Graphene effectively activating "dead" water molecules between manganese dioxide layers in potassium-ion battery

Aqueous potassium-ion batteries(APIBs),recognized as safe and reliable new energy devices,are considered as one of the alternatives to traditional batteries.Layered MnO_(2),serving as the main cathode,exhibits a lower specific capacity in aqueous electrolytes compared to organic systems and operates through a different reaction mechanism.The application of highly conductive graphene may effectively enhance the capacity of APIBs but could complicate the potassium storage environment.In this study,a MnO_(2) cathode pre-intercalated with K~+ions and grown on graphene(KMO@rGO) was developed using the microwave hydrothermal method for APIBs.KMO@rGO achieved a specific capacity of 90 mA h g^(-1) at a current density of 0.1 A g^(-1),maintaining a capacity retention rate of>90% after 5000 cycles at 5 A g^(-1).In-situ and exsitu characterization techniques revealed the energy-storage mechanism of KMO@rGO:layered MnO_(2)traps a large amount of "dead" water molecules during K~+ions removal.However,the introduction of graphene enables these water molecules to escape during K~+ ions insertion at the cathode.The galvanostatic intermittent titration technique and density functional theory confirmed that KMO@rGO has a higher K~+ions migration rate than MnO_(2).Therefore,the capacity of this cathode depends on the interaction between dead water and K~+ions during the energy-storage reaction.The optimal structural alignment between layered MnO_(2) and graphene allows electrons to easily flow into the external circuit.Rapid charge compensation forces numerous low-solvent K~+ions to displace interlayer dead water,enhancing the capacity.This unique reaction mechanism is unprecedented in other aqueous battery studies.

Influence of interlayer water molecules in Ni-based catalysts for oxygen evolution reaction

Nickel-iron layered double hydroxides(NiFe LDHs) have been identified as one of the best promising electrocatalysts-candidates for oxygen evolution reaction(OER). However, the catalytic activity effected by interlayer water molecules is ignored and rarely reported. Herein, Ni(OH)_2, NiFe LDHs vertically aligned Ni foam are designed for OER. As a contrast, the corresponding electrocatalysts with the removal of the interlayer water molecules(Ni(OH)_2-AT, NiFe LDHs-AT) are developed to probe into the influence of the interlayer water molecules towards OER. As expected, NiFe LDH nanoplates exhibit excellent catalytic performance and durability for water electrolysis in alkaline conditions with lower overpotential and smaller Tafel slope compared to those of NiFe LDHs-AT, which are influenced mainly by stability of crystal structure due to the existence of interlayer water molecules. The discovery opens up a similar pathway by controlling the amount of water molecules to boost catalytic performance for studying other electrocatalysts with heteroatom dopant.

Orientation and Motion of Water Molecules at Air/Water Interface

Here we report a quantitative study of the orientational structure and motion of water molecule at the air/water interface. Analysis of Sum Frequency Generation （SFG） vibrational peak of the free O-H stretching band at 3700 cm^-1 in four experimental configurations showed that orientational motion of water molecule at air/water interface is libratory within a limited angular range. The free OH bond of the interracial water molecule is tilted around 33°from the interface normal and the orientational distribution or motion width is less than 15°. This picture is significantly different from the previous conclusion that the interracial water molecule orientation varies over a broad range within the ultrafast vibrational relaxation time, the only direct experimental study concluded for ultrafast and broad orient, ational motion of a liquid interface by Wei et al. （Phys. Rev. Lett. 86, 4799, （2001）） using single SFG experimental configuration.

Detailed investigation on single water molecule entering carbon nanotubes

The behavior of a water molecule entering carbon nanotubes （CNTs） is stud- ied. The Lennaxd-Jones potential function together with the continuum approximation is used to obtain the van der Waals interaction between a single-walled CNT （SWCNT） and a single water molecule. Three orientations are chosen for the water molecule as the center of mass is on the axis of nanotube. Extensive studies on the variations of force, energy, and velocity distributions axe performed by vaxying the nanotube radius and the orientations of the water molecule. The force and energy distributions are validated by those obtained from molecular dynamics （MD） simulations. The acceptance radius of the nanotube for sucking the water molecule inside is derived, in which the limit of the radius is specified so that the nanotube is favorable to absorb the water molecule. The velocities of a single water molecule entering CNTs axe calculated and the maximum entrance and the interior velocity for different orientations axe assigned and compared.

