Water Intercalation Research Articles

Intercalated water mediated electromechanical response of graphene oxide films on flexible substrates

The confinement of water between sub-nanometer bounding walls of layered two-dimensional materials has generated tremendous interest. Here, we examined the influence of confined water on the mechanical and electromechanical response of graphene oxide films, prepared with variable oxidative states, casted on polydimethylsiloxane substrates. These films were subjected to uniaxial strain under controlled humid environments (5 to 90% RH), while dc transport studies were performed in tandem. Straining resulted in the formation of quasi-periodic linear crack arrays. The extent of water intercalation determined the density of cracks formed in the system thereby, governing the electrical conductance of the films under strain. The crack density at 5% strain, varied from 0 to 3.5 cracks mm−1 for hydrated films and 8 to 22 cracks mm−1 for dry films, across films with different high oxidative states. Correspondingly, the overall change in the electrical conductance at 5% strain was observed to be ∼5 to 20 folds for hydrated films and ∼20 to 35 folds for the dry films. The results were modeled with a decrease in the in-plane elastic modulus of the film upon water intercalation, which was attributed to the variation in the nature of hydrogen bonding network in graphene oxide lamellae.

Bi2S3 and MoS2 Soft Coatings: A Comparative Study of Their Frictional Behavior Under Different Humidity Levels, Normal Loads, and Sliding Speeds

Bi2S3 is a promising solid lubricant for demanding applications, such as oil extraction, heavy mining, and aerospace components. However, its tribological behavior has not been studied in depth. Burnished Bi2S3 soft coatings were evaluated utilizing reciprocating sliding tests under different levels of relative humidity level, normal load, and sliding speed and the results were benchmarked against MoS2 coatings. In addition, ab initio calculations using density functional theory modeling were employed for studying the interaction between the sulfides and the steel substrates and the effect of water intercalation at an atomic level. It was found that Bi2S3 coatings present excellent environmental adaptability and substrate protection over a wide range of testing conditions, thanks to their characteristic crystal structure.

Performance enhancement of subcooled flow boiling on graphene nanostructured surfaces with tunable wettability

Modifying the surface wettability at the solid-liquid interface can significantly improve flow boiling heat transfer. The graphene nanoplatelets (GNPs) and epoxy additives form nanocomposites coatings with tunable wettability (superhydrophilic, superhydrophobic and hydrophobic) via a thermal curing process. They are applied for enhancing the subcooled flow boiling heat transfer in a minichannel. By comparing with the uncoated surface, the superhydrophilic GNPs coating shows the highest boiling heat transfer coefficient with a maximum enhancement of 64.9 %. The nanocapillary-networks of the superhydrophilic GNPs coatings facilitate the fast water permeation effect and induce an effective filmwise boiling heat transfer. Moreover, the superhydrophilic GNPs coatings facilitate bubble detachment process and suppress the formation of dry spot during the boiling process. On the contrary, the hydrophobic and superhydrophobic GNPs coatings act as impervious blankets for the intercalation of water and deteriorate the flow boiling rates. The effects of the subcooled degree and the mass flux of the bulk flow on the performance enhancement are also investigated. This study aims to investigate the flow boiling enhancement attributed to the graphene functionalized coatings and provides interesting insights of the ultrafast water permeation mechanism of graphene into the subcooled flow boiling heat transfer.

Reversible Molecular and Ionic Storage Mechanisms in High-Performance Zn0.1V2O5·nH2O Xerogel Cathode for Aqueous Zn-Ion Batteries.

The cathode is a critical component for aqueous Zn-ion batteries (ZIBs) to achieve high capacity and long stability. In this work, we demonstrate a dissolution-free, low-Zn-preinserted bilayer-structured V2O5 xerogel cathode, Zn0.1V2O5·nH2O (ZnVO), with excellent capacity and stability using a low-cost ZnSO4 electrolyte. Its discharge capacity reaches 463 mAh g-1 at 0.2 A g-1 and 240 mAh g-1 at 10 A g-1, while 93% and 88% of its capacity are retained at 0.2 A g-1 for 200 cycles and at 10 A g-1 for 20 000 cycles, respectively. We then show that the outstanding performance of ZnVO is derived from the enlarged gallery spacing by the solvent water intercalation and the water stable V2O5 bilayer structure. We further unveil via ab initio molecular dynamics that H+ is largely originated from the dissociation of the gallery water, while OH- moves out of the gallery to form Zn4(SO4)(OH)6·5H2O with ZnSO4 electrolyte on the surface of ZnVO; the intercalated Zn2+ forms aquo complex [Zn(H2O)6]2+ with the gallery water. Our theoretical analysis also suggests that the gallery water and solvent water in the electrolyte are statistically the same and functionally equivalent. Overall, this study shows the promise of ZnVO as a practical cathode for ZIBs and offers fundamental insights into the roles of gallery water, solvent water, bilayer V2O5 structure, and dual Zn2+/H+ intercalation mechanisms in achieving high capacity and long stability.

