New insights into the degradation mechanism of ibuprofen in the UV/H2O2 process: role of natural dissolved matter in hydrogen transfer reactions.

Ibuprofen (IBU), a widely used antipyretic and analgesic, has been frequently detected in various natural water systems. Advanced oxidation processes (AOPs) are effective ways to remove pollutants from water. The degradation of IBU under UV/H2O2 conditions in the presence of various kinds of natural dissolved matter was investigated using density functional theory (DFT). The eco-toxicological properties were predicted based on a quantitative structure-activity relationship (QSAR) model. The calculated results showed that two H-abstraction reactions occurring at the side chain are predominant pathways in the initial reaction. H2O, NH3, CH3OH, C2H5OH, HCOOH and CH3COOH can catalyze the H transfer in the degradation process through decreasing the energy barriers and the catalysis effects follow the order of NH3 > alcohols > acids > H2O. The catalysis effects differ under acid or alkaline conditions. The overall rate coefficient of the reaction of IBU with ˙OH is calculated to be 5.04 × 109 M-1 s-1 at 298 K. IBU has harmful effects on aquatic organisms and human beings and the degradation process cannot significantly reduce its toxicity. Among all products, 2-(4-formylphenyl)propanoic acid, which is more toxic than IBU, is the most toxic with acute and chronic toxicity, developmental toxicity, mutagenicity, genotoxic carcinogenicity and irritation/corrosivity to skin. The findings in this work provide new insights into the degradation of IBU and can help to assess its environmental risks.

Liquid-Liquid Phase Separation of Aqueous Ionic Liquids in Covalent Organic Frameworks for Thermal Switchable Proton Conductivity.

Covalent organic frameworks (COFs) have regular channels that can accommodate guest molecules to provide highly conductive solid electrolytes. However, designing smart, conductive COFs remains a great challenge. Herein, we report the first example of PEG-functionalized ionic liquids (ILs) anchored on the COF walls by strong hydrogen bonding to fabricate thermally responsive COFs (ILm@COF). We found that similar to the traditional IL/water mixture, the ILs undergo lower critical solution temperature (LCST)-type phase behavior within COF nanopores under high moisture levels. However, the phase separation temperature of aqueous IL decreases in COF channels due to the strong interaction between the IL and COF. Thus, the proton conductivity of ILm@COF can be reversibly switched by phase miscibility and separation in COF nanopores, and there is no obvious decrease even after 20 switching cycles. Our work provides important clues for understanding liquid-liquid phase separation in a confined nanospace and opens a new pathway to switchable proton conductivity.

Rational design of MXene-based single atom catalysts for Na-Se batteries from sabatier principle.

Na-Se batteries have attracted great attention because of their high-energy density and low cost, though the shuttle effect of polyselenides and sluggish reaction dynamics still limit their practical applications. Herein, MXenes were decorated with single zinc atom as selenium hosts, and the effect of interfacial electrochemical reaction was studied via first-principles simulation. The embedding of single zinc atom into MXenes was found to enhance the anchoring ability to inhibit the shuttle effect. However, Zn-MXenes as single atom catalysts had different effects on interfacial electrochemical reactions, which can be attributed to the increased interaction strengths between Zn-MXenes and polyselenides. For Ti-based MXenes, the enhanced interaction was found to be beneficial for the electrochemical reaction, whereas the overly strong anchoring strength of Zn-Cr2CO2 would inhibit charging-discharging kinetics. Therefore, the matching of MXenes and metal atoms should be considered to adjust the anchoring ability based on the Sabatier principle. This work provides new insights into the design of SACs and high-performance Na-Se batteries.

The ionic liquid-based electrolytes during their charging process: Movable endpoints of overscreening effect near the electrode interface.

HYPOTHESIS: Adding solvents to ionic liquids (ILs) can lead to the suppression of the overscreening effect near an electrode interface. Also, this suppression can be observed in neat ILs by elongating the length of the nonpolar chains on their ions. Most neat ILs, unlike the ideal model, do not exhibit a crowding effect in experiments. Through molecular dynamics (MD) simulations, researchers can model and analyze these systems in order to understand them. SIMULATIONS: In this study, the dynamic change near the electrode interface of ILs-based electrolytes was investigated using MD simulations. The phenomena observed in MD simulations are generally understandable because factors can attenuate charge densities calculated from these simulations. FINDINGS: The study findings reveal that both the solvents or nonpolar chains contributed to the formation of nonpolar domains. Also, the microscopic mechanisms and influences of these nonpolar domains were clearly identified. The results are important for real life applications. Some ions form a "point to surface" layer near the electrode of neat ILs. When ILs contain long nonpolar chains, they can suppress the crowding effect through self-assembly behavior. However, when they do not have any chains or short nonpolar chains, it can be difficult to stop the overscreening effect. This means it can become challenging to begin the next stage of the crowding effect.