Geometrical structures, vibrational frequencies, force constants and dissociation energies of isotopic water molecules (H_2O, HDO, D_2O, HTO, DTO, and T_2O) under dipole electric field

The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311＋＋G（3df,3pf）. The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H-O increases whereas the bond angle of H-O H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H2O, HDO, HTO, D2O, DTO, and T2O under the same external electric fields.

Control water molecules across carbon-based nanochannels

It is important to know the mechanisms of water molecules across carbon-based nanochannels, which is not only beneficial for understanding biological activities but also for designing various smart devices. Here we review the recent progress of research tbr water transfer across carbon-based nanochannels. In this review, we summarize the recent methods which can affect water molecules across these nanochannels. The methods include exterior factors （i.e., dipolar molecules and gradient electric fields） and interior factors （namely, cone-shaped structures, nonstraight nanochannels, and channel defects）. These factors can control water permeation across nanochannels efficiently.

The Gravito-Chemical Bond and Structures of Hydrocarbons and Water Molecules with Real Magnetic Charges

Experimental and theoretical studies of the author (period: 1968-present) have shown that true sources of the magnetic field are magnetic fundamental particles (magnetic charges), and not moving electrons. The main reason for ignoring real magnetic charges, as well as true antielectrons in physical science is the hard conditions for confinement of these particles in atoms and substances, which is radically different from the confinement of electrons. Magnetic charges together with electric charges form the shells atoms which are electromagnetic, and not electronic. Namely, electromagnetic shells are sources of gravitational field which is a vortex electromagnetic field and described by the vortex rot [E - H]. Depending on the state polarization of vortex vectors rot [E - H] in compositions of atomic gravitational fields it is subdivided into paragravitational (PGF) and ferrogravitational fields (FGF). The overwhelming number of atoms emits PGF. Between the masses (bodies, atoms, nucleons and others) emitting PGF areas of negative gravitational “Dark Energy” are realized the forces of which press the masses towards each other. Namely, the compression of atoms by the forces of paragravitational “Dark Energy” underlies the chemical bond. The exception here is the ionic bond in ionic crystals. However, all ions have electromagnetic shells that generate the gravitational field. Consequently, ionic bonding is a relatively rare addition to gravito-chemical bond processes. The direct gravito-chemical bond of carbon atoms with hydrogen (1H) is physically forbidden due to the manifestation of the effect of ferrogravitational levitation between them and the repulsion of atoms from each other. Paradoxically, but all existing ideas about the structural device of hydrocarbons are based on such physically forbidden bonds which, moreover, must be realized through ionic bonds which in reality do not exist. Chemical bonding of carbon and hydrogen atoms to form hydrocarbons molecules is possible only if the hydrogen atoms are in the molecular form (1H2). In the composition of water, within the framework of the chemical formula H2O, two stable isomorphic molecular structures are formed. The chemical bond in the first structure is similar to the hydrocarbon scenario described above, i.e. in the process of combining paragravitational oxygen with a hydrogen molecule 1H2. The second molecular structure in water is formed under conditions of ferropolarization of the gravitational field of oxygen atoms under the influence of FGF of neighboring 1H atoms. In this case, the chemical bond is realized under the conditions of ferropolarization of the vortex vectors rot [E - H] of the gravitational fields of all atoms in the molecule and the co-directionality of them vectors Pfp ferropolarization. The gravito-physical properties of the presented molecular structures in the composition of water make it possible to name them, respectively, as heavy and light clusters.

