Guozhong Wu

Double-Layer Formation of [Bmim][PF6] Ionic Liquid Triggered by Surface Negative Charge

Applications of ionic liquids (ILs) in electrified interfaces and electrochemical systems require insight into the molecular-level structure and properties of the interfacial ILs. Using atomistic molecular dynamics (MD) simulations, we show here that a new double-layer stacking formation of the [Bmim][PF(6)] IL can be triggered by the surface negative charge. We also found that the double-layer formation induced by the surface charge thoroughly extended into the bulk phase, implying a strong unscreened ion effect in our IL system. Further study indicated that the double-layer formation in the bulk phase was due to a rapid structural transition. Different IL formations, including the conventional adsorption layer and the double-layer formation, can be achieved in sequence by increasing the surface negative charge. Moreover, the diffusion ability of the new double-layer formation in the bulk phase is much lower when compared to that observed in its original uncharged condition. The structure and properties of the ILs formation may be attributed to the tail-tail aggregation hypothesis of the nonpolar domain in the IL.

Unravelling the Role of the Compressed Gas on Melting Point of Liquid Confined in Nanospace

Phase behaviors of the liquids in nanospaces are of particular interest to understand the thermodynamics of the liquid on the nanoscale and for their applications that involve the confined systems. However, in many cases, the inconsistent observations of melting point variation for confined liquids are often revealed by different groups. Ionic liquids are a special kind of liquid. Here, by using the merits of the nonvolatile nature of ionic liquids, we realized the encapsulation of ionic liquids inside of mesopores silica oxide nanoparticles with a complete removal of compressed gas under high-vacuum condition; the completely confined ionic liquid formed a crystalline-like phase. It was found that compressed gas plays an important role in changing the melting point of the confined ionic liquid.

Structural Analysis of [ChCl]m[ZnCl2]n Ionic Liquid by X-ray Absorption Fine Structure Spectroscopy

The components and structures of ionic liquid ChCl-ZnCl(2) in different ChCl:ZnCl(2) ratios were investigated using XAFS (X-ray absorption fine structure) technique. The average coordination number and distance of Zn species at different x(ZnCl(2)) (mole fraction of ZnCl(2) when synthesizing) were calculated. It is shown that x(ZnCl(2)) has a regular influence on the coordination number of Zn species, due to the change of anion forms and structures in the ChCl-ZnCl(2) ionic liquid. The possible forms and structures of Zn species in the ionic liquids were analyzed according to the coordination number. XAFS and DSC (differential scanning calorimetry) analysis imply that besides ZnCl(3)(-) and Zn(2)Cl(5)(-) anions, the Cl-Zn-Cl ion pair is a main species in the ionic liquid at higher x(ZnCl(2)). This newly discovered Zn species has substantial influence on the properties of the ionic liquid. From the analysis of the coordination numbers and coordination distance, a new mechanism of interactions between Ch(+) cation and Cl-Zn-Cl ion pairs or Cl(-) is proposed.

Dilute or Concentrated Electrolyte Solutions? Insight from Ionic Liquid/Water Electrolytes

When room-temperature ionic liquids (IL) are used as an electrolyte, their transport behaviors are still under heavy debate due to their complicated ion-associations. In this article, we conducted molecular dynamics simulations to study the molecular scale ion associations from the very dilute 1-butyl-3-methylimidazolium iodide/water solution to the pure IL. It revealed that ions are localized in a multicoordinated ion cage structure with nanoseconds in concentrated IL solutions. Dynamics analyses indicate that the transport of this solution can be depicted by the Debye-Hückel model only in dilute IL/water electrolyte. The velocity and rotational correlation functions showed that the lifetime of translational and rotational motions are at the level of picoseconds and nanoseconds, respectively, because of the ion cage effect. The lifetime of ion association demonstrated that the recombination of association ions was prevalent in IL solutions. It means that the dipolar or stable contact ion-pairs model may not be suitable for depicting the IL transport.

Optimum complexation of uranyl with amidoxime in aqueous solution under different pH levels: density functional theory calculations

This study aims to understand the complexation of uranyl with amidoxime in aqueous solution under different pH levels using density functional theory calculations. The geometries, relative stabilities of complexes, and changes in Gibbs free energies for different complexing reactions were investigated. Amidoximate ions were gradually added to the equatorial plane of uranyl to understand the complexation process. We modelled the effect of pH by varying the number of OH− and H2O ligands accompanying amidoximate ions in the equatorial plane of uranyl. The ŋ2 binding motif was the most favourable form, regardless of the uranyl/amidoximate ratio and the pH level. Compared with low and high pH, neutral pH condition was more beneficial to the complexation of uranyl with amidoxime.

The Influence of Silica Nanoparticles on Ionic Liquid Behavior: A Clear Difference between Adsorption and Confinement

The phase behaviors of ionic liquids (ILs) confined in nanospace and adsorbed on outer surface of nanoparticles are expected to be different from those of the bulk. Anomalous phase behaviors of room temperature ionic liquid tributylhexadecylphosphonium bromide (P44416Br) confined in ordered mesoporous silica nanoparticles with average pore size 3.7 nm and adsorbed on outer surface of the same silica nanoparticles were reported. It was revealed that the melting points (Tm) of confined and adsorbed ILs depressed significantly in comparison with the bulk one. The Tm depressions for confined and adsorbed ILs are 8 °C and 14 °C, respectively. For comparison with the phase behavior of confined P44416Br, 1-butyl-3-methylimidazolium bromide (BmimBr) was entrapped within silica nanopores, we observed an enhancement of 50 °C in Tm under otherwise similar conditions. The XRD analysis indicates the formation of crystalline-like phase under confinement, in contrast to the amorphous phase in adsorbed IL. It was confirmed that the behavior of IL has clear difference. Moreover, the complex π-π stacking and H-bonding do not exist in the newly proposed phosphonium-based IL in comparison with the widely studied imidazolium-based IL. The opposite change in melting point of P44416Br@SiO2 and BmimBr@SiO2 indicates that the cationic species plays an important role in the variation of melting point.