Alginate Fiber-Grafted Polyetheramine-Driven High Ion-Conductive and Flame-Retardant Separator and Solid Polymer Electrolyte for Lithium Metal Batteries.

Traditional polymer-based separators and solid polymer electrolytes (SPEs) often suffer from inherent poor flame retardancy and unsatisfied ionic conductivity, which seriously affect the safety and energy storage performance of lithium metal batteries (LMBs). Inspired by the mechanism of Li+ conductivity, an alginate fiber (AF)-grafted polyetheramine (AF-PEA) separator with efficient Li+ transport and excellent flame retardancy is dedicatedly designed, which also can act as the backbone for PEO-based SPEs (PEO@AF-PEA). Based on the intrinsic flame retardancy of the AF, the AF-PEA shows self-extinguishing ability, and its Li+ transport ability (1.8 mS cm-1 at 25 °C) is enhanced by grafting the ion-conductive PEA chain segment. By simulating the transport and distribution of Li+ in the AF-PEA, the PEA with 7-segment chain lengths can uniformly fill the Li+ transport space between the alginate backbone to promote the Li+ adsorption and the utilization of Li+ anchoring points in PEA side chains, increasing the Li+ transport rate and migration capacity. The LiFePO4/Li solid-state battery assembled using PEO@AF-PEA SPEs exhibits high safety and excellent cycling performance (exceeding 100 mAh g-1 after 1500 cycles at 2 C current density and 80 °C with less than 0.016% capacity decay for each cycle).

A High-Performance Quasi-Solid-State Aqueous Zinc-Dual Halogen Battery.

Aqueous zinc-based batteries are promising candidates for the grid-scale energy storage owing to their nonflammability, ecofriendliness, and low cost. Nevertheless, their practical applications are hindered by the relatively low capacity and energy density. Herein, we develop a quasi-solid-state aqueous zinc-dual halogen battery composed of freestanding carbon cloth-iodine cathode and in situ prepared concentrated aqueous gel electrolyte. The freestanding composite cathode and aqueous gel electrolyte can afford iodine source and bromide ions, respectively, thus activating the I-/I0/I+ reaction by forming [IBr2]- interhalogen. Furthermore, the conversion reaction of Br-/Br0 in [IBr2]- interhalogen is stimulated due to the catalytic effect of iodine. Therefore, this rationally designed aqueous dual halogen conversion chemistry enables three successive redox reactions (i.e., I-/I0, I0/I+, and Br-/Br0). Additionally, the LiNO3 additive and acrylamide (AM)-based polymer matrix not only stabilizes the anode/electrolyte interface but also restrains the side reactions and dissolution/diffusion of active species. Consequently, the as-assembled aqueous zinc-dual halogen battery exhibits high areal capacity and energy density.

Ti2CT2 MXene as Anodes for Metal Ion Batteries: From Monolayer to Bilayer to Pillar Structure.

The electrochemical performances of Ti2CT2 (T = F, O, and OH) MXenes with different layer structures (monolayer, bilayer, and pillared structures) as anodes for mono-/multivalent metal ion (Li+, Na+, Mg2+, and Al3+) batteries (MIBs) were studied via first-principles simulations. First, metal ions (MIs) adsorbed on Ti2CT2 monolayers were investigated to reveal the influence of MXene terminated groups on MIB performance. This indicated that O-terminated MXenes would be more suitable as electrodes. In particular, the theoretical capacity of Mg2+ on a Ti2CO2 monolayer could be more than 1500 mA h g-1. Then, MIs intercalated into MXene bilayers were considered to better understand the charging/discharging mechanism. In a Ti2CO2 bilayer with larger interlayer spacing, monovalent MIs and Mg2+ could form a multilayer accompanied by drastic expansion/contraction of the electrode, which still needs to be solved. Finally, imidazolium-based ionic liquids were used to preintercalate into MXene due to the matching size of the imidazolium cation, which effectively improved MXene stability and inhibited the self-stacking of layered MXenes. Our research would be helpful for theoretically regulating MXene functional groups and adjusting the interlayer spacing of MXenes via selecting guest molecules for designing MIBs and other energy storage devices.

Screening ionic liquids for dissolving hemicellulose by COSMO-RS based on the selective model.

