Toluene-water Interface Research Articles

Massive Vacancy Concentration Yields Strong Room-Temperature Ferromagnetism in Two-Dimensional ZnO.

Two-dimensional (2D) ZnO nanosheets with highly concentrated Zn vacancies (VZn) of up to approximately 33% were synthesized by ionic layer epitaxy at the water-toluene interface. This high cation vacancy concentration is unprecedented for ZnO and may provide unique opportunities to realize exotic properties not attainable in the conventional bulk form. After annealing, the nanosheets showed characteristic magnetic hysteresis with saturation magnetization of 57.2 emu/g at 5 K and 50.9 emu/g at room temperature. This value is 1 order of magnitude higher than other ZnO nanostructures and comparable to the conventional ferrimagnetic Fe3O4. Density functional theory calculations, with the support of experimental results, suggest that a high concentration of VZn (approximately one-third of the Zn sites) can form spontaneously during synthesis when stabilized by H ions, and the formation of VZn could be further facilitated by the presence of grain boundaries. It is essential to remove the H for the nanosheets to show ferromagnetism. The mechanisms identified for the origin of the high magnetism in ZnO nanosheets presents an intriguing example of a kinetically stabilized, non-equilibrium, highly defective 2D nanomaterial with a significantly enhanced physical property.

X-Ray Reflectometry of the Adsorption Octadecanamide Film at the Toluene–Water Interface

The structure of an adsorption octadecanamide film at the planar toluene-water interface is studied by X-ray reflectometry using synchrotron radiation with photon energy of 15 keV. The electron density (polarizability) profiles, according to which the interface structure is determined by the pH level in the water subphase, are reconstructed from experimental data with the help of a model-independent approach. For a high pH~11, the adsorption film is a crystalline octadecanamide monolayer with a thickness of about 2.6 nm, in which aliphatic tails of surfactant are extended along the normal to the surface. For low pH ~ 2, the thickness of the surface structure consisting of the crystalline monolayer directly on the toluene-water interface and a thick layer of deposited octadecanamide micelles reaches about 50 nm. In our opinion, the condensation of nonionogenic surfactant micelles for which the surface concentration of the surfactant increases significantly is caused by a change in the polarization direction upon a decrease in the pH level in the electric double layer at the interface between the water subphase and the octadecanamide monolayer. The shape of the reconstructed electron density profiles also indicates the existence of a plane of the closest approach of surfactant micelles to the interface at a distance of about 7 nm from it.

Carbon Quantum Dot Assisted Adsorption of Graphene Oxide to the Oil–Water Interface for Copper Sensing Emulsions

AbstractA nanocomplex of graphene oxide (GO) and nitrogen‐doped carbon quantum dots (N‐CQDs) is utilized for effective stabilization of the toluene–water interface in high surface area oil‐in‐water emulsions to assist in detection and extraction of Cu(II) ions. CQDs are nitrogen‐doped to produce a positively charged material that readily adsorbs to GO through charge interactions, forming a surface‐active complex. N‐CQDs serve two key purposes: first, to screen the surface charge of GO and thereby lower the electrostatic barrier to adsorption at the toluene–water interface, and second to detect Cu(II) ions via fluorescence quenching. This combined system is far more effective in lowering the interfacial tension between toluene and water, and thus stabilizing toluene‐in‐water emulsions, than either component alone. The complex comprises cheap and easy to prepare materials, and overcomes the limitations of the individual components through synergistic effects. Additionally, the noncovalent nature and self‐assembly of this system allows for facile use and potential recovery of the materials, and therefore enables utilization in industrial applications such as solvent extraction for mineral processing.

One-Step Preparation Method of Flexible Metafilms on the Water-Oil Interface: Self-Assembly Surface Plasmon Structures for Surface-Enhanced Raman Scattering Detection.

The present study demonstrated a one-step method for the first time to fabricate self-assembled gold nanoparticle (AuNP) metafilms at the water-toluene interface by adding polystyrene-polyisoprene-polystyrene as the support layer. The thiolated polyethylene glycol and ethanol were used to tune the surface charge density on the AuNPs, constructing a balanced situation at the water-toluene interface. The flexible (AuNP) metafilm can be easily obtained after evaporation of the toluene phase and further used as a surface-enhanced Raman scattering (SERS) substrate for trace thiram detection. The SERS sensitivity was tested using standard Raman probes such as crystal violet and malachite green, both with the detect concentration reaching 1 × 10-11 M. Moreover, the excellent reproducibility and elastic properties make the metafilm promising in practical detection. Hence, the trace thiram detection on an orange pericarp was inspected with the detection limit of 0.5 ppm (1 × 10-6 M) as well as a favorable linearity relation with a correlation coefficient of 0.979, exactly matching the realistic application requirements.

