Polar Water Molecules Research Articles

(Digital Presentation) Investigation of the Hexylamine Adsorption on Platinum By Potentiostatic and Potentiodynamic Methods

Adsorption is one of the electrochemical process stages often. The adsorption of polar organic molecules (surfactants) on metal electrodes is of significant interest. In particular, the surfactant adsorption affects the exchange current value and determines the metal corrosion rate. Therefore, the explanation of the adsorption mechanism is the most important problem in the investigation of the electrochemical kinetics.The kinetics of the Fe2+ and Fe3+ oxidation-reduction reaction on a platinum electrode in 1 M HClO4 was investigated by potentiodynamic and chronoamperometric methods in the presence of hexylamine as a surfactant. The main kinetic characteristics of the reaction (exchange current density, transfer coefficient, diffusion coefficients of iron ions) have been determined.The dependence of the exchange current density on the hexylamine concentration is analyzed. The surface coverage with a surfactant was estimated at various hexylamine concentrations. It was shown that the hexylamine adsorption on platinum is described by the Dhar-Flory-Huggins adsorption isotherm. The values of the adsorption constant and the adsorption free energy are obtained. These values are close to the corresponding values for the hexylamine adsorption on mild steel in hydrochloric acid. Consequently, the objective laws for the hexylamine adsorption depend low on the acid type and the electrode nature. This indicates the physical adsorption of the surfactant.It is possible that adsorption occurs due to the hydrophobic interaction of the surfactant molecules with polar water molecules. Then, the displacement of surfactant molecules to the interface takes place regardless of the nature of the acid and the metal contacting with the solution. The latter assumption requires further investigations of the surfactant adsorption on various metals.

(Digital Presentation) On the Nature of Surfactant Adsorption on Metals: Adsorption of Hexylamine on Platinum

The kinetics of the Fe2+ and Fe3+ oxidation-reduction reaction on a platinum electrode in 1 M HClO4 was investigated by the EIS method in the presence of hexylamine as a surfactant. With surfactant adsorption, the effective area of the solution-electrode interface decreases. A proportional increase in charge transfer resistance takes place. This resistance values obtained at various hexylamine concentrations. The surface coverage θ(R) for the solution-platinum interface have been calculated.The hexylamine adsorption at the solution-air interface was investigated by the maximum bubble pressure method. The surface tension γ at various hexylamine concentrations are obtained. The surface coverage θ(γ) for the solution-air interface has been calculated. The area occupied by the hexylamine molecule at the interface and the adsorption layer thickness are estimated.It is shown that adsorption process is described by the Dhar-Flory-Huggins isotherm at both interfaces. The slope tg α of the θ(R) and θ(γ) dependence on the hexylamine concentration is close to the theoretical unit in the Dhar-Flory-Huggins coordinates. The main parameters of the hexylamine adsorption (adsorption constant Kad, free adsorption energy ΔGad) were calculated for both interfaces (see Table). Solution-platinum interface Solution-air interface tg α 0.94±0.09 0.98±0.18 K ad / L mol-1 10.0±4.0 15.8±0.3 ΔG ad / kJ mol-1 –(14.8 ± 5.0) –(16.7±0.3) In the general case, the surfactant adsorption on a metal electrode can be due to the interaction of surfactant molecules with the metal or the hydrophobic effect of the surfactant displacement molecules onto the solution surface by polar water molecules. For the solution-air interface, the hydrophobic effect is the main reason for surfactant adsorption at this interface. The values of the main adsorption characteristics on both interfaces are close. Probably, the hydrophobic effect is also the predominant reason for the hexylamine adsorption on platinum. This assumption requires additional studies of the surfactant adsorption on other metals.

Submolecular Insights into Interfacial Water by Hydrogen-Sensitive Scanning Probe Microscopy.

