14 research outputs found
First-principles investigation of aluminum intercalation and diffusion in TiO2 materials: Anatase versus rutile
Aluminum-ion batteries, emerging as a promising post-lithium battery solution, have been a subject of increasing research interest. Yet, most existing aluminum-ion research has focused on electrode materials development and synthesis. There has been a lack of fundamental understanding of the electrode processes and thus theoretical guidelines for electrode materials selection and design. In this study, by using density functional theory, we for the first time report a first-principles investigation on the thermodynamic and kinetic properties of aluminum intercalation into two common TiO 2 polymorphs, i.e., anatase and rutile. After examining the aluminum intercalation sites, intercalation voltages, storage capacities and aluminum diffusion paths in both cases, we demonstrate that the stable aluminum intercalation site locates at the center of the O 6 octahedral for TiO 2 rutile and off center for TiO 2 anatase. The maximum achievable Al/Ti ratios for rutile and anatase are 0.34375 and 0.36111, respectively. Although rutile is found to have an aluminum storage capacity slightly higher than anatase, the theoretical specific energy of rutile can reach 20.90 Wh kg −1 , nearly twice as high as anatase (9.84 Wh kg −1 ). Moreover, the diffusion coefficient of aluminum ions in rutile is 10 −9 cm 2 s −1 , significantly higher than that in anatase (10 −20 cm 2 s −1 ). In this regard, TiO 2 rutile appears to be a better candidate than anatase as an electrode material for aluminum-ion batteries
Selective heavy metal removal and water purification by microfluidically-generated chitosan microspheres: Characteristics, modeling and application
Many industrial wastewater streams contain heavy metals, posing serious and irreversible damage to humans and living organisms, even at low concentrations due to their high toxicity and persistence in the environment. In this study, high-performance monodispersed chitosan (CS) microspheres were prepared using a simple microfluidic method and evaluated for metal removal from contaminated water. Batch experiments were carried out to evaluate the adsorption characteristics for the removal of copper ions, one representative heavy metal, from aqueous solutions. The inherent advantages of microfluidics enabled a precise control of particle size (CV = 2.3%), while exhibiting outstanding selectivity towards target ions (adsorption capacity 75.52 mg g−1) and fair regeneration (re-adsorption efficiency 74% after 5 cycles). An integrated adsorption mechanism analytic system was developed based on different adsorption kinetics and isotherms models, providing an excellent adsorption prediction model with pseudo-second order kinetics (R2 = 0.999), while the isotherm was fitted best to the Langmuir model (R2 = 0.998). The multi-step adsorption process was revealed via quantitative measurements and schematically described. Selective adsorption performance of CS microspheres in the present of other competitive metal ions with different valence states has been demonstrated and studied by both experimental and density functional theory (DFT) analysis
A Site Density Functional Theory for Water: Application to Solvation of Amino Acid Side Chains
We
report a site density functional theory (SDFT) based on the
conventional atomistic models of water and the universality <i>ansatz</i> of the bridge functional. The excess Helmholtz energy
functional is formulated in terms of a quadratic expansion with respect
to the local density deviation from that of a uniform system and a
universal functional for all higher-order terms approximated by that
of a reference hard-sphere system. With the atomistic pair direct
correlation functions of the uniform system calculated from MD simulation
and an analytical expression for the bridge functional from the modified
fundamental measure theory, the SDFT can be used to predict the structure
and thermodynamic properties of water under inhomogeneous conditions
with a computational cost negligible in comparison to that of brute-force
simulations. The numerical performance of the SDFT has been demonstrated
with the predictions of the solvation free energies of 15 molecular
analogs of amino acid side chains in water represented by SPC/E, SPC,
and TIP3P models. For theTIP3P model, a comparison of the theoretical
predictions with MD simulation and experimental data shows agreement
within 0.64 and 1.09 kcal/mol on average, respectively
Mesoscopic Simulations of Adsorption and Association of PEO-PPO-PEO Triblock Copolymers on a Hydrophobic Surface: From Mushroom Hemisphere to Rectangle Brush
The dissipative particle dynamics
(DPD) method is used to investigate the adsorption behavior of PEO-PPO-PEO
triblock copolymers at the liquid/solid interface. The effect of molecular
architecture on the self-assembled monolayer adsorption of PEO-PPO-PEO
triblock copolymers on hydrophobic surfaces is elucidated by the adsorption
process, film properties, and adsorption morphologies. The adsorption
thicknesses on hydrophobic surfaces and the diffusion coefficient
as well as the aggregation number of Pluronic copolymers in aqueous
solution observed in our simulations agree well with previous experimental
and numerical observations. The radial distribution function revealed
