Interlayer Water Molecules Research Articles

Intermolecular dynamics of ultraconfined interlayer water in tobermorite: influence on mechanical performance.

Ultraconfined interlayer water within the tobermorite molecular structure is responsible for changes in the uniaxial tensile and compressive response of the family of tobermorites: 9, 11 and 14 Å. These confined interlayer water molecules are engaged in solvation of cations and anions within the tobermorite structure, which has been demonstrated through the intermolecular vibrational spectra and hydrogen bond lifetime of the water molecules. This study demonstrates that instead of ionization of water molecules (as proposed in an earlier study), breaking of hydrogen bonds of water is more plausible leading to solvation of ions within the molecular structure of tobermorite. A schematic of the coordinate covalent bonds between the water molecules and the cations and anions of the tobermorite structure has been proposed in this study.

Driving force for the swelling of montmorillonite as affected by surface charge and exchangeable cations: A molecular dynamic study

Abstract Swelling of montmorillonite (MMT) is a nonnegligible factor in many industrial processes owing to its great ability to absorb water in interlayer space. It is not easy to determine whether the exchangeable cations or the MMT layers interacts much stronger with water molecules to provide the dominant driving force for the swelling of MMT. In this work, driving force for the swelling of montmorillonite as affected by surface charge and exchangeable cations has been investigated through molecular dynamics simulations (MDs). The adsorption energy between water molecules and MMT layers and between interlayer cations and water molecules was calculated to qualitatively characterize the driving force for the swelling of MMT, and higher negative adsorption energy means greater driving force. It is found that the adsorption energy between interlayer cations and water molecules are far higher than that between MMT layers and water molecules. Thus, it is the exchangeable cations that provide the dominant driving force for MMT to swell. Besides, it is observed that interlayer cations with stronger hydration ability (Mg > Ca > Na > K) have more negative adsorption energy to water molecules, which indicates that the stronger the hydration ability of exchangeable cations the greater contribution they make to the total driving force for the swelling of MMT.

Crystalline Swelling Process of Mg-Exchanged Montmorillonite: Effect of External Environmental Solicitation

This work reports characterization of the possible effects that might distress the hydration properties of Mg-exchanged low-charge montmorillonite (SWy-2) when it undergoes external environmental solicitation. This perturbation was created by an alteration of relative humidity rates (i.e., RH%) over two hydration-dehydration cycles with different sequence orientations. Structural characterization is mainly based on the X-ray diffraction (XRD) profile-modeling approach achieved by comparing the “in situ” obtained experimental 00l reflections with other ones calculated from theoretical models. This method allows assessing the evolution of the interlayer water retention mechanism and the progress of diverse hydration state’s contributions versus external strain. Obtained results prove that the hydration behavior of the studied materials is strongly dependent on the RH sequence orientation which varied over cycles. The interlayer organization of Mg-exchanged montmorillonite (i.e., SWy-2-Mg) is characterized by a heterogeneous hydration behavior, which is systematically observed at different stages of both cycles. By comparing the interlayer water process evolution of Mg-exchanged montmorillonite with the observed SWy-2-Ni sample hydration behaviors, a same hysteresis thickness characterized by obvious fluctuations of interlayer water molecule abundances is observed. Nevertheless, in the case of Hg and Ba-saturated montmorillonite, the retention water process versus the applied cycles was steadier comparing with Mg ions.

Dilithium (citrate) crystals and their relatives.

New compounds of the type LiMHC6H5O7 (M = Li, Na, K, Rb) have been prepared from the metal carbonates and citric acid in solution. The crystal structures have been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. The compounds crystallize in the triclinic space group P-1 and are nearly isostructural. The structures are lamellar, with the layers in the ab plane. The boundaries of the layers consist of hydrophobic methylene groups and very strong intermolecular O-H...O hydrogen bonds. The O...O distances range from 2.666 Å for M = Li to 2.465 Å for M = Rb. The Li-O bonds exhibit significant covalent character, while the heavier M-O bonds are ionic. The Li atoms are four-, five-, or six-coordinate, while the coordination numbers of the larger cations are higher, i.e. eight for Na and nine for K and Rb. The citrate anion occurs in the trans,trans conformation, one of the two low-energy conformations of an isolated citrate anion. The crystal structure of LiRbHC6H5O7·H2O was also solved and refined. It consists of the same layers as in the anhydrous M = Rb compound, with interlayer water molecules and a different hydrogen-bonding pattern.