Partial Transformation of Imogolite by Decylphosphonic Acid Yields an Interface Active Composite Material.

The phosphonic acid moiety is commonly used as an anchoring group for the surface modification of imogolite. However, the impact of the reaction on its structure has never been clearly analyzed before. We study the reaction of imogolite and decylphosphonic acid by combining infrared spectroscopy, X-ray scattering, scanning electron microscopy, transmission electron microscopy, and solid-state nuclear magnetic resonance spectroscopy. Instead of a surface functionalization, we observe the formation of a lamellar phase interconnected with imogolite bundles. Although we find no evidence for grafted imogolite tubes, we observe the expected dispersion characteristics and stabilization of water in toluene emulsions described in the literature. Based on the surface chemistry of imogolite, we propose an explanation for the observed reactivity and link the structural features of the obtained composite material to its dispersibility in toluene and its observed properties at the toluene-water interface.

Synthesis of C−C Bonded Two‐Dimensional Conjugated Covalent Organic Framework Films by Suzuki Polymerization on a Liquid–Liquid Interface

AbstractSynthesis of free‐standing two‐dimensional (2D) conjugated covalent organic framework (COF) films linked by C−C bonds is highly desirable. Now a very simple and mild strategy has been developed to synthesize them by Suzuki polymerization on a water–toluene interface in a refrigerator. The versatility of this strategy was confirmed by the successful synthesis of two different 2D‐COF films: a porous graphene and a porphyrin‐contained 2D‐COF. Both 2D‐COF films have large lateral size and their crystalline domains were visualized by high resolution TEM. Based on the wide compatibility of Suzuki reaction, our breakthrough work opened a door for the synthesis of various 2D conjugated COF films. For application studies, the porous graphene exhibits a good carrier mobility, which is much higher than −C=N− linked 2D COF films and a good catalytic activity for hydrogen evolution reaction, which is comparable with nitrogen‐ or phosphorus‐doped graphene.

Synthesis of C-C Bonded Two-Dimensional Conjugated Covalent Organic Framework Films by Suzuki Polymerization on a Liquid-Liquid Interface.

Synthesis of free-standing two-dimensional (2D) conjugated covalent organic framework (COF) films linked by C-C bonds is highly desirable. Now a very simple and mild strategy has been developed to synthesize them by Suzuki polymerization on a water-toluene interface in a refrigerator. The versatility of this strategy was confirmed by the successful synthesis of two different 2D-COF films: a porous graphene and a porphyrin-contained 2D-COF. Both 2D-COF films have large lateral size and their crystalline domains were visualized by high resolution TEM. Based on the wide compatibility of Suzuki reaction, our breakthrough work opened a door for the synthesis of various 2D conjugated COF films. For application studies, the porous graphene exhibits a good carrier mobility, which is much higher than -C=N- linked 2D COF films and a good catalytic activity for hydrogen evolution reaction, which is comparable with nitrogen- or phosphorus-doped graphene.

A thermo-responsive polymer-tethered and Pd NP loaded UiO-66 NMOF for biphasic CB dechlorination

As a thermo-responsive MOF-based emulsifier, Pd@UiO-66-S-PNIPAM can highly promote the biphasic chlorobenzene dechlorination at the toluene–water interface at room temperature.

Visible-Light-Driven Efficient Hydrogen Production from CdS NanoRods Anchored with Co-catalysts Based on Transition Metal Alloy Nanosheets of NiPd, NiZn, and NiPdZn

Investigation of new catalysts to improve artificial photosynthesis efficiencies is an absolute need concerning energy demands and environmental issues. In the present study, nanosheets of NiPd, NiZn, and NiPdZn metal alloys, synthesized at the toluene–water interface, have been employed as co-catalysts for hydrogen evolution from water in the presence of CdS nanorods (NRs) as a photosensitizer. Anchoring of alloy nanosheets with CdS NRs resulted in exceptional enhancement in hydrogen evolution activity. Interestingly earth abundant cost-effective CdS/NiZn photocatalyst showed higher hydrogen evolution reaction (HER) activity than comparatively precious photocatalyst CdS/NiPd. Trimetallic alloy nanosheets of NiPdZn further exhibited superior HER activity concerning bimetallic alloys, NiZn and NiPd. An enhancement of 21 times in the hydrogen evolution activity of CdS has been achieved by optimum loading of NiPdZn. Hydrogen yields of 21347.3 μmol h–1 g–1 (AQY = 11.35%) and 53361.3 μmol h–1 g–1 (AQY = 28%) h...