that the ability of self-assembly on hydrophobic surfaces is P123 >
P84 > L64 > P105 > F127, which increased with the EO ratio
of the Pluronic copolymers. Moreover, the shape parameter and the
degree of anisotropy increase with increasing molecular weight and
mole ratio of PO of the Pluronic copolymers. Depending on the conformation
of different Pluronic copolymers, the morphology transition of three
regimes on hydrophobic surfaces is present: mushroom or hemisphere,
progressively semiellipsoid, and rectangle brush regimes induced by
decreasing molecular weight and mole ratio of EO of Pluronic copolymers
Unraveling Flow Effect on Capacitive Energy Extraction from Salinity Gradients
The harvesting of salinity gradient energy through a
capacitive
double-layer expansion (CDLE) technique is directly associated with
ion adsorption and desorption in electrodes. Herein, we show that
energy extraction can be modulated by regulating ion adsorption/desorption
through water flow. The flow effects on the output energy, capacitance,
and energy density under practical conditions are systematically investigated
from a theoretical perspective, upon which the optimal operating condition
is identified for energy extraction. We demonstrate that the net charge
accumulation displays a negative correlation with the water flow velocity
and so does the surface charge density, and this causes a nontrivial
variation in the magnitude of output energy when water flows are introduced.
When high water flows are introduced in both the charging and discharging
processes, the energy extraction can be significantly reduced by 47.69–49.32%.
However, when a high flow is solely exerted in the discharging process,
the energy extraction can be enhanced by 12.94–14.49% even
at low operation voltages. This study not only offers a comprehensive
understanding of the microscopic mechanisms of surface-engineered
energy extraction with water flows but also provides a novel direction
for energy extraction enhancement
Mesoscopic Simulations of Adsorption and Association of PEO-PPO-PEO Triblock Copolymers on a Hydrophobic Surface: From Mushroom Hemisphere to Rectangle Brush
The dissipative particle dynamics
(DPD) method is used to investigate the adsorption behavior of PEO-PPO-PEO
triblock copolymers at the liquid/solid interface. The effect of molecular
architecture on the self-assembled monolayer adsorption of PEO-PPO-PEO
triblock copolymers on hydrophobic surfaces is elucidated by the adsorption
process, film properties, and adsorption morphologies. The adsorption
thicknesses on hydrophobic surfaces and the diffusion coefficient
as well as the aggregation number of Pluronic copolymers in aqueous
solution observed in our simulations agree well with previous experimental
and numerical observations. The radial distribution function revealed
that the ability of self-assembly on hydrophobic surfaces is P123 >
P84 > L64 > P105 > F127, which increased with the EO ratio
of the Pluronic copolymers. Moreover, the shape parameter and the
degree of anisotropy increase with increasing molecular weight and
mole ratio of PO of the Pluronic copolymers. Depending on the conformation
of different Pluronic copolymers, the morphology transition of three
regimes on hydrophobic surfaces is present: mushroom or hemisphere,
progressively semiellipsoid, and rectangle brush regimes induced by
decreasing molecular weight and mole ratio of EO of Pluronic copolymers
Mesoscopic Simulations of Adsorption and Association of PEO-PPO-PEO Triblock Copolymers on a Hydrophobic Surface: From Mushroom Hemisphere to Rectangle Brush
The dissipative particle dynamics
(DPD) method is used to investigate the adsorption behavior of PEO-PPO-PEO
triblock copolymers at the liquid/solid interface. The effect of molecular
architecture on the self-assembled monolayer adsorption of PEO-PPO-PEO
triblock copolymers on hydrophobic surfaces is elucidated by the adsorption
process, film properties, and adsorption morphologies. The adsorption
thicknesses on hydrophobic surfaces and the diffusion coefficient
as well as the aggregation number of Pluronic copolymers in aqueous
solution observed in our simulations agree well with previous experimental
and numerical observations. The radial distribution function revealed
that the ability of self-assembly on hydrophobic surfaces is P123 >
P84 > L64 > P105 > F127, which increased with the EO ratio
of the Pluronic copolymers. Moreover, the shape parameter and the
degree of anisotropy increase with increasing molecular weight and
mole ratio of PO of the Pluronic copolymers. Depending on the conformation
of different Pluronic copolymers, the morphology transition of three
regimes on hydrophobic surfaces is present: mushroom or hemisphere,
progressively semiellipsoid, and rectangle brush regimes induced by
decreasing molecular weight and mole ratio of EO of Pluronic copolymers
Dissipative Particle Dynamics Study on the Aggregation Behavior of Asphaltenes under Shear Fields
In
the present work, the effects of shear fields on the aggregation
of asphaltene molecules in heptane were investigated by means of dissipative
particle dynamics simulations. The geometries of asphaltene aggregates
without shear fields were studied, and the simulation results provide
an interpretation of the experimental results on the microscopic level.
