Water Molecules In Layer Research Articles

Effect of Fe3+ doping on the electronic structure and surface hydration properties of quartz

In this study, the effects of Fe3+ doping on the crystal structure and surface properties of quartz were analyzed using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The crystal structure, surface model, and adsorption model of the water molecule layer for Fe3+-doped α-quartz were established. The DFT calculations reveal that Fe3+ doping affects the α-quartz lattice parameters and surface active sites. The adsorption energy near the sites occupied by Fe3+ is −66.20 kJ/mol, which is considerably lower than that of the undoped system (−42.35 kJ/mol). This makes it easier for water molecules to be adsorbed on the Fe3+-doped α-quartz (001) surface. The frontier orbital energy, electron density difference, charge density, and Mulliken bond population analyses indicate that the presence of Fe3+ improves the ability of the (001) surface of α-quartz to attract and bind water molecules. This improvement is mainly due to the formation of hydrogen bonds between the surface hydroxyl groups and water molecules on the surface of Fe3+-doped quartz and the equilibrium of the electrostatic interaction between the cation and water molecules. MD simulations show that a hydration layer with a thickness of approximately 8 Å is formed on the surface of Fe3+-doped α-quartz. Compared with the undoped system, the hydration film on the surface of the doped system is thicker, indicating that the incorporation of Fe3+ impurities in the lattice enhances the surface hydration characteristics of quartz. These results offer theoretical guidance for achieving efficient separation and thorough purification of quartz.

Unraveling the adsorption dynamics of asphaltene molecules on silica surfaces

Understanding the adsorption behavior of heavy oil components on reservoir solids is crucial for improving oil recovery, yet the molecular mechanism remains unclear. This study used molecular dynamics simulations to explore the adsorption kinetics and thermodynamics of asphaltene molecules on silica surfaces. The adsorption process was divided into three stages: free, adsorption, and equilibrium. In the adsorption stage, asphaltenes must pass through two dense hydration layers and adhere to the silica surface in a flat configuration. Carboxyl groups increase asphaltene hydrophilicity, raising interaction energy with water molecules and hindering adsorption. In addition, two distinct hydration layers of water molecules on the silica surface. The first hydration layer, with a peak density of 2000 kg m−3, was located around 0.6 nm from the surface, driven by hydrogen bonding between Si-OH groups and water molecules. The second layer, found at 1.44–1.80 nm, had a lower density of 1200 kg m−3, formed through hydrogen bonding between water molecules. This study aims to enhance the understanding of the physicochemical mechanisms governing oil droplet adsorption on silica surfaces, potentially informing the design of improved oil recovery strategies.

Analysis of foaming mechanism and adhesion of foam rubberised asphalt from the perspective of molecular scale

ABSTRACT Rubberised asphalt faces challenges such as viscosity and construction energy consumption. These problems can be ameliorated by the use of foaming technology. However, existing studies lack a microscopic-level understanding of the foaming mechanism and interfacial properties of foam rubberised asphalt. Therefore, this study used molecular dynamics simulation methods to establish foam rubberised asphalt models and interface models. The models were analysed from the aspects of model density, energy change, molecular agglomeration behaviour and adhesion work. Results revealed that increased temperature and water consumption caused difficulties in the volumetric compression of the model. The diffusion and aggregation behaviour of water molecules altered the distribution of other molecules in the model, effectively reducing the viscosity of the rubberised asphalt without affecting the chemical structure. In the interfacial model, water molecules contribute to the migration of asphalt molecules to the mineral surface, which exists in two forms: aggregating within asphalt and diffusing to the interface. The interface water molecules enhance the electrostatic interaction between asphalt and minerals. However, due to the random nature of water molecule diffusion, it is difficult to form a regular layer of water molecules at the interface, which leads to failure of the adhesion work.

