Water Intercalation Research Articles

Enhancement of Friction by Water Intercalated between Graphene and Mica.

Common experience shows that friction converts mechanical energy into heat. The first part of this process is vibrational excitation of atoms at the interface between rubbing bodies. The second part is the removal of the vibration energy by transferring it from the interface to the substrate. However, it is difficult to disentangle the excitation and energy transfer processes. We solved this by using a system consisting of a SiO2-terminated tip sliding over graphene deposited on mica with intercalated water between them. The intercalated water was found to increase friction by a factor of ∼3 relative to dry mica. Density functional theory calculations show that water broadens the spectral range of graphene vibrations-particularly the low-frequency flexural modes-thus providing new excitation channels and also by increasing the overlap with the atomic vibrations of the mica substrate, which facilitates coupling and energy transfer.

Microstructure characterization of hydrothermally synthesized PANI/V2O5·nH2O heterojunction photocatalyst for visible light induced photodegradation of organic pollutants and non-absorbing colorless molecules

Polyaniline intercalated vanadium oxide xerogel (PV) hybrid nanocomposite (NC) with novel structure has been successfully synthesized through a simple hydrothermal route. Detailed structure and microstructure characterization of PV NC is illustrated through Rietveld refinement of XRD data and FESEM/HRTEM images. Both FTIR and XPS spectra confirm the presence of PANI and water molecules within the NC and partial reduction of V5+ to V4+, corroborating with the results of XRD pattern analysis. Core-shell structure of PV NC, where PANI sheath layer acts as a shell covering around V2O5·nH2O crystalline core is confirmed from HRTEM images. Successive morphological changes of PV NC with different reaction time have been revealed from FESEM images. UV–vis spectra also confirm the formation of PV NC. Intercalation of water and PANI layers into V2O5·nH2O layer leads to a structural phase transition from orthorhombic to monoclinic phase due to substantial increase in interplanar spacing of (00l) of orthorhombic V2O5. The photocatalytic property of the as synthesized PV NC has been reported for the first time, with a promising photocatalytic activity for the degradation of organic dye, Rhodamine B (RhB) under visible light irradiation. It is attributed to a synergic effect in between PANI and V2O5·nH2O xerogel. The photocatalyst also shows remarkable real visible light photocatalytic activity with non-absorbing colorless test molecules like phenol and antibiotic kanamycin.

Photocatalytic activity and physicochemical characteristics of modified potassium polytitanates in the reaction of decomposition of aqueous-alcoholic solutions

Study of the photocatalytic activity of nanomaterials based on potassium polytitanate modified with transition metal ions (Ni2+, Cr3+, Cu2+) demonstrated that the cation composition, morphology of photocatalyst particles, and their size strongly affect the photocatalytic activity. The rate of the photoinduced hydrogen evolution from the aqueous-alcoholic solution grows in the series of potassium polytitanates modified with Cu2+, Ni2+, Cr3+ ions, and that from pure water, for potassium polytitanates modified with Ni2+,Cr3+, Cu2+ ions. The capacity for intercalation of water into the interlayer space does not strongly affect the rate of the photoinduced hydrogen evolution. It was shown that potassium polytitanate modified with Cr3+ ions has the maximum quantum efficiency (30%).

Effects of Water Intercalation and Tribochemistry on MoS2 Lubricity: An Ab Initio Molecular Dynamics Investigation.

To date, no clear conclusion has been reached on the atomistic mechanisms that govern the observed decrease of lubricating capabilities of MoS2 in humid environments. Based on ab initio molecular dynamic calculations, we show that intercalated water molecules hinder the sliding motion of both regular and defective layers considerably, with the velocities decaying exponentially with time. However, in the presence of an applied load and exposed edge terminations, water is rapidly removed from the interface and is adsorbed on the edges either in undissociated form or as OH/H fragments. These outcomes suggest that the interlayer slipperiness can be reduced by the presence of water even in the absence of any chemical oxidation. Our work could help to set up more dedicated experiments to further tackle a technologically relevant issue for the applications of MoS2 -based lubricants.

Effects of Applied Potential and Water Intercalation on the Surface Chemistry of Ti2C and Mo2C MXenes

Two-dimensional transition metal carbides and nitrides, also known as MXenes, represent an attractive class of materials for a multitude of electrochemical and other applications. While single sheets of MXenes have been widely studied theoretically, there have been much fewer studies on layered bulk MXenes, which are more representative of multi- or few-layer MXenes used in actual applications. Herein, we investigate the structural and electronic effects of water intercalation, multiple functional groups and applied potential on layered bulk Ti2C and Mo2C MXenes using density functional theory. The out-of plane lattice parameter, c, was found to vary significantly with the functional group, and is greatly increased upon intercalation of water. Experimental results confirm the change in lattice constant due to addition or removal of intercalated water. Under zero applied potential, both Ti2C and Mo2C were found to be functionalized by one monolayer of O; bare MXenes were never found to be stable, regardles...