The effects of shear fields on asphaltene aggregates were also investigated
by accessing the radial distribution functions, spatial orientation
correlation functions, and the radii of gyrations. We show that the
shear fields can destroy the conformational order of the aggregates
by damaging the organized structure and isolating the asphaltenes.
As the radius of gyration results show, the asphaltene molecules are
elongated to be alike-polymers by shear fields. Moreover, the reason
why the viscosity decreases under shear fields is that the shear fields
lead to the increase of dimerization free energies
Efficient Fabrication of Self-Assembled Polylactic Acid Colloidosomes for Pesticide Encapsulation
Colloidosomes are
microcapsules whose shells are composed of cumulated
or fused colloidal particles. When colloidosomes are used for in situ
encapsulation, it is still a challenge to achieve a high encapsulation
efficiency and controllable release by an effective fabrication method.
Herein, we present a highly efficient route for the large-scale preparation
of colloidosomes. The biodegradable polylactic acid (PLA) nanoparticles
(NPs) as shell materials can be synthesized using an antisolvent precipitation
method, and the possible formation mechanism was given through the
molecular dynamics (MD) simulation. The theoretical values are basically
consistent with the experimental results. Through the use of the modified
and unmodified PLA NPs, the colloidosomes with controllable shell
porosities can be easily constructed using spray drying technology.
We also investigate the mechanism of colloidosomes successfully self-assembled
by PLA NPs with various factors of inlet temperature, feed rate, and
flow rates of compressed air. Furthermore, avermectin (AVM) was used
as a model for in situ encapsulation and a controllable release. The
spherical modified colloidosomes encapsulating AVM not only achieve
a small mean diameter of 1.57 μm but also realize a high encapsulation
efficiency of 89.7% and impermeability, which can be further verified
by the MD simulation. AVM molecules gather around and clog the shell
pores during the evaporation of water molecules. More importantly,
the PLA colloidosomes also reveal excellent UV-shielding properties,
which can protect AVM from photodegradation
Dynamics of Pickering Emulsions in the Presence of an Interfacial Reaction: A Simulation Study
Pickering
emulsions combining surface-active and catalytic properties
offer a promising platform for conducting interfacial reactions between
immiscible reagents. Despite the significant progress in the design
of Pickering interfacial catalysts for a broad panel of reactions,
the dynamics of Pickering emulsions under reaction conditions is still
poorly understood. Herein, using benzene hydroxylation with aqueous
H<sub>2</sub>O<sub>2</sub> as a model system, we explored the dynamics
of benzene/water Pickering emulsions during reaction by dissipative
particle dynamics. Our study points out that the surface wettability
of the silica nanoparticles is affected to a higher extent by the
degree of polymer grafting rather than an increase of the chain length
of hydrophobic polymer moieties. A remarkable decline of the oil-in-water
(O/W) interfacial tension was observed when increasing the yield of
the reaction product (phenol), affecting the emulsion stability. However,
phenol did not alter to an important extent the distribution of immiscible
reagents around the nanoparticles sitting at the benzene/water interface.
A synergistic effect between phenol and silica nanoparticles on the
O/W interfacial tension of the biphasic system could be ascertained