xO11 (x = 0.04), has been discovered and its structure determined by powder X-ray diffraction (Space group P6322 (#182), a = 6.2539(2) Å; c = 12.3417(2) Å). The compound derives from the cation exchange of Na2Ta4O11, via a reaction with EuBr2 at 1173 K, and replacement by half the number of divalent Eu cations. Rietveld refinements show preferential ordering of the Eu cations over one of the two possible cation sites, i.e., Wyckoff site 2d (∼94%; Eu1) versus 2b (∼6%; Eu2). Total energy calculations confirm an energetic preference of the Eu cation in the 2d site. Tantalum vacancies of ∼1% occur within the layer of Eu cations and TaO6 octahedra, and ∼20% partial oxidation of Eu(II) to Eu(III) cations from charge balance considerations. 151Eu Mössbauer spectroscopy measured at 78 K found a Eu(II):Eu(III) ratio of 69:31, with a relatively broad line width of the former signal of Γ = 7.6(2) mm s–1. Also, the temperature-dependent magnetic susceptibility could be fitted to a Curie Weiss expression, giving a μeff = 6.2 μB and θCW = −10 K and confirming a mixture of Eu(II)/Eu(III) cations. The optical bandgap of EuTa4-xO11 was found to be ∼1.5 eV (indirect), significantly redshifted as compared to ∼4.1 eV for Na2Ta4O11. Spin-polarized electronic structure calculations show that this redshift stems from the addition of Eu 4f7 states as a higher-energy valence band. Thus, these results demonstrate a new cation-exchange approach that represents a useful synthetic pathway to new Eu(II)-containing oxides for tunable magnetic and optical properties.

Synergistic Effect of Aluminum Lactate and Sodium Molybdate on Freshwater Corrosion of Carbon Steel Under Irradiation

In this study, a corrosion inhibitor suitable for the corrosion inhibition of primary containment vessels at the Fukushima Daiichi Nuclear Power Station is investigated. Considering the internal environment of the primary containment vessels, the corrosion inhibitor should inhibit the freshwater corrosion of carbon steel under irradiation and should not come under effluent standards in Japan. Herein, a corrosion inhibitor was devised by combining Al lactate and Na molybdate that met the above conditions, and its corrosion mechanism was investigated. It was found that 0.75 mM Al lactate and 0.25 mM Na molybdate were the most inhibitive to the corrosion of carbon steel. As Al lactate has never been reported as a corrosion inhibitor for metallic materials, it could be developed as a novel corrosion inhibitor in this study. The corrosion inhibitor inhibited the freshwater corrosion of carbon steel even under gamma irradiation of 200 Gy/h. Al and molybdate ions in the solution formed a metal cation layer on carbon steel with few defects and without iron. This metal cation layer inhibited both the cathodic oxygen reduction reaction and the anodic iron dissolving reaction, thereby enhancing the corrosion protection of carbon steel in freshwater.

Irreversible Structural Phase Transition in [(9‐triptycylammonium) ([18]crown‐6)][Ni(dmit)2]: Origin and Effects on Electrical and Magnetic Properties

AbstractMaterials exhibiting irreversible phase transitions, leading to changes in their properties, have a potential for novel application in electronic components such as a non‐rewritable high‐security memory. Here, we focused on the two salts, [(9‐triptycylammonium)([18]crown‐6)][Ni(dmit)2] (1) and [(9‐triptycylammonium)([15]crown‐5)][Ni(dmit)2] (2), which featured 2D sheet structures with alternately stacked cation and anion layers. Both salts exhibit similar cation arrangements, however, their anion arrangements differ significantly. The temperature‐dependent magnetic susceptibilities of 1 and 2 were well reproduced by the alternating chain model (JAC1/kB=−306(8), JAC2/kB=−239(3) K) and the Curie‐Weiss model (θ=−3.9(1) K), respectively. 1 experience a reversible phase transition around 40–60 K, causing anomalies in magnetic behavior. Moreover, an irreversible single‐crystal‐to‐single‐crystal phase transition to 1′ undergo at ~381 K, inducing a rearrangement of [Ni(dmit)2]− anions and a resistivity decrease from 6.5×106 to 6.5×102 Ω cm. The susceptibility curve of 1′ was reproduced by a combination of the Curie‐Weiss and dimer models (Jdimer/kB=−407(5), θ=−26.7(5) K). The irreversible transition of 1 is the first example for such supramolecule and [Ni(dmit)2]− system to our knowledge, in opening potential new‐type materials.

