32 research outputs found
Ice-like Water Structure in Carbon Nanotube (8,8) Induces Cationic Hydration Enhancement
It
is well recognized that ice-like water can be formed in carbon nanotubes
(CNTs). Here, we perform molecular dynamics simulations of the hydration
of Na<sup>+</sup>, K<sup>+</sup> and Cl<sup>–</sup> in armchair
CNTÂ(<i>n</i>,<i>n</i>) (<i>n</i> = 6,
7, 8, 9 and 10) at 300 K to elucidate the effect of such water structures
on ionic hydration. It is found that the interaction of Na<sup>+</sup> and K<sup>+</sup> with the water molecules is enhanced in CNTÂ(8,8),
but is similar or weaker than in bulk in the other CNTs. In bulk,
water molecules orient in specific directions around ions due to the
electrostatic interaction between them. Under the confinement of CNTs,
the hydrogen bonds formed in the first hydration shell of Na<sup>+</sup> and K<sup>+</sup> disturb this orientation greatly. An exception
is in CNTÂ(8,8), where the dipole orientation is even more favorable
for cations than in bulk due to the formation of a unique ice-like
water structure that aligns the water molecules in specific directions.
In contrast, the coordination number is more important than hydration
shell orientation in determining the Cl<sup>–</sup>–water
interaction. Additionally, the preference for ions to adopt specific
radial positions in the CNTs also affects ionic hydration
Two-Dimensional PC-SAFT-DFT Adsorption Models for Carbon Slit-Shaped Pores with Surface Energetical Heterogeneity and Geometrical Corrugation
Studying the effects of surface curvature and energetic
heterogeneity
on adsorption on carbon surfaces has aroused great interest. Utilizing
the PC-SAFT-DFT model may be a promising approach for it. However,
efficient algorithms are needed to obtain the two-dimensional (2D)
PC-SAFT-DFT calculation results efficiently. In this work, first,
the Chebyshev pseudospectral collocation method was extended to 2D
PC-SAFT-DFT calculation with complex boundary conditions. In addition,
an efficient approach to calculate the matrices required in the Chebyshev
pseudospectral collocation method has been proposed which significantly
reduces the computation time. Based on the accelerated PC-SAFT-DFT
program, a preliminary study of the effects of the surface curvature
and energetic heterogeneity for pure and mixed gas adsorption was
conducted
Developing Electrolyte Perturbed-Chain Statistical Associating Fluid Theory Density Functional Theory for CO<sub>2</sub> Separation by Confined Ionic Liquids
The
electrolyte perturbed-chain statistical associating fluid theory
(ePC-SAFT) classical density functional theory (DFT) was developed
to describe the behavior of pure ionic liquid (IL) and CO<sub>2</sub>/IL mixture confined in nanopores, in which a new ionic functional
based on the ionic term from ePC-SAFT was proposed for electrostatic
free-energy contribution. The developed model was verified by comparing
the model prediction with molecular simulation results for ionic fluids,
and the agreement shows that the model is reliable in representing
the confined behavior of ionic fluids. The developed model was further
used to study the behavior of pure IL and CO<sub>2</sub>/IL mixture
in silica nanopores where the IL ions and CO<sub>2</sub> were modeled
as chains that consisted of spherical segments with the parameters
taken from the bulk ePC-SAFT. The results reveal that the nanoconfinement
can lead to an increased CO<sub>2</sub> solubility, and the solubility
increases with increasing pressure. The averaged density of pure IL
and solubility of CO<sub>2</sub> are strongly dependent on pore sizes
and geometries. In addition, the choice of IL ions is very important
for the CO<sub>2</sub> solubility. Overall, the modeling results for
silica-confined systems are consistent with available molecular simulation
and experimental results
Bioinspired Graphene Nanopores with Voltage-Tunable Ion Selectivity for Na<sup>+</sup> and K<sup>+</sup>
