Gas-solution Interface Research Articles

Interface-assisted synthesis of Ag/Ceria composites for the detection and photodegradation of organic dyes

A simple method for creating Ag/CeO2 composites involves the reaction between components of an aqueous salt solution and ammonia vapor at the gas-solution interface. The concentrations of the reagents and the reaction time determine the structure and composition of the composite films formed on the solution surface. When the concentration ratio AgNO3/Ce(NO3)3 in the solution is 1/1, a composite film is formed consisting of Ag nanowires and Ceria nanoflakes. A model of the interaction at the liquid-gas interface is proposed. Ag/CeO2 composites have dual capabilities, enabling efficient photodegradation of Methylene Blue organic molecules and improved SERS detection of Rhodamine 6 G dye at concentrations as low as 10−9 mol/L. The synergistic effect of composition and morphology on properties was observed for the composites obtained within 7 minutes of interaction.

Investigation of crystal growth of CO2 hydrate in aqueous fructose solution for the potential application in carbonated solid foods

CO2 hydrate is applicable to solid carbonated foods. The hydrate crystal morphology, which represents the crystal size and shape, is an important characteristic that changes the texture of foods. We report an observational study of the crystal growth of CO2 hydrate in aqueous fructose solution. The difference between the phase equilibrium temperature and the experimental temperature, ΔTsub, is applied as an index of the driving force. Experiments were performed at ΔTsub range of 0.9 K to 5.4 K. At all ΔTsub, initial crystal formed at the gas-solution interface and grew along the interface. After covering the interface, the crystals grew in the liquid phase The individual crystals were identified as polyhedral with facets (ΔTsub = 0.9 K), skeletal crystals (ΔTsub = 2.0 K) and dendrites (ΔTsub = 3.0 K and 5.4 K). Based on these results, the potential effect of gas hydrate morphology on texture of foods has been discussed.

Anomalously High Fluorine Mobility in Tysonite-Like LaF3:ScF3 Nanocrystals: NMR Diffusion Data

Nanosized La0.93Sc0.07F3 superionic conductor with tysonite structure was obtained at the gas–solution interface after interaction of aqueous salt solution with gaseous HF. NMR diffusion studies show that homovalent substitution of La3+ by Sc3+ with a smaller ionic radius leads to around four orders of magnitude faster fluorine diffusion as compared with crystalline LaF3 and faster as in all previously studied nanosized LaF3 and heterovalent-doped nanosized La0.95Sr0.05F2.95. The homovalent doping is a new route to improve the conductivity of tysonite-structured nanomaterials.

Effect of Additives on the Foam Behavior of Aviation Coolants: Tendency, Stability, and Defoaming.

The foam tendency of aviation coolants (ACs) can be greatly influenced by additives. This study investigates the effect of additives on foam behaviors based on four commercial ACs and glycol aqueous solutions added with different additives. Experimental results show that the foam tendency of ACs can be greatly influenced by surfactants; however, inorganic salts have little effect on foam tendency. The volume of generated foam reaches up to 350 mL after ventilation for an AC with a surfactant, much larger than 40 mL of an AC with an inorganic salt. The surface tension of ACs reduces with the addition of surfactants, the lower the surface tension, the more the foam formation. Furthermore, the presence of arranged surfactants at the gas–solution interface can increase the intermolecular forces and enhance the liquid and viscosity of film elasticity, thereby enhancing the foam stability. Besides, the surfactants would weaken the gas diffusion of foams and affect the defoaming property of ACs accordingly.

Synthesis of the FeOOH Microtubes with Inner Surface Modified by Ag Nanoparticles.

Lepidocrocite (γ-FeOOH) microtubes with scroll morphology prepared by gas–solution interface technique (GSIT) have been modified by silver nanoparticles (Ag NPs). The successive ionic layer deposition (SILD) was first used for the synthesis of the Ag NPs on the lower surface of a solid film freely lying on the surface of a solution. The sizes of Ag NPs are about 15 nm after one synthesis cycle, and their diameters reach 35 nm after three SILD cycles. As a result of vacuum-drying, the modified film is transformed into microtubes with a diameter of about 10 μm and a length of 150 μm in such a way that the inner surface of the microtube is modified by Ag NPs. The catalytic properties of the microtubes have been observed by the decomposition of H2O2 in aqueous solution. The Ag/FeOOH microtubes move in hydrogen peroxide solutions with an average speed of 117 μm/s. This result is based on the synergetic effect between lepidocrocite nanosheets and Ag NPs, which results in the modified microtubes having enhanced mobility.