Role of intercalated water in calcium hydroxide interlayers for carbonation reaction

Carbonation of calcium hydroxide (Ca(OH)2) is an indispensable process with applications in the stable storage of CO2, geological disposal of radioactive waste, and cement manufacture for the construction industry. In the carbonation reaction of Ca(OH)2, water plays an important role in the conversion of CO2 and increases the thermodynamic stability of calcium carbonate. Therefore, understanding the interaction between water and Ca(OH)2 is essential for controlling the kinetics and thermodynamics of the carbonation reaction of Ca(OH)2. In this study, changes in the physical and chemical properties of Ca(OH)2 that appear before the carbonation of hydrated Ca(OH)2 were observed through XRD and NMR analyses. Through XRD analysis, the interplanar distance of hydrated Ca(OH)2 increased by approximately 0.39% compared to that of the pristine Ca(OH)2. Furthermore, we quantified the intercalated water through NMR analysis based on water signal appearing around 0.9 ppm, which was approximately 3.0–7.0 wt% of Ca(OH)2. Through theoretical calculations, the hydrated Ca(OH)2 formed a stable structure with intercalated water molecules, resulting in lower reaction barrier and heat of reaction of the Ca(OH)2 carbonation. For the first time, the intercalation of water between the Ca(OH)2 interlayers is observed, and its importance in the carbonation reaction is established.

Multidimensional analysis of excitonic spectra of monolayers of tungsten disulphide: toward computer-aided identification of structural and environmental perturbations of 2D materials

Despite 2D materials holding great promise for a broad range of applications, the proliferation of devices and their fulfillment of real-life demands are still far from being realized. Experimentally obtainable samples commonly experience a wide range of perturbations (ripples and wrinkles, point and line defects, grain boundaries, strain field, doping, water intercalation, oxidation, edge reconstructions) significantly deviating the properties from idealistic models. These perturbations, in general, can be entangled or occur in groups with each group forming a complex perturbation making the interpretations of observable physical properties and the disentanglement of simultaneously acting effects a highly non-trivial task even for an experienced researcher. Here we generalise statistical correlation analysis of excitonic spectra of monolayer WS2, acquired by hyperspectral absorption and photoluminescence imaging, to a multidimensional case, and examine multidimensional correlations via unsupervised machine learning algorithms. Using principal component analysis we are able to identify four dominant components that are correlated with tensile strain, disorder induced by adsorption or intercalation of environmental molecules, multi-layer regions and charge doping, respectively. This approach has the potential to determine the local environment of WS2 monolayers or other 2D materials from simple optical measurements, and paves the way toward advanced, machine-aided, characterization of monolayer matter.

Adsorption of water on epitaxial graphene

Graphene and its functionalization are still one of the most prominent two‐dimensional crystals. In recent years, the wetting properties of graphene for water (i.e., its hydrophobic, hydrophilic, and also icophobic features) were controversially discussed as well as water intercalation and confined water, that have unusual characteristics. The dispute about wetting properties was originally based on contact angle (/engineering) measurements conducted at ambient pressure. In the meanwhile, detailed ultra‐high vacuum (UHV) surface science works and theoretical studies are available. This brief review describes the current knowledge available in the literature about the water/graphene system as well as our own work using experimental UHV surface science techniques. The review starts with a definition of hydrophobicity and briefly touches on a possible correlation with icephobicity as well as discusses briefly confined water. Next, theoretical studies are reviewed, and finally, experimental works are described on which the review focusses. Finally, a brief outlook section discusses water adsorption on functionalized graphene.

Nanoscale Hydration in Layered Manganese Oxides.

