Search

Herein, a highly sensitive volatile organic compound (VOC) gas sensor is demonstrated using immobilized ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, onto surfaces functionalized by the quaternary ammonium group -N

In situ changes in the nanofriction and microstructures of ionic liquids (ILs) on uncharged and charged surfaces have been investigated using colloid probe atomic force microscopy (AFM) and molecular dynamic (MD) simulations. Two representative ILs, [BMIM][BF4] (BB) and [BMIM][PF6] (BP), containing a common cation, were selected for this study. The torsional resonance frequency was captured simultaneously when the nanoscale friction force was measured at a specified normal load; and it was regarded as a measure of the contact stiffness, reflecting in situ changes in the IL microstructures. A higher nanoscale friction force was observed on uncharged mica and highly oriented pyrolytic graphite (HOPG) surfaces when the normal load increased; additionally, a higher torsional resonance frequency was detected, revealing a higher contact stiffness and a more ordered IL layer. The nanofriction of ILs increased at charged HOPG surfaces as the bias voltage varied from 0 to 8 V or from 0 to —8 V. The simultaneously recorded torsional resonance frequency in the ILs increased with the positive or negative bias voltage, implying a stiffer IL layer and possibly more ordered ILs under these conditions. MD simulation reveals that the [BMIM]+ imidazolium ring lies parallel to the uncharged surfaces preferentially, resulting in a compact and ordered IL layer. This parallel “sleeping” structure is more pronounced with the surface charging of either sign, indicating more ordered ILs, thereby substantiating the AFM-detected stiffer IL layering on the charged surfaces. Our in situ observations of the changes in nanofriction and microstructures near the uncharged and charged surfaces may facilitate the development of IL-based applications, such as lubrication and electrochemical energy storage devices, including supercapacitors and batteries.

The interaction parameters of ionic liquids with SiO2 are derived from colloid probe atomic force microscopy force–distance data, and used directly in molecular dynamics simulations to compute the self-diffusion coefficients of confined ionic liquids.

Atomic force microscopy (AFM) with a gold colloid probe modeled as the electrode surface is employed to directly capture the contact resonance frequency of two phosphonium-based ionic liquids (ILs) containing a common anion [BScB]

The fungicide folpet is rapidly degraded into phthalimide (PI) during both thermal processing and analytical procedures in sample preparation; thus, its residue definition has been modified into the sum of itself and PI. Tea is one of the world's most popular nonalcoholic beverages, where folpet is not listed as an applicable pesticide. To demonstrate how serious false-positives and overestimation in dietary risk are caused by the application of a new residue definition, the residue pattern of PI in made tea and processed tea leaves, along with its transfer rate during tea brewing and corresponding dietary risk, were investigated in the present study. The results revealed that PI residue in tea ranged from10 μg/kg to 180 μg/kg with a median value of 10 μg/kg, 7.3 % of which was over the maximum residue limit established by EU (100 μg/kg, expressed as folpet). The PI residue in green tea was obviously higher than that in black, dark and oolong tea. Simulated heating experiments revealed that PI can arise from improper heating of folpet-free fresh tea leaves, and thus green tea bears a higher risk for its manufacturing employing a comparatively higher temperature. The transfer rate of PI during tea brewing was 104 ± 14 %. Nevertheless, the risk of PI through drinking tea was negligible to humans depending on the risk quotient (RQ) value, which was significantly lower than 1.

