Viscous Organic Solvents Research Articles

A Single-Walled Carbon Nanotube/Covalent Organic Framework Nanocomposite Ultrathin Membrane with High Organic Solvent Resistance for Molecule Separation.

Covalent organic framework (COF)-based membranes are burgeoning candidates for separation technologies owing to their well-ordered channel structures. The exponential interest in the stability of the COF membrane on exposure to harsh organic solvents is directed to develop a composite membrane for dye separations in polar aprotic solvents. Here, we reported a nanocomposite membrane composing of a single-walled carbon nanotube (SWCNT)/COF (an imine-based COF) hybrid on a commercial polytetrafluoroethylene (PTFE) substrate, with a thickness of ∼58 nm prepared in a diffusion cell. This membrane displayed high permeability and stability toward nonpolar and aprotic solvents. It exhibited high permeability for lower viscous organic solvents such as hexane (66 L m-2 h-1 bar-1), acetone (60 L m-2 h-1 bar-1), and acetonitrile (59 L m-2 h-1 bar-1) with a desirable dye rejection (92.8% for Brilliant blue in acetone). The long-time operation demonstrated the excellent stability of the nanocomposite membrane. We herein reported a facile and mild method to prepare an ultrathin COF-based nanocomposite membrane with a porous, robust structure coupled with solvent durability capable of efficient dye separation.

Features of injection and chromatographic separation of samples in high boiling viscous organic solvents using the capillary columns at a low split ratio

The features of injection and gas chromatographic separation of stock analytes in their solutions in high boiling viscous polar organic solvents (on the example of 1,3-butanediol) using a short capillary column of large internal diameter (Megabore type) at low split ratios are considered. The manifestation of so-called discrimination effects is confirmed, with the main of them being the dependence of absolute peak areas vs . injection temperature as well as similar dependence of relative peak areas in different solvents. However, these effects are manifested in a lesser degree than the same effects for the samples dissolved in low boiling solvents. It is demonstrated that the dependencies of peak areas vs . injector temperature ( S = aT + b ) are principally different for solvents with various boiling points. Thus, for the solutions of butyl acetate, cyclohexanone, anisol, butyl butyrate, and acetophenone in low boiling 2-propanol the linear dependencies S ( T ) are revealed for the injector temperature range of 120-180°С only (with correlation coefficients r = 0.986 – 0.999), while at the higher injector temperatures (210-240°С) the significant deviations from linearity are typical. At the same time, the solutions of the same components in higher boiling 1,3-butanediol demonstrate the linear S ( T ) dependencies within the whole temperature range (120-240°С). It is confirmed that the discrimination effects have no significant influence on the results of gas chromatographic analyses of the samples in high boiling solvents if the method of internal normalization is used. The main uncertainties of the results are caused by the column’s overloading with the solvent, which leads to the broadening and asymmetry of its peaks and their overlapping with the peaks of some analytes. DOI: http://dx.doi.org/10.15826/analitika.2018.22.3.005 Keywords : High boiling viscous organic solvents, gas chromatographic analysis, capillary columns, discrimination effects (Russian) Igor G. Zenkevich, Eugene Leleev St. Petersburg State University, Russian Federation, 198504, St. Petersburg, Universitetskii prosp., 26

Pressure-driven liquid-liquid separation in Y-shaped microfluidic junctions

On-chip phase separation of multiphase microflows at the divergence point of Y-shaped microfluidic junctions is an effective way for integrating continuous microstructured devices. In this study, flow pattern maps of various solvent pairs based on the volumetric flow rates of both phases have been drawn experimentally and compared with numerical prediction to investigate the effective domain for which complete phase separation occurred. Furthermore, sufficient separation of aqueous and organic phases at the end of the microchannel was achieved by controlling the pressure difference at the liquid-liquid interface via loading back-pressure on the organic phase. A mathematical model based on interfacial pressure balance was derived. It was found that organic phase outlet tube should be kept between the upper and lower values calculated from the model. Only narrow discrepancy between the model and experimental observation can be seen in using viscous organic solvents.

Site selective Cu2+ substitution in single crystal Fe3O4 biocompatible nanospheres by solvothermal reflux method