A dynamic electrostatic shielding layer toward highly reversible Zn metal anode

Aqueous Zn-ion batteries (AZIBs) have gained considerable attention due to their inherent safety, cost-effectiveness, and environmental friendliness. However, their application in large-scale energy storage system is hindered by uncontrollable dendrite growth and severe side reactions at the electrode-electrolyte interface. To address these challenges, we propose the incorporation of trivalent yttrium (Y3+) ions in ZnSO4 electrolyte, which can form a cationic electrostatic shielding layer on the Zn anode to regulate the deposition behavior of Zn2+ ions. The inert Y3+ ions with a lower effective reduction potential will selectively adsorb on the active sites, facilitating uniform Zn deposition through a sustained dynamic electrostatic shielding effect. Moreover, the adsorbed Y3+ ions create a protective interface for the Zn anode, mitigating the corrosion reactions caused by water molecules. Consequently, the Zn//Zn cell with 0.1 M Y3+ ions demonstrates dendrite-free Zn plating/stripping over 2080 h at 5 mA cm−2, and the assembled Zn//NH4V4O10 cell delivers a high capacity retention of 89.6% after 2000 cycles at 5 A g−1. This work develops a new rare earth ion additive and confirms its sustained dynamic electrostatic shielding effect for dendrite-free Zn deposition, providing theoretical support and an exploration direction for further investigation of unexplored rare earth elements.

Rational design of a membrane-coated cathode for selective electrochemical hydrogen evolution in chlorate electrolysis

The industrial chlorate process has traditionally used chromium(VI) as an electrolyte additive for high Faraday efficiency. However, due to its recognized toxicity and carcinogenic properties, the EU has regulated its usage, prompting the need for alternative approaches. In this study, we propose the adoption of a polymeric membrane-coated cathode (MCC) as a straightforward yet highly efficient solution to enhance the selectivity of the hydrogen evolution reaction (HER) in chlorate electrolysis. Proof-of-concept MCCs were fabricated by coating roughened titanium substrates with cation and anion exchange membrane layers, which function as selective barriers for anodic hypochlorite species. The study revealed that a thin membrane coating on the electrode surface effectively suppressed the permeation of anodic intermediates, without compromising the current density for HER. By optimizing the coating layer thickness and substrate surface properties of MCC, the chlorate electrolysis cell demonstrated an impressive Faradaic efficiency of up to 95% at a current density of 150 mA/cm², while maintaining exceptional stability. The outcome of this study can potentially advance the feasibility of industrial chlorate production in meeting regulatory requirements and effectively mitigating environmental consequences.

Crystal structure of danofloxacin mesylate (C19H21FN3O3)(CH3O3S)

The crystal structure of danofloxacin mesylate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Danofloxacin mesylate crystallizes in space groupP1(#1) witha= 6.77474(8),b= 12.4973(4),c= 12.82826(28) Å,α= 84.8709(29),β= 87.7501(10),γ= 74.9916(4)°,V= 1044.723(11) Å3, andZ= 2. The protonation of the danofloxacin cations was established by the analysis of potential intermolecular interactions and differs from that expected from isolated-cation calculations. The crystal structure consists of alternating layers of cations and anions parallel to theac-plane. There is parallel stacking of the oxoquinoline rings along thea-axis. The expected N–H⋯O hydrogen bonds between the cations and anions are not present. Each cation makes an N–H⋯O hydrogen bond with the other cation, resulting in zig-zag chains along thea-axis. Both cations have strong intramolecular O–H⋯O hydrogen bonds. There are several C–H⋯O hydrogen bonds between the danofloxacin cations and mesylate anions. The powder pattern has been submitted to ICDD® for inclusion in the Powder Diffraction File™ (PDF®).