Multifunctional Water Additive Enabling Stable Cycling of Chloride‐Free Magnesium Metal Batteries Based on Carbonate Electrolyte

AbstractRechargeable magnesium batteries (RMBs) face with the challenge of interphase passivation between electrolytes and Mg anodes. Compared with ether electrolytes, carbonate solvents possess the superior electrochemical stability at cathode side, but their incompatibility with Mg metal, high viscosity, and desolvation energy barrier restrict their practical utilization in RMBs. Herein, the “unwanted‐impurity” water with high concentration is revisited and employed as multifunctional additive in carbonate electrolyte to improve the reversibility of RMBs. Water additive enables the localized deep eutectic effect, reduces the viscosity of carbonate electrolyte, and improves the Mg ion conductivity. The water molecules also participate the solvation sheath of Mg ions, resulting in the reduction of Mg deposition overpotential and inhibition of parasitic reaction. Furthermore, the co‐intercalated water molecules in V2O5 cathode layers enable the stabilization of intercalation structure and supply of additional magnesiophilic sites. Cooperated with the binder‐decorated Mg powder anode, the propylene carbonate electrolyte with water additive endows Mg||Mg symmetric cells and Mg||V2O5 full cells with satisfactory cycling performance and high‐voltage stability. This work revisits the impact of impurity water and provides a practical strategy for the utilization of conventional low‐cost carbonate electrolyte family, broadening the design and formulation of electrolytes for chlorine‐free and high‐voltage RMBs.

Molecular simulation of the effect of water content on CO2, CH4, and N2 adsorption characteristics of coal

The objective of this work was to investigate the sorption behavior of gases, namely CO2, CH4, and N2, by molecules of coal sampled from Linglu mine under different water inclusion rates. To this end, the adsorption, diffusion, adsorption heat, and potential energy distribution characteristics of the gases in the coal pores at different water inclusion rates were analyzed using molecular dynamics and grand canonical ensemble Monte Carlo methods. The results showed that the adsorption relationship of the coal molecules on CO2, CH4, and N2 exhibited a downtrend followed by an uptrend when the water content was increased from 0 to 3.6%. The adsorption amount of CO2 was approximately twice as much as those of CH4 and N2, indicating that the competitive adsorption advantage of CO2 compared with those of CH4 and N2 was unaffected by the water content. The trend in the average heat of adsorption was generally consistent with the trend in the density of coal molecules under different moisture contents. Under the same conditions, the diffusion coefficient within a coal molecule was negatively related to the water content in the system. The layer spacing of the water molecules (2.875 Å) was greater than the liquid–water layer spacing, indicating the formation of a water molecule layer at this point, which inhibited gas adsorption. This study lays a theoretical foundation for further investigating the microscopic mechanism of coal–water interaction.

Hydration mechanism of molybdenite affected by surface oxidation: New insights from DFT and MD simulations

The oxidation and hydration of molybdenite surfaces cannot be avoided during the crushing and flotation processes in industry, which adversely affects its clean separation and extraction. In this study, the hydration mechanism under the influence of molybdenite surface oxidation was investigated using density functional theory (DFT) and molecular dynamics (MD) simulations. The results showed that the adsorption energy of a single water molecule on the molybdenite (0 0 1) surface changed from −0.33 kcal/mol to −2.07 kcal/mol after oxidation. Dissociated O acted as a bridging link on the molybdenite (0 0 1) surface, inducing hybridization of the Hw 1 s orbitals with the Os 2p orbitals, thereby enhancing the adsorption of water molecules. The adsorption energy of a single water molecule on the molybdenite (1 1 0) surface changed from −33.97 kcal/mol to −3.37 kcal/mol after oxidation. The dissociated O hindered the hybridization of the Mo 4d and Ow 2p orbitals, thus preventing the adsorption of water molecules on the (1 1 0) surface. After oxidation, the interfacial interaction between the molybdenite (0 0 1) surface and water molecules was enhanced, while the interfacial interaction between the molybdenite (1 1 0) surface and water molecules was weakened. The water molecules near the surface of molybdenite are adsorbed through hydrogen bonding and gradually form a hydrated film consisting of three layers of water molecules with a thickness of 8–9 Å as the water coverage increases.

