Fei Lu

Aggregation behavior of 1-dodecyl-3-methylimidazolium bromide in aqueous solution: effect of ionic liquids with aromatic anions.

The effects of ionic liquids (ILs), 1-butyl-3-methylimidazolium methylsulfonate (bmimMsa), 1-butyl-3-methylimidazolium benzenesulfonate (bmimBsa), and 1-butyl-3-methylimidazolium 2-naphthalenesulfonate (bmimNsa), on the aggregation behavior of 1-dodecyl-3-methylimidazolium bromide (C12mimBr) in aqueous solution were investigated by surface tension, dynamic light scattering measurements, and (1)H NMR spectroscopy. The ability to promote the surfactant aggregation is in the order bmimNsa > bmimBsa > bmimMsa. Nevertheless, only bmimNsa distinctly reduces both the CMC value and the surface tension at CMC. Due to the penetration of C10H7SO3(-)anions into the surfactant aggregate, bmimNsa is found to induce a phase transition from micelles to vesicles, whereas the other ILs only slightly increase the sizes of micelles. The combined effect of intermolecular interactions, such as hydrophobic effect, electrostatic attractions, and π-π stacking interactions, is supposed to be responsible for this structural transformation, in which π-π stacking plays an important role.

Protein-decorated reduced oxide graphene composite and its application to SERS.

A globular protein, β-lactoglobulin (BLG), was used to decorate reduced graphene oxide sheets (RGO) and the obtained BLG-RGO composite can be dispersed in aqueous solution with pH-sensitive solubility. The morphology of the BLG-RGO composite was studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results indicate that BLG-RGO is effectively exfoliated with an average thickness of 2.5 nm. UV-vis spectra were performed to examine the reduction degree and determine the optimum concentration of β-lactoglobulin and appropriate pH value. Furthermore, Raman spectra demonstrate that β-Lactoglobulin promotes the chemical reduction process of graphene oxide and benefits to repair the crystal defects. Due to the adsorption of β-Lactoglobulin on the surface of graphene sheets, the BLG-RGO composite was further used as template for Au nanoparticles assembly. These Au nanoparticles assembled on the BLG-RGO composite were shown to yield a large SERS enhancement for Rhodamine 6G.

Preparation and characterization of nonaqueous proton-conducting membranes with protic ionic liquids.

Hybrid Nafion membranes were successfully fabricated by incorporating with protic imidazolium ionic liquids 1-(2-aminoethyl)-3-methylimidazolium chloride ([MimAE]Cl), 1-(2-hydroxylethyl)-3-methylimidazolium chloride ([MimHE]Cl), and 1-carboxylmethyl-3-methylimidazolium chloride ([MimCM]Cl) for high-temperature fuel cells. The composite membranes were characterized by impedance spectroscopy, small-angle X-ray scattering (SAXS), scanning electronic microscopy (SEM), and thermogravimetric analysis (TGA). The incorporated protic ionic liquids enhance the doping of phosphoric acid (PA) and result in a relatively high ionic conductivity. The Nafion/10 wt % [MimAE]Cl/PA composite membrane exhibits an ionic conductivity of 6.0 mS/cm at 130 °C without humidification. [MimAE]Cl can swell the Nafion matrix more homogeneously than [MimHE]Cl or [MimCM]Cl, which results in a better ionic conductivity. It is notable that the composite Nafion/IL/PA membranes have a better thermal stability than the pristine Nafion membranes.

Spontaneous vesicle phase formation by linear pseudo-oligomeric surfactant in aqueous solutions.

In the present work, we reported a novel linear pseudo-oligomeric surfactant, which is formed by mixing dodecyl benzenesulfonate (SDBS) and a linear tricationic imidazolium bromide salt (LTIB) in a molar ratio of 3:1. The aggregation behavior, aggregate structures, and interactions between SDBS and LTIB were investigated by surface tension measurement, dynamic light scattering, turbidity, cryogenic transmission electron microscopy, and (1)H NMR techniques. When SDBS is mixed with LTIB in aqueous solutions, three SDBS molecules may be bridged to one cationic LTIB molecule by intermolecular interactions, behaving like a linear oligomeric surfactant. Vesicles can be formed by this kind of linear pseudo-oligomeric surfactant. The aggregation behavior of the LTIB/SDBS mixed aqueous solutions behaves ratio- and concentration- dependence. Our work paves a convenient way for constructing surfactant systems with the characteristics of linear pseudo-oligomeric surfactant through intermolecular interactions between commercially available single-chain surfactants and linear tricationic imidazolium counterions.