ConspectusWater-solid interfaces have attracted extensive attention because of their crucial roles in a wide range of chemical and physical processes, such as ice nucleation and growth, dissolution, corrosion, heterogeneous catalysis, and electrochemistry. To understand these processes, enormous efforts have been made to obtain a molecular-level understanding of the structure and dynamics of water on various solid surfaces. By the use of scanning probe microscopy (SPM), many remarkable structures of H-bonding networks have been directly visualized, significantly advancing our understanding of the delicate competition between water-water and water-solid interactions. Moreover, the detailed dynamics of water molecules, such as diffusion, clustering, dissociation, and intermolecular and intramolecular proton transfer, have been investigated in a well-controlled manner by tip manipulation. However, resolving the submolecular structure of surface water has remained a great challenge for a long time because of the small size and light mass of protons. Discerning the position of hydrogen in water is not only crucial for the accurate determination of the structure of H-bonding networks but also indispensable in probing the proton transfer dynamics and the quantum nature of protons.In this Account, we focus on the recent advances in the H-sensitive SPM technique and its applications in probing the structures, dynamics, and nuclear quantum effects (NQEs) of surface water and ion hydrates at the submolecular level. First, we introduce the development of high-resolution scanning tunneling microscopy/spectroscopy (STM/S) and qPlus-based atomic force microscopy (qPlus-AFM), which allow access to the degrees of freedom of protons in both real and energy space. qPlus-AFM even allows imaging of interfacial water in a weakly perturbative manner by measuring the high-order electrostatic force between the CO-terminated tip and the polar water molecule, which enables the subtle difference of OH directionality to be discerned. Next we showcase the applications of H-sensitive STM/AFM in addressing several key issues related to water-solid interfaces. The surface wetting behavior and the H-bonding structure of low-dimensional ice on various hydrophilic and hydrophobic solid surfaces are characterized at the atomic scale. Then we discuss the quantitative assessment of NQEs of surface water, including proton tunneling and quantum delocalization. Moreover, the weakly perturbative and H-sensitive SPM technique can be also extended to investigations of water-ion interactions on solid surfaces, revealing the effect of hydration structure on the interfacial ion transport. Finally, we provide an outlook on the further directions and challenges for SPM studies of water-solid interfaces.

Fingerprints of Critical Phenomena in a Quantum Paraelectric Ensemble of Nanoconfined Water Molecules.

We have studied the radio frequency dielectric response of a system consisting of separate polar water molecules periodically arranged in nanocages formed by the crystal lattice of the gemstone beryl. Below T = 20-30 K, quantum effects start to dominate the properties of the electric dipolar system as manifested by a crossover between the Curie-Weiss and the Barrett regimes in the temperature-dependent real dielectric permittivity ε'(T). When analyzing in detail the temperature evolution of the reciprocal permittivity (ε')-1 down to T ≈ 0.3 K and comparing it with the data obtained for conventional quantum paraelectrics, like SrTiO3, KTaO3, we discovered clear signatures of a quantum-critical behavior of the interacting water molecular dipoles: Between T = 6 and 14 K, the reciprocal permittivity follows a quadratic temperature dependence and displays a shallow minimum below 3 K. This is the first observation of "dielectric fingerprints" of quantum-critical phenomena in a paraelectric system of coupled point electric dipoles.

Low-Temperature Mixing of Polar Hydrogen Bond-Forming Molecules in Amorphous Solid Water

The level of mixing of guest molecules within low-temperature amorphous solid water (ASW) (as a host) is of interest and relevance to model studies of photochemistry that take place in the interstellar medium (ISM). In this study, we explore how the physical properties of guest molecules, methanol and ammonia, which strongly interact with ASW films, affect the level of mixing and distribution of these molecules throughout the ASW film at adsorption temperatures of 35–100 K, while they are deposited on a Ru(0001) substrate under ultra-high vacuum conditions. Both methanol and ammonia have gas-phase dipole moments similar to that of water, and they are both capable of forming hydrogen bonds with water. The level of mixing and dispersion of these molecules in ASW films is explored through the isothermal noninvasive contact potential difference (ΔCPD) measurements and temperature programmed contact potential difference experiments (TP-ΔCPD). Upon adsorption at 35 K, both molecules form hydrogen bonds with the surrounding water molecules but do not move too far from their initial location in the ASW film. This is confirmed by the observation of an “inverse volcano” process, where guest molecules initially placed within the interaction range of the ruthenium substrate migrate to the substrate upon water crystallization instead of desorbing to the vacuum as expected in a typical “volcano” process. The adsorption temperature at which extensive mixing is achieved is correlated to the glass transition and crystallization temperatures of the guest molecules, which in this case is lower for both guest molecules than that of water. Homogeneous mixing is only achieved when the films are heated above the glass transition temperature of the host (water) molecules.