The utilization of biomass resources has attracted more and more attention due to the consumption of non-renewable resources. Compared with cellulose and lignin, hemicellulose has been less studied. Some ionic liquids (ILs) have been proved to be excellent solvents for lignocellulosic pretreatment. However, screening of more efficient ILs is difficult due to numerous possible ILs. Computational chemistry has been proved effective in solvent screening, but a precise model is indispensable. In this work, we focused on building several appropriate models and selected the most suitable one. According to the structure of hemicellulose, six hemicellulose models were constructed and the mid-dimer of the xylan chain hemicellulose (MDXC) model was proved to be the best compared with the reported experimental results. Based on the MDXC model, 1368 ILs were screened to evaluate their ability to dissolve hemicellulose by Conductor-like Screening Model for Real Solvents (COSMO-RS). The activity coefficient (γ), excess enthalpy (HE), and σ-profile indicated that the hydrogen-bond (H-bond) played a vital role in the dissolution of hemicellulose. Anions played a more critical role than cations, where small anions with H-bond acceptor groups could enhance the molecular interactions with hemicellulose. This work provided a thermodynamic understanding of hemicellulose and IL solvent systems. It highlights the importance of building appropriate solute models, which may be necessary to predict of the other thermodynamic properties in the future.

Insight into the dual effect of water on lignin dissolution in ionic liquids.

The dual regulation of water on lignin in ionic liquids was studied at the molecular level by molecular dynamics simulation. The simulation results show that a small amount of water will destroy the ion association in ionic liquids, that is, it will produce more free anions and cations. The free ions around lignin are conducive to the dissolution of lignin. On the contrary, excess water will seriously solvate anions and cations. By changing the number of lignin clusters, it is more intuitive to observe that the dissolution of lignin in ILs containing a small amount of water is stronger than that in pure IL, however, the dissolution ability of lignin is reduced after adding a large amount of water in ILs. It is concluded that with the increase of water content, water changes from co-solvent to anti-solvent in the dissolution process. This study provides ideas for the design of IL-water system for economic pretreatment of biomass.

First-principles calculations on the resistance and electronic properties of H2 adsorption on a CoO-SnO2 heterojunction surface.

Compared with pure metal oxides, heterojunctions greatly change the response to gas by the synergistic effect of the interface. In this work, density functional theory was used to reveal the adsorption performance of H2 on the heterojunction under oxygen conditions. First, we determined the most reasonable heterojunction structure based on the adhesion work. According to the adsorption energy, the presence of SnO2(100)(I)/CoO(110)(II) made the adsorption of H2 more stable. The DOS results showed that the resistance of the heterojunction increased with H2 adsorption, following the same trend as that of CoO(110) with H2 adsorption, although that of the heterojunction increased more. The electron density and electron density difference indicated that the heterojunction improved the reaction between H2 and oxygen ions on CoO(110). However, the resistance of CoO(110)(II)/SnO2(100)(II) increased after H2 adsorption, contrary to the resistance change of SnO2(100). Besides, the bonding energy between H2 and the adsorption site became worse. The above results demonstrated that the presence of the heterojunction could indeed change the response trend and the adsorption behavior of H2. Interestingly, the adsorption sites and effects of H2 were different when two metal oxides were used as the substrate of the heterojunction, respectively.

Structural Reorganization of Ionic Liquid Electrolyte by a Rapid Charge/Discharge Circle.

The behavior of forming layers near the electrode surface is an important topic for the energy storage with ionic liquid (IL) electrolytes. Here, molecular dynamics (MD) simulations were used to study the behavior of surface active ionic liquid (SAIL) electrolytes near positive electrodes. With the increase of electrode surface charge density, a V-type conformation of the anion [AOT]- for energy storage was shown. The V conformation is easier to replace the latent voids, which is like wedging ions into the layer near the electrodes. Meanwhile, after a rapid charge/discharge circle, there would be more V-type anions appearing in this optimized electrolyte. It is a significant point for the mechanism of nanoscale and microscale energy storage, which provides a theoretical basis for the optimization of efficient IL electrolytes and the design of related experimental research.

Water desalination of a new three-dimensional covalent organic framework: a molecular dynamics simulation study.