Comparison Study on the Effect of Interlayer Hydration and Solvation on Montmorillonite Delamination

The effect of water and isopropanol intercalation on montmorillonite (MMT) delamination was investigated in order to compare the roles of hydration and solvation in the delamination. Transmittance results showed that water has a significant effect on the delamination of MMT compared with isopropanol. This observation was attributed to the difference of the intercalation of water and isopropanol. Thermogravimetric (TG) results illustrate that the intercalation mass of water was greater than that of isopropanol when the pressure remained constant. Weighing test results show that the intercalation mass of water was smaller than that of isopropanol when the volume of MMT remained constant. Molecule dynamic simulation results show that the water and isopropanol molecules were interacting with Na+ and siloxane surface of MMT, respectively. It was demonstrated that the hydration of the MMT interlayer followed two steps: in step 1, the Na+ in the interlayer was hydrated, thereby expanding the interlayer spacing; in step 2, additional water molecules were absorbed into the expanded interlayer space. It was found that step 2 could not be actuated until the completion of step 1. For the solvation of the MMT interlayer with isopropanol, however, only one step was required, in which isopropanol was absorbed onto the siloxane sites of the interlayer while maintaining the interlayer spacing.

One-dimensional nanowires of pseudoboehmite (aluminum oxyhydroxide γ-AlOOH)

We report the discovery of a 1D crystalline structure of aluminum oxyhydroxide. It was found in a commercial product of fibrous pseudoboehmite (PB), γ-AlOOH, synthesized easily with low cost. The thinnest fiber found was a ribbon-like structure of only two layers of an Al-O octahedral double sheet having a submicrometer length along its c axis and 0.68-nm thickness along its b axis. This thickness is only slightly larger than half of the lattice parameter of the b-axis unit cell of the boehmite crystal (b/2 = 0.61 nm). Moreover, interlayer splittings having an average width of 1 nm inside the fibrous PB are found. These wider interlayer spaces may have intercalation of water, which is suggested by density functional theory (DFT) calculation. The fibers appear to grow as almost isolated individual filaments in aqueous Al-hydroxide sols and the growth direction of fibrous PB is always along its c axis.

ChemInform Abstract: Multidimensional Perovskites: A Mixed Cation Approach Towards Ambient Stable and Tunable Perovskite Photovoltaics

AbstractReview: [92 refs.

Multidimensional Perovskites: A Mixed Cation Approach Towards Ambient Stable and Tunable Perovskite Photovoltaics.

Although halide perovskites are able to deliver high power conversion efficiencies, their ambient stability still remains an obstacle for commercialization. Thus, promoting the ambient stability of perovskites has become a key research focus. In this review, we highlight the sources of instability in conventional 3 D perovskites, including water intercalation, ion migration, and thermal decomposition. Recently, the multidimensional perovskites approach has become one of the most promising strategies to enhance the stability of perovskites. As compared to pure 2 D perovskites, multidimensional perovskites typically possess more ideal band gaps, better charge transport, and lower exciton binding energy, which are essential for photovoltaic applications. The larger organic cations in multidimensional perovskites could also be more chemically stable at higher temperatures than the commonly used methylammonium cation. By combining 3 D and 2 D perovskites to form multidimensional perovskites, halide perovskite photovoltaics can attain both high efficiency and increased stability.

Green synthesis route for WS2 nanosheets using water intercalation

The exfoliation of layered materials has attracted a lot of attention in recent times. In this report, we have exfoliated WS2 in deionized water (without using any chemical solvents, surfactants, etc) using the thermal coefficient mismatch between WS2 and H2O along with other anomalous properties of water, such as the formation of five-, six- and seven-ring structures while freezing. Two different green synthesis routes have been proposed for WS2 exfoliation. We call them the ‘hard’ and ‘soft’ quenching methods. The nanosheets were investigated using different characterization tools and we found the exfoliation of the bulk into <4 layers with an average lateral dimension of 200 nm. The exfoliation method is unique in the sense of producing pristine nanosheets due to the absence of any organic solvents, which are difficult to remove.