Nanostructured Proton Conductors Formed via in Situ Polymerization of Ionic Liquid Crystals

Ionic liquid crystals (ILCs) with hexagonal and lamellar phases were successfully fabricated by the self-assembly of a polymerizable amphiphilic zwitterion, which is formed by 3-(1-vinyl-3-imidazolio)propanesulfonate (VIPS) and 4-dodecyl benzenesulfonic acid (DBSA) based on intermolecular electrostatic interactions. The microstructures and phase behaviors of ILCs were studied by polarized microscope (POM) and small-angle X-ray scattering (SAXS). The ILC topological structures can be considered as proton pathways and further fixed by photopolymerization to prepare nanostructured proton-conductive films. The introduction of highly ordered and well-defined ILC structures into these polymeric films radically improves the ionic conductivities.

Nanostructured aqueous lithium-ion conductors formed by the self-assembly of imidazolium-type zwitterions.

In the present study, we have synthesized a room-temperature ionic liquid by mixing imidazolium-type zwitterions with lithium bis(trifluoromethanesulfonyl)imide. We constructed nanostructured aqueous lithium-ion conductors having hexagonal, lamellar, and bicontinuous cubic structures by the self-assembly of this amphiphilic ionic liquid. These nanostructured lithium-ion conductors exhibited an assembled-structure dependent lithium-ion conduction behavior. The introduction of highly ordered and well-defined liquid crystal structures into room-temperature ionic liquid radically changes the conduction mechanism from diffusion to hopping.

Aqueous dispersion of graphene sheets stabilized by ionic liquid-based polyether

Graphene sheets can be effectively dispersed by a novel ionic liquid-based polyether, poly(1-glycidyl-3-methylimidazolium chloride) (PGMIC), in aqueous solution. The reduction of graphene oxide to graphene is confirmed by UV–Vis and Raman spectrum in aqueous solution of PGMIC. TEM image showed that the stable and uniform dispersion of graphene sheets were obtained. Both the TGA and AFM analysis indicated that the graphene sheet was covered by PGMIC. FTIR spectra demonstrated that n–π, cation–π interactions and electrostatic repulsions played important roles in the dispersion of graphene sheets.

Photoresponsive Self-Assembly of Surface Active Ionic Liquid

A novel photoresponsive surface active ionic liquid (SAIL) 1-(4-methyl azobenzene)-3-tetradecylimidazolium bromide ([C14mimAzo]Br) with azobenzene located in the headgroup was designed. Reversible vesicle formation and rupture can be finely controlled by photostimuli without any additives in the aqueous solution of the single-tailed ionic liquid. The photoisomerization of the azobenzene derivative was investigated by (1)H NMR and UV-vis spectroscopy. Density functional theory (DFT) calculations further demonstrate that trans-[C14mimAzo]Br has less negative interaction energy, which is beneficial to aggregate formation in water. The incorporation of trans-azobenzene group increases the hydrophobicity of the headgroup and reduces the electrostatic repulsion by delocalization of charge, which are beneficial to the formation of vesicles. However, the bend of cis-azobenzene makes the cis-isomers have no ability to accumulate tightly, which induces the rupture of vesicles. Our work paves a convenient way to achieve controlled topologies and self-assembly of single SAIL.

Facile one-step preparation of hierarchical α-Fe2O3 nanostructures with enhanced performance in energy and environmentally related applications

Hierarchical α-Fe2O3 nanostructures have been successfully synthesized in aqueous solution of sodium dodecyl sulfonate (SDS), 1-dodecyl-3-methylimidazolium bromide (C12mimBr) and ethylene glycol (EG) on the basis of a polyol process. Based on a series of experiments, the possible growth mechanism and fabrication process of the hierarchical structures were proposed. The addition of EG and utilizing Fe2+ ions as the source of iron were our “protection” reactions to guarantee the equilibrium between hydrolysis and oxidation of Fe3+. Furthermore, electrochemical measurements demonstrated that the as-prepared hierarchical α-Fe2O3 nanocrystals are ideal candidates for lithium-ion batteries. In addition, the photocatalytic activity of the as-prepared α-Fe2O3 was superior to that of the previously reported hierarchical α-Fe2O3 nanomaterials and the Fe2O3-based photocatalyst (α-Fe2O3/SnO2).

Aggregation behavior of alkyl triphenyl phosphonium bromides in aprotic and protic ionic liquids

The aggregation behavior of alkyltriphenylphonium bromides, CnTPB (nu2009=u200912 and 14), has been investigated in two different room-temperature ionic liquids (ILs), the aprotic 1-butyl-3-metyllimidazolium tetrafluoroborate ([bmim][BF4]), and the protic ethylammonium nitrate (EAN). The critical micelle concentration was determined by the surface tension measurements. The calculated thermodynamic parameters based on surface tension measurements at various temperatures indicate that the micellization for CnTPB in both aprotic [bmim][BF4] and protic EAN is enthalpy-driven. But stronger solvophobic interactions presented between CnTPB and protic EAN than aprotic [bmim][BF4]. 1H NMR spectra were further conducted to reveal that ethylammonium cation can insert into the micelle while imidazole cation only locates among the head groups of CnTPB.