Haiying Fu

Molecular dynamics simulation of the interfacial structure of [Cnmim][PF6] adsorbed on a graphite surface: effects of temperature and alkyl chain length

The structures and diffusion behaviors of a series of ionic liquids [C(n)mim][PF(6)] (n = 1, 4, 8 and 12) on a graphite surface have been investigated by means of molecular dynamics simulation. It was found that three or four ordering layers of ionic liquids were formed near the graphite surface, and this layering structure was stable over the temperature range investigated. At the liquid/vacuum interface, the ionic liquid with a butyl chain had a monolayer ordering surface, while [C(8)mim][PF(6)] and [C(12)mim][PF(6)] exhibited a bilayer ordering with a polar domain sandwiched between two orientational nonpolar domains. More impressively, the simulated results showed that for the ionic liquids with alkyl chains longer than C(4), the adjacent alkyl chains in the whole film tended to be parallel to each other, with the imidazolium rings packed closely together. This indicated that the ionic liquids have a better regulated short-range structure than was previously expected. It was also found that both in the bottom layer and in the bulk region, the diffusion of the alkyl chains was much faster than that of the polar groups. However, as the alkyl chain length increased, the charge delocalization in the cation and the enhanced van der Waals interaction between the nonpolar groups contributed by reducing this difference in the diffusivity of major groups.

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.

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.

Crystallization and temperature-dependent structure deflection of C6mimBr ionic liquid intercalated in LAPONITE®

The physicochemical properties of large molecules confined in nanopores are expected to be different from those of the bulk. This study investigates the cation–anion relative position and the molecular orientation of the 1-hexyl-3-methylimidazolium bromide (C6mimBr) ionic liquid intercalated in LAPONITE® by a temperature-dependent X-ray absorption fine structure (XAFS) and some traditional methods (TEM, DSC, XRD, and IR). DSC and TEM analyses revealed the formation of C6mimBr crystals intercalated in LAPONITE®. The XAFS and XRD analyses at ambient temperature revealed that an ordered monolayer structure, with C6mim+ cations intercalated in the interlayer nanospace and Br located on the edge of the LAPONITE®, was formed when ILs were intercalated in LAPONITE®. The results also demonstrated that the enhanced interactions, the formed hydrogen bonds, as well as the ordered monolayer arrangement induced the formation of C6mimBr crystals when intercalated in LAPONITE®. In situ XAFS analysis with a combination of XRD patterns at varied temperatures revealed that the structure orientation of the intercalated C6mim+ cations tends to deflect and maintain the ordered monolayer arrangement with the elevation of temperature. The ordered crystal structure still exists at 120 °C and disappears at a higher temperature.

Probing the spontaneous reduction mechanism of platinum ions confined in the nanospace by X-ray absorption fine structure spectroscopy

The reduction mechanism of Pt(4+) ions confined in the channel of multi-walled carbon nanotubes was mainly investigated using X-ray absorption fine structure (XAFS) spectroscopy, with the aid of TEM, Raman, XRD and ICP-AES studies. The XAFS spectra revealed the spontaneous formation of Pt nanoparticles when H2PtCl6 was confined in multi-walled carbon nanotubes (MWCNTs). The Pt L3-edge X-ray absorption near edge structure (XANES) coupled with the C K-edge NEXAFS results indicated that the reduction of Pt(4+) from tetravalent to zerovalent was attributed to the electron transfer from MWCNTs. The Fourier transform R-space of the Pt L3-edge XAFS data displayed that the nanoconfinement effect of MWCNTs promoted the formation of Pt nanoparticles. Moreover, the Pt-Pt bond length in confined Pt nanoparticles became shorter than that of Pt in the bulk state. Furthermore, by varying the inner diameter of MWCNTs from 15 nm to 10 nm and 5 nm, the Pt-Pt bond length of nanoconfined Pt nanoparticles decreased gradually. The results clearly revealed that MWCNTs acting as enriched electron donors can continuously reduce the confined Pt ions to Pt nanoparticles, thereby showing a great potential for the design of a new type of confined nanocatalysts.