Preparing a nanoporous membrane with high density and ordered pore sizes which allows high water permeability and salt rejection rate is the key to realize highly efficient desalination. However, preparing a nanoporous membrane with high density and order pore sizes is still extremely hard due to the limitation of experimental techniques. Recently, a 3D covalent organic framework (3D-COF) material named as the 3D-OH-COF with good crystallinity and large specific surface areas has been synthesized. Based on the structural features of the 3D-OH-COF, we speculate that it may be a good candidate for the desalination application derived from its high-density sub-nanometer pore. In this work, using molecular dynamics simulations, the possibility of the 3D-OH-COF for desalination application was explored, the influence of membrane thickness on its desalination performance was also studied, and the detailed structure and dynamics of ions and water transport in the channel of the 3D-OH-COF was discussed. The results show that the rectangular channel structure and charged H atoms are responsible for the excellent salt rejection rate (100%) and high water flux (41.44 Lit cm-2 day-1 MPa-1), respectively. Furthermore, the water flux is three orders of magnitude higher than that of the commercial reverse osmosis membrane and is four times higher than that of the theoretically reported monolayer nanoporous MoS2 membrane. It is also about 28% higher than that of the recently reported 2D-CAP membrane. This work theoretically confirms that the 3D-OH-COF is a promising membrane material for desalination applications and the underlying molecular mechanisms are clarified.

Precise Mesoscopic Model Providing Insights into Polymerization-Induced Self-Assembly.

Self-assembly of copolymer is an important approach to obtain multifarious nanostructures. Polymerization-induced self-assembly (PISA) is a recently developed and powerful copolymer self-assembly strategy. However, some researchers have reported a different morphology prepared by PISA and the traditional copolymer self-assembly using the same copolymer system. In this work, to explore the mystery, we develop a precise mesoscopic dissipative particle dynamics (DPD) model to reveal insights into the PISA of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS). It is observed that P4VP-b-PS nanotubes can be obtained via TSA rather than PISA, which is consistent with reported experimental results. By carefully investigating the dynamics of PISA under specific solvent and monomer conditions and different polymerization rates, we propose that combining excessive monomers with multistep PISA can help to enhance the morphological regulation ability of PISA and retain a high solid content simultaneously. The findings in this study not only provide a precise modeling method for investigating copolymer self-assembly but also serve as a rational guide for future studies toward optimization of the PISA strategy.

Optimal aggregation number of reverse micelles in supercritical carbon dioxide: a theoretical perspective.

The aggregation number is one of the most fundamental and important structural parameters for the micelle or reverse micelle (RM) system. In this work, a simple, reliable method for the determination of the aggregation number of RMs in supercritical CO2 (scCO2) was presented through a molecular dynamics simulation. The process of pulling surfactants out of the RMs one by one was performed to calculate the aggregation number. The free energies of RMs with different numbers of surfactants were calculated through this process. We found an RM with the lowest free energy, which was considered to have the optimal number of surfactants. Therefore, the optimal aggregation number of RMs was acquired. In order to explain the existence of an optimal aggregation number, detailed analyses of surfactant accumulation were conducted by combining molecular dynamics with quantum chemistry methods. The results indicated that in the RMs with the lowest free energy, the head-group and tail-terminal of the surfactants accumulated on an equipotential surface. In this case, the surfactant film could effectively separate water and CO2; thus, the lowest free energy was expected. This method determined the aggregation number of RMs by theoretical calculations that did not depend on experimental measurements. This presented approach facilitates the evaluation of the characteristics of RMs in scCO2 and can be further applied in the RM system of organic solvents or even in the micellar system.

Dissipative Particle Dynamics Simulation on Vesicles Self-Assembly Controlled by Terminal Groups.

Block copolymer vesicles have been widely used in the field of drug delivery, microreactors, and cell membrane mimetics. Introducing terminal groups to the block copolymer can control the structures of vesicles, which is important for improving the application of vesicles. In this paper, the effects of terminal groups on the structure of vesicles were studied by dissipative particle dynamics simulation. We considered different locations, hydrophobicity, and numbers of terminal groups. When the terminal group located at the end of a hydrophobic block, the increase of wall thickness and the decrease of cavity size of vesicles were observed with the hydrophobicity of the terminal group increasing. In contrast, when the terminal group located at the end of the hydrophilic block, with the hydrophobicity of terminal groups increasing, the vesicular cavity size increased but the wall thickness of vesicles remained nearly unchanged. Finally, increasing the number of terminal groups lead to a decrease of cavity size and an increase of wall thickness of vesicles. The hydrophobic changes of polymer molecules are regarded as the origin of the structural changes of vesicles. This simulation study supplies a potential approach that controls the structures of vesicles and is expected to facilitate its further applications.

Shape transition of water-in-CO2 reverse micelles controlled by the surfactant midpiece.