Birnessite is a layered MnO2 mineral capable of intercalating nanometric water films in its bulk. With its variable distributions of Mn oxidation states (MnIV, MnIII, and MnII), cationic vacancies, and interlayer cationic populations, birnessite plays key roles in catalysis, energy storage solutions, and environmental (geo)chemistry. We here report the molecular controls driving the nanoscale intercalation of water in potassium-exchanged birnessite nanoparticles. From microgravimetry, vibrational spectroscopy, and X-ray diffraction, we find that birnessite intercalates no more than one monolayer of water per interlayer when exposed to water vapor at 25 °C, even near the dew point. Molecular dynamics showed that a single monolayer is an energetically favorable hydration state that consists of 1.33 water molecules per unit cell. This monolayer is stabilized by concerted potassium–water and direct water–birnessite interactions, and involves negligible water–water interactions. Using our composite adsorption–condensation–intercalation model, we predicted humidity-dependent water loadings in terms of water intercalated in the internal and adsorbed at external basal faces, the proportions of which vary with particle size. The model also accounts for additional populations condensed on and between particles. By describing the nanoscale hydration of birnessite, our work secures a path for understanding the water-driven catalytic chemistry that this important layered manganese oxide mineral can host in natural and technological settings.

Structure and Dynamics of Aqueous Electrolytes Confined in 2D-TiO2/Ti3C2T2 MXene Heterostructures

The synthesis of heterostructures of different two-dimensional (2D) materials offers an approach to combine advantages of different materials constituting the heterostructure and ultimately enhance their performance for applications such as electrochemical energy storage, achieving high energy, and high-power densities. Understanding the behavior of ions and solvents in confinement between these dissimilar layers is critical to understand their performance and control. Considering aqueous electrolytes, we explore the heterostructure of 2D lepidocrocite-type TiO2 (2D-TiO2) and hydroxylated or O-terminated Ti3C2 MXene using ReaxFF molecular dynamics simulations and elastic/quasielastic neutron scattering techniques. Simulating a bilayer water intercalation, we find that the extent of interlayer hydration is impacted most by the surface terminations on the MXene and is marginally affected by 2D-TiO2. However, the introduction of 2D-TiO2 decreases the water self-diffusion due to the notch sites (i.e., surface oxygen ridges) entrapping water molecules. Intercalating alkali cations into the heterostructures, we find that Li+ is predominantly adsorbed at the 2D-TiO2 surface instead of the MXenes with the preferential occupation of the notch sites. In contrast, Na+ forms a planar solvation with water, while K+ is adsorbed both at the O-terminated MXene and 2D-TiO2. This behavior is altered when OH-terminated MXene is involved-the repulsion from the protons on the MXene surface forces the K+ ions to be adsorbed exclusively to 2D-TiO2, while Na+ retains some of its solvation in the water layer due to its smaller size. In OH-terminated MXenes, we see a consistent transfer of protons from the MXene surface toward 2D-TiO2, implying a greater capacity to store protons in the heterostructures. Of the three cations simulated, Na+ hinders the proton migration the least and Li+ the most because of its position near the 2D-TiO2 surface. Therefore, 2D-TiO2/MXene heterostructures are likely to exhibit a higher energy density but lower power density, especially with Na+ intercalation.

Graphene and graphene oxide on Ir(111) are transparent to wetting but not to icing

Anti-icing coatings reduce the freezing onset temperature for water by changing the chemical and physical environment at the water-substrate interface to prevent ice nucleation and growth. Graphene oxide has several attributes that make it attractive as an anti-icing coating and it has been theoretically predicted that graphene oxide has a lower freezing onset temperature than pristine graphene. Here, we test this hypothesis using carefully prepared, well-characterized graphene oxide substrates. We compare the water contact angle for graphene and graphene oxide coatings, both prepared on iridium(111) surfaces. The results show both materials to be transparent to wetting, but indicate a lower freezing onset temperature for graphene oxide than for pristine graphene. The measured water contact angles are dominated by the properties of the underlying Ir(111) substrate while the freezing onset temperature is dictated by the functional groups present on the graphene basal plane. We suggest that the lowering of the freezing onset temperature is caused by the formation of a viscous water layer on the surface. Scanning tunneling microscopy and x-ray photoelectron spectroscopy data are used to evaluate the robustness of the coating material and suggest ways to improve the long-term performance, namely by advancing strategies to avoid water intercalation.