Nanoporous nickel with rich adsorbed oxygen for efficient alkaline hydrogen evolution electrocatalysis

Sluggish water dissociation kinetics severely limits the rate of alkaline electrocatalytic hydrogen evolution reaction (HER). Therefore, finding highly active electrocatalysts and clarifying the mechanism of water dissociation are challenging but important. In this study, we report an integrated nanoporous nickel (np-Ni) catalyst with high alkaline HER performance and the origin of the corresponding enhanced catalytic activity. In 1 mol L−1 KOH solution, this np-Ni electrode shows an HER overpotential of 20 mV at 10 mA cm−2, along with fast water dissociation kinetics. The excellent performance is not only attributed to the large surface area provided by the three-dimensional interconnected conductive network but also from the enhanced intrinsic activity induced by the unique surface properties. Further studies reveal that the types of oxygen species that naturally form on the Ni surface play a key role in water dissociation. Remarkably, when the lattice oxygen almost disappears, the Ni surface terminates with adsorbed oxygen (Oads), exhibiting the fastest water dissociation kinetics. Density functional theory calculation suggests that when Oads acts as the surface termination of Ni metal, the orientation and configuration of polar water molecules are strongly affected by Oads. Finally, the H—OH bond of interfacial water molecules is effectively activated in a manner similar to hydrogen bonding. This work not only identifies a high-performance and low-cost electrocatalyst but also provides new insights into the chemical processes underlying water dissociation, thus benefiting the rational design of electrocatalysts.

Submolecular-resolution imaging of water clusters on the Cu(110) surface by atomic force microscopy

<p indent="0mm">Water/solid interfaces are important to a wide range of scientific and technological processes such as ice nucleation and growth, corrosion, lubrication, heterogeneous catalysis and electrochemistry. It is a key issue to understand the structure and dynamics of water on solid surfaces. However, the atomic-scale characterization of the weakly bonded water clusters on metal surfaces remains challenging. Here, we report submolecular-resolution imaging of the water clusters on the Cu(110) surface using a qPlus-based noncontact atomic force microscope with a CO tip. The configurations of water clusters, including the detailed OH directionalities, could be identified unambiguously by probing the weak high-order electrostatic force between the CO-tip and polar water molecules, which is further confirmed by theoretical simulations. Water clusters composed of 4, 5, and 6 water molecules are observed on the Cu(110) surface, which are mainly built from cyclic tetramers and pentamers. We notice that water hexamers contain three different types of H-bonding configurations, one cyclic tetramer with two additional water molecules adsorbed at <italic>ortho</italic>- or <italic>para</italic>-sites of the tetramer and one pentagonal ring with one additional water molecule. More interestingly, these structures could be interconverted by the tip manipulation, because of the similar adsorption energies. The isolated pentamer would act as a nucleation core for the growth of 1D pentagonal chains on the Cu(110) surface.

Quality Evaluation of Lemon Cordial Stored at Different Times with Microwave Heating (Pasteurization)