Large-Scale Synthesis and Comprehensive Structure Study of δ-MnO2.

Layered δ-MnO2 (birnessites) are ubiquitous in nature and have also been reported to work as promising water oxidation catalysts or rechargeable alkali-ion battery cathodes when fabricated under appropriate conditions. Although tremendous effort has been spent on resolving the structure of natural/synthetic layered δ-MnO2 in the last few decades, no conclusive result has been reached. In this Article, we report an environmentally friendly route to synthesizing homogeneous Cu-rich layered δ-MnO2 nanoflowers in large scale. The local and average structure of synthetic Cu-rich layered δ-MnO2 has been successfully resolved from combined Mn/Cu K-edge extended X-ray fine structure spectroscopy and X-ray and neutron total scattering analysis. It is found that appreciable amounts (∼8%) of Mn vacancies are present in the MnO2 layer and Cu2+ occupies the interlayer sites above/below the vacant Mn sites. Effective hydrogen bonding among the interlayer water molecules and adjacent layer O ions has also been observed for the first time. These hydrogen bonds are found to play the key role in maintaining the intermediate and long-range stacking coherence of MnO2 layers. Quantitative analysis of the turbostratic stacking disorder in this compound was achieved using a supercell approach coupled with anisotropic particle-size-effect modeling. The present method is expected to be generally applicable to the structural study of other technologically important nanomaterials.

Structure, Dynamics, and Mechanical Properties of Cross-Linked Calcium Aluminosilicate Hydrate: A Molecular Dynamics Study

C-A-S-H is the main hydration product of environmental friendly concrete with cement material partially substituted by the industrial waste. The molecular structure of C-A-S-H gel determines the durability of the material. In this study, the cross-linking C-A-S-H models with Al/Si ratios of 0, 0.05, 0.10, 0.15, and 0.2 are constructed, and the structure, reactivity, and mechanical properties of the C-A-S-H gel are investigated by the reactive force field molecular dynamics. The incorporation of aluminate species in the C-A-S-H gel modifies the silicate-aluminate skeleton and interlayer water molecules. On the one hand, the bridging silicate tetrahedron is substituted by the aluminate species that polymerize with defective silicate chains, improve the crystalline order, enhance the Q species connectivity, and transform the layered C-S-H structure to cross-linked branch of C-A-S-H gel. On the other hand, the Al–Si substitution enhances the reactivity of the bridging oxygen sites in Si–O–Al, which contribute...

Optimized photoreduction of CO2 exclusively into methanol utilizing liberated reaction space in layered double hydroxides comprising zinc, copper, and gallium

Layered double hydroxides (LDHs), typically comprising Zn, Cu, and Ga, photoreduce CO2 into methanol and CO, however, selective methanol synthesis using CO2 and heterogeneous photocatalyst is very rare. In this study, the amount of interlayer water molecules is reduced to 31% of that for as-synthesized LDHs by preheating the LDHs at 423 K in vacuum, and the performance for CO2 photoreduction using 0–0.28 MPa of CO2 and 0–0.56 MPa of H2 was investigated. If the LDHs are preheated in vacuum and never in contact with air prior to the photoreduction tests, methanol was produced exclusively in all experiments of this study. LDHs comprising inlayer Cu sites were more active compared to [Zn3Ga(OH)8]2CO3·mH2O, [Zn3Ga(OH)8]2Cu(OH)4·mH2O, and [Zn3Ga(OH)8]2Pd(OH)4·mH2O LDHs. A contour plot for methanol formation rates was drawn for the most active [Zn1.5Cu1.5Ga(OH)8]2CO3·mH2O and the volcano top positioned at 0.12 MPa of CO2 and 0.28 MPa of H2; 2.8 μmol-methanol h−1 gcat−1 and the selectivity was >97 mol%-methanol. 13CH3OH formation in the presence of 13CO2 and [Zn1.5Cu1.5Ga(OH)8]2CO3·mH2O confirmed photocatalytic methanol synthesis. Under 0.12 MPa of CO2 and 0.28 MPa of H2, the intensity of the Cu K preedge peak progressively decreased at the rate of 170 μmol-Cu h−1 gcat−1 upon the UV–visible light irradiation for the [Zn1.5Cu1.5Ga(OH)8]2CO3·mH2O LDH, demonstrating photogenerated electron accumulation at the CuII/I sites for subsequent CO2 reduction.