Unsaturated transport properties of water molecules and ions in graphene oxide/hydrated calcium silicate nanochannels:from basic principles to complex environmental performance effects

The problems of traditional concrete such as brittleness,poor toughness and short service life of concrete engineering under acid rain or marine environment need to be solved urgently.Hydrated calcium silicate(C-S-H)is a key component to improve the mechanical properties and durability of concrete.However,the traditional method of concrete material design based on empirical models or comparative tests has become a bottleneck restricting the sustainable development of concrete.The synthesis method,molecular structure and properties of C-S-H were systematically described in this paper;The interface structure and interaction of graphene oxide/calcium silicate hydrate(C-S-H/GO)were discussed.On this basis,the saturated and unsaturated transport characteristics of ions and water molecules in C-S-H/GO nanochannels under the environment of ocean and acid rain were introduced.The contents of this review provide the basis for improving the multi-scale transmission theory and microstructure design of concrete.It has important guiding significance for analyzing and improving the service life of concrete in complex environment.

Molecular dynamics study of water molecules nucleation for fine particle removal:Effects of wettability and aggregation modes and comparison with experiment Author links open overlay panel

Water vapor nucleation on particle's surface plays an important role in dust removal,cloud formation,and particle measurement.However,the selectivity of nucleation sites and the nucleation characteristic of water molecule on the particle's surface are still unclear,especially for the aggregated particles.In this paper,the effects of particle wettability and aggregation modes on the selectivity of nucleation sites and the nucleation characteristics were investigated using molecular dynamics simulation.The results were compared with our earlier experimental findings.It illustrates how the contact angle of clusters,the growth velocity,and the growth duration are all influenced by the interaction coefficient between water and particles.Moreover,the nucleation sites of water molecules on the particle aggregation surface exhibit a definite selectivity.The primary indicator of this selectivity is the preferential nucleation of water molecules at the interfaces of linear chain aggregation particles,at the inner side of non-linear chain aggregation particles,and at the centers of ring aggregation.These results are in good agreement with our previous experimental findings.More significantly,additional research has revealed that subcritical-size clusters typically aggregate on two-particle surfaces spacing when the spacing smaller than the critical cluster size.

Water molecule-induced hydrogen bonding between cellulose nanofibers toward highly strong and tough materials from wood aerogel

Lightweight,highly strong and bio-based structural materials remain a long-lasting challenge.Here,inspired by nacre,a lightweight and high mechanical performance cellulosic material was fabricated via a facile and effective top-down approach and the resulting material has a high tensile strength of149.21 MPa and toughness of 1.91 MJ/m^(3).More specifically,the natural balsawood(NW) was subjected to a simple chemical treatment,removing most lignin and partial hemicellulose,follow by freeze-drying,forming wood aerogel(WA).The delignification process produced many pores and exposed numerous aligned cellulose nanofibers.Afterwards,the WA absorbed a quantity of moisture and was directly densified to form above high-performance cellulosic material.Such treatment imitates highly ordered"brick-and-mortar" arrangement of nacre,in which water molecules plays the role of mortar and cellulose nanofibrils make the brick part.The lightweight and good mechanical properties make this material promising for new energy car,aerospace,etc.This paper also explains the strengthening mechanism for making biomimetic materials by water molecules-induced hydrogen bonding and will open a new path for designing high-performance bio-based structural materials.

Using a water-confined carbon nanotube to probe the electricity of sequential charged segments of macromolecules

The detection of macromolecular conformation is particularly important in many physical and biological applications. Here we theoretically explore a method for achieving this detection by probing the electricity of sequential charged segments of macromolecules. Our analysis is based on molecular dynamics simulations, and we investigate a single file of water molecules confined in a half-capped single-walled carbon nanotube （SWCNT） with an external electric charge of ＋e or -e （e is the elementary charge）. The charge is located in the vicinity of the cap of the SWCNT and along the centerline of the SWCNT. We reveal the picosecond timescale for the re-orientation （namely, from one unidirectional direction to the other） of the water molecules in response to a switch in the charge signal, -e -＋ ＋e or ＋e -＋ --e. Our results are well understood by taking into account the electrical interactions between the water molecules and between the water molecules and the external charge. Because such signals of re-orientation can be magnified and transported according to Tu et al. [2009 Proc. Natl. Aead. Sci. USA 106 18120], it becomes possible to record fingerprints of electric signals arising from sequential charged segments of a macromolecule, which are expected to be useful for recognizing the conformations of some particular macromolecules.