First-Principles Modeling of Sodium Ion and Water Intercalation into Titanium Disulfide Interlayers for Water Desalination

Recent experiments revealed the possibility of using titanium disulfide (TiS2) as the cathode material in capacitive deionization (CDI) devices for water desalination. Although it performed stably ...

Hydroplastic foaming of graphene aerogels and artificially intelligent tactile sensors.

Direct foaming from solids is the most efficient method to fabricate porous materials. However, the ideal foaming fails to prepare aerogel of nanoparticles because the plasticity of their solids is denied by the overwhelming interface interactions. Here, we invent a hydroplastic foaming method to directly convert graphene oxide solids into aerogel bulks and microarrays, replacing the prevalent freezing method. The water intercalation plasticizes graphene oxide solids and enables direct foaming instead of catastrophic fragmentation. The bubble formation follows a general crystallization rule and allows nanometer-precision control of cellular wall thickness down to 8 nm. Bubble clustering generates hyperboloid structures with seamless basal connection and renders graphene aerogels with ultrarobust mechanical stability against extreme deformations. We exploit graphene aerogel to fabricate tactile microarray sensors with ultrasensitivity and ultrastability, achieving a high accuracy (80%) in artificially intelligent touch identification that outperforms human fingers (30%).

Humidity effect on peeling of monolayer graphene and hexagonal boron nitride

Ambient humidity introduces water adsorption and intercalation at the surfaces and interfaces of low-dimensional materials. Our extensive molecular dynamics (MD) simulations reveal the completely opposite contributions of interfacial water to the peeling of monolayer graphene and hexagonal boron nitride (h-BN) sheets from graphite and BN substrates. For graphene, interfacial water decreases the peeling force, due to lower adhesion at the graphene/water interface. The peeling force of h-BN increases with an increase in the thickness of interfacial water, owing to stronger adhesion at the h-BN/water interface and the detachment of the water layer from the substrates. In this work, a theoretical model considering graphene/water and water/substrate interfacial adhesion energies is established, to predict the peeling forces of graphene and h-BN, which coincides well with the peeling forces predicted by the MD simulations. Our results should provide a deeper insight into the effect of interfacial water, induced by ambient humidity, on mechanical exfoliation and the transfer of two-dimensional van der Waals crystals.

Adsorption of water on epitaxial graphene

Abstract

Study of n-alkylamine Intercalated Layered Perovskite-Like Niobates HCa2Nb3O10 as Photocatalysts for Hydrogen Production From an Aqueous Solution of Methanol.

A series of hybrid niobates HCa2Nb3O10×RNH2, containing n-alkylamines (R = Me, Et, Pr, Bu, Hx, Oc) intercalated into the interlayer space, has been thoroughly studied concerning the photocatalytic hydrogen production from a model aqueous solution of methanol for the first time. All the hybrid photocatalysts were synthesized by the conventional ceramic technique followed by protonation and intercalation of n-alkylamines. The products were characterized using XRD, Raman, IR and diffuse reflectance spectroscopy, TGA, CHN-analysis and SEM. Photocatalytic measurements were conducted according to an advanced scheme taking into account possible changes in the photocatalyst concentration because of sedimentation, pH shifts and exfoliation of the samples into nanoplatelets. Special attention was also paid to the feasible improvement of the photocatalytic activity of the samples via their modification with Pt nanoparticles as a cocatalyst. In the series of amine derivatives, the highest rate of hydrogen generation was demonstrated by the Pt-loaded HCa2Nb3O10×BuNH2 reaching apparent quantum efficiency of 13% in the 220–340 nm range. The initial HCa2Nb3O10 showed comparable efficiency of 8.3% that is greater than for other amine derivatives. It was demonstrated that for the investigated samples the photocatalytic activity correlates with their ability of water intercalation.