First-principles study of a MXene terahertz detector.

2D transition metal carbides, nitrides, and carbonitrides called MXenes have attracted increasing attention due to their outstanding properties in many fields. By performing systematic density functional theory calculations, here we show that MXenes can serve as excellent terahertz detecting materials. Giant optical absorption and extinction coefficients are observed in the terahertz range in the most popular MXene, namely, Ti3C2, which is regardless of the stacking degree. Various other optical properties have been investigated as well in the terahertz range for in-depth understanding of its optical response. We find that the thermoelectric figure of merit (ZT) of stacked Ti3C2 flakes is comparable to that of carbon nanotube films. Based on excellent terahertz absorption and decent thermoelectric efficiency in MXenes, we finally suggest the promise of MXenes in terahertz detection applications, which includes terahertz bolometers and photothermoelectric detectors. Possible ZT improvements are discussed in large-scale MXene flake films and/or MXene-polymer composite films.

Molecular Dynamics Study of Crystalline Swelling of Montmorillonite as Affected by Interlayer Cation Hydration

Swelling of montmorillonite (Mt) is an important factor for many industrial applications. In this study, crystalline swelling of alkali-metal- and alkaline-earth-metal-Mt has been studied through energy optimization and molecular dynamics simulations using the clay force field by Materials Studio 8.0. The delamination and exfoliation of Mt are primarily realized by crystalline swelling caused by the enhanced interlayer cation hydration. The initial position of the interlayer cations and water molecules is the dominated factor for the accuracy of the Mt simulations. Crystalline swelling can be carried out in alkali-metal-Mt and Mg-Mt but with difficulty in Ca-Mt, Sr-Mt and Ba-Mt. The crystalline swelling capacity values are in the order Na-Mt > K-Mt > Cs-Mt > Mg-Mt. This order of crystalline swelling of Mt in the same group can be attributed to the differences between the interlayer cation hydration strengths. In addition, the differences in the crystalline swelling between the alkali-metal-Mt and alkaline-earth-metal-Mt can be primarily attributed to the valence of the interlayer cations.

Crystal chemistry of zinc incorporation in strunzite-group minerals containing zeolitic water

AbstractA comparative study is presented of the chemistry and crystallography of zinc-bearing strunzites from Hagendorf Süd, Bavaria, Germany and the Sitio do Castelo mine, Folgosinho, Portugal. Electron microprobe analyses of samples from the two localities show quite different cation substitutions. The Hagendorf Süd mineral is a Zn-bearing ferristrunzite, with compositional zoning due to Zn2+replacing predominantly Fe3+as well as minor Mn2+, whereas the Portugese mineral is a Zn-bearing strunzite, in which Zn2+replaces Mn2+, with minor replacement of Fe3+by Mn3+. Zincostrunzite, with dominant Zn in the interlayer octahedrally coordinated site, is a new strunzite-group mineral that has been characterized at both locations. Analysis of single-crystal synchrotron data for zinc-bearing ferristrunzite and zincostrunzite crystals from Hagendorf Süd show that the structures of both minerals contain zeolitic water in the interlayer region. The formula for strunzite-group minerals containing the zeolitic water isMFe23+(PO4)2(OH)2·6.5H2O, M=Fe, Mn, Zn. This formulation agrees with that found for zincostrunzite from the Sitio do Castelo mine, but differs from that reported previously for strunzite,MFe2+(PO4)2(OH)2·6H2O, which has no interlayer water. Interestingly, the zincostrunzites from the two localities differ in the location of the interlayer water molecule, with a corresponding difference in the H bonding.