Molecular Insight into the Processes and Mechanisms of N2 Adsorption and Accumulation at the Hydrophobic Solid/Liquid Interface.

In this study, molecular dynamics (MD) simulations were employed to elucidate the processes and underlying mechanisms that govern the adsorption and accumulation of gas (represented by N2) at the hydrophobic solid-liquid interface, using the GROMACS program with an AMBER force field. Our findings indicate that, regardless of surface roughness, the presence of water molecules is a prerequisite for the adsorption and aggregation of N2 molecules on solid surfaces. N2 molecules dissolved in water can cluster even without a solid substrate. In the gas-solid-liquid system, the exclusion of water molecules at the hydrophobic solid-liquid interface and the adsorption of N2 molecules do not occur simultaneously. A loosely arranged layer of water molecules is initially formed on the hydrophobic solid surface. The two-stage process of N2 molecule adsorption and accumulation at the hydrophobic solid/liquid interface involves initial adsorption to the solid surface, displacing water molecules, followed by N2 accumulation via self-interaction after saturating the substrate's surface. The process and underlying mechanisms of gas adsorption and accumulation at hydrophobic solid/liquid interfaces elucidated in this study offer a molecular-level understanding of nano-gas layer formation.

A cost-effective and high efficient Janus membrane for the treatment of oily brine using membrane distillation

Membrane distillation technology could utilize low-grade heat to desalinate brine, but the membrane material often suffers from disadvantages of low permeation flux and weak robustness to contaminants. To address these issues, the commercial polytetrafluoroethylene (PTFE) membrane was modified by cost-effective chemicals of tannic acid and (3-Aminopropyl)-triethoxysilane (APTES) to construct hydrophilic/underwater superoleophobic nano-rough structures on the surface to enhance its flux and oil-fouling resistance in direct contact membrane distillation. The results show that a high underwater oil contact angle of 180° is observed to the membrane surface due to the rough nanostructures functionalized by abundant hydroxyl groups. Despite the additional mass transfer resistance provided by the rough nanostructures, the flux was increased noticeably. This is mainly attributed to the strong interactions between the abundant hydroxyl groups of hydrophilic layer surface and water molecules, leading to a part of free water staying at intermediate transition state (IW). The mass transfer resistance of the hydrophilic layer itself is reduced as a consequence of decreased evaporation enthalpy of water, thereby increasing the flux. Moreover, while the flux of the pristine membrane is reduced by 84.18%, the flux of Janus membrane remains the same when treating mineral oil brine emulsions with oil concentration up to 1500 ppm in comparison with the result for 35 g l−1 brine solution, indicating that the Janus membrane is safe from the oil contamination. Our work provides a fine guidance for membrane distillation to treat high oily brine.

High-energy density cellulose nanofibre supercapacitors enabled by pseudo-solid water molecules

Compared with conventional electrochemical supercapacitors and lithium-ion batteries, the novel amorphous cellulose nanofibre (ACF) supercapacitor demonstrates superior electric storage capacity with a high-power density, owing to its fast-charging capability and high-voltage performance. This study unveils introduces an ACF supercapacitor characterised by a substantial energy density. This is achieved by integrating a singular layer of pseudo-solid water molecules (electrical resistivity of 1.11 × 108 Ω cm) with cellulose nanofibers (CNFs), establishing forming an electric double layer at the electrode interface. The enhanced energy storage in these high-energy density capacitors (8.55 J/m2) is explicated through the polarisation of protons and lone pair electrons on oxygen atoms during water electrolysis, commencing at 1.23 V. Improvements in energy density are attainable through CNF density enhancements and charging-current optimisation. The proposed ACF supercapacitor offers substantial promise for integration into the power sources of flexible and renewable paper-based electronic devices.