Designing CO2-philic surfactants for generating wormlike reverse micelles (RMs) is an effective approach to enhance the viscosity of supercritical CO2 (scCO2), however this remains challenging. Modifying the middle piece (midpiece) of surfactant tails is a potential method to generate wormlike RMs, but the underlying mechanism is still unclear. Herein, by adopting molecular dynamics simulations, the self-assembly of the hybrid surfactant FC6-HC5 in scCO2 was investigated. It was found that the FC6-HC5 with an alkyl midpiece could form spherical RMs. By introducing phenyl on the surfactant midpiece, a transformation of the RMs from a spherical shape to a wormlike shape was achieved. The improved fusion free energy was demonstrated to promote the fusion of the spherical RMs to form wormlike RMs. Further analysis indicated that, originating from the π-π interaction, the introduced phenyl assists the parallel arrangement of FC6-HC5, resulting in the improved fusion ability. Moreover, according to the analysis on interfacial properties, introducing phenyl had little effect on the surfactant CO2-philicity. Therefore, modifying the midpiece is a great method for designing hybrid surfactants to generate wormlike RMs while maintaining their high CO2-philicity. This strategy of generating wormlike RMs is expected to facilitate the application of scCO2 meeting industrial requirements.

CO2 activating hydrocarbon transport across nanopore throat: insights from molecular dynamics simulation.

In tight oil reservoirs, nanopore throat acting as the narrowest section of fluidic channel determines the oil transport performance; injecting CO2 is found to significantly promote the oil flow. Despite substantial efforts, the underlying transport mechanism of above phenomenon remains unclear. Employing molecular dynamics simulation, the oil transport through a nanopore throat is studied. A high energy barrier derived of conformation deformation, oil/pore interaction and Jamin effect is found to impede the oil transport. The CO2 activating effect for oil transport is present, and a dependence on CO2 amount is observed. The underlying mechanism was well documented from the aspects of oil swelling, interfacial tension and surface sliding. Our study provides fundamental insight into the oil transport across nanopore throat and CO2 activating effect; the results have promising applications in enhanced oil recovery in CO2 flooding.

Molecular-Scale Design of Hydrocarbon Surfactant Self-Assembly in Supercritical CO2.

Forming wormlike reverse micelles (RMs) by hydrocarbon surfactant self-assembly is an economic and environmental strategy to improve the physicochemical properties of supercritical carbon dioxide (scCO2), but it remains challenging. Introducing cosurfactant in hydrocarbon surfactant self-assembly system is a potential method to generate wormlike RMs. Here, adopting molecular dynamics simulations, we performed hydrocarbon surfactant (TC14) self-assembly with introducing cosurfactants (C8Benz). It is found that adding the C8Benz molecules will induce the spherical RMs to a short rodlike form. In this case, the microstructure of the short rodlike RMs shows a dumbbell-like form that is composed by three parts including a middle part of C8Benz and two parts of TC14 aggregation at both ends of rodlike RMs, which is regarded as the origin of RMs shape transition. Further, the analysis of free energy for RMs fusion indicates that the high fusion ability of C8Benz aggregation drives the formation of the dumbbell-like RMs. Accordingly, enhancing the affinity of the C8Benz is found to be effective strategy to further fusion of rodlike RMs in end-to-end manner, yielding a wormlike RMs with a beads-on-a-string structure. It is expected that this work will provide a valuable information for design the hydrocarbon wormlike RMs and facilitate the potential application of scCO2.

The self-assembly structure and the CO2-philicity of a hybrid surfactant in supercritical CO2: effects of hydrocarbon chain length.

Hybrid surfactants containing both fluorocarbon (FC) and hydrocarbon (HC) chains, as effective CO2-philic surfactants, could improve the solubility of polar substances in supercritical CO2. Varying the length of the HC of hybrid surfactants is an effective way to improve the CO2-philicity. In this paper, we have investigated the effects of the HC length on the self-assembly process and the CO2-philicity of hybrid surfactants (F7Hn, n = 1, 4, 7 and 10) in water/CO2 mixtures using molecular dynamics simulations. It is found that the self-assembly time of F7Hn exhibits a maximum when the length of the HC is equal to that of the FC (F7H7). In this case, the investigation of H-bonds between the water core and CO2 phase shows that F7H7 has the strongest CO2-philicity because it has the best ability to separate water and CO2. To explain the origin of the differences in separation ability, the analysis of the structures of the reverse micelles shows that there are two competing mechanisms with a shortening HC. Firstly, the volume of F7Hn is reduced, which thus decreases the separation ability. Moreover, this also leads to the curved conformation of the FC. As a result, the separation ability is enhanced. These two mechanisms are balanced in F7H7, which has the best ability to separate water and CO2. Our simulation results demonstrate that the increased volume and the curved conformation of the hybrid surfactant tail could enhance the CO2-philicity in F7Hn surfactants. It is expected that this work will provide valuable information for the design of CO2-philic surfactants.