Solid–Liquid Phase Transition in the Octadecanoic Acid Film Adsorbed on the Toluene–Water Interface

The structure of the soluble protonated (pH=2) octadecanoic acid film adsorbed on the saturated hydrocarbon (n-hexane) - water and aromatic hydrocarbon (toluene)-water interfaces is studied by X-ray reflectometry using synchrotron radiation. The experimental data demonstrate that a solid phase of a Gibbs monolayer (26 +/- 1) Angstrom thick, in which aliphatic tails are perpendicular to the surface and the area per molecule is A=(18 +/- 2) Angstrom^2, forms in the film at the n-hexane - water interface. The solid monolayer on the toluene - water interface in the adsorbed film melts when temperature increases, and this transition is caused by disordering the hydrocarbon tails of the acid. During the solid - liquid transition, the Gibbs monolayer thickness remains almost the same, (22 +/- 1) Angstrom. In the solid phase, we have A=(20+/- 2) Angstrom^2 and the angle of deviation of the molecular tails from the normal to the surface is about ~ 30 deg. The density of the liquid monolayer phase with A=(24 +/- 2) Angstrom^2 corresponds to liquid n-octadecane.

Mithrene Is a Self-Assembling Robustly Blue Luminescent Metal–Organic Chalcogenolate Assembly for 2D Optoelectronic Applications

Crystalline metal–organic chalcogenolate assemblies are a class of semiconducting hybrid nanomaterials that consist of well-defined arrays of nanostructured inorganic coordination polymers with a supramolecular lattice of organic ligands. Growing crystals of periodic arrays of nanostructured hybrid chalcogenolates at biphasic liquid–liquid interfaces has been used to prepare semiconducting hybrid materials for potential applications in sensing, catalysis, mechanochemistry, organic light-emitting devices, and photovoltaics. However, a distinct lack of a systematic framework for quantifying the relationship between experimental parameters and the structure–function relationship of the prepared materials has been one of the largest hurdles for the emerging field of hybrid chalcogenolates and related hybrid coordination polymer systems. Here we examine the crystallization of silver benzeneselenolate, coined here as mithrene, at a toluene–water interface and demonstrate that silver ion concentration is the cri...

Ionic liquid-assisted synthesis of Pt nano thin films at toluene–water interface: Enhanced CO tolerance in methanol fuel cells and adsorptive removal of p-nitrophenol from water

In this investigation, we report a one-pot method for the synthesis of Pt/ionic liquid nano thin films at organic-aqueous media at room temperature without using any harsh conditions. Synthesized Pt/ionic liquid thin films were characterized with common analytical techniques. Transmission electron microscope images confirmed the formation of spherical particles having a size distribution in the range of 4–12 nm. Ionic liquids have a key role in the control of better size distribution and prevent from agglomeration of nanostructures by preparing a shell around particles. These catalysts were applied for the reduction of toxic p-nitrophenol into non-toxic p-aminophenol and exhibited good catalytic activity. Also, they exhibit excellent CO tolerance in methanol oxidation process of fuel cells. This method provides a novel, rapid, low cost and economical alternative for the reduction of toxic organic pollutants in water and also to prepare high quality catalysts with low metal loading for methanol fuel cells. Pt/1-aminoethyl-3-methylimidazolium bromide exhibits better CO tolerance than Pt/1-methyl-3-octylimidazolium chloride and Pt/1-methyl-3-octylimidazolium tetrafluoroborate thin films.

Contrasting Mechanisms of Spontaneous Adsorption at Liquid-Liquid Interfaces of Nanoparticles Constituted of and Grafted with pH-Responsive Polymers.