Interface-Assisted Synthesis of the Mn3-xFexO4 Gradient Film with Multifunctional Properties.

Anisotropic gradient materials are considered as promising and novel in that they have numerous functional properties and are able to transform into hierarchical microstructures. We report a facile method of gradient inorganic thin film synthesis through diffusion-controlled deposition at the gas-solution interface. To investigate the reaction of interfacial phase boundary controllable hydrolysis by gaseous ammonium, an aqueous solution of FeCl3 and MnCl2 was chosen, as the precipitation pH values for the hydroxides of these metals differ gradually. As a result of synthesis using the gas-solution interface technique (GSIT), a thin film is formed on the surface of the solution that consists of Mn2+(Fe,Mn)23+O4 nanoparticles with hausmannite crystal structure. The ratio between iron and manganese in the film can be adjusted over a wide range by varying the synthetic procedure. Specific conditions are determined that allow the formation of a Mn-Fe mixed oxide film with a gradient of composition, morphology, and properties, as well as its further transformation into microscrolls with a diameter of 10-20 μm and a length of up to 300 μm, showing weak superparamagnetic properties. The technique reported provides a new interfacial route for the development of functional gradient materials with tubular morphology.

Influence of Morphology of LaF3 Nano-crystals on Fluorine Dynamics Studied by NMR Diffusometry

Ionic dynamics in nano-structured 2D superionic conductors LaF3 obtained by a synthesis at the gas–solution interface has been analyzed using 19F NMR Static Field Gradient (SFG) diffusometry in a temperature range up to 800 K. The fluorine diffusion in 2D materials is significantly higher as compared to that in bulk LaF3 and is strongly dependent on the nano-crystalline sheet thickness. Its decrease from 18 nm to 6 nm leads to an increase of mobility by almost two orders of magnitude, resulting in an overall mobility enhancement of more than three orders of magnitude compared to mono-crystalline LaF3. Moreover, the activation energy is reduced from 1.2 eV for mono-crystals to 0.23 eV for 6 nm thin nano-crystalline powder samples.

Formation of Fe and Fe2O3 Microspirals via Interfacial Synthesis

AbstractA new method is reported for obtaining microspirals of iron‐based compounds by interfacial interaction. A thin film of Fe(OH)3 is obtained as a result of interaction between an aqueous solution of iron salts and gaseous ammonia. Upon drying, it is transformed into Fe(OH)3 microspirals with a diameter of up to 10 µm. These microspirals can be transformed into Fe2O3 microspirals by annealing in air. As a result of hydrogen reduction, Fe microspirals are formed. Both the annealing in air and that in hydrogen allow the retaining of the morphology. The material synthesized is characterized by electronic microscopy methods, X‐ray diffraction, diffuse reflectance Fourier transform infrared, and Mössbauer and photoelectron spectroscopies. The electrocatalytic properties of the electrode based on Fe2O3 microspirals as a catalyst of hydrogen evolution and the magnetic properties of Fe microspirals are tested. A hypothesis is proposed on the formation of microspirals by the gas–solution interface technique.

Synthesis of Fe(OH)3 Microtubes at the Gas–Solution Interface and Their Use for the Fabrication of Fe2O3 and Fe Microtubes

A straightforward and effective method is reported for obtaining microtubes of iron‐based compounds by interfacial interaction between a solution and gaseous reagents. A thin amorphous film of Fe(OH)3 was synthesized on the surface of a mixed FeCl2/FeCl3/ascorbic acid aqueous solution as a result of the interaction with gaseous ammonium. When dried in air, the film was oxidized and transformed into microtubes. These Fe(OH)3 microtubes were converted into α‐Fe2O3 ones by annealing in air. As a result of thermal hydrogen reduction, α‐Fe microtubes were formed. Both the annealing in air and reduction in a hydrogen flow at a temperature of 1,000 °C preserve the tubular morphology of the product. The microtubes synthesized were characterized by optical and scanning microscopy, structural and compositional analyses, and Mössbauer spectroscopy. A hypothesis is proposed about the model of microtube formation resulting from the chemical reaction at the gas–solution interface.