Consumer interest in food quality and safety has shifted over time, as consumers increasingly prefer minimally processed items. As a result, numerous non-thermal approaches have been implemented due to their potential to preserve the nutritional profile of products along with lengthening their storability. Microwaving, a green processing technique, volumetrically heats the product because of the interactions developed between charged ions, polar water molecules of foodstuff and the incoming electromagnetic waves. The study was mapped out to investigate the effect of microwave exposure time (60, 90 and 120 s) at fixed power (1000 W) and frequency (2450 MHz) on physicochemical properties, phytochemical constituents, antioxidant potential and microbial counts of lemon cordial stored at refrigerated temperature (4 ± 2 °C). The mentioned parameters were analyzed after an interval of 30–90 days. Statistical findings illustrated a highly significant (p ≤ 0.01) impact of microwave treatment and storage on titratable acidity, pH, total soluble solids, total phenolic contents, total flavonoids contents, antioxidant potential and total plate count. Sample microwaved for 120 s showed the highest pH values (2.45 ± 0.050), total soluble solids (56.68 ± 2.612 °B) and antioxidant activity (1212.03 ± 716.5 µg—equivalent of ascorbic acid per 100 mL of cordial); meanwhile, it exhibited the lowest total plate counts (1.75 ± 0.144 Log 10 CFU/mL). Therefore, microwaving can be suggested as a suitable alternate to traditional pasteurization techniques as well as to chemical preservatives.

Hydrophilic carbon monoliths derived from metal-organic frameworks@resorcinol-formaldehyde resin for atmospheric water harvesting

Atmospheric water harvesting (AWH) is considered a promising technique to address the problem of global water shortage. Adsorption-based AWH technology, has the advantages of a simple device structure, high energy efficiency, wide application range, etc., and has attracted much attention. For the adsorption, one of the key issues is to find high-performance porous adsorbents. Porous carbons have exceptional stability, high porosity and low cost, but are usually highly hydrophobic with a low affinity for polar water molecules. A class of monolithic porous carbons with good hydrophilicity was prepared by the pyrolysis of composites consisting of a metal-organic framework in a resorcinol-formaldehyde resin matrix, in which the metal-organic parts developed polar sites in the final products. AWH tests showed that in a relative humidity of 40%-80%, the water capture capacity of the adsorbents reached 20 wt.%.

Microscopic adsorption properties of methyl acrylate on lignite surface: Experiment and molecular simulation study

Quality improvement of low-rank lignite is highly desirable for sustaining the increasing demand for primary fossil fuel. In order to characterize the microscopic adsorption behavior of nonionic methyl acrylate (MA) on the low-rank lignite, the Fourier transform infrared (FTIR) experiments, contact angle instruments, Grand Canonical Monte Carlo (GCMC), and molecular dynamics (MD) simulations were adopted in this study. The FTIR results suggested that the MA can be adsorbed in the oxygen-containing functional group region of lignite during the adsorption process. The adsorption performance of the hydrophilic organic matter of lignite to methyl acrylate was better than that of ash minerals. Contact angle results showed that the adsorption of methyl acrylate can improve the hydrophobicity of lignite. The adsorption of MA on lignite can be divided into monolayer adsorption stage (0–0.8 g/L), towards the critical micelle concentration (CMC) adsorption stage (0.8 g/L-CMC), micellar adsorption stage (CMC-1.6 g/L). From the perspective of saving the dosage of surfactant and improving the hydrophobicity of lignite, 0.8 g/L is the most suitable MA concentration. Finally, molecular simulations demonstrated that the adsorption isotherm of methyl acrylate on lignite surface conformed to the type-Ⅰ Langmuir model, and the adsorption of methyl acrylate on lignite belongs to physical adsorption. Polar water molecules have advantages in the competitive adsorption process between water molecules and MA, while water molecules are greatly affected by temperature.

Insights on the proton translocation pathways in FоF1-ATP synthase using molecular dynamics simulations

Proton translocation through the Fo fraction of FoF1-ATP synthase is one of the crucial processes in the catalytic cycle of the enzyme. However, the exact trace of protons movement has not been finally established yet because the location and structure of the half-channels are still the subject of investigation. We described the possible network of polar amino acids residues and water molecules that can favor the preferential proton pathway using molecular dynamics simulation of the membrane part of the E. coli ATP synthase embedded in the lipid bilayer and water environment. The inlet half-channel was a complex structure with two entrances in the form of aqueous lacunae and a highly conservative proton transfer chain near Asp61 of c-subunit including amino acids residues and three structural water molecules (W1–W3), while the outlet half-channel was just a water cavity through which a proton can easily move into the cytoplasm. Moreover, the side chains of Asn214 and Gln252 of a-subunit had the stable spatial positions (SP1-SP3). аAsn214 in position SP3 and аGln252 in SP1, SP2 were oriented towards cAsp61 and could presumably protonate it via W1. Herewith aAsn214 in SP1, SP2 was oriented to aHis245. Thus, the proton transfer chain is always unclosed, and switching between positions SP1/SP2 and SP3 of aAsn214 determines the time of proton transport and the movement in this region is the rate-limiting step. In addition, we found another rare position SP3, in which aGln252 is oriented to aAsn116 and aSer144, located outside of the "main H+ route" and being a dead end. The new findings would help to evaluate the whole process of the proton translocation through FoF1-ATP synthase.

