Preparation of poly(acrylamide)/nanoclay organic-inorganic hybrid nanoparticles with average size of ∼250 nm via inverse Pickering emulsion polymerization

In this study, the preparation of poly(acrylamide)/nanoclay organic-inorganic hybrid nanoparticles via surfactant-free inverse emulsion polymerization by using organically modified clay platelets as stabilizers was discussed. Colloidally stable inverse Pickering emulsions of aqueous acrylamide solution in cyclohexane (solvent) stabilized by hydrophobic Cloisite 20A (MMT20) were prepared. Polymerization was carried out via 2,2′-azobis(isobutyronitrile) and composite particles with an average size of ～250 nm were obtained. The effect of initiator and solvent type on the stability, size, size distribution, and morphology of the produced composite particles was examined. It was observed that in the presence of xylene as solvent, particles with bigger sizes and broader size distribution were obtained. Furthermore, using an ionic initiator resulted in a slight coagulation during polymerization and smaller particles. Moreover, the effect of various polymerization conditions such as temperature, initiator, and crosslinking agent concentration and clay content on the polymerization rate was evaluated. The experimental results showed that polymerization rate increases with an increase in polymerization temperature, crosslinking agent concentration, and initiator content. However, increasing in clay content results in a lower polymerization rate.     

Characterizing colloidal behavior of non-ionic emulsifiers in non-polar solvents using electrical impedance spectroscopy

Colloidal behavior of a widely used non-ionic emulsifier, sorbitan monooleate (Span80), was investigated in non-polar solvents (cyclohexane and xylene) using electrical impedance spectroscopy (EIS). The electrical characteristics of the colloidal mixtures were measured with frequency scans ranging from 1 Hz to 200 kHz. The conductances at low frequencies were found to increase with an increase in Span80 concentration. The source of conductivity for non-polar solvents using non-ionic emulsifiers is usually attributed to ionic impurities either in the Span80 or in the non-polar solvents. The measured electrical characteristics for pure Span80 and pure non-polar solvents revealed that the source of ionic conduction is impurities in Span80. It was confirmed that the ionic impurities in the non-polar solvents are in form of aggregate of ions, ion-pairs, and triple ions which is unaffected with the emulsifier concentration. Analyses using equivalent electrical circuits confirmed that the critical Maxwell-Wagner frequency is 0.6–1.8 Hz for the mixtures. The conductance-concentration profiles for the mixtures at 1 Hz showed transitions from a square root to a linear concentration dependence at the CMC. This indicated that the dissociation model holds below the CMC, while the fluctuation model applies above the CMC. The conductance profiles enabled estimates of the relative hydrophilic core radius and the fraction of charged micelles in both non-polar solvents. Figure

CMC determination of non-ionic emulsifier in non-polar solvents     

Mechanistic Investigation on Dynamic Interfacial Tension Between Crude Oil and Ionic Liquid Using Mass Transfer Concept

Ionic liquids (ILs) are a new kind of solvents that have recently gained an upsurge in attention in light of their unique potential for different applications. With respect to this, in the present study, applicability of an IL called 1-octadecyl-3-methylimidazolium chloride ([C18mim] [Cl]) as a new class of surfactant was investigated. Different interfacial tension (IFT) measurements were performed to find the effect of IL concentration and temperature on the IFT of water/crude oil system. The observed trend was explained based on mass transfer mechanisms including diffusion and convective mass transfer. In addition, the effect of rotational speed, ranging between 3000 and 9000 rpm, on the IFT was examined with the hypothesis that it can modify the convective mass transfer. Finally, since it has been reported that the Marangoni effect enhances the mass transfer flux in the surfactant solutions, two different methods of IFT measurements including the spinning drop and pendant drop methods were applied to investigate the effects of convective mass transfer on the equilibrium IFT.     