Rational design of novel NiBi-LDH with enhanced overall water splitting activity

Layered double hydroxides (LDHs) are among the most important materials considered in the redox reaction of water electrolysis. In this study, a new LDH containing Ni and Bi in the cationic layers was synthesized through a solvothermal method. The physicochemical characteristics of the synthesized LDH were investigated using various techniques such as XRD, FE-SEM, EDX, BET, FT-IR, and Raman. The efficiency of the NiBi-LDH catalyst supported on nickel foam (NB/NF) was evaluated for the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). To improve the overall water-splitting performance of the synthesized LDH, it was modified with NiMoO4 (NMO). The electrochemical activity, kinetics, mechanism, and stability of the modified samples were studied using various techniques such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The electrochemical results showed that the NB/NF catalyst had overpotentials of 202 and 264 mV for HER and OER, respectively. However, the addition of NMO to the NB/NF catalyst resulted in a significant improvement in the overall performance, with a small overpotential of only 84 and 160 mV (at 10 mA cm−2) for HER and OER, respectively, and a very small Tafel slope of 45.7 and 74.9 mV.dec−1. The potential for overall water-splitting was found to be 1.424 V. The NB-NMO/NF catalyst demonstrated excellent kinetics, stability, and durability.

Crystal structure and cation-anion interactions of potassium (Difluoromethanesulfonyl) (trifluorome thanesulfonyl)imide.

Sulfonimide salts are of great interest for battery use thanks to their special properties including sufficient superior chemical/thermal stabilities, structural flexibility, etc. In particular, the hydrogen-containing sulfonimide (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide anion {[N(SO2CF2H) (SO2CF3)]-, DFTFSI-}, stands out owing to its suppressed anion mobility and superior electrochemical properties. We herein report the structural analyses of potassium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide {K [N(SO2CF2H) (SO2CF3)], KDFTFSI} by virtue of single crystal X-ray diffraction and computational approaches. Our results reveal that KDFTFSI crystallizes in a orthorhombic cell (space group: Pbcn) comprising of cationic and anionic layers, which is similar to the conventional sulfonimide salt, potassium bis(trifluoromethanesulfonyl)imide {K [N(SO2CF3)2], KTFSI}. Gas-phase density functional theory calculations show that the conversion from trans to cis DFTFSI- anions is hindered due to the presence of stabilizing intramolecular H-bonding interactions in the trans conformer; yet interaction with K+ substantially minimizes the energy difference between the two conformers due to the formation of strong tridentate K+ coordination with oxygen atoms in the cis KDFTFSI. This work is anticipated to provide further understanding on the structure-property relations of hydrogenated sulfonimide anions, and thus inspire the structural design of new anions for battery research.

Carbonates of alkaline earth metals: Impact of the cation size on strengths of interionic interactions and polymorphic preferences

The energies of all types of pair-wise interionic interactions between atoms of the representative (MCO3)13 clusters sampled from X-ray structures of rhombohedral magnesite (M = Mg) and calcite (M = Ca), on one hand, and orthorhombic aragonite (M = Ca) and cerussite (M = Pb), on the other hand, are evaluated theoretically to ascertain how the size of a divalent metal cation governs the preferable existence of rhombohedral or (and) orthorhombic polymorph (polymorphs) at ambient temperature and pressure. The carbonates studied and their clusters are considered as those consisting of (i) columns of carbonate anions (CAs) separated by trios of cations, (ii) ribbons and layers of CAs, and (iii) rods and layers of cations. For each cluster, coordination energies of six CAs by a cation and six cations by a CA are evaluated. Energies of interactions of C and O atoms of columns and ribbons with cations and energies of inter-anionic C···O, O···O, and C···C interactions in column and ribbons of clusters are compared. Strengths of cation – cation repulsions are also evaluated. Analyses of the interaction energies, interionic distances in the carbonates studied, and thermodynamic properties of carbonates of alkaline earth metals allow one to understand how the size of a particular divalent metal cation affects relative thermodynamic stabilities and the very existence of its rhombohedral or (and) orthorhombic crystalline phase (phases).