The role of water lubrication in critical state fault slip

The conventional driving mechanisms including elevating the pore pressure or far-reaching poroelastic effects, may not necessarily explain the injection-triggered seismicity that can be up to 35–90 km far away from injection wells. In this experimental study, we examined the mechanism of water lubrication for the triggered seismicity where the fluid pressure was negligible compared to the in-situ stresses. The results show that fault slip can occur upon saturation when the ratio of the applied shear stress to the fault peak shear strength exceeds a critical threshold, which is defined to quantitatively assess the critical stress state for faults. The microscale slip test using atomic force microscopy reveals the mechanism responsible for the significant reduction of friction between granite surfaces from dry to wet state. A nanometer-thick water layer was attached on the granite surfaces, causing the shear plane shifting from the direct granite/granite interface to the water layer, and meanwhile the adhesive force between granite surfaces was significantly reduced by water intercalation, both of which played the dominate role in triggering fault slip. In practice, slip may be associated with in-situ fluid flow into far-field faults, which causes the increase of water and lubricates the fault zone.

Self-Assembly Evolution of N-Terminal Aromatic Amino Acids with Transient Supramolecular Chirality.

Deep understanding and fine tailoring of spontaneous structural evolution of self-assembled arrays are pivotal in the rational design of advanced soft materials. However, an indistinct structure-property relationship and pathway complexity in self-assembly lead to a considerable challenge. Herein, we reveal the self-assembly pathway complexity in spontaneous aggregation of several N-terminated aromatic amino acids. By primarily tuning the incubation time, building blocks appended with alanine and serine selectively form 1:1 hydrated clathrates, enabling the microfiber to transition to crystals. The dynamic water intercalation process was studied by incubation time-dependent morphological changes, powder X-ray diffraction, and single-crystal structure analysis. A pronounced amino acid residue effect on the self-assembly evolution was reflected by supramolecular chirality inversion of the building block having the phenylalanine residue, accomplishing dynamic M- to P-helicity transition within a confined time scale.

A 3D-RISM study of water and potassium ion adsorption in Montmorillonite nanoclay

In this study, we investigated the intercalation of water and K+ to interlayer of Montmorillonite (MMT) nanoclay by using the statistical mechanics theory of molecular liquids or three-dimensional reference interaction site model (3D-RISM). The results from 3D-RISM show that the distribution of water and K+ bound to the MMT’s surfaces with different sites. Moreover, the results from 3D-RISM show the amount of water corresponds to the d-basal spacing of the clay, which are in good agreements with other simulation methods as well as experimental.

Disentangling the effects of doping, strain and disorder in monolayer WS2 by optical spectroscopy

Monolayers of transition metal dichalcogenides (TMdC) are promising candidates for realization of a new generation of optoelectronic devices. The optical properties of these two-dimensional materials, however, vary from flake to flake, or even across individual flakes, and change over time, all of which makes control of the optoelectronic properties challenging. There are many different perturbations that can alter the optical properties, including charge doping, defects, strain, oxidation, adsorbed molecules and water intercalation. Identifying which perturbations are present is usually not straightforward and requires multiple measurements using multiple experimental modalities, which presents barriers when attempting to optimise preparation of these materials. Here, we apply high-resolution photoluminescence and differential reflectance hyperspectral imaging in situ to CVD-grown WS2 monolayers. By combining these two optical measurements and using a statistical correlation analysis we are able to disentangle three contributions modulating optoelectronic properties of these materials: electron doping, strain and disorder arising from adsorbates, substrate fluctuations and/or defects. In separating these contributions, we also observe that the B-exciton energy is less sensitive to variations in doping density than A-excitons. Our approach is not limited to monolayers of WS2 and is also applicable to other 2D materials with optical transitions, and the general approach could be extended to other characterization modalities.

Graphene-Subgrain-Defined Oxidation of Copper.

The correlation between the crystal structure of chemical vapor deposition (CVD)-grown graphene and the crystal structure of the Cu growth substrate and their mutual effect on the oxidation of the underlying Cu are systematically explored. We report that natural oxygen or water intercalation along the graphene-Cu interface results in an orientation-dependent oxidation rate of the Cu surface, particularly noticeable for bicrystal graphene domains on the same copper grain, suggesting that the relative crystal orientation of subgrains determines the degree of Cu oxidation. Atomistic force field calculations support these observations, showing that graphene domains have preferential alignment with the Cu(111) with a smaller average height above the global Cu surface as compared to intermediate orientations, and that this is the origin of the heterogeneous oxidation rate of Cu. This work demonstrates that the natural oxidation resistance of Cu coated by graphene is highly dependent on the crystal orientation and lattice alignment of Cu and graphene, which is key information for engineering the interface configuration of the graphene-Cu system for specific functionalities in mechanical, anticorrosion, and electrical applications of CVD-grown graphene.