Transition metal cations distribution among tetrahedral and octahedral sites in Fe3O4 has profound influence on it properties. The cations distribution among these sites were influenced by crystal field stabilization energy (CFSE) of a substituent ion. It was reported that Cu2+ substitutes both Fe3+ in tetrahedral and Fe2+ in octahedral sites of magnetite though it has high CFSE for octahedral sites. Thus it promotes mixed (normal & inverse) spinel structure and hence the properties deviate from the prediction. Here we show that selective octahedral site substitution of Fe2+ by Cu2+ in single crystal Fe3O4 nanoparticles was possible by solvothermal reflux method at moderate temperatures (≈300°C). It was attributed to reduced energy barrier for crystallization and high diffusion coefficient of the metal cations at moderate temperature in low viscous organic solvents mixture, at ambient pressure, compared to coprecipitation and solid state reaction protocols. In addition, effective removal of exothermic crystal lattice energy, released during nucleation and growth process, by natural gas bubbles formed in the reflux organic solvent mixture. This promotes effective diffusion of cations during the growth process and easy octahedral occupation by Cu2+ in Fe1−xCuxFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5 & 0.6) single crystal nanospheres. The octahedral substitution was confirmed by reduction of crystal lattice parameter as well as ferromagnetic strength of octahedral sublattice with enhanced Cu2+ concentration. In addition, morphology, lattice vibrational frequency and electron excitation spectra of the nanospheres were studied. The Langevin function fit analysis reveals that superparamagnetic domain diameter were slightly less than the particle diameter obtained from TEM micrograph.

3-D dumbbell-like LiNi1/3Mn1/3Co1/3O2 cathode materials assembled with nano-building blocks for lithium-ion batteries

Dumbbell-like microsphere carbonate precursors including multi-transition metal components (Ni1/3Mn1/3Co1/3CO3) assembled with nano-building blocks were synthesized by urea-assisted solvo/hydrothermal method, and layered cathode materials (LiNi1/3Mn1/3Co1/3O2) were subsequently prepared using the similarly shaped carbonate precursors for Li-ion batteries. For the synthesis of hierarchical microsphere structures, the partial addition of viscous organic solvent (e.g. ethylene glycol) in aqueous solution played a crucial role, not only in suppressing the sudden particle growth but also in regulating the directional crystallization of carbonate particles on the surface. The dumbbell-like LiNi1/3Mn1/3Co1/3O2 assembled with nanocubes prepared via the urea-assisted solvo/hydrothermal method exhibited better electrochemical characteristics, such as initial discharge capacity, cyclic performance, and rate-capability as a cathode material of Li-ion batteries, compared with the LiNi1/3Mn1/3Co1/3O2 materials prepared via the conventional co-precipitation method.

Excited-State Kinetics of the Hydrophobic Probe Nile Red in Membranes and Micelles

Nile red is a widely used hydrophobic dye for probing the structure, dynamics, and environment in many biological and microheterogeneous systems. This paper reports emission-wavelength-dependent fluorescence intensity decay of Nile red in membranes and micelles. Global analysis of these multiple fluorescence decays reveals a double-exponential decay with negative amplitudes for the short-lifetime component at longer emission wavelengths. This indicates an excited-state kinetics leading to the formation of a new species in the excited state from the initially excited state. In both the cases, the short lifetime corresponds to that of the initially excited species. This excited-state kinetics is also observed in the case of viscous organic solvents such as 1-octanol and glycerol and is attributed to that of an excited-state solvent relaxation.

Physico-Chemical Properties of the Most Suitable Spray Reagent for Fluorescence Enhancement in Thin-Layer Chromatography

Abstract In a fluorescence-enhancing method by spraying with a viscous organic solvent in thin-layer chromatography(TLC), the relationship between fluorescence enhancement and the properties of spray reagents was investigated, using 5-dimethylamino-1-naphthalene-sulfondimethylamide(DNS-DMA) as a fluorescent compound. A stuitable reagent should have two properties of giving high fluorescence intensity to a fluorescent compound and good transmigration from an adsorbent to the reagent medium, i.e., having the large product of relative fluorescence quantum number(RFQN) in the reagent solution and Rf value of the fluorescnet compound in TLC using the reagent as a developing solvent. A mixture of Triton X-100 and chlofoform(2:8) showed the largest product for DNS-DMA, so that the mixture was expected to be the most suitable reagent, and DNS-amine fluorescences on a plate were enhanced about 100-fold practically. Standard curves for DNS-amines were linear in the range of 1 to 20 pmole per spot. The Triton X-100 ...

Fluorescence enhancement in thin-layer chromatography by spraying viscous organic solvents

Spraying of the fluorescence spot on a thin-layer plate with a non-volatile and viscous organic solvent after development enhanced the fluorescence. The elucidation of the physicochemical factors that affect such an enhancing effect was investigated. The effect was not related to the transmissibility of light through the thin layer but to the properties of the spraying reagent (polarity, viscosity and acidity). The appropriate reagents for 5-dimethylamino-1-naphthalenesulphonamides (DANS-amines) are non-polar, viscous and non-acidic solvents such as a mixture of liquid paraffin and n-hexane, which enhanced the fluorescence internsity 10-fold. With benzo( a)pyrene, the use of a solvent such as this liquid paraffin mixture enhanced the fluorescence intensity 35-fold.