Crystal structure of meglumine diatrizoate, (C7H18NO5)(C11H8I3N2O4)

The crystal structure of meglumine diatrizoate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Meglumine diatrizoate crystallizes in space group P21 (#4) with a = 10.74697(4), b = 6.49364(2), c = 18.52774(7) Å, β = 90.2263(3), V = 1292.985(5) Å3, and Z = 2. Two different crystal structures, which yielded essentially identical refinement residuals and positions of the non-H atoms, were obtained. The differences were in the H atom positions and the hydrogen bonding. One structure was 123.0 kJ/mol/cell lower in energy than the other and was adopted for the final description. The crystal structure consists of alternating double layers of cations and anions along the c-axis. The hydrogen bonds link the cations and anions into a three-dimensional framework. Each of the hydrogen atoms on the ammonium nitrogen of the cation acts as a donor in a strong N–H⋯O hydrogen bond. One of these is to a hydroxyl group of another cation, and the other is to the carboxylate group of the anion. Each of the amide nitrogen atoms of the anion forms a strong N–H⋯O intermolecular hydrogen bond, one to a carbonyl and the other to a carboxylate group. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

Self-Assembly and In Situ Quaternization of Triblock Bottlebrush Block Copolymers via Organized Spontaneous Emulsification for Effective Loading of DNA.

Microspheres bearing large pores are useful in the capture and separation of biomolecules. However, pore size is typically poorly controlled, leading to disordered porous structures with limited performances. Herein, ordered porous spheres with a layer of cations on the internal surface of the nanopores are facilely fabricated in a single step for effective loading of DNA bearing negative charges. Triblock bottlebrush copolymers (BBCPs), (polynorbornene-g-polystyrene)-b-(polynorbornene-g-polyethylene oxide)-b-(polynorbornene-g-bromoethane) (PNPS-b-PNPEO-b-PNBr), are designed and synthesized for fabrication of the positively charged porous spheres through self-assembly and in situ quaternization during an organized spontaneous emulsification (OSE) process. Pore diameter as well as charge density increase with the increase of PNBr content, resulting in a significant increase of loading density from 4.79 to 22.5ngµg-1 within the spheres. This work provides a general strategy for efficient loading and encapsulation of DNA, which may be extended to a variety of different areas for different real applications.

Harmonizing nanomaterial exposure methodologies in ecotoxicology: the effects of two innovative nanoclays in the freshwater microalgae Raphidocelis subcapitata

Layered double hydroxides (LDHs) are innovative nanomaterials (NMs) with a typical nanoclay structure (height <40 nm) consisting of layers of metallic cations and hydroxides stabilized by anions and water molecules. Upon specific triggers, anions can exchange by others in the surrounding environment. Due to this stimuli-responsive behavior, LDHs are used as carriers of active ingredients in the industrial or pharmaceutical sectors. Available technical guidelines to evaluate the ecotoxicity of conventional substances do not account for the specificities of NMs, leading to inaccuracies and uncertainty. The present study aimed to assess two different exposure methodologies (serial dilutions of the stock dispersion vs. direct addition of NM powder to each concentration) on the ecotoxicological profile of different powder grain sizes of Zn–Al LDH-NO3 and Cu–Al LDH-NO3 (bulk, <25, 25–63, 63–125, 125–250, and >250 µm) in the growth of the freshwater microalgae Raphidocelis subcapitata. Results revealed that the serial dilutions methodology was preferable for Zn–Al LDH-NO3, whereas for Cu–Al LDH-NO3 both methodologies were suitable. Thus, the serial dilutions methodology was selected to assess the ecotoxicity of different grain sizes for both LDHs. All Zn–Al LDH-NO3 grain sizes yielded similar toxicity, while Cu–Al LDH-NO3 powders with smaller grain sizes caused a higher effect on microalgae growth; thus, grain size separation might be advantageous for future applications of Cu–Al LDH-NO3s. Considering the differences between exposure methodologies for the Zn–Al LDH-NO3, further research involving other NMs and species must be carried out to achieve harmonization and validation for inter-laboratory comparison.