Biological protein channels have many remarkable properties such as gating, high permeability, and selectivity, which have motivated researchers to mimic their functions for practical applications. Herein, using molecular dynamics simulations, we design bioinspired nanopores in graphene sheets that can discriminate between Na<sup>+</sup> and K<sup>+</sup>, two ions with very similar properties. The simulation results show that, under transmembrane voltage bias, a nanopore containing four carbonyl groups to mimic the selectivity filter of the KcsA K<sup>+</sup> channel preferentially conducts K<sup>+</sup> over Na<sup>+</sup>. A nanopore functionalized by four negatively charged carboxylate groups to mimic the selectivity filter of the NavAb Na<sup>+</sup> channel selectively binds Na<sup>+</sup> but transports K<sup>+</sup> over Na<sup>+</sup>. Surprisingly, the ion selectivity of the smaller diameter pore containing three carboxylate groups can be tuned by changing the magnitude of the applied voltage bias. Under lower voltage bias, it transports ions in a single-file manner and exhibits Na<sup>+</sup> selectivity, dictated by the knock-on ion conduction and selective blockage by Na<sup>+</sup>. Under higher voltage bias, the nanopore is K<sup>+</sup>-selective, as the blockage by Na<sup>+</sup> is destabilized and the stronger affinity for carboxylate groups slows the passage of Na<sup>+</sup> compared with K<sup>+</sup>. The computational design of biomimetic ion-selective nanopores helps to understand the mechanisms of selectivity in biological ion channels and may also lead to a wide range of potential applications such as sensitive ion sensors, nanofiltration membranes for Na<sup>+</sup>/K<sup>+</sup> separation, and voltage-tunable nanofluidic devices
Bioinspired Graphene Nanopores with Voltage-Tunable Ion Selectivity for Na<sup>+</sup> and K<sup>+</sup>
Biological protein channels have many remarkable properties such as gating, high permeability, and selectivity, which have motivated researchers to mimic their functions for practical applications. Herein, using molecular dynamics simulations, we design bioinspired nanopores in graphene sheets that can discriminate between Na<sup>+</sup> and K<sup>+</sup>, two ions with very similar properties. The simulation results show that, under transmembrane voltage bias, a nanopore containing four carbonyl groups to mimic the selectivity filter of the KcsA K<sup>+</sup> channel preferentially conducts K<sup>+</sup> over Na<sup>+</sup>. A nanopore functionalized by four negatively charged carboxylate groups to mimic the selectivity filter of the NavAb Na<sup>+</sup> channel selectively binds Na<sup>+</sup> but transports K<sup>+</sup> over Na<sup>+</sup>. Surprisingly, the ion selectivity of the smaller diameter pore containing three carboxylate groups can be tuned by changing the magnitude of the applied voltage bias. Under lower voltage bias, it transports ions in a single-file manner and exhibits Na<sup>+</sup> selectivity, dictated by the knock-on ion conduction and selective blockage by Na<sup>+</sup>. Under higher voltage bias, the nanopore is K<sup>+</sup>-selective, as the blockage by Na<sup>+</sup> is destabilized and the stronger affinity for carboxylate groups slows the passage of Na<sup>+</sup> compared with K<sup>+</sup>. The computational design of biomimetic ion-selective nanopores helps to understand the mechanisms of selectivity in biological ion channels and may also lead to a wide range of potential applications such as sensitive ion sensors, nanofiltration membranes for Na<sup>+</sup>/K<sup>+</sup> separation, and voltage-tunable nanofluidic devices
Coupled Chemical and Thermal Drivers in Microwaves toward Ultrafast HMF Oxidation to FDCA
Fast
reaction rate under mild reaction conditions is highly desired
in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic
acid (FDCA). Continuous control of pH and temperature is the key to
accelerate the reaction rate. This work offers a binary addition method
enabling continuous control of solution pH during the entire reaction
period and thus expedites reaction rate in each step along the reaction
path. The fluctuation of reaction temperature from binary addition
is then addressed by a coupled microwave heating method. FDCA yield
of >99 mol % can be achieved within 30 min under mild reaction
conditions
of atmospheric pressure and low temperature of <100 °C
Some Insight into Stability of Amorphous Poly(ethylene glycol) Dimethyl Ether Polymers Based on Molecular Dynamics Simulations
PolyÂ(ethylene glycol) dimethyl ether
(PEGDME) polymers are widely
used as drug solid dispersion reagents. They can cause the amorphization
of drugs and improve their solubility, stability, and bioavailability.