Flower-like silver nanocrystals: facile synthesis via a gas–solution interface technique

In this paper, flower-like Ag nanocrystals and their fractal networks were successfully synthesized by gas–solution interface technique at the surface of AgNO3 water solution with the assistance of ammonium citrate and of gaseous N2H4 used as reductant. The synthesized flower-like silver structure consisted of a large number of petal-like silver nanoplates. They were characterized by scanning and transmission electron microscopy, absorption UV–Vis spectroscopy, and X-ray diffraction. In addition to the standard silver fcc modification, the nanostructures contained the hexagonal polymorph (4H-Ag) in the amount of about 5%. The effect of pH of the solution on the morphology of nanoparticles and on the silver crystal structure was examined. Depending on the time of treatment with gaseous hydrazine, it was possible to obtain either separate flower-like nanoparicles and their fractal networks, or continuous films formed by rather closely packed petal-like nanoparticles. The surface-enhanced Raman scattering effect was observed, and the most intense interaction of laser beam with the silver nanoparticles occurred when the solution side of the synthesized film was irradiated.

Facile synthesis of 2D silver nanocrystals by a gas–solution interface technique

The templateless and surfactant-free facile synthesis of 2D silver nanocrystals was carried out for the first time by a gas–solution interface technique using an aqueous solution of AgOAc and gaseous N2H4 as reactants.

The effect of microtube formation with walls, containing Fe3O4 nanoparticles, via gassolution interface technique by hydrolysis of the FeCl2 and FeCl3 mixed solution with gaseous ammonia

The effect of microtube formation with walls, containing Fe3O4 nanoparticles, via gassolution interface technique by hydrolysis of the FeCl2 and FeCl3 mixed solution with gaseous ammonia

Effect of N2/O2 composition on inactivation efficiency of Escherichia coli by discharge plasma at the gas-solution interface

PurposeBacterial inactivation by discharge plasma is affected by many factors including gas type. No uniform conclusion for the effect of working gas type on the inactivation efficiency has been reached until now. In this work, the gas type and composition on the bactericidal efficiency of discharge plasma were systemically investigated. MethodsThe inactivation behaviors of Escherichia coli (E. coli) by corona discharge plasma at the gas-solution interface produced using needle high-voltage electrode above the liquid with shielding O2, N2, and air were systemically compared. The reactive species produced in solution were detected and their correlation with the bactericidal efficiency was found. ResultsAir plasma has strong sterilization capability, followed by N2 plasma, while O2 plasma has the lowest sterilization capability. The bactericidal abilities of different gas plasma is in positive correlation with the produced nitrite concentration in solution. ConclusionThe reason for the gas type and composition to influence the sterilization capability was due to that they influenced the nitrite production in solution which further reacted with plasma-produced hydrogen peroxide in acidified medium to form a strong oxidant peroxynitrite. The produced peroxynitrite could damage both the membrane and DNA, especially the former, and consequently inactivate the bacteria lethally.

Facile synthesis of scandium fluoride oriented single-crystalline rods and urchin-like structures by a gas–solution interface technique

ScF3 rod-like oriented crystals and urchin-like structures were synthesized at the gas–solution interface for the first time.

Sodium Atom Emission from Aqueous Surfactant Solutions Exposed to Ultrasound.

Emission from electronically excited sodium atoms (Na*) was observed when argon saturated aqueous solutions of the anionic surfactants, sodium dodecyl sulfate, sodium octyl sulfate, sodium 1-pentanesulfonate, and sodium 1-octanesulfonate were sonicated using 358 kHz ultrasound. The same emission band, centered at about 590 nm, was also obtained in aqueous NaCl solutions, although a ∼100-fold higher concentration than that used for the surfactant solutions was required to obtain an emission of comparable intensity. The results have been interpreted in terms of the surfactant adsorbing at the gas-solution interface of the bubbles generated by the ultrasound, generating an electrostatic surface potential, and attracting Na+ counterions to the bubble surface. It is reasoned that Na+ ions are simultaneously reduced and electronically excited at the bubble-solution interface during the final stages of the collapse phase of the acoustically driven bubble. It is proposed that sodium ion bound water molecules reduce interfacial Na+ under the extreme, perhaps supercritical, conditions the interface experiences on bubble implosion.

Influence of Bubbling of “Passive” Gases on the Properties of Water and Aqueous Solutions of Sodium Chloride

It is experimentally established that, in the course of bubbling of “passive” gases through the aqueous solutions of NaCl, we observe not only the wash-out of soluble CO2 and O2 but also the continuous generation a new gas–solution interface, which has a pronounced acid character. This is why bursting of gas bubbles on the surface is accompanied by the formations of acid aerosols and the appearance of a specific bubbling chemical effect (BCE), when the pH value of the solution independently increases (alkaline BCE) or decreases (acid BCE). The form of the BCE is determined by the type of aerosol (finely or coarsely divided) and the rate of its removal from the system. In distilled water, the BCE is not observed. Structural changes in water may serve as a cause of the acidity of interface in gas bubbles.