With the increasing importance of nanoconfined water in various heterostructures, it is quite essential to clarify the influence of nanoconfinement on the unique properties of water molecules in the pivotal heterojunction. In this work, we reported a series of classical molecular dynamics (MD) simulations to explore nanoconfined water in the subnanometer-sized and nanometer-sized heterostructures by adjusting one-dimensional (1-D) carbon nanotubes with different diameters and two-dimensional (2-D) graphene sheets with different interlayer distances. Our simulation results demonstrated that water molecules in the 1-D/2-D heterojunction show an obvious structural rearrangement associated with the remarkable breaking and formation of hydrogen bonds (HBs), and such rearrangements in the subnanometer-sized systems are much more pronounced than those in the nanometer-sized ones. When water molecules in the 1-D/2-D heterojunctions migrate from 2-D to 1-D confinements, the ordered multi-layer structure in the 2-D confinement are completely destroyed and then transform into different circular HB networks near the nanotube orifice for better connecting to the single-file or helical HB network in the 1-D nanotubes. Furthermore, water molecules in the 1-D/2-D heterojunctions can form stronger HBs with those water molecules further away from the 1-D confinement, leading to an asymmetrical orientational distribution near the orifice. More importantly, our comparison results revealed that the 1-D confinement plays a more important role than the 2-D confinement in determining both the structures and dynamics of water molecules in the 1-D/2-D heterojunction.

Here we report a series of nonequilibrium dynamic Monte Carlo simulations combined with dual control volume (DCV-DMC) to explore the separation selectivity of CH4/CO2 gas mixtures in the ZIF-8 membrane with a thickness of up to about 20 nm. Meanwhile, an improved DCV-DMC approach coupled with the corresponding potential map (PM-DCV-DMC) is further developed to speed up the computational efficiency of conventional DCV-DMC simulations. Our simulation results provide the molecular-level density and selectivity profiles along the permeation direction of both CH4 and CO2 molecules in the ZIF-8 membrane, indicating that the parts near membrane surfaces at both ends play a key role in determining the separation selectivity. All densities initially show a sharp increase in the individual maximum within the first outermost unit cell at the feed side and follow a long fluctuating decrease process. Accordingly, the corresponding selectivity profiles initially display a long fluctuating increase in the individual maximum and follow a sharp decrease near the membrane surface at the permeation side. Furthermore, the effects of feed composition, temperature, and pressure on the relevant separation selectivity are also discussed in detail, where the temperature has a greater influence on the separation selectivity than the feed composition and pressure. More importantly, the predicted separation selectivities from our PM-DCV-DMC simulations are well consistent with previous experimental results.

Here, we perform a series of classical molecular dynamics simulations for two different [HEMIM][DCA] and [BMIM][BF

To put adsorbed natural gas for applicable vehicle fuel use, one has to achieve adequate delivery capacities of CH4 (the main component of natural gas) in porous adsorbent materials. A computational screen has been performed to investigate factors that influence the deliverable capacity of CH4 in carbon-based porous adsorbents, including unique textural properties (volumetric specific surface area, porosity, pore size distribution, surface chemical properties) and adsorption operation condition (temperature and pressure) using Monte Carlo simulations. By a systematic study of 580 models with unique textural properties at different adsorption operation conditions, general trends of improving CH4 deliverable capacity have been identified. Also, structural property thresholds were obtained assuming the target of U.S. department of energy's Advanced Research Projects Agency. The suggested method and results obtained from this work can facilitate a fast screening and guide the development of new synthesis routes for carbonaceous materials targeted at effective deliveries of natural gas for vehicle fuel.

Clarifying the microstructures and time-dependent stability of ionic liquids (ILs) within the confinement of the meso-slit of carbon is the first step to understand the intrinsic synergy effect bet...

Here we report a series of nonequilibrium dynamic Monte Carlo simulations combined with dual control volume (DCV-DMC) to explore the separation selectivity of CH

The ionic liquid (IL)/titanium dioxide (TiO2) interface exists in many application systems, such as nanomaterial synthesis, catalysis, and electrochemistry systems. The nanoscale interfacial properties in the above systems are a common issue. However, directly detecting the interfacial properties of nanoconfined ILs by experimental methods is still challenging. To help better learn about the interfacial issue, molecular dynamics simulations have been performed to explore the structures, vibration spectra, and hydrogen bond (HB) properties at the IL/TiO2 interface. Ethylammonium nitrate (EAN) ILs confined in TiO2 slit pores with different pore widths were studied. A unique vibrational spectrum appeared for EAN ILs confined in a 0.7 nm TiO2 slit, and this phenomenon is related to interfacial hydrogen bonds (HBs). An analysis of the HB types indicated that the interfacial NH3+ group of the cations was in an asymmetric HB environment in the 0.7 nm TiO2 slit, which led to the disappearance of the symmetric N–H...

