14 research outputs found

    First-principles investigation of aluminum intercalation and diffusion in TiO2 materials: Anatase versus rutile

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    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

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    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

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    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

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    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

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    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

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    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

    No full text
    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

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    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

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    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

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    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
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