Numerical simulation of the air-water interface effects of an airboat

This paper describes the Air-Water Interface (AWI) occurrence effects of the airboat at various speed, draught, and trim angle. This evaluates the dynamics of AWI with focus on the mechanisms involved in air displacement, the formation of air cushion, boundary layer turbulence, surface tension and wave generation. The analysis involves the change in speed, draught, and trim (0, 1, 1.5 and 2 degrees). The speed of 1.01 and 3.35m/s for displacement and planning regions of the airboat operation were examined. At the AWI, the thin layer of water molecules is affected by the airboat movement at the said trim, it is observed that the layer at the boundary will experience turbulence due to passing air over the layer and the interaction between the air and water at the interface causes mixing and creates waves or ripples at that trim. The wave generated at various trim angles will also create unique wave even at the same speed and draught with a change in trim. The difference in wave formation is seen not to be the same with the change in trim and these changes are observed at the bow and the aft of the vessel. This is also connected to the volume displacement of the boat, the resistance of the vessels, the angle of trim of the airboat and the hull form of the boat. This shows that displacement, resistance, angle of trim and hull form of the boat play critical and crucial roles in wave formation especially for the airboat.

Atomistic exploration of unfrozen water film connection modes in CSH gel pores

Significant changes in concrete's internal structure profoundly affect its performance across varied environmental conditions. Concrete behaves differently in low-temperature environments compared to room temperature due to phase transitions and the freezing of pore water within its matrix. However, understanding the microstructure within cementitious material's gel pores under low-temperature conditions, especially the ice-water-matrix connection mode, has remained elusive. Our molecular dynamics simulations have unveiled that pore size and temperature wield a considerable influence on the connection mode within these gel pores. We have delved deeply into the melting process of ice crystals and the intricate nature of unfrozen water films (UWFs) across different temperatures and pore sizes. The results elucidate that pore size's impact on the connection mode largely hinges on whether gel pores of specific sizes can retain an intact ice layer. At lower temperatures, thinner UWFs emerge, revealing at the nanoscale a reduction in the layers of water molecules within the connection structure. Additionally, we have observed the pivotal role played by calcium ions and water-like molecules in substituting within the matrix's connection structure. These findings offer theoretical insights for construction practices in cold regions, enhancing our ability to predict concrete behavior under low-temperature conditions.

Acoustothermal dynamic characteristics of water-based copper nanofluids on a vibrating nanosurface

The high-frequency vibration is a potential method to induce evaporation and boiling of nanofilm by acoustothermal effect. Here, we investigate the acoustothermal dynamic characteristics of water-based copper nanofluids on a vibrating nanosurface using molecular dynamics simulation. Regimes of the evaporation, nucleate boiling and film boiling can be classified at different amplitudes (A) and frequencies (f). Under the same vibration condition, the introduction of the nanoparticle is conducive to the evaporation and boiling outcome, which becomes superior with the increase of the nanoparticle diameter. Change rules of acoustothermal atomization modes depend on A and f, which are similar for basefluid and nanofluids. There is a negative linear relationship between the nonevaporating layer height and Af3/2 when Af3/2 is smaller than the turning point. Underlying reasons for the enhancement of the evaporation and boiling by adding the nanoparticle rest with the irregular Brownian motion and spinning motion of the nanoparticle, which intensifies disturbance in the water nanofilm. Moreover, a layer of water molecules is absorbed around the nanoparticle to ameliorate heat transfer and thus facilitates the evaporation and boiling of the water nanofilm on a vibrating nanosurface.