The flow behaviour of water molecules in a slit compose of a two-dimensional material slit offers very important information that can be used for the design of high-flux seawater-desalination membr...

Based on our previous experimental research, we studied the absorption of CO2 in the ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), immobilized on TiO2 [rutile (110) ] with different thickness by molecular dynamics simulation. The effects of the properties (hydrophobicity and hydrophilicity) of solid interfaces were also studied with IL immobilized on graphite and TiO2, respectively. We studied the influence of the thickness of IL immobilized on TiO2 on the absorption of CO2 via structural and dynamical properties. The results show that the self-diffusion coefficients of IL and CO2 increase as the thickness of immobilized IL decreases. And the CO2 absorption capacity increases as the thickness of immobilized IL decreases as well. Additionally, more CO2 molecules are absorbed in the region near the solid interface as the thickness of IL decreases. For IL immobilized on graphite, the self-diffusion coefficients of cations and anions are larger than that of IL imm...

The changes of wetting state of water droplet on the solid surface featuring pillared structures are quantitatively studied by Coarse Grained simulation. Our results demonstrate that wetting state ...

The hydrophilicity/hydrophobicity of heterogeneous interface of the electrode material is critical for the performance of ionic liquids supercapacitors. However, the behavior of electrolytes at the electrode interface, especially the interface microstructure and properties is not yet clear. We investigated the electric double-layer of [emim][DCA] on slit pore of TiO2/C composite with the heterogeneous surface by combining molecular dynamics simulation and experimental measurements. The results of simulation show that coverage ratio of carbon on the surface affect the number density distribution, orientation and diffusion coefficient of [emim][DCA]. Moreover, we calculated the charge distribution of electric double-layer of [emim][DCA] and the capacitance. The results indicate that the capacitance of slit pore with the surface of TiO2 with 78.7% carbon coverage ratio has the highest capacitance at high surface charge density. We performed an electrochemical experiment using composite of TiO2 covered with carbon as the electrode material, and obtained the capacitance from cyclic voltammetry (CV). The experimental results also indicate there is an optimal coverage ratio of carbon, which achieves the highest capacitance. Our researches could provide a microscopic perspective of the electric double layer at the heterogeneous interface and the guidance for the design of electrode material.

With the emergence of membrane separation and heterogeneous catalysis applications that are associated with confined ethanol/water binary mixture in the pores of two-dimensional (2D) nanomaterials, understanding their confined microstructures is the first step for further relevant applications. In this work, molecular dynamics was performed to investigate the microstructure of ethanol/water binary mixture of 5% mole fraction confined within the four typical 2-nm width 2D-nanoslits (i.e. hBN, GO-0.2, GO-0.4 and Ti3C2(OH)2). Results demonstrated that different chemical properties of solid surfaces can induce distinctive microstructures of mixed fluid within the interfacial contact (adsorbed) layer and thus can result in different mobility of water molecules within the subcontact layer. The residence times of water molecules in the subcontact layer were found in the sequence of Ti3C2(OH)2 > hBN > GO-0.4 > GO-0.2, whereas their sequence of diffusion coefficient within the x-z plane was Ti3C2(OH)2 > hBN > GO-0.2 > GO-0.4. Detailed hydrogen bond (HB) microstructure analysis showed that a high average number of HBs (between fluid molecules of the interfacial contact layer and water molecules of the subcontact layer) induced by solid surfaces could facilitate water molecules to reside in the subcontact layer. Moreover, the small average number of HBs between the water molecules themselves in the subcontact layer could lead to high in-plane diffusion coefficients.

Based on our previous experimental research, we studied the absorption of CO