Features of adsorption phenomena in strontium salt solutions in the presence of some cavitands of cucurbituril family

The influence of the electrolyte nature and cation charge on the adsorption properties of cucurbit[6]uril supramolecular complexes are established and discussed. The results show the narrowing of the adsorption potential region of these complexes with increasing cation charge, and the possibility to form an adsorbate layer of supramolecular cations associated with surface-active electrolyte anions at the positive boundary of the adsorption potential region.

Intermolecular arrangement facilitated broadband blue emission in group-12 metal (Zn, Cd) hybrid halides and their applications

Various fluorescent organic materials are widely known for their potential applications in light-emitting diodes, organic lasers, anti-counterfeiting and bio-imaging. However, poor emission efficiency and stability issues limit their usability. Here we report the syntheses, crystal and electronic structures, and optical characterizations of two new hybrid organic-inorganic group 12 halides, (P-xd)ZnCl4 and (P-xd)CdCl4 (where (P-xd) = p-xylylenediammonium). Single crystals of both compounds can be conveniently synthesized by solution chemistry methods from their low-cost, low toxicity and easily available precursors. (P-xd)ZnCl4 possesses a crystal structure featuring alternating layers of organic cations and completely separated anionic [ZnCl4]2- tetrahedral units of zero-dimensional (0D) connectivity. In contrast, (P-xd)CdCl4 adopts similar layering of organic cations sandwiched between perovskite sheets of two-dimensional (2D) connectivity, which are formed by corner-sharing anionic [CdCl6]4- octahedral units. The structural, optical, and electronic studies suggest that the incorporation of organic and inorganic structural units into a hybrid structure improves its blue emission efficiency with nearly 23 times and 4 times higher photoluminescence quantum yield (PLQY) values in (P-xd)ZnCl4 and (P-xd)CdCl4, respectively, as compared to the organic precursor. Notably, PLQY of 23% for (P-xd)ZnCl4 is the highest reported to date for Zn-based hybrid organic-inorganic metal halides, where emission originates from the organic component. Both (P-xd)ZnCl4 and (P-xd)CdCl4 demonstrate considerably improved air-, thermal- and photostability, which suggest their suitability for potential practical applications such as fingerprint detection and solid-state lighting.

Supramolecular Structure of Tris(1,10-phenanthroline)zinc(II)-Cation and N,N′,N″-tris(carboxymethyl)-1,3,5-benzenetricarboxamide-Anion: Synthesis, Crystal Structure, Vibrational Spectra, and Theoretical Investigations

The present work reports on the synthesis, structural, spectroscopic, and theoretical studies of a new solid state ionic compound mainly composed of tris(1,10-phenanthroline)zinc(II) cations and N,N′,N″-tris(carboxymethyl)-1,3,5-benzenetricarboxamide anions. Colorless and well-shaped crystals were obtained from an alkaline aqueous methanolic solution, and single-crystal X-ray diffraction revealed a distinct supramolecular network. Powder diffraction techniques and Rietveld analysis confirmed the phase purity of the crystalline probes. The compound crystallizes in the orthorhombic space group Pbca with a cell volume of 9517.0 Å3. The complex cations [Zn(phen)3]2+ are interconnected via π–π-interactions and form a cationic layer network with holes. The organic counterion, as a dianion, forms dimeric units through π–π-interactions and hydrogen bonds, which also form an anionic layer network with honeycomb-like holes through cooperative classical hydrogen bonds of the O∙∙∙H–O and O∙∙∙H–N type with attractive secondary electrostatic interactions. Using the holes, the resulting supramolecular framework can be described as an interpenetrated network of separate anionic and cationic layers linked by further weaker non-covalent interactions such as C–H∙∙∙π and lone-pair∙∙∙π interactions. DFT calculations confirmed the experimentally observed spectroscopic (IR and Raman) findings. For a deeper insight into the structural arrangement in the crystal, the different Hirshfeld surfaces of the cation and anion, the pairwise interaction energies as well as the energy framework were calculated, supporting the dominance of attractive and repulsive electrostatic forces between the ions.