Experimental and mechanism studies on high CaCO3 fouling inhibition of PTFE coating with enhanced stability and anti-corrosion

Surface coatings are an effective technique for mitigating fouling in heat exchangers. In this study, a stable polytetrafluoroethylene (PTFE) coating was prepared with improved corrosion resistance and CaCO3 fouling inhibition rate. The prepared PTFE coating remains strongly stable even undergoing tape stripping, sandpaper abrasion, water impacting and immersion. The corrosion-suppression efficiency of the coating is 95.09 % compared to the stainless steel surface. Fouling tests reveal that the coating possesses an inhibition rate of 86.25 %, and it retains a high level of fouling inhibition rate even after 100 cycles of tape stripping and 400 mm of sandpaper abrasion. Additionally, molecular dynamics simulation was performed to gain insight into the anti-fouling mechanism of the PTFE coating. The results demonstrate the presence of two dense adsorption layers of water molecules in close proximity to the metal surface, which is found to be a crucial role in facilitating the adsorption of CaCO3 ions due to their strong attraction (Einteraction = -15.47 eV) towards the ions. In contrast, the weaker interaction (Einteraction = -1.52 eV) between PTFE and water molecules results in the absence of dense water adsorption layers on the PTFE coating. Consequently, the PTFE coating effectively reduces the rate of ion adsorption on the metal surfaces in the initial stage of CaCO3 fouling formation.

Conformational Properties of Aβ Peptide Oligomers in Aqueous Ionic Liquid Solution: Insights from Molecular Simulation Studies.

Alzheimer's disease is a progressive irreversible neurological disorder with abnormal extracellular deposition of amyloid β (Aβ) peptides in the brain. We have carried out atomistic molecular dynamics simulations to investigate the size-dependent conformational properties of aggregated Aβ oligomers of different orders, namely, pentamer [O(5)], decamer [O(10)], and hexadecamer [O(16)] in aqueous solutions containing the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). The calculations revealed reduced peptide conformational fluctuations in O(5) and O(10) in the presence of the IL. In contrast, the higher order oligomer [O(16)] has been found to exhibit greater structural distortion due to enhanced flexibilities of its peptide units in the presence of the IL. Based on the distributions of the solvent (water) and the cosolvent (IL) components, it is demonstrated that exchange of water by the IL ion pairs at the exterior surface of the oligomers primarily occurs beyond the first layer of surface-bound water molecules. Importantly, a reduced number of relatively weaker peptide salt bridges have been found in O(16) in binary water-IL solution as compared to the other two smaller-sized oligomers [O(5) and O(10)]. Such differential influence of the IL on peptide salt bridges results in less favorable binding free energies of peptide monomers to O(16), which leads to its greater structural distortion and reduced stability compared to those of O(5) and O(10).

Interaction and Inhibition Mechanism of Sulfuric Acid with Fluorapatite (001) Surface and Dolomite (104) Surface: Flotation Experiments and Molecular Dynamics Simulations

The natural wettability of apatite and dolomite and the effect of sulfuric acid (H2SO4) and sodium oleate (NaOl) on the floatability and wettability of both minerals were studied using single-mineral flotation and contact angle measurement. The flotation experiments demonstrated that adding NaOl, apatite, and dolomite had good floatability. After adding H2SO4, the floatability of apatite decreased significantly. H2SO4 effectively inhibits apatite flotation. Contact angle measurements show that the use of H2SO4 induces a significant difference in surface wettability between apatite and dolomite. The moderate addition of H2SO4 can increase the contact angle of dolomite. In order to study the selective inhibition mechanism of H2SO4 in phosphorite flotation, molecular dynamics simulations (MDSs) were conducted to investigate the interaction between H2SO4 and fluorapatite and dolomite at the atomic–molecular level. The results of MDSs reveal that H2SO4 interacts with Ca sites on both fluorapatite and defective dolomite surfaces, hindering the interaction of NaOl with Ca sites on both mineral surfaces. SO42− ions cannot prevent the interaction of oleate ions with Mg sites on dolomite surface. It is worth mentioning that SO42− ions occupy the defective vacancies formed due to the dissolution of CO32− on the surface of dolomite and interact with Ca sites. The remaining H2SO4 is subsequently adsorbed onto the surface of dolomite. Experimental and simulation results show that, due to the interaction of H2SO4 and NaOl, the surface of apatite can still undergo hydration forming a water molecule layer and maintaining a macroscopic hydrophilic property. In contrast, the oleate ions form an adsorption layer on dolomite transitioning it from a hydrophilic to a hydrophobic state. During the phosphate flotation process, the addition of an appropriate amount of sulfuric acid can further diminish the hydration of the dolomite surface, so that the surface of dolomite is more hydrophobic.