Unprecedentedly rapid transport of single-file rolling water molecules

The realization of rapid and unidirectional single-file wate^molecule flow in nanochannels has posed a challenge to date. Here, we report unprecedentedly rapid unidirectional single-file water-molecule flow under a translational terahertz electric field, which is obtained by developing a Debye double- relaxation theory. In addition, we demonstrate that all the single-file molecules undergo both stable translation and rotation, behaving like high-speed train wheels moving along a railway track. Inde- pendent molecular dynamics simulations help to confirm these theoretical results. The mechanism involves the resonant relaxation dynamics of H and O atoms. Purther, an experimental demon- stration is suggested and discussed. This work has implications for the design of high-efficiency nanochannels or smaller nanomachines in the field of nanotechnology, and the findings also aid in the understanding and control of water flow across biological nanochannels in biology-related research.

First-principles study on the co-adsorption of water and oxygen molecules on chalcopyrite(112)-M surface

Chalcopyrite is a common copper-bearing mineral with antiferromagnetic properties.However,this property has rarely been considered in previous studies for detailed adsorption behaviors of molecules on chalcopyrite.Based on density functional theory(DFT),new adsorption pathways by H_(2)O and O_(2)on the chalcopyrite metal terminated(112)surface((112)-M)is found in this work.First,through simulating the adsorption of an isolated water molecule and monolayer water molecules,it is confirmed that H_(2)O molecules tend to adsorb on the surface Fe atoms more than on the surface Cu atoms.Then,we studied various adsorption behaviors of the O_(2)molecule.It is found that the adsorption on the hollow FeAFe site is the most stable case;however,O_(2)is undissociated.Two adsorption cases will happen when H_(2)OAO_(2)adsorb simultaneously on the surface.For the S site,the H_(2)O molecule thoroughly dissociated and formed SAO species,and the other case is H_(2)O undissociated adsorbing at the Cu site.For the former case,it is interesting that H_(2)O is dissociated before O_(2).

Effect of Explicit Water Molecules on the Color-Tuning Mechanism of the Firefly

The contributions of explicit water molecules to color-tuning mechanism of firefly were studied. The explicit water molecules cause two different structures in the geometrical parameters of keto（-1） both in vacuo and aqueous solution. There are somewhat larger influences on absorption and emission spectra. When water molecules were added only on the side of benzothiazole ring, the spectra shift to the blue. In contrast, when waters were added only on the side of the thiazoline ring, the spectra shift to red. In a word, the color modulation of the emitted light depends on charge redistribution of molecule keto（-1）, mainly the charge change of the benzothiazole and thiazole tings at the two terminal in keto（-1）.

Water Molecule-Triggered Anisotropic Deformation of Carbon Nitride Nanoribbons Enabling Contactless Respiratory Inspection

The exploitation of the interaction between nanostructured matter and small molecules,such as H_(2)O at interfaces via dynamic hydrogen bonding,is essentially the key for smart,responsive nanodevices but remains challenging.Herein,the authors report that the carbon nitride nanoribbons(CNNRs)with an anisotropic intraplanar and interplanar molecular arrangement underwent a deformation by H_(2)O triggering.Both experiments of bulk samples and single nanoribbons disclosed that the reversible formation of a hydrogen-bonded H_(2)O adsorption layer was the source of the CNNRs deformation,reminiscent of the hydration-triggered twist of natural bean pods in seeding.Nonetheless,CNNRs had a more balanced H_(2)O affinity,enabling a superior response and recovery time.By coupling with carbon nanotubes,the authors also converted the deformation of CNNRs into more straightforward electrical readouts with record-fast response time.Further applied to capture fluctuations in humidity in real-time respiration,a higher detection sensitivity was obtained in a contactless mode,which compared favorably with the clinical breath-testing station.Given the carbon nitride family with various C/N ratios,surface properties,and topography,this finding that CNNRs are an outstanding H_(2)O transducer would significantly pave the way for the H_(2)O-triggered smart devices in broad prospective applications.

