Colloidal suspensions of N-modified graphene nano-platelets in water and organic solvent/water mixed systems

The production of colloidal suspensions of graphene-based nano-platelets in large scale is highly important for their use in practical applications. In this work, we developed a new route for generation of colloidal suspensions of N-modified graphene-based nano-platelets (A-rG-O) with high concentration in water or organic solvent/water mixed systems by the reaction between graphene oxide and ammonium hydroxide. Graphene oxide was reduced by the ammonium hydroxide and N atoms (up to 6 at%) were introduced into A-rG-O materials using solution process without further thermal treatment. Such A-rG-O nano-platelets were well dispersed as individual layers in both systems. Macroscopic free-standing A-rG-O paper materials with good electrical conductivity were produced by filtration of such colloidal suspensions.     

Preferable solvatation of decane and benzene in 1-octanol-N,N-dimethylformamide mixed solvent

Heat effects of the dissolution of decane and benzene in a model system of 1-octanol (OctOH)-N,N-dimethylformamide are measured at 298 and 318 K using a variable temperature calorimeter with an isotermic shell. The state of hydrocarbon molecules in the mixed solvent is studied using an extended coordination model and is compared to earlier data for ethyl acetate (EtOAc), DMF, OctOH, and tetramethyl hematoporphyrin (TMHP). It is shown that the polar carboxylic groups of porphyrin are preferably solvated by amide molecules due to stronger interaction with DMF, while nonpolar aliphatic groups are solvated by alcohol molecules. We conclude that a solvate shell of aromatic benzene is strongly enriched with DMF over the range of compositions, suggesting that the weakening of the preferable solvatation of porphyrin relative to EtOAc is due primarily to the influence of nonpolar substituents.     

A theoretical study on the specific interaction of hexafluorobenzene with benzene and p -xylene

A cndo/2 study has been carried out for C₆F₆ + C₆H₆aad C₆F₆ + C₆H₁₀ composites and individual molecules. The favoured configurations of the adducts have been decided on the basis of energy calculations of various geometries. For the C₆F₆+C₆H₆ adduct the lowest energy corresponds to the configuration in which the molecular planes are parallel to each other with a twist angle of 30°. For the C₆F₆+ C₈H₁₀ adduct lowest energy corresponds to a geometry in which the two molecular planes are inclined by a small angle with the angle of twist between the molecular planes being 30°. It is shown that the complexes are not of the charge transfer type.     

Reference values of vapour pressure the vapour pressures of benzene and hexafluorobenzene

The vapour pressures of benzene and hexafluorobenzene in the range 10 to 100 kPa were measured in the course of developing a comparative ebulliometric apparatus, and the results of four sets of measurements on benzene and of one on hexafluorobenzene are given. There is excellent agreement between the measurements made in this laboratory and those made at the Bartlesville laboratory of the U.S. Department of Energy and equations are given that reproduce the results of the work in the two laboratories within 0.01 per cent of the pressure in a range around atmospheric pressure, corresponding to differences in temperature of not more than 0.005 K.     

Photoactive graphene sheets prepared by "click" chemistry

Graphene sheets modified by phenylacetylene moieties provide a facile platform for attaching various photoactive functional molecules via"click" chemistry. The produced photoactive graphene materials are well-dispersed in various solvents and show dramatically improved photo-current responses.     

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.     

Size fractionation of graphene oxide sheets by pH-assisted selective sedimentation

Graphene oxide (GO) sheets prepared by Hummers' method have been separated into two portions with large (f1) or small (f2) lateral dimensions from their aqueous dispersion. This method is based on the selective precipitation of GO sheets with lateral dimensions mostly (>90%) larger than 40 μm(2) at a pH value of 4.0 because of their larger hydrophobic planes and fewer hydrophilic oxygenated groups. The hydrazine reduced Langmuir-Blodgett (LB) films of f1 showed much higher conductivities than those of f2. Furthermore, the thin film of f1 prepared by filtration exhibited a smaller d-space and much higher tensile strength and modulus than those of f2 films. The one-step size fractionation method reported here is simple, cheap, efficient, and environmentally friendly, which can be used for the size fractionation of GO sheets in large scale.     

Towards free-standing graphene/carbon nanotube composite films via acetylene-assisted thermolysis of organocobalt functionalized graphene sheets

A novel approach towards highly conductive free-standing chemically reduced graphene/carbon nanotube composite films via an in situ thermolysis of functionalized graphene/organic cobalt complexes was developed. By combining 1D-CNT and 2D-graphene, a synergistic effect of conductivity was established.     