New semiconductor halocadmate [CdnXm](2n–m) crystal structure, molecular conformation and theoretical investigations

The new chemical compound (C6H5ClF3N2)3[Cd2Cl7] has been crystallized as an organic-inorganic hybrid. This structure is one of the rarely known examples, with exhibiting both [CdCl3]1- and [CdCl4]2- anionic environments. Two layers of mono-protoned fluoro organic cations orientated into preferred intermolecular and intramolecular A-H ….X (A ​= ​N,C and X ​= ​Cl,F) hydrogen bonds separate the one-dimensional inorganic zigzag chain [Cd2Cl7]3-.To better understand the cohesion and interactions within the crystal, an examination has been made using the Hirshfeld surface analysis method, as well as another method which is topological analysis using Atom In Molecules (AIM) theory which was carried out to find the Bond Critical Point (BCP).In addition, this compound has been theoretically studied using DFT calculations, in order to examine its compatibility with the experimental results and which may be a means of verifying the homogeneity and purity of the synthesized compound. An experimental studies with infrared (FT-IR) and Raman spectroscopy are used to conduct and discuss the vibration modes of the existing groups in this new salt, this experimental study is compared to the theory. The energy gap, which is Eg ​= ​3.64 ​eV and the UV–visible absorption spectra were used which enabled us to determine the nature of the material in question and is a semiconductor. The emission of this compound covers a significant portion of the visible light spectrum.

Surface-induced ferromagnetism and anomalous Hall transport at Zr2S(001)

Two-dimensional layered electrides possessing anionic excess electrons in the interstitial spaces between cationic layers have attracted much attention due to their promising opportunities in both fundamental research and technological applications. Using first-principles calculations, we predict that the layered bulk electride ${\mathrm{Zr}}_{2}\mathrm{S}$ is nonmagnetic with massive Dirac nodal-line states arising from $\mathrm{Zr}\text{\ensuremath{-}}4d$ cationic and interlayer anionic electrons. However, the ${\mathrm{Zr}}_{2}\mathrm{S}(001)$ surface increases the density of states at the Fermi level due to the surface potential, thereby inducing a ferromagnetic order at the outermost Zr layer via the Stoner instability. Consequently, the time-reversal symmetry breaking at the surface not only generates spin-polarized topological surface states with intricate helical spin textures but also hosts an intrinsic anomalous Hall effect originating from the Berry curvature generated by spin-orbit coupling. Our findings offer a playground to investigate the emergence of ferromagnetism and anomalous Hall transport at the surface of nonmagnetic topological electrides.

Investigation of Imidazolium-Based Ionic Liquids as Additives for the Separation of Urinary Biogenic Amines via Capillary Electrophoresis

Ionic liquids (ILs), such as imidazoles, can be used to prevent the sorption of analytes onto the walls of the capillary. Prior works have confirmed that coating the capillary wall with a cationic layer can increase its surface stability, thereby improving the repeatability of the separation process. In this study, micellar electrokinetic chromatography (MEKC) is employed to evaluate how two ILs with different anions—namely, 1-hexyl-3-methylimidazolium chloride [HMIM+Cl−] and 1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM+BF4−]—affect the separation efficiency for biogenic amines (BAs) such as metanephrine (M), normetanephrine (NM), vanilmandelic acid (VMA), and homovanillic acid (HVA) in urine samples. To this end, solid-phase extraction (SPE) is employed using different sample pH values, with the results demonstrating that HVA and VMA is easily extracted at a sample pH of 5.5, while a sample pH of 9.0 facilitated the extraction of M and NM. In the applied SPE protocol, selected analytes were isolated from urine samples using hydrophilic–lipophilic-balanced (HLB) columns and eluted with methanol (MeOH). The validation data confirmed the method’s linearity (R2 &gt; 0.996) for all analytes within the range of 0.25–10 µg/mL. The applicability of the optimized SPE-MEKC-UV method was confirmed by employing it to quantify clinically relevant BAs in real urine samples from pediatric neuroblastoma (NBL) patients.