Anisotropic amplification of proton transport in proton exchange membrane fuel cells

Though graphene oxide (GO) membrane shuttles protons under humid conditions, it suffer severe disintegration and anhydrous conditions lead to abysmal ionic conductivity. The trade-off between mechanical integrity and ionic conductivity challenge the amplification of GO’s ionic transport under anhydrous conditions. We show anisotropic amplification of GO’s ionic transport with a selective amplification of in plane contribution under anhydrous conditions by doping it with a plant extract, phytic acid (PA). The hygroscopic nature of PA stabilized interlayer water molecules and peculiar geometry of OH functionalities around saturated hydrocarbon ring anisotropically enhanced ionic transport amplifying the fuel cell performance metrics.

Structural and thermodynamic investigation of the hydration-dehydration process of Na +-Montmorillonite using DFT calculations

This work is mainly focused on investigating the atomic structure of the interlayer water molecules inside Na+-Montmorillonite, their key interactions in the structure and the thermodynamics of the dehydration process. A theoretical study of the different degrees of hydration was performed using calculations based on DFT with several exchange-correlation functionals. The weak layer–water molecules interactions suggested the need of dispersion corrections to simulate correctly the basal spacing and the thermodynamic potentials for the dehydration process. The existence of the structures with sodium cation in planar geometry, representative of the one-water layer model and in octahedral geometry in a two-water layer model was confirmed. The stages of the dehydration of Na+–Mt were evaluated by thermodynamics calculations leading to a good description of the results from TGA/DTG studies. The thermodynamic data suggest also that the one-water layer structure as an intermediate with a metastable configuration.

Stacking changes of KLi[Sb2(C4H2O6)2] homochiral layers mediated by interlayer solvent molecules

Abstract A new compound KLi[Sb2(C4H2O6)2]·4H2O, 1, was synthesized in single crystal form by slowly evaporating an aqueous solution of potassium antimony tartrate and lithium nitrate. The structure of 1 consists of homochiral layers of antimony tartrate dimers linked by LiO4 tetrahedra. The interlayer water molecules can be reversibly driven out by heating or exchanged by small alcohol molecules under ambient conditions, occurring via single-crystal to single-crystal transformations. To accommodate different interlayer molecules, the interlayer space is changed by adjusting the relative lateral shift of neighboring layers. A similar adjustment in the layer stacking also occurs in a structural phase transition caused by order-disorder transformation of the arrangement of interlayer methanol molecules at low temperature.

Size-dependent hydration mechanism and kinetics for reactive MgO and Al2O3 powders with respect to the calcia-free hydraulic binder systems designed for refractory castables

This work investigates the time-dependent hydration behavior of 1:1 molar ratio mixture of reactive α-Al2O3 nano- or micro-powder and reactive MgO in relation to the development of new hydraulic binder systems for in situ spinel refractory corundum castables. Mg–Al–CO3 hydrotalcite-like phases formed in the cementitious matrices cured in the corresponding curing condition up to 280 days of age at 50 °C were subjected to morphological, chemical and structural characterization using XRD, FT-IR, NMR, SEM and TEM techniques. The observations indicate that both the short-term cured MgO–nano-Al2O3 cementitious matrix and the long-term cured one containing micro-Al2O3 contain mainly OH–(Mg3) hydroxyl group, whereas the long-term cured MgO–nano-Al2O3 cementitious matrix is dominated by OH–(Mg2Al) hydroxyl group. The thermal stability of hydrotalcite-like compounds (Mg0.667Al0.333(OH)2(CO3)0.167(H2O)0.5, Mg6Al2CO3(OH)16·4H2O) (HTlcs) through combined DTA–TGA–EGA–MS analyses shows that HTlcs undergo dehydration first and then dehydroxylation overlapping with decarbonization processes. According to EGA–MS and FT-IR measurements, the Mg–Al cementitious matrices were progressively carbonated over curing time and then interlayer water molecules were preferably coordinated by interlayer CO32− ions that exist in a complex network of hydrogen bonds between octahedral layers. In the near-fully-hydrated binder paste, dehydration of crystalline water molecules occurs at 262 °C and the thermal stability of hydroxyl groups in HTlcs is OH–(Mg2Al) (422 °C) > OH–(Mg3) (337 °C) at a ramping rate of 10 °C/min. The basic information provided by the microcalorimetric measurement is such that the starting grain size significantly affects the heat flow curve. From the SEM and TEM images, the hydrates are found to be hexagonal in shape.