Heat transfer mechanism for abnormal enhancement of thermal conductivity in a nanofluidic system by molecular dynamics

Molecular dynamics simulation was used to investigate effects of microscopic characteristics of interfacial layer of ZnO/W and Zn/W nanofluids to reveal abnormal enhancement of thermal conductivity. The thermal conductivities of ZnO/W nanofluids were higher than those of Zn/W nanofluids. It was found that fewer water molecules with slower velocities leave the interfacial layer and trajectory lines of water molecules are more concentrated to form a more stable interfacial layer in the ZnO/W nanofluidic system. A higher number of nanoparticle atoms and the probability of finding molecules evaluated by mean square displacement and radial distribution function, lead to the formation of a more stable interfacial layer. This study presents a new parameter S to evaluate the stability of the interfacial layer to determine the effect of its on the thermal conductivity and a new perspective to improve the heat transfer characteristics of nanofluids.

Quantification of Stern Layer Water Molecules, Total Potentials, and Energy Densities at Fused Silica:Water Interfaces for Adsorbed Alkali Chlorides, CTAB, PFOA, and PFAS.

We have employed amplitude- and phase-resolved second-harmonic generation spectroscopy to investigate ion-specific effects of monovalent cations at the fused silica:water interface maintained under acidic, neutral, and alkaline conditions. We find a negligible dependence of the total potential (as negative as -400 mV at pH 14), the second-order nonlinear susceptibility (as large as 1.5 × 10-21 m2 V-1 at pH 14), the number of Stern layer water molecules (1 × 1015 cm-2 at pH 5.8), and the energy associated with water alignment upon going from neutral to high pH (ca. -24 kJ mol-1 to -48 kJ mol-1 at pH 13 and 14, close to the cohesive energy of liquid water but smaller than that of ice) on chlorides of the alkali series (M+ = Li+, Na+, K+, Rb+, and Cs+). Attempts are presented to provide estimates for the molecular hyperpolarizability of the cations and anions in the Stern layer at high pH, which arrive at ca. 20-fold larger values for αtotalions(2) = αM+(2) + αOH-(2) + αCl-(2) when compared to water's molecular hyperpolarizability estimate from theory and point to a sizable contribution of deprotonated silanol groups at high pH. In contrast to the alkali series, a pronounced dependence of the total potential and the second-order nonlinear susceptibility on monovalent cationic (cetrimonium bromide, CTAB) and anionic (perfluorooctanoic and perfluorooctanesulfonic acid, PFOA and PFOS) surfactants was quantifiable. Our findings are consistent with a low surface coverage of the alkali cations and a high surface coverage of the surfactants. Moreover, they underscore the important contribution of Stern layer water molecules to the total potential and second-order nonlinear susceptibility. Finally, they demonstrate the applicability of heterodyne-detected second-harmonic generation spectroscopy for identifying perfluorinated acids at mineral:water interfaces.