Synthesis of Tungsten Oxide Nanorods by the Controlling Precipitation Reaction: Application for Hydrogen Evolution Reaction on a WO3 Nanorods/Carbon Nanotubes Composite Film Modified Electrode

Tungsten trioxide nanorods (WO₃) were prepared by controlling the precipitation reaction of sodium tungstate dehydrates solution and hydrothermal process. The synthesized tungsten trioxide nanorods have been characterized by X‐ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Electrochemical activity for hydrogen evolution reaction (HER) on WO₃ nanorods / carbon nanotube (WO₃/CNT) composite electrocatalyst was first studied in acid solution (0.1 M H₂SO₄) at room temperature. The overall experimental results revealed that the electrocatalytic activity for HER on WO₃/CNT is two order magnitude higher than those obtained with WO₃ nanorods and is four times than in the case of commercial WO₃ in 0.1 M H₂SO₄. On the other hand, the kinetic reaction mechanisms were discussed on WO₃/CNT electrocatalysts in acid solution for HER. However, the rate‐determining step carries through Tafel reaction on commercial WO₃, CNT, WO₃ nanorods and WO₃/CNT electrocatalysts in acidic solution was introduced.     

Label-free colorimetric detection of picomolar amounts of hydrazine using a gold nanoparticle-based assay

We report the development of a simple and rapid colorimetric detection method for hydrazine in boiler feed water using label-free aggregation-based gold nanoparticles as probe. This assay relies upon the distance-dependent optical properties of gold nanoparticles. Hydrazine could rapidly induce the aggregation of gold nanoparticles, thereby resulting in visual color change from red to blue (or purple). The concentration of hydrazine can be determined by the naked eye or by a UV–vis spectrometer. Calibration curve was linear ranging from 1.0 × 10^?11 to 1.0 × 10^?7 M of hydrazine. The present limit of detection for hydrazine was 1.0 × 10^?12 M. The method is rather simple, and the whole process including sample pretreatment takes only 15 min at room temperature. The merits (such as simplicity, rapidity, low cost and visual colorimetry) make the proposed method especially useful for on-site screening of hydrazine levels well in boiler feed water.     

S−H…O and O−H…O Hydrogen Bonds-Comparison of Dimers of Thiocarboxylic and Carboxylic Acids

ωB97-XD/aug-cc-pVTZ calculations were performed on dimers of selected thiocarboxylic acids and on analogous carboxylic acids. The sample of calculated thiocarboxylic acids is an extension of the Cambridge Structural Database search that contains only a few such structures. The Natural Bond Orbital (NBO) method, Symmetry-Adapted Perturbation Theory (SAPT) approach, Non-Covalent Interaction (NCI) method and Quantum Theory of Atoms in Molecules (QTAIM) were applied additionally to analyse interactions in dimers of thiocarboxylic and carboxylic acids. The insights into crystal structures as well as into results of calculations show that the formation of S−H…O hydrogen bonds between molecules of thiocarboxylic acids is steered by the same mechanisms as the formation of much stronger O−H…O hydrogen bonds in carboxylic acids. The intramolecular O−H…O and C−H…S hydrogen bonds occurring in few considered structures are also analysed.     

Supramolecular stabilization of acid tolerant L-arabinose isomerase from Lactobacillus sakei

L-Arabinose isomerase stability is a crucial criterion for the industrial application of this biocatalyst. Noria and NoriaPG are capable of increasing the L-arabinose isomerase stability not only at high temperatures but also at low pH. Such results highlight, for the first time, the use of the Noria series of molecules for protein stabilization and activation.     

Ionic Strength Effect on the Stability of the V(V) + IDA Complex

In this research the interaction of dioxovanadium(V) with iminodiacetic acid has been considered at 25 °C and pH=1.00–2.50 in an ionic strength range of 0.1 to 1.0 mol⋅dm⁻³ of NaClO₄ by UV spectrophotometric and potentiometric techniques. Only one species, VO₂H₂L⁺, was assumed on the basis of two stoichiometric models. The extended Debye-Hückel theory predicts the first order effects in simple electrolyte solutions. Interactions between the reacting species and the ionic medium are taken into account in the specific ion interaction model. Parabolic, specific ion interaction, and extended Debye-Hückel models have been compared and it has been shown that the parabolic model with two coefficients is satisfactory for this complexation reaction. The results have also been compared with the literature values.     

Trichloroacetonitrile as a Source of Positive Chlorine Ion for Trapping Huisgen's Zwitterions

The zwitterionic 1 : 1 intermediates generated by addition of N‐heterocycles to activated acetylenes are trapped by trichloroacetonitrile to afford 1,2‐ or 1,4‐disubstituted N‐heterocycles in moderate to good yields under mild reaction conditions.