Interactions of ammonium-smectite with volatile organic compounds from leachates

AbstractThe percolation of water through waste landfills produces leachates with high concentrations of which can generate -exchanged clays within geochemical barriers. These leachates also contain several volatile organic compounds (VOCs) which can interact with the clay barrier. The aim of the present study was to characterize the sorption of eight short-chain VOCs (acetonitrile, methyl tert-butyl ether, dichloromethane, benzene, phenol, ethanol, acetone and aniline) on -smectite, and to identify their sorption mechanisms. The samples treated were characterized by carbon and nitrogen elemental analysis, infrared spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. For acetonitrile, methyl tert-butyl ether, dichloromethane and benzene, no sorption was detected. Phenol, ethanol and acetone were sorbed very weakly, through Van der Waals interactions. Aniline molecules were sorbed strongly on -smectite mainly with hydrogen bonds between aniline and interlayer water molecules. However, aniline sorption decreased the hydrophilic character of the -smectite, which may increase the permeability of the clay barrier.

Reactive molecular dynamics and experimental study of graphene-cement composites: Structure, dynamics and reinforcement mechanisms

The remarkable properties of graphene and graphene oxide (GO) make it as an ideal candidate for high performance cement-based composites. This paper firstly investigated the effects of graphene and GO on the hydration, microstructures and mechanical properties of cement paste. The incorporation of 0.16 wt % GO into the cement matrix can enhance the flexural strength of the material by 11.62% due to the higher hydration degree, nano-filler effect and cracking-bridging effect. On the other hand, graphene reduces the hydration development and mechanical behavior of cement paste due to its poor dispersibility in alkaline environments. Furthermore, the different interaction mechanisms between graphene/GO and cement hydrates have been deeply studied by reactive force field molecular dynamics (MD), revealing that the functional hydroxyl groups in GO provide non-bridging oxygen (NBO) sites that accept hydrogen-bonds of interlayer water molecules in the calcium silicate hydrate (CSH). In the presence of interface counter-ions, protons transfer from the OH in GO to the NBO sites in CSH, which further contributes to the polarity of the GO surface and enhances the bonding with neighboring species. Besides the H-bond connections, the Ca2+ and Al3+ ions near the surface of CSH play a mediating role in bridging oxygen atoms in silicate chains and hydroxyl groups in GO, which increases the silicate chain length and heals the defective GO structure. Dynamically, the aluminate-silicate chains, calcium ions and functional hydroxyl groups establish the “cages”, and strongly prevent the freely diffusion of the interface water molecules, stabilizing the connections between CSH and GO structures. Finally, the uniaxial tensile simulation indicated that while the high cohesive force and enhance plasticity in the GO modified cement composite is mainly contributed by the strong structural H-bonds and calcium aluminate skeleton, the weakest mechanical behavior of the graphene/CSH composite is attributed to poor bonding and the instability of atoms in the interface region. Reactive force field couples the chemical and mechanical responses that the water dissociation, protons exchange between CSH and GO structures and silicate-aluminate-carbon network de-polymerization occurred to resist the tensile loading.