Aggregation behavior of derivatives of sodium alginate and N-octyl-β-d-glucopyranoside in aqueous solutions

Abstract In this study, the aggregation of N-octyl-β- d -glucopyranoside (OGP) and cholesteryl grafted sodium alginate derivative (CSAD) in solutions was investigated by surface tension method, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. Results showed that cholesteryl of CSAD and OGP were adsorbed competitively to the gas–solution interface. Four different conformations of complexes were found with the increasing of OGP concentration (C). When C 2 ), the quantity of pearl-chain structure complexes increases, they interact to form core–shell structure complexes, and several core–shell structure complexes formed short string-structures by association of CSAD molecule. When C > C 2 , adsorption amount of OGP to CSAD reached saturation, OGP molecules formed small single OGP micelles, while the string-structures were dissolved because the cholesteryl among the micelles were replaced by the single OGP micelles.

Interfacial nanobubbles are leaky: permeability of the gas/water interface.

Currently there is no widespread agreement on an explanation for the stability of surface nanobubbles. One means by which several explanations can be differentiated is through the predictions they make about the degree of permeability of the gas-solution interface. Here we test the hypothesis that the gas-solution interface of surface nanobubbles is permeable by experimental measurements of the exchange of carbon dioxide. We present measurements by attenuated total reflection Fourier transform infrared (ATR-FTIR) and atomic force microscopy (AFM), demonstrating that the gas inside surface nanobubbles is not sealed inside the bubbles, but rather exchanges with the dissolved gas in the liquid phase. Such gas transfer is measurable by using the infrared active gas CO2. We find that bubbles formed in air-saturated water that is then perfused with CO2-saturated water give rise to distinctive gaseous CO2 signals in ATR-FTIR measurements. Also the CO2 gas inside nanobubbles quickly dissolves into the surrounding air-saturated water. AFM images before and after fluid exchange show that CO2 bubbles shrink upon exposure to air-equilibrated liquid but remain stable for hours. Also air bubbles in contact with CO2-saturated water increase in size and Ostwald ripening occurs more rapidly due to the relatively high gas solubility of CO2 in water.

Molecularly Smooth Single-Crystalline Films of Thiophene–Phenylene Co-Oligomers Grown at the Gas–Liquid Interface

Single crystals of thiophene–phenelyne co-oligomers (TPCOs) have previously shown their potential for organic optoelectronics. Here we report on solution growth of large-area thin single-crystalline films of TPCOs at the gas–liquid interface by using solvent–antisolvent crystallization, isothermal slow solvent evaporation, and isochoric cooling. The studied co-oligomers contain identical conjugated core (5,5′-diphyenyl-2,2′-bithiophene) and different terminal substituents, fluorine, trimethylsilyl, or trifluoromethyl. The fabricated films are molecularly smooth over areas larger than 10 × 10 μm2, which is of high importance for organic field-effect devices. The low-defect structure of the TPCO crystals is suggested from the monoexponential kinetics of the PL decay measured in a wide dynamic range (up to four decades) and from low crystal mosaicity assessed by microfocus X-ray diffraction. The TPCO crystal structure is solved using a combination of X-ray and electron diffraction. The terminal substituents affect the crystal structure of TPCOs, bringing about the formation of a noncentrosymmetric crystal lattice with a crystal symmetry Cc for the bulkiest trimethylsilyl terminal groups, which is unusual for linear conjugated oligomers. Comparing the different crystal growth techniques, it is concluded that the solvent–antisolvent crystallization is the most robust for fabrication of single-crystalline TPCOs films. The possible nucleation and crystallization mechanisms operating at the gas–solution interface are discussed.

Inactivation of Microcystis aeruginosa by DC glow discharge plasma: Impacts on cell integrity, pigment contents and microcystins degradation

We proposed a method to inactivate M. aeruginosa by using discharge plasma taking at the gas-solution interface supplied by DC power. Multiple analysis techniques including fluorescence excitation–emission matrix (EEM) and flow cytometry (FCM) were used to reveal the inactivation mechanism of M. aeruginosa. The photosynthetic pigment contents including phycocyanin, chlorophyll and metabolites were examined quantitatively. The DC glow discharge plasma caused an increased level of reactive oxygen species (ROS), and the damage of M. aeruginosa cells are mainly attributed to the oxidative stress including OH attack and H2O2 oxidation. Our findings demonstrate that plasma oxidation is a promising technology for inactivation of M. aeruginosa cells with simultaneous removal of microcystins and so it may lead us to a new route to efficient treatment of cyanobacterial blooms.