Single-particle and collective excitations of polar water molecules confined in nano-pores within a cordierite crystal lattice.

Recently, the low-temperature phase of water molecules confined within nanocages formed by the crystalline lattice of water-containing cordierite crystals has been reported to comprise domains with ferroelectrically ordered dipoles within the a, b-planes which are antiferroelectrically alternating along the c-axis. In the present work, comprehensive broad-band dielectric spectroscopy is combined with specific heat studies and molecular dynamics and Monte Carlo simulations in order to investigate in more detail the collective modes and single-particle excitations of nanoconfined water molecules. From DFT-MD simulations we reconstruct the potential-energy landscape experienced by the H2O molecules. A rich set of anisotropic temperature-dependent excitations is observed in the terahertz frequency range. Their origin is associated with the complex rotational/translational vibrations of confined H2O molecules. A strongly temperature dependent relaxational excitation, observed at radio-microwave frequencies for the electric field parallel to the crystallographic a-axis, E||a is analyzed in detail. The temperature dependences of loss-peak frequency and dielectric strength of the excitation together with specific heat data confirm a ferroelectric order-disorder phase transition at T0 ≈ 3 K in the network of H2O dipoles. Additional dielectric data are also provided for polarization E||b, too. Overall, these combined experimental investigations enable detailed conclusions concerning the dynamics of the confined water molecules that develop within their microscopic energy landscapes.

Hybrid effect of the activated carbon and the CuO catalyst on vegetable oil steam reforming

This study aims to utilize of bio material to produce green hydrogen energy through hybrid of the activated carbon and the CuO catalyst in vegetable oil steam reformer. The experiment was done in the atmospheric pressure steam reformer. The results show that activated carbon and CuO individually performs the same trend in producing hydrogen. Their combination accelerates hydrogen production. This indicates that heat energy makes CuO alters the electron density around the reactant by combining the van der Waals force with the induction due to electron jump in its narrow ban gap. Therefore, CuO activate effectively the polar water (H2O) molecules. More energy is needed to alter the electron in stable large molecule triglyceride of vegetable oil. On the other hand, the activated carbon does it by combining the van der Waals force with the induction due to delocalized of the pi electrons travelling between carbon atoms in the graphite structure. Consequently, only the nonpolar triglyceride molecules are attracted while the polar H2O are repelled by hydrophobic force. Thus, larger energy is needed to activate electrons in H2O. When they are combined, the CuO works only on H2O while activated carbon does only on triglyceride which is highly effective. Copyright © 2018 VBRI Press.

Quantitative Measurements of Membrane Lipid Order in Yeast and Fungi.

Membrane lateral heterogeneity, historically referred to as the lipid raft hypothesis, has been extensively investigated through physiochemical experiments on model membranes. Currently, the basic principles are well understood; however, the physiological relevance of these structures in living organisms is still not clear. Thus, studying membrane organization in vivo is extremely important and elucidates the role of such structures in various membrane-associated processes. This is particularly true when a whole single-celled organism can be studied rather than an isolated cell. The ordered and disordered membrane phases are characterized by the degree of acyl chain packing in the lipid bilayer. Polar water molecules can penetrate into the low-density lipid packing of the disordered phase, but are more excluded from the tightly packed ordered phase. Here, polarity-sensitive probes, embedded in the lipid bilayer, are used to report on membrane organization and to quantitate this parameter via 2-channel fluorescence microscopy. Coupling genetic approaches, which are easily accessible in yeast model organisms, with the imaging approach described here provides a great opportunity to investigate how membrane heterogeneity impacts physiology.