However, the mechanism about why amorphous PEGDME 2000 polymer is
highly stable is unclear so far. Molecular dynamics (MD) simulation
is a unique key technique to solve it. In the current work, we systematically
investigate structure, aggregate state, and thermodynamic and kinetic
behaviors during the phase-transition processes of the PEGDME polymers
with different polymerization degree in terms of MD simulations. The
melting and glass-transition temperatures of the polymers are in good
agreement with experimental values. The amorphous PEGDME2000 exhibits
high stability, which is consistent with the recent experiment results
and can be ascribed to a combination of two factors, that is, a high
thermodynamic driving force for amorphization and a relatively low
molecular mobility
Bioinspired Graphene Nanopores with Voltage-Tunable Ion Selectivity for Na<sup>+</sup> and K<sup>+</sup>
Biological protein channels have many remarkable properties such as gating, high permeability, and selectivity, which have motivated researchers to mimic their functions for practical applications. Herein, using molecular dynamics simulations, we design bioinspired nanopores in graphene sheets that can discriminate between Na<sup>+</sup> and K<sup>+</sup>, two ions with very similar properties. The simulation results show that, under transmembrane voltage bias, a nanopore containing four carbonyl groups to mimic the selectivity filter of the KcsA K<sup>+</sup> channel preferentially conducts K<sup>+</sup> over Na<sup>+</sup>. A nanopore functionalized by four negatively charged carboxylate groups to mimic the selectivity filter of the NavAb Na<sup>+</sup> channel selectively binds Na<sup>+</sup> but transports K<sup>+</sup> over Na<sup>+</sup>. Surprisingly, the ion selectivity of the smaller diameter pore containing three carboxylate groups can be tuned by changing the magnitude of the applied voltage bias. Under lower voltage bias, it transports ions in a single-file manner and exhibits Na<sup>+</sup> selectivity, dictated by the knock-on ion conduction and selective blockage by Na<sup>+</sup>. Under higher voltage bias, the nanopore is K<sup>+</sup>-selective, as the blockage by Na<sup>+</sup> is destabilized and the stronger affinity for carboxylate groups slows the passage of Na<sup>+</sup> compared with K<sup>+</sup>. The computational design of biomimetic ion-selective nanopores helps to understand the mechanisms of selectivity in biological ion channels and may also lead to a wide range of potential applications such as sensitive ion sensors, nanofiltration membranes for Na<sup>+</sup>/K<sup>+</sup> separation, and voltage-tunable nanofluidic devices
Bioinspired Graphene Nanopores with Voltage-Tunable Ion Selectivity for Na<sup>+</sup> and K<sup>+</sup>
Biological protein channels have many remarkable properties such as gating, high permeability, and selectivity, which have motivated researchers to mimic their functions for practical applications. Herein, using molecular dynamics simulations, we design bioinspired nanopores in graphene sheets that can discriminate between Na<sup>+</sup> and K<sup>+</sup>, two ions with very similar properties. The simulation results show that, under transmembrane voltage bias, a nanopore containing four carbonyl groups to mimic the selectivity filter of the KcsA K<sup>+</sup> channel preferentially conducts K<sup>+</sup> over Na<sup>+</sup>. A nanopore functionalized by four negatively charged carboxylate groups to mimic the selectivity filter of the NavAb Na<sup>+</sup> channel selectively binds Na<sup>+</sup> but transports K<sup>+</sup> over Na<sup>+</sup>. Surprisingly, the ion selectivity of the smaller diameter pore containing three carboxylate groups can be tuned by changing the magnitude of the applied voltage bias. Under lower voltage bias, it transports ions in a single-file manner and exhibits Na<sup>+</sup> selectivity, dictated by the knock-on ion conduction and selective blockage by Na<sup>+</sup>. Under higher voltage bias, the nanopore is K<sup>+</sup>-selective, as the blockage by Na<sup>+</sup> is destabilized and the stronger affinity for carboxylate groups slows the passage of Na<sup>+</sup> compared with K<sup>+</sup>. The computational design of biomimetic ion-selective nanopores helps to understand the mechanisms of selectivity in biological ion channels and may also lead to a wide range of potential applications such as sensitive ion sensors, nanofiltration membranes for Na<sup>+</sup>/K<sup>+</sup> separation, and voltage-tunable nanofluidic devices
Investigation of Structural, Thermal, and Dynamical Properties of Pd–Au–Pt Ternary Metal Nanoparticles Confined in Carbon Nanotubes Based on MD Simulation
We
apply molecular dynamics (MD) simulations to investigate structural,
thermal, and dynamical properties of Pd–Au–Pt trimetallic
nanoparticles confined in armchair single-walled carbon tubes ((<i>n</i>,<i>n</i>)-SWNTs). The metal–carbon interactions
are described by a Lennard-Jones (LJ) potential, while the metal–metal
interactions are represented by the second-moment approximation of
the tight-binding (TB-SMA) potentials. Results illustrate that the
confined Pd–Au–Pt metal nanoparticles appear to be of
cylindrical multishelled structure, similar to those of gold (or Au–Pt)
nanoparticles confined in SWNT and different from free Pd–Au–Pt
nanoparticles or bulk gold. For each confined Pd–Au–Pt
nanoparticle, gold atoms preferentially accumulate near the tube center,
while Pt atoms preferentially distribute near the tube wall. These
results are in qualitative agreement with previous observations on
Au–Pt nanoparticles confined in SWNT. Importantly, Pd atoms
disperse thorough the confined Pd–Au–Pt nanoparticle,
which is consistent with caltalytic observations in experiment. The
melting temperatures of the confined Pd–Au–Pt nanoparticles
are controlled by platinum with greater cohesive energy. The melting
temperatures of the confined Pd–Au–Pt nanoparticles
are significantly higher than those of the free Pd–Au–Pt
nanoparticles, which are caused by the confined interaction of SWNT.
Some important dynamic results are obtained in terms of the classical
nucleation theory