NOVEL WATER SOLUBLE HOST MOLECULE DERIVED FROM CALIXARENE

Reaction of p-t-butylcalix[6]arene with ethylene oxide gives a water soluble host compound with a hydrophobic cavity and it can include organic molecules and ions in aqueous solution.

Molecular Simulations of Water Transport Resistance in Polyamide RO Membranes: Interfacial and Interior Contributions

Understanding the transport resistance of water molecules in polyamide(PA)reverse osmosis(RO)membranes at the molecular level is of great importance in guiding the design,preparation,and applications of these membranes.In this work,we use molecular simulation to calculate the total transport resistance by dividing it into two contributions:the interior part and the interfacial part.The interior resistance is dependent on the thickness of the PA layer,while the interfacial resistance is not.Simulation based on the 5 nm PA layer reveals that interfacial resistance is the dominating contribution(>62%)to the total resistance.However,for real-world RO membranes with a 200 nm PA layer,interfacial resistance plays a minor role,with a contribution below 10%.This implies that there is a risk of inaccuracy when using the typical method to estimate the transport resistance of RO membranes,as this method involves simply multiplying the total transport resistance of the simulated value based on a membrane with a 5 nm PA layer.Furthermore,both the interfacial resistance and the interior resistance are dependent on the chemistry of the PA layer.Our simulation reveals that decreasing the number of residual carboxyl groups in the PA layer leads to decreased interior resistance;therefore,the water permeability can be improved at no cost of ion rejection,which is in excellent agreement with the experimental results.

Effect Mechanism of Structure-Changed Water on Heat Stability of Lysozyme

Based on the mechanism of the effect of hydration on the heat stability of lysozyme and the theory of water molecule clusters, the effect of structure-changed water on heat stability of lysozyme has been studied. The results obtained by differential scanning calorimetry (DSC) showed that the thermal denaturation temperature of lysozyme had been elevated 8.47 K through hydration of lysozyme with processed water whose structure had been changed so it was called "structured water" compared to ordinary water. The reason is that structured water changed the dipole moment of water molecules and easily formed cyclic water hexamer or cage-like water hexamer, so that the interacting force of maintaining three-dimensional conformation of lysozyme could be reinforced.

Correlation between surface charge and hydration on mineral surfaces in aqueous solutions: A critical review

Surface charges and hydration are predominant properties of colloidal particles that govern colloidal stability in aqueous suspensions.These properties usually coexist and interact with each other.The correlation between the surface charge and hydration of minerals is summarized on the basis of innovative experimental,theoretical,and molecular dynamics simulation studies.The factors affecting the adsorption behavior of ions and water molecules,such as ion concentration,ion hydration radius and valence,and surface properties,are discussed.For example,the hydration and adsorption states completely differ between monovalent and divalent ions.For ions of the same valence,the effect of surface charge on the hydration force follows the Hofmeister adsorption series.Electrolyte concentration exerts a significant effect on the hydration force at high ion concentrations.Meanwhile,the ion correlations in high-concentration electrolyte systems become long range.The interfacial water structure largely depends on surface chemistry.The hydration layer between different surfaces shows large qualitative differences.

Electricity resonance-induced phase transition of water confined in nanochannels

The phase transition of water molecules in nanochannels under varying external electric fields is studied by molecular dynamics simulations.It is found that the phase transition of water molecules in nanochannels occurs by changing the frequency of the varying electric field.Water molecules maintain the ice phase when the frequency of the varying electric field is less than 16 THz or greater than 30 THz,and they completely melt when the frequency of the varying electric field is 24 THz.This phenomenon is attributed to the breaking of hydrogen bonds when the frequency of the varying electric field is close to their inherent resonant frequency.Moreover,the study demonstrates that the critical frequency varies with the confinement situation.The new mechanism of regulating the phase transition of water molecules in nanochannels revealed in this study provides a perspective for further understanding of the phase transition of water molecules in nanochannels,and has great application potential in preventing icing and deicing.