Effect of solvent on two-photon absorption by vinyl benzene derivatives

Two-photon absorption cross sections and spectral profiles were determined for three centrosymmetric vinyl benzenes in solvents of differing polarity and polarizability. The data do not correlate with parameters that characterize dielectric properties of the solvents. Rather, the effect of solvent depends on the solute, and even subtle structural changes in the latter can result in pronounced solvent-dependent differences in the absorption cross section. Our data highlight the need for more sophisticated models that can simulate the perturbing effects of a solvent in the two-photon process.     

Neutron activation analysis of high purity nickel by solvent extraction using 2-benzylpyridin/benzene

A radiochemical neutron activation analysis using solvent extraction has been applied for the determination of trace impurities in high purity nickel. Because of the high activity of⁵⁸Co produced by the nuclear reaction,⁵⁸Ni(n,p)⁵⁸Co, cobalt should be separated from the impurities. Removal of cobalt from the other trace elements in the aqueous acidic solution containing 1M thiocyanate ion (KSCN) was achieved by extraction with 1M2-benzylpyridin (BPy) in benzene. From the result of tracer experiments, cobalt was completely separated from most other elements except Fe, Mo and Zn. To determine the experimental accuracy, NIST SRM 673 nickel oxide was analyzed and the results agreed well within 10% deviation. This established radiochemical method was applied to the analysis of high purity nickel samples.     

Effects of molecular association on polarizability relaxation in liquid mixtures of benzene and hexafluorobenzene

In this work we have studied the relaxation dynamics of the many-body polarizability anisotropy in liquid mixtures of benzene (Bz) and hexafluorobenzene (Hf) at room temperature by femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) experiments and molecular dynamics (MD) simulations. The computed polarizability response arising from intermolecular interactions was included using the first-order dipole-induced-dipole model with the molecular polarizability distributed over the carbon sites of each molecule. We found good qualitative agreement between experiments and simulations in the features exhibited by the nuclear response function R(t) for pure liquids and mixtures. The long-time diffusive decay of R(t) was observed to vary substantially with composition, slowing down noticeably with dilution of each of the species as compared with that in the corresponding pure liquids. MD simulation shows that the effect on R(t) is due to the formation of strong and localized intermolecular association between Bz and Hf species that hinder the rotational diffusive dynamics. The formation of these Bz-Hf complexes in the liquid mixtures also modifies the rotational diffusive dynamics of the component species in such a way that cannot be explained solely in terms of a viscosity effect. Even though the computed orientational diffusive relaxation times associated with Bz and Hf are larger by a factor of approximately 2 than those from experiments, we found similar trends in experiments and simulations for these characteristic times as a function of composition. Namely, the collective and single-molecule orientational correlation times associated with Bz are observed to grow monotonically with the dilution of Bz, while those corresponding to Hf species exhibit a maximum at the equimolar composition. We attribute the quantitative discrepancy between experiments and simulations to the use of the Williams potential, which seems to overestimate the intermolecular interactions and thus predicts not only a slower translational dynamics but also a slower rotational diffusion dynamics than in real fluids.     

The orbital interpretation of the photoelectron spectrum of benzene, 1,3,5-trifluorobenzene and hexafluorobenzene

An interpretation of certain features in the vibrational pattern of the 11.5 to 13.0 eV photoelectron spectrum of benzene in terms of a Jahn-Teller effect is presented. This supports Lindholm's orbital assignment of the ionization processes in this region. A change in the assignment of some of the higher systems in the photoelectron spectra of 1,3,5,-trifluorobenzene and hexafluorobenzene is proposed. Some discussion of Rydberg series found in these molecules is also given.     

Flexible graphene films via the filtration of water-soluble noncovalent functionalized graphene sheets

Flexible graphene films were prepared by the filtration of water-soluble noncovalently functionalized graphene sheets with pyrenebutyrate. The work presented here will not only open a new way for preparing water-soluble graphene dispersions but also provide a general route for fabricating conducting films based on graphene.     

Development of rectangular column structured titanium oxide photocatalysts anchored on silica sheets by a wet process

Commercially available powdered photocatalysts such as P-25 are known to show high photocatalytic performance. However, in practical use, their anchoring onto a substrate without any binders is still very difficult. The purpose of this study is to design and develop high-performance photocatalysts that can be anchored onto a substrate, and to this end we have prepared a titanium oxide photocatalyst using a wet process. The results of this study led to the successful development of rectangular column structured titanium oxide crystals which could be anchored onto silica sheets. The rectangular columnar crystal was 100- 500 nm wide and 1000- 5000 nm long. Moreover, investigations on the complete oxidation reaction of acetaldehyde into CO₂ and H₂O showed a high performance equivalent to that of the most efficient marketed powdered photocatalysts.