Iso-conversional kinetics study on thermal degradation of Ni-Al layered double hydroxide synthesized by ‘soft chemical’ sol-gel method

The iso-conversional kinetic parameters evaluation study from thermogravimetric analysis (TGA) data of Ni-Al-LDH was carried out under non-isothermal condition. Ni-Al-LDH was prepared by soft chemical sol-gel method using metal acetylacetonate as precursors. It was characterised by PXRD, FT-IR, TGA and SEM. Ni-Al-LDH showed three step thermal degradations where first step correspond to the loss of surface and interlayer water molecules; the second and third step correspond to the loss of intercalated water molecules and ions from the hydroxidic brucite like layers. The kinetic parameters such as activation energy (Ea), pre-exponential factor (A) and reaction order (n) were determined for the second and third step degradations by Flynn-Wall-Ozawa (FWO), Friedman, Coats-Redfern and Phadnis-Deshpande methods respectively. The activation energy obtained from Friedman method was in good agreement with the value obtained from Flynn-Wall-Ozawa method. The solid state decomposition mechanism obtained from Coats-Redfern method for the second step degradation was an A3 type nucleation and growth mechanism and for the third step a D4 type three –dimensional diffusion control mechanism which was further confirmed by Phadnis-Deshpande method.

Promising zinc-ion battery cathode created

The projected low cost and inherent safety of rechargeable aqueous zinc-ion batteries make energy storage devices based on the technology seem like a real winner. Large stationary versions of such batteries could be particularly useful for grid storage applications involving intermittent power sources such as wind turbines and solar panels. But the batteries haven’t gotten off the ground yet, mainly because of unsatisfactory cathodes, which cause the devices to act sluggishly and die quickly. University of Waterloo researchers led by Linda F. Nazar have now come up with a layered vanadium oxide featuring interlayer zinc ions and water molecules that seems to bypass those problems (Nat. Energy 2016, DOI: 10.1038/nenergy.2016.119). The team used a microwave-driven hydrothermal method to synthesize ribbonlike single crystals of Zn0.25V2O5•nH2O (n = 0.85–1.0) and fashioned cathodes from thin films of the material. They paired the cathodes with metallic zinc anodes to make test cells. Analyses based

Thermogravimetry–mass spectrometry investigations of montmorillonite interlayer water perturbations caused by aromatic acid adsorbates

Mass loss and m/z 18 mass spectrometric ion signal temperature profiles are used to characterize interactions between benzoic acid, salicylic acid, and acetylsalicylic acid adsorbates and potassium, sodium, and calcium montmorillonites. Temperature-dependent water desorption trends show that all three adsorbates cause significant disruptions to clay interlayer water molecule environments. Results suggest that the source of this disruption is the formation of adsorbate–water molecule–cation bridging through the adsorbate acid functionality. Salicylic and acetylsalicylic acids perturb interlayer water molecule environments more than benzoic acid. This is most likely due to the additional hydrogen bond-forming capabilities afforded by the hydroxyl (salicylic acid) and ester (acetylsalicylic acid) groups attached to the aromatic rings of these adsorbates.

Cation and Water Structure, Dynamics, and Energetics in Smectite Clays: A Molecular Dynamics Study of Ca–Hectorite

The incorporation of Ca2+ into smectite minerals is well-known to have a significant effect on the swelling behavior and mechanical properties of this environmentally and technologically important group of materials. Relative to common alkali cations such as Na+, K+, and Cs+, Ca2+ has a larger charge/ionic radius ratio and thus interacts very differently with interlayer water molecules and the oxygens of the clay basal surface. Recent 2H and 43Ca NMR studies of the smectite mineral, hectorite, show that the molecular scale interlayer dynamics is quite different with Ca2+ than with alkali cations. Classical molecular dynamics (MD) simulations presented here use a newly developed hectorite model with a disordered distribution of Li+/Mg2+ substitutions in the octahedral sheet and provide new insight into the origin of the effects of Ca2+ on the structure, dynamics, and energetics of smectite interlayers. The computed basal spacings and thermodynamic properties suggest the potential for formation of stable mo...