Effect of water intercalation on the structure and electrophysical properties of YBa2Cu3O6.9

The influence of water vapors and plastic deformation on the structure and electrophysical properties of YBa2Cu3O6.9 (123) has been studied. It has been established that, at T = 200°C, the introduction of water into the structure of YBa2Cu3O6.9 leads to its transition into a defect tetragonal phase of the 124 type as a result of the formation of planar stacking faults. After annealing at T = 930°C, these defects are partially retained and are efficient centers of pinning in the magnetic fields applied perpendicularly to the c axis, which makes it possible to increase (by an order of magnitude) the critical current density in the high-textured ceramics at 77 K in the external magnetic field of 5–10 T. The plastic deformation of the hydrated ceramics favors the reverse transition of the arising 124 phase to the 123 phase at T = 930°C and is accompanied by a recrystallization of the material, which leads to the appearance of a texture and an increase the critical current density.

First-Principles Study of the Role of O2 and H2O in the Decoupling of Graphene on Cu(111).

The structural and electronic properties of graphene coated on a Cu(111) surface can be strongly influenced by the arrangement of adsorbates at the graphene edges. Oxygen and water intercalation at the graphene edges could lead to oxidation and hydrolysis at the graphene/Cu(111) interface, eventually causing decoupling of graphene from the Cu substrate. However, the reaction pathways for oxygen or water (or both) intercalation at the graphene edges are not well understood at the molecular level. Using ab initio density functional theory calculations, we observed a strong hybridization of π orbitals at a zigzag edge of a graphene nanoribbon (GNR) on a bare Cu(111) surface, whereas such hybridization was absent for the corresponding armchair edge under otherwise identical conditions. These results indicate that the edge type influences the oxidation chemistry beneath the GNR. Moreover, we demonstrate that the presence of oxygen species, as well as GNR, facilitates the propagation of H2O. The following decoupling mechanisms are discussed: (i) GNRs with armchair edge configurations on Cu(111) can be decoupled via a sequential reaction that involves O2 dissociation followed by H2O intercalation, whereas (ii) GNRs with zigzag edge configurations on Cu(111) can be decoupled by oxygen intercalation.

Graphene and MoS2 interacting with water: A comparison by ab initio calculations

Although very similar in many technological applications, graphene and MoS2 bear significant differences if exposed to humid environments. As an example, lubrication properties of graphene are reported to improve while those of MoS2 to deteriorate: it is unclear whether this is due to oxidation from disulfide to oxide or to water adsorption on the sliding surface. By means of ab initio calculations we show here that these two layered materials have similar adsorption energies for water on the basal planes. They both tend to avoid water intercalation between their layers and to display only mild reactivity of defects located on the basal plane. It is along the edges where marked differences arise: graphene edges are more reactive at the point that they immediately prompt water splitting. MoS2 edges are more stable and consequently water adsorption is much less favoured than in graphene. We also show that water-driven oxidation of MoS2 layers is unfavoured with respect to adsorption.

Superconducting water derivatives of Sr2Can−1CunO2+2n-δ (n = 2–4) high-Tc superconductors

We prepared two new phases of high-Tc superconductors with water molecules as the main constituents of the charge-reservoir block and refined the synthesis method for another phase. These water-containing phases form from high-pressure-synthesized Sr2Can−1CunO2+2n±δ or 0(Sr)2(n−1)n (n = 2–4) superconducting phases through a topotactic water-intercalation process when the parent phases are exposed to open air at 80 °C. Upon the water intercalation the body-centered unit cell of the parent phase is elongated along the c-axis direction by ∼6.2 Å. Despite the elongated unit cell the Tc value is not changed upon the water intercalation. The water-based H-m(Sr)2(n−1)n copper-oxide superconductors are new exotic members of the yet tiny family of superconductors with Tc values higher than 100 K.

TG and DSC investigation of water intercalation and protonation processes in perovskite-like layered structure of titanate K2Nd2Ti3O10

The article presents results of the complex study of hydration and protonation processes of promising photocatalysts K2Nd2Ti3O10, belonging to the family of perovskite-type layered Ruddlesden–Popper phases. K2Nd2Ti3O10 was synthesized by solid-state method and was monitored using powder X-ray diffraction. The behavior in water has been studied by means of thermogravimetric analysis, simultaneous thermal analysis and differential scanning calorimetry. The substitution of potassium cations for protons and the water intercalation into the interlayer space of the crystal structure were observed. Proton-containing layered oxides with general formula HxK2−xNd2Ti3O10·yH2O (0.07 ≤ x ≤ 1.7, 0.06 ≤ y ≤ 0.44) have been obtained.

Robust Phonon-Plasmon Coupling in Quasifreestanding Graphene on Silicon Carbide.