Non‐Local Electrostatic Gating Effect in Graphene Revealed by Infrared Nano‐Imaging

AbstractElectrostatic gating lies in the heart of field effect transistor (FET) devices and modern integrated circuits. To achieve efficient gate tunability, the gate electrode has to be placed very close to the conduction channel, typically a few nanometers. Remote control of a FET device through a gate electrode located far away is highly desirable, because it not only reduces the complexity of device fabrication, but also enables the design of novel devices with new functionalities. Here, a non‐local electrostatic gating effect in graphene devices using scanning near‐field optical microscopy (SNOM)—a technique that can probe local charge density in graphene—is reported. Remarkably, the charge density of the graphene region tens of micrometers away from a local gate can be efficiently tuned. The observed non‐local gating effect is initially driven by an in‐plane electric field induced by the quantum capacitance of graphene, and further largely enhanced by adsorbed polarized water molecules. This study reveals a non‐local phenomenon of Dirac electrons, provides a deep understanding of in‐plane screening from Dirac electrons, and paves the way for designing novel electronic devices with remote gate control.

The Correlation Between the Electronegativities and the Standard Potentials

The linear correlations are analyzed between the empirical electronegativities χ a of metals and non-metals and their standard potentials E o . The correlation intersection corresponds to the transfer from metals to non-metals, characterized by the intermediate electronegativity χ a,interm and the standard potential E o ∼+ 0.5 V SHE which is close to Billiter potential +0.475 V SHE. The electronegativity χ a,interm and E o ∼ +0.5 V SHE would correspond to some hypothetical substance (neither metal nor non-metal) without own chemical actiity. This would be due to the intermediate non-specific (definite coulomb) bond of its outer electrons. This bond is not enough unstable (as metallic bonds) for breaking and not enough stable (as non-metallic bonds) for accepting electrons. Spontaneous half-reactions-interactions of Red - and Ox - forms on electrodes are due to the break Red + H2O → Ox + ne interm and formation Ox + ne interm + H2O → Red of specific (chemical) electron bonds with Ox-forms, where ne interm are electrons without specific bond with Ox-forms. The instant division of electrons ne interm, ions and polarized water molecules of formed intermediate complexes leads to the appearance of double-electric layers on electrodes.

DC electric polarization of cured cement paste being unexpectedly hindered by free water

AbstractElectric polarization is basic to the dielectric behavior, which is pertinent to the science and applications of cement‐based materials. This work reports the dynamics of the DC‐current‐induced electric polarization/depolarization of cured cement paste and their dependence on the water/cement ratio. This dependence has not been previously reported for any cement‐based material. The extent of the polarization is unexpectedly found in this work to decrease as the water/cement ratio increases, indicating that the free water hinders the polarization. This hindrance is due to (i) the dominance of ions behind the polarization (as supported by the previously reported increase in permittivity with increasing temperature), and (ii) the polar water molecules partly shielding the ions from the applied electric field. The fraction of ions in the pore solution that participates in the polarization increases with the polarization time and is 4.5 × 10‐14 for 570 s of polarization at a current of 1 μA for water/cement ratio 0.35. Upon increasing the water/cement ratio (0.3–0.4), the polarization rate decreases, the polarization extent at a given polarization time decreases, and the time to reach polarization saturation decreases. The polarization/depolarization rate decreases as the current application progresses because the polarization/depolarization hinders further polarization/depolarization. The degree of this hindrance increases with increasing water/cement ratio. Thus, a higher water/cement ratio is preferred if less polarization is desired as in resistance‐based self‐sensing, whereas a lower water/cement ratio is preferred if more polarization is desired as in capacitance‐based self‐sensing.