Elucidating the mechanisms responsible for spontaneous adsorption of nanoparticles (NPs) at interfaces is important for their application as emulsifiers, bubble stabilizers, or foaming agents. In order to investigate the key factors that control the spontaneous adsorption of NPs at liquid-liquid interfaces, we synthesized seven different types of NPs from pH-responsive polymers poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) and poly(2-dimethylamino)ethyl methacrylate) (PDMAEMA) via surfactant-free emulsion polymerization or via "grafting from" polystyrene (PS) NPs. The dynamic interfacial tension (IFT) measurements at the toluene-water (Tol-H2O) interface reveal that when PDEAEMA and PDMAEMA are grafted from the surface of PS NPs the solubility of the grafted pH-responsive polymers in toluene is the key factor determining the NPs' interfacial adsorption. Under acidic conditions (pH < 6.0), PDEAEMA and PDMAEMA are protonated and show no solubility in toluene, and as a result, the grafted NPs do not adsorb at the Tol-H2O interface. Oppositely, under basic conditions (pH > 7.0), PDMAEMA dissolves in toluene and therefore the PDMAEMA-grafted NPs can adsorb at the Tol-H2O interface. Interestingly, when NPs are constituted of PDEAEMA, they can adsorb spontaneously at the Tol-H2O interface under acidic conditions (pH < 6.0) but not under basic conditions (pH > 7.0). In this case, the key factor determining the NPs' spontaneous adsorption at the Tol-H2O interface is the degree of softness of the NPs rather than the solubility of PDEAEMA in toluene. Furthermore, we found that the adsorption of NPs constituted of PDEAEMA- (pH 2.0-6.0) and PDMAEMA-grafted PS NPs (pH 7.0-10.0) at the Tol-H2O interface is a combination of diffusion-controlled and energy-barrier-controlled. The opposite trends observed for the interfacial attachment Δ E and activation energies Ea for the "constituted of" and "grafted from" NPs with pH suggest an opposite mechanisms of adsorption at the Tol-H2O interface. Finally, the synthesized NPs prove to be effective emulsifiers, where the phase of the Pickering emulsions can be changed dynamically by pH adjustment.

Effect of humic acids on bitumen films at the oil-water interface and on emulsion stability: Potential implications for groundwater remediation

This study investigates the effect of humic acids (HA) on the stability of toluene/water emulsions in the presence of bitumen. Bottle tests showed that emulsions were unstable with bitumen or HA added separately, but were stable when HA and bitumen were simultaneously present in the system. The stability of the mixed HA/bitumen system was explained on the basis of the synergistic interactions between HA and bitumen, which produced interfacial films with high compressional and shear visco-elastic moduli, as probed with the oscillating barrier method using a Langmuir trough and with an interfacial shear rheometer, respectively. The shear rigidity of HA and bitumen films was measured at pH 3, 5.5 and 10 and was found to exhibit a marked pH-dependence. The shear visco-elastic moduli were greatest at pH = 3, at which the electrostatic repulsion between HA and bitumen was likely lower than at pH 5.5 and 10. In addition to changing the bitumen’s films rigidity, HA affected the morphology of interfacial bitumen films, as probed in situ using Brewster Angle Microscopy at the toluene-water interface.

Deposition of Ag and Ag-Au nanocrystalline films with tunable conductivity at the water-toluene interface.

Thin films of Au, Ag and Ag–Au alloy nanocrystals extending to areas of several square centimetres are obtained by deposition at the interface of water and toluene. Toluene containing chlorotris(triphenylphosphine)silver(i) and/or chlorotriphenylphosphine gold(i) is reacted with aqueous tetrakishydroxymethylphosphonium chloride to obtain nanocrystalline films adhered to the interfacial region. Alloying was induced by varying the composition of the toluene layer. The composition change results in regular and reproducible variation in the transport characteristics of the films, with the initially metallic deposits turning non-metallic with increased Au content. The films at the interface were transferred to different substrates and characterised using atomic force microscopy, UV-visible spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy.