Photoinduced electron transfer between 2-methylanthraquinone and triethylamine in an ionic liquid: Time-resolved EPR and transient absorption spectroscopy study

Photoinduced electron transfer between 2-methylanthraquinone (MeAQ) and triethylamine (TEA) in a room-temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), was investigated by comparing the time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy and the transient absorption spectroscopy. The results of TR-EPR spectroscopy, in which MeAQ was 8 mmol L(-1) and TEA was 150 mmol L(-1), indicated that the transient radical would exist longer time in [bmim][PF6] than in acetonitrile. At the delay time of 8 μs after laser excitation, the TR-EPR signal transformed from an emissive peak into an absorptive peak when the experiment was performed in [bmim][PF6]. The results of the transient absorption spectroscopy, in which MeAQ was 0.1 mmol L(-1) and TEA was 2.2 mmol L(-1), showed that the efficiency and the rate of the photoinduced electron transfer reaction in [bmim][PF6] were obviously lower than that in acetonitrile. It was concluded that various factors, such as concentration, viscosity and local structural transformation of the solution, have an influence on the process of photoinduced electron transfer in [bmim][PF6].

Improvement of Radiation Resistance and an Estimate of Solvated Electron Yield of the Ionic Liquid [Bmim]Cl by the Addition of FeCl3

Abstract The radiation stability of the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) was investigated after 60Co &ggr; irradiation at doses up to 600 kGy. Thermal and spectroscopic analysis revealed the formation of a small quantity of radiolytic products and an evident change in the physicochemical properties of the ionic liquid. The presence of anionic FeCl4− (up to 5 mol%), as measured by UV-vis absorption, differential scanning calorimetry, and Raman spectroscopy, significantly improved the radiation resistance of [Bmim]Cl. The increased resistance may be due to the capture of a solvated electron (esolv−) by FeCl4− to form FeCl42− and results in the radiation protection of the organic cation. The radiation yield of the reductive species (Fe(II)) was estimated to be 0.217 ± 0.010 µmol/J (2.09 ± 0.10/100 eV), which is considered close to the radiation yield of the solvated electrons of [Bmim]Cl.

Influence of FeCl3 on radiation stability of ionic liquid BmimCl

This study investigates the effect FeCl3 on the radiation stability of the ionic liquid, 1-butyl-3-methylimidazolium chloride (BmimCl) over a wide dose range of 0 to 1000 kGy under γ-ray radiation. The ionic liquid species, BmimFeCl4, was formed by adding FeCl3 into BmimCl. The results showed that the presence of FeCl4− significantly improved the radiation resistance of BmimCl, wherein the effect was more pronounced at higher FeCl4− content. Meanwhile, under irradiation, Fe(II) was generated from Fe(III), which was reduced by solvated electron. In addition, the concentration of Fe(II) increased with low level of absorbed dose, but leveled off at higher doses. Moreover, the radiation yield of the solvated electrons of BmimCl was further estimated at approximately 0.358±0.01 μmol/J in BmimCl-7 mol% FeCl3 system.

Functionalization of cotton fabrics with highly durable polysiloxane–TiO2 hybrid layers: potential applications for photo-induced water–oil separation, UV shielding, and self-cleaning

Using a facile strategy to prepare multifunctional cotton fabrics with switchable superhydrophobicity–superhydrophilicity, UV-resistance, photo-induced water–oil separation, and self-cleaning properties is an important and urgent issue in the sustainable development of natural fibers. Herein, a new type of surface modified cotton fabric with a polysiloxane–TiO2 hybridized coating (Cot-g-PMAPS/TiO2) was prepared through radiation-induced graft polymerization and sol–gel technology. The hybridized coating was composed of two sub-layers: an inner part consisting of an organic–inorganic hybrid layer to address the issue of self-degradation of TiO2-loaded polymeric materials while simultaneously improving the adhesion of the TiO2 film to its support, and an outer part consisting of nanocrystalline anatase TiO2 to endow the cotton fabric with multifunctionality. The influence of the polysiloxane–TiO2 on the structure and integrated performance of Cot-g-PMAPS/TiO2 was systematically studied. The results showed that the polysiloxane–TiO2 coating improved the UV absorption capacity 5.6-fold compared with that of the untreated cotton fabric. In addition, the retention of the break strength of Cot-g-PMAPS/TiO2 was 95.6% after 192 h of UV irradiation. Since the polysiloxane–TiO2 coating is chemically bound to the cotton fibers, the Cot-g-PMAPS/TiO2 fabric possesses long-term stability, ultra-high durability, and robustness. After 20 commercial or domestic launderings, the UV absorption intensity and WCAs were almost the same as those of the newly fabricated material. The Cot-g-PMAPS/TiO2 also exhibits photo-induced water–oil separation and self-cleaning based on the switchable superhydrophobicity–superhydrophilicity and the photoactivity of TiO2. This study provides an interesting insight into the design of a novel functional material based on a controllable surface structure.