Industrially relevant CHA membranes for CO2/CH4 separation

In the present work, single channel tubular zeolite CHA membranes with a length of 50 cm and a membrane area of 100 cm2 were evaluated by SEM and permeation experiments with single components and industrially relevant humid mixtures. The membranes comprised well-intergrown and smooth CHA films with a thickness of <500 nm supported on the inside of a highly porous tube. For single component permeation, a very low SF6 permeance of 4.5 × 10−10 mol/(m2‧s‧Pa) was observed, which indicated nearly defect free membranes. On the contrary, the membranes displayed a very high CO2 permeance of 128 × 10−7 mol/(m2‧s‧Pa), which illustrated the very high permeability of the CHA pores. Finally, the membranes displayed excellent selectivity for separation of industrially relevant CO2/CH4/H2O mixtures, which was attributed to selective interaction between the CO2 molecules and the polar water molecules in the pores. The highest observed CO2/CH4 separation selectivity was as high as 198 in combination with a CO2 permeance of 14 × 10−7 mol/(m2‧s‧Pa) at a feed pressure of 600 kPa (including 2.2 kPa water) and 293K. The corresponding CO2 flux was 0.39 mol/(m2‧s) and the corresponding CO2/CH4 separation factor was 162. The observed membrane performance was reduced by concentration polarisation due to the limited feed flow in the experimental setup. The corresponding selectivity and CO2 permeance corrected for concentration polarisation were as high as 236 and 16 × 10−7 mol/(m2‧s‧Pa), and the corrected CO2 flux was 0.44 mol/(m2‧s) and corrected separation factor was 198. An estimate showed that even at a low feed pressure of 500 kPa, it would be sufficient with as few as 64 membranes for processing of a feed of 100 Nm3/h raw biogas, i.e. the capacity of a typical biogas plant at a large farm, to biomethane with high purity. These results illustrated that the membranes are promising candidates for industrial separation of CO2 from e.g. natural gas and biogas.

Distinct Chemistries Explain Decoupling of Slip and Wettability in Atomically Smooth Aqueous Interfaces.

Despite essentially identical crystallography and equilibrium structuring of water, nanoscopic channels composed of hexagonal boron nitride and graphite exhibit an order-of-magnitude difference in fluid slip. We investigate this difference using molecular dynamics simulations, demonstrating that its origin is in the distinct chemistries of the two materials. In particular, the presence of polar bonds in hexagonal boron nitride, absent in graphite, leads to Coulombic interactions between the polar water molecules and the wall. We demonstrate that this interaction is manifested in a large typical lateral force experienced by a layer of oriented hydrogen atoms in the vicinity of the wall, leading to the enhanced friction in hexagonal boron nitride. The fluid adhesion to the wall is dominated by dispersive forces in both materials, leading to similar wettabilities. Our results rationalize recent observations that the difference in frictional characteristics of graphite and hexagonal boron nitride cannot be explained on the basis of the minor differences in their wettabilities.

Humidification of high-performance and multifunctional polyimide/carbon nanotube composite foams for enhanced electromagnetic shielding

Though conductive polymer composite (CPC) foams have been investigated widely for electromagnetic interference (EMI) shielding owing to their low density and high EM absorption, fabricating high-performance CPC foams through a simple and easy-to-scale preparation process, as well as exploring new approach to achieve the shielding enhancement of CPC foams under mild conditions for meeting some special circumstances that needing higher shielding effectiveness (SE) in a short time, is still of great importance. In this work, multifunctional polyimide/carbon nanotube composite foams (PIF/CNT) were manufactured by the combination of effective chemical-foaming method and simple solution dip-coating approach. The resultant PIF/CNT with ultralow density exhibited the integration of excellent performances on absorbing-dominant EMI shielding with the extreme-temperature adaptability, flame retardancy, thermal insulation, infrared stealth and Joule-heating functions. On the other hand, the idea of humidifying-enhanced EMI shielding is proposed, and the EMI SE of wetted PIF/CNT samples can be massively improved due to the easy adsorption of strongly polar water molecules on the open-cell foam skeleton with hydrophilic poly (vinyl pyrrolidone). By the humidifying-drying cycles to enhance or restore the SE performance, our PIF/CNT material can be adjusted within a certain SE range to achieve intelligent electromagnetic response, providing another important guide for the design of novel intelligent EMI shields.