Water State in Hemoglobin Solutions: Microwave Dielectric Spectroscopy Study

In this review, we discuss the dielectric relaxation of water in the Hemoglobin (Hb) aqueous solutions in different states (MetHb, OxyHb, and DeoxyHb)). The interpretation of the results was performed by the 3D trajectory approach, which considers dielectric parameters of water relaxation and protein concentration. It has been shown that the interaction of amino acid dipole residues, located on the surface of a protein macromolecule, with water dipoles determines the protein hydration. In addition, ions of the buffer, in which proteins are dissolved, are also hydrated. The transition from a dipole-ion interaction of water molecules to a dipole-dipole interaction of water with an increase in protein concentration is observed. We proposed a new approach to calculate hemoglobin hydration shells. The theoretical model defines the change in the ratio between the content of free and bound water molecules (BWM) as a function of MetHb concentration in ion-free and ion-containing aqueous solutions. It considers the number of positive and negative charges at the surface of the protein molecule, the number of BWMs in its hydration shells, and the partition of water molecules bound to MetHb and the inorganic ions. The theoretical evaluation of the ratio of free-to-bound water reveals that, in the absence of ions, MetHb binds about 1400 water molecules, which is in good agreement with experimental data. At MetHb concentrations close to physiological, Hb is dominating in binding water over the inorganic ions, and the amount of BWM remains at the level of ~20% of total cytosol water as the concentration of Hb increases above 15 g/dL. These results suggest that in the physiological concentration diapason (29 - 35g/dL), molecules of MetHb are so close together that their hydration shells interact and shrink from four to one layer of water molecules. In contrast, Hb molecules aggregate to neutralize their surface charges mutually.

All-printed wearable humidity sensor with hydrophilic polyvinylpyrrolidone film for mobile respiration monitoring

In this study, a capacitive-type wearable humidity sensor comprising a polyvinylpyrrolidone (PVP) film, as active sensing dielectric, and carbon nanotube (CNT) random networks, as electrodes, all-printed on flexible substrates in ambient air, is demonstrated for real-time respiration monitoring. The PVP-based humidity sensor achieved a high sensing response of 3.0 ± 0.15 nF/RH%∙cm2 (where RH stands for relative humidity) and a sensitivity of 6.4 ± 0.1 pF/%RH in the RH range of 40–90%. A significantly small hysteresis window, fast response/recovery (∼ 30 ms), and high reliability were noted. The sensing mechanism of the capacitive response toward humidity was investigated, and it is attributed to continuous proton hopping through water molecule layers. The operational stability of the proposed humidity sensor under temperature variations and mechanical deformation, was investigated to address existing issues related to wearable electronics. Finally, the feasibility of a mobile respiration monitoring device is demonstrated by developing an armband-type wireless-communication monitoring system equipped with the wearable humidity sensor. Real-time biophysical information can be analyzed by monitoring the changes in the respiration intensity and frequency, which were wirelessly transmitted to the user’s mobile interface. We note that very few studies have focused on all-printed wearable humidity sensors consisting of pristine PVP and immobilized CNT random networks for real-time mobile respiration monitoring of human breath regardless of bent and relaxed state.

On the Challenge of Obtaining an Accurate Solvation Energy Estimate in Simulations of Electrocatalysis

The effect of solvation on the free energy of reaction intermediates adsorbed on electrocatalyst surfaces can significantly change the thermochemical overpotential, but accurate calculations of this are challenging. Here, we present computational estimates of the solvation energy for reaction intermediates in oxygen reduction reaction (ORR) on a B-doped graphene (BG) model system where the overpotential is found to reduce by up to 0.6 V due to solvation. BG is experimentally reported to be an active ORR catalyst but recent computational estimates using state-of-the-art hybrid density functionals in the absence of solvation effects have indicated low activity. To test whether the inclusion of explicit solvation can bring the calculated activity estimates closer to the experimental reports, up to 4 layers of water molecules are included in the simulations reported here. The calculations are based on classical molecular dynamics and local minimization of energy using atomic forces evaluated from electron density functional theory. Data sets are obtained from regular and coarse-grained dynamics, as well as local minimization of structures resampled from dynamics simulations. The results differ greatly depending on the method used and the solvation energy estimates are deemed untrustworthy. It is concluded that a significantly larger number of water molecules is required to obtain converged results for the solvation energy. As the present system includes up to 139 atoms, it already strains the limits of computational feasibility, so this points to the need for a hybrid simulation approach where efficient simulations of much larger number of solvent molecules is carried out using a lower level of theory while retaining the higher level of theory for the reacting molecules as well as their near neighbors and the catalyst. The results reported here provide a word of caution to the computational catalysis community: activity predictions can be inaccurate if too few solvent molecules are included in the calculations.