Effect of coating nanostructure on the electrokinetics of polyelectrolyte-coated particles. Grafted vs adsorbed polymer

In this work, the electrokinetic response of nanoparticles suspensions under the action of alternating electric fields is analyzed for the case that the particles are coated with a shell of polyelectrolyte. This is an important field of application of colloidal systems, as the coating is necessary or even unavoidable for control of the stability or functionalization of the particles for a specific use. Characterization of the coating in situ is not an easy task, and electrokinetics can help in answering this question, if one goes beyond the simple routine evaluation of the electrophoretic mobility of the particles, which will provide information on the sign (and perhaps a sort of effective amount) of the surface charge and potential, but little more. The richness and rigour of the information is much more significant if AC fields are used. This is the case for the techniques evaluated in the present investigation, namely, AC electrophoresis and dielectric dispersion. They jointly sweep several decades in frequency, and are sensitive in different manners to the size of the particles, the charge of the core and the shell, the thickness and rigidity of the latter, etc. In addition, an important distinction is made between coatings with a soft or adsorbed layer structure and those with a grafted, ideally radially arranged (brush-like) polyelectrolyte. A model is first described for the AC electrokinetics in both cases, and it is demonstrated that the brush structure magnifies the Maxwell-Wagner (or double layer) polarization, leading to an elevation in the AC mobility for frequencies around the MHz, and it very much raises the amplitude of the alpha- or concentration-polarization relaxation detected in the dielectric dispersion. The distribution of the charge in a thicker region for the brush structure explains these results. Experimental investigations are carried out with silica spheres coated by PDADMAC (+) and PSS (-) polyelectrolytes in the soft-layer case, and by (vinylbenzyl)trimethylammonium chloride (+) and sodium 4-vinylbenzenesulfonate (-) monomers that were polymerized (grafted) on the particles. The results show that the brush coating produces the expected MW elevation of the mobility, mostly in the case of the cationic polymer, apparently better attached to the particles by electrostatic attraction to the negative charge of the core silica particles. In contrast, a rather monotonous decrease of the mobility in absolute value is measured for the soft coatings, indicating that the inertia of the particles sets out at lower frequencies because of aggregation. Dielectric spectra confirm the better stability in the presence of the grafted polymer, although a low-frequency elevation in the logarithmic derivative of the permittivity is a proof of the existence of aggregates, less abundant in any case than for soft coatings. Dielectric data also confirm the different amounts of charge, larger for grafted cationic layers than for anionic ones. Finally, the model elaborated can fit the experimental results yielding quantitative values of the main parameters of the coated particles, namely, effective size, overall charge of the coating, and thickness and ionic permeability of the latter.

The hydration of Li+ and Mg2+ in subnano carbon nanotubes using a multiscale theoretical approach.

The separation of brines with high Mg/Li mass ratios is a huge challenge. To provide a theoretical basis for the design of separation materials, the hydration of Li+ and Mg2+ in confinement using carbon nanotubes (CNTs) as the 1-D nanopore model was investigated using a multiscale theoretical approach. According to the analysis of the first coordination layer of cations, we determined that the coordination shells of two cations exist inside CNTs, while the second coordination shells of the cations are unstable. Moreover, the results of the structure analysis indicate that the hydration layer of Li+ is not complete in CNTs with diameters of 0.73, 0.87, and 1.00nm. However, this does not occur in the 0.60nm CNT, which is explained by the formation of contact ion pairs (CIP) between Li+ and Cl- that go through a unstable solvent-shared ion pair [Li(H2O)4]+, and this research was further extended by 400ns in the 0.60nm CNT to address the aforementioned results. However, the hydration layer of Mg2+ is complete and not sensitive to the diameter of CNTs using molecular dynamics simulation and an ab initio molecular dynamics (AIMD) method. Furthermore, the results of the orientation distribution of Li+ and Mg2+ indicate that the water molecules around Mg2+ are more ordered than water molecules around Li+ in the CNTs and are more analogous to the bulk solution. We conclude that it is energetically unfavorable to confine Li+ inside the 0.60-nm diameter CNT, while it is favorable for confining Li+ inside the other four CNTs and Mg2+ in all CNTs, which is driven by the strong electrostatic interaction between cations and Cl-. In addition, the interaction between cations and water molecules in the five CNTs was also analyzed from the non-covalent interaction (NCI) perspective by AIMD.