Using inelastic electron scattering in combination with dielectric theory simulations on differently prepared graphene layers on silicon carbide, we demonstrate that the coupling between the 2D plasmon of graphene and the surface optical phonon of the substrate cannot be quenched by modification of the interface via intercalation. The intercalation rather provides additional modes like, e.g., the silicon-hydrogen stretch mode in the case of hydrogen intercalation or the silicon-oxygen vibrations for water intercalation that couple to the 2D plasmons of graphene. Furthermore, in the case of bilayer graphene with broken inversion symmetry due to charge imbalance between the layers, we observe a similar coupling of the 2D plasmon to an internal infrared-active mode, the LO phonon mode. The coupling of graphene plasmons to vibrational modes of the substrate surface and internal infrared active modes is envisioned to provide an excellent tool for tailoring the plasmon band structure of monolayer and bilayer graphene for plasmonic devices such as plasmon filters or plasmonic waveguides. The rigidity of the effect furthermore suggests that it may be of importance for other 2D materials as well.

In situ spectroscopic study of water intercalation into talc: New features of 10 Å phase formation

The synthesis of 10 A phase via the reaction of talc plus water at 8 GPa and 500 °C was studied by in situ Raman spectroscopy using a diamond-anvil cell. The initial fast (2 h) incorporation of interlayer H2O molecules into the talc structure is traced by gradual growth of new OH stretching bands at 3592 and 3621 cm−1 and the shift of several framework bands. Further monitoring at HP-HT conditions over 7 h reveals gradual weakening of the 3592 cm−1 band, which can probably be related to the onset of the formation of “long-run” 10 A phase through the appearance of silanol groups following the model proposed by Pawley et al. (2010), influencing the interlayer hydrogen bonding.

Mixed conduction properties of pristine bulk graphene oxide

We investigated the conduction properties of pristine bulk graphene oxide (GO) with different oxidation degrees. GO with a low oxidation degree shows the electron/hole conduction behavior. Interestingly, however, GO with high oxidation degree exhibits mixed conduction behaviors (electron/hole conduction and proton conduction), depending on the water content. For GO with a high oxidation degree, electron/hole conduction dominates the electrical transport in the water-lean state, while the proton conduction dominates the electrical transport in the water-rich state. Among different oxygen-containing functional groups, the epoxide groups, which could influence the band gap, interlayer distance and water intercalation process, play a critical role in the conduction properties of GO. In electrical transport process, epoxide groups act as conduction barriers for electron/hole conduction while serving as active sites for proton conduction. Both graphite and GOs exhibit a clear anisotropic behavior in electrical transport.. These observations will provide insightful information for the applications of GO in fuel cells, humidity sensors and supercapacitors.

Water Intercalation for Seamless, Electrically Insulating, and Thermally Transparent Interfaces.

The interface between functional nanostructures and host substrates is of pivotal importance in the design of their nanoelectronic applications because it conveys energy and information between the device and environment. We report here an interface-engineering approach to establish a seamless, electrically insulating, while thermally transparent interface between graphene and metal substrates by introducing water intercalation. Molecular dynamics simulations and first-principles calculations are performed to demonstrate this concept of design, showing that the presence of the interfacial water layer helps to unfold wrinkles formed in the graphene membrane, insulate the electronic coupling between graphene and the substrate, and elevate the interfacial thermal conductance. The findings here lay the ground for a new class of nanoelectronic setups through interface engineering, which could lead to significant improvement in the performance of nanodevices, such as the field-effect transistors.

High-temperature conductivity and structure of Y2(WO4)3 ceramics

The magnitude and character of conductivity were studied for Y2(WO4)3 ceramics synthesized by the ceramic (from oxides) and organic-nitrate procedures. Investigation of the dependence \(\sigma \left( {{\alpha _{{o_2}}}} \right)\) and measurements of the ion transport numbers of charge carriers by the EMF method showed that Y2(WO4)3 is basically an ion conductor. The conductivity is largely determined by the sample preparation conditions related to the dependence of the specific surface area and powder grain size on the synthetic procedure. The maximum high-temperature conductivity of Y2(WO4)3 was 2.51 × 10–4 S/cm, which roughly corresponds to the conductivities of Sc2(WO4)3 and In2(WO4)3 measured under the same conditions. It was confirmed that Y2(WO4)3 crystallizes as a mixed monoclinic-orthorhombic structure at 1000°C. The character of water incorporation in hydrated Y2(WO4)3 crystals was studied by thermogravimetry and diffuse reflectance IR spectroscopy. A qualitative model of water intercalation was suggested.