Facile synthesis of PtSnZn nanosheet thin film at oil–water interface by use of organometallic complexes: An efficient catalyst for methanol oxidation and p‐nitrophenol reduction reactions

PtSnZn nanosheet thin film with stable and high activity towards methanol electro‐oxidation was synthesized via a simple reduction of organometallic precursors including [PtCl2(cod)] (cod = cis,cis‐1,5‐cyclooctadiene) and [Sn(CH3)4] complexes, in the presence of [Zn(acac)2] (acac = acetylacetonate) complex at toluene–water interface. Catalytic activities of PtSnZn nanosheets were investigated in the p‐nitrophenol (p‐Nip) reduction and methanol oxidation reactions. The obtained results demonstrate that PtSnZn nanosheets exhibit a good electrocatalytic performance for methanol oxidation reaction, the catalytic activity of the PtSnZn nanosheets being at least 3.5 times higher than that of Pt nanoparticle thin film. Also, the apparent rate constant obtained for p‐Nip reduction with the PtSnZn nanosheets is at least 2.3 times higher than that for Pt nanoparticle thin film due to the appropriate interaction between platinum, tin and zinc metals and geometric properties of PtSnZn nanosheet thin film. Nanosheets are highly favourable for superior catalytic performances due to their geometric properties. A facile and efficient route was used to synthesize trimetallic alloy thin film at oil–water interface.

Correction to Interfacial Films Adsorbed from Bitumen in Toluene Solution at a Toluene–Water Interface: A Langmuir and Langmuir–Blodgett Film Approach

Correction to Interfacial Films Adsorbed from Bitumen in Toluene Solution at a Toluene–Water Interface: A Langmuir and Langmuir–Blodgett Film Approach

Characteristics of nanocrystalline thin films of cadmium sulphide deposited at the water-oil interface

Thin films of nanocrystalline CdS were obtained at the water-toluene interface by reacting cadmium diethyldithiocarbamate in toluene with aq. Na2S. Three parameters unique to the topical deposition scheme: the effect of column heights, stirring and the action of molecular surfactants are systematically investigated. The obtained nanocrystalline aggregates are characterized by scanning- and transmission electron microscopy, X-ray diffraction and profilometric measurements. Conditions for obtaining smooth device quality thin films have been identified during these experiments.

Palladium–cadmium sulfide nanopowder at oil–water interface as an effective catalyst for Suzuki–Miyaura reactions

A simple and effective strategy is described for the synthesis of Pd–CdS nanopowder by the reduction of an organopalladium(II) complex, [PdCl2(cod)] (cod = cis,cis‐1,5‐cyclooctadiene), in the presence of CdS quantum dots (QDs) at a toluene–water interface. We investigated the impact of addition of CdS QDs on catalytic activity of Pd nanoparticles (NPs). The Pd–CdS nanopowder functions as an efficient catalyst for Suzuki–Miyaura reactions for the formation of carbon–carbon bonds. There is a high electron density on Pd NPs and due to their high electron affinity they behave as an electron scavenger from CdS increasing the rate of oxidative addition, which is the rate‐determining step of the catalytic cycle, and, just as we expect, the C─C coupling reaction with the Pd–CdS nanopowder is faster and occurs in less time than that with Pd nanocatalysts. Compared to classical reactions, this method consistently has the advantages of short reaction times, high yields in a green solvent, reusability of the catalyst without considerable loss of catalytic activity and low cost, and is a facile method for the preparation of the catalyst.

Evidence of contact epitaxy in the self-assembly of HgSe nanocrystals formed at a liquid–liquid interface

The grazing incidence x-ray scattering results presented here show that the self-assembly process of HgSe nanocrystals formed at a liquid–liquid interface is quite different along the in-plane direction and across the interface. In situ x-ray reflectivity and ex situ microscopy measurements suggest quantized out-of-plane growth for HgSe nanoparticles of a size of about nm initially. Grazing incidence small-angle x-ray scattering measurements for films transferred from the water–toluene interface at various stages of reaction show that these nanoparticles first form random clusters with an average radius of 2.2 nm, giving rise to equally spaced rings of several orders. Finally, these clusters self-organize into face-centered cubic superstructures, giving sharp x-ray diffraction peaks oriented normal to the liquid–liquid interface with more than 100 nm-coherent domains. We also observed the x-ray diffraction pattern of the HgSe crystalline phase, with the superlattice peaks in these grazing incidence measurements of the transferred films. The electron microscopy and atomic force microscopy results support the x-ray observation of the self-organization of HgSe nanocrystals into close-packed superlattices. These results show that capillary wave fluctuation promotes the oriented attachment of clusters at the liquid–liquid interface, giving direct experimental evidence of contact epitaxy.