Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation

We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble’s surface temperature between 21–135 °C and its encapsulated water temperature between 21–74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12‐fold superior reaction rate constant for methylene blue degradation than at room temperature.     

Measurement of the surface tension of liquid marbles

The capillary rise and Wilhelmy plate methods have been used to study the "surface tension" of water marbles encapsulated with polytetrafluoroethylene (PTFE) powders of 1-, 35-, and 100-μm particle size. With the capillary rise technique, a glass capillary tube was inserted into a water marble to measure the capillary rise of the water. The Laplace pressure exerted by the water marble was directly measured by comparing the heights of the capillary rise from the marble and from a flat water surface in a beaker. An equation based on Marmur's model was proposed to calculate the water marble surface tension. This method does not require the water contact angle with the supporting solid surface to be considered; it is therefore a simple but efficient method for determining liquid marble surface tension. The Wilhelmy method was used to measure the surface tension of a flat water surface covered by PTFE powder. This method offers a new angle for investigating liquid marble shell properties. A discussion on the nature and the realistic magnitude of liquid marble surface tension is offered.     

Glassy carbon electrodes modified by multiwalled carbon nanotubes and poly(neutral red): A comparative study of different brands and application to electrocatalytic ascorbate determination

The electrochemical behaviour of glassy carbon electrodes coated with multiwalled carbon nanotubes (MWCNT) from three different sources and with different loadings has been compared, with a view to sensor applications. Additionally, poly(neutral red) (PNR) was electrosynthesised by potential cycling on bare glassy carbon and on MWCNT-modified glassy carbon electrodes, and characterised by cyclic voltammetry and scanning electron microscopy. Well-defined voltammetric responses were observed for hexacyanoferrate (II) oxidation with differences between the MWCNT types as well as from loading. The MWCNT and PNR/MWCNT-modified electrodes were applied to the oxidative determination of ascorbate, the electrocatalytic effects observed varying according to the type of nanotubes. Comparison was made with electrodes surface-modified by graphite powder. All modified electrode configurations with and without PNR were successfully employed for ascorbate oxidation at +0.05 V vs saturated calomel electrode with detection limits down to 4 μM; good operational stability and storage stability were also obtained.     

A simple transflective liquid crystal display with composite dielectric layer

ABSTRACT

A simple transflective liquid crystal display with a vertically aligned cell using a composite dielectric layer is demonstrated. The top substrate has a top planar common electrode, two transparent dielectric layers with different dielectric constants are coated on the bottom planar pixel electrode to generate linearly varying electric potential from the transmissive region (T region) to the reflective region (R region), while two bumpy reflectors are coated under the bottom substrate. In this device, with the composite dielectric layer, the common and pixel electrodes generate a strong electric potential in the T region and a relatively weak electric potential in the R region. Consequently, the T and R regions accumulate the same electro-optical characteristics. The simulation results show that the display exhibits reasonably low operating voltage, high optical efficiency and well-matched voltage-dependent transmittance (VT) and reflectance (VR) curves. Besides, the driving mode and the fabrication process of the transflective liquid crystal display are fairly simple and it is suitable for mobile applications.     

New Preparation Method of Nanocrystalline Materials by Impulse Plasma in Liquid

A new method to fabricate nanomaterials by using Impulse Plasma in Liquid is presented. Impulse plasma appears from inter-electrode space break-down in high potential difference between two electrodes submerged into a dielectric liquid, while the power supply is relatively small that is insufficient to excite an arc discharge. By changing the dielectric liquid, we can obtain metallic particles, oxides, carbides. This method does not require vacuum chamber and high energy, thus, can provide economical preparation of various types of nanomaterials. Nanocrystalline powder of titanium oxide was prepared using purified water as a dielectric liquid. Metallic nanoparticles of ytterbium, silver and copper were also prepared by the impulse plasma between a pair of the same material electrodes submerged in styrene. In addition, fullerene C₆₀ was synthesized by the impulse plasma in toluene. Nanoparticles of TiC, WC, TaC were also synthesized by the impulse plasma in styrene.     

Electrochemical Impedance Characterization of Nafion‐Coated Carbon Film Resistor Electrodes for Electroanalysis

Carbon film disk electrodes with Nafion coatings have been characterized by electrochemical impedance spectroscopy (EIS) with a view to a better understanding of their advantages and limitations in electroanalysis, particularly in anodic stripping voltammetry of metal ions. After initial examination by cyclic voltammetry, spectra were recorded over the full potential range in acetate buffer solution at the bare electrodes, electrodes electrochemically pretreated in acid solution, and Nafion‐coated pretreated electrodes in the presence and absence of dissolved oxygen. EIS equivalent circuit analysis clearly demonstrated the changes between these electrode assemblies. In order to simulate anodic stripping voltammetry conditions, spectra were also obtained in the presence of cadmium and lead ions in solution at Nafion‐coated electrodes, both after metal ion deposition and following re‐oxidation. Permanent changes to the structure of the Nafion film occurred, which has implications for use of these electrode assemblies in anodic stripping voltammetry at relatively high trace metal ion concentrations.     

二氧化钛涂覆多壁碳纳米管的制备及可见光催化活性

以多壁碳纳米管(MWCNTs)为反应性模板, 金属钛粉为钛源, 采用熔盐法制备碳化钛涂覆的MWCNTs中间体, 然后通过控制氧化制备二氧化钛涂覆的MWCNTs复合光催化剂. 考察了熔盐反应温度、MWCNTs和钛粉的摩尔比及氧化温度等对产物的结构和形貌的影响. 采用X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等技术对其进行了系统的表征; 以亚甲基蓝(MB)溶液的脱色降解为模型反应, 考察了催化剂的可见光(λ>420 nm)催化活性. 结果表明: 所制备的催化剂基本保持了原始MWCNTs的纤维状形貌, 二氧化钛涂层在MWCNTs表面分布均匀, 并与MWCNTs之间结合紧密, 形成了Ti－O－C键. MWCNTs增强了污染物亚甲基蓝在催化剂表面的吸附, Ti－O－C键的形成使得在二氧化钛价带附近形成了杂质能级, 提高了对可见光的吸收和利用, 因此所制备的TiO₂/MWCNTs复合光催化剂表现出较高的可见光催化活性.     

Polarisation-independent blue-phase liquid crystal microlens array with different dielectric layer

A fast response (sub-milliseconds) and polarisation-independent blue-phase liquid crystal (BPLC) microlens array with periodical double layer electrodes using different dielectric layers is proposed. The bottom double layer electrodes are coated with transparent and different dielectric layers to generate linearly varying electric potential from the centre to the edge, while the top planar electrode iridium tin oxide (ITO) electrode has a constant potential. As a result, gradient vertical electric fields are generated, and a gradient refractive index profile is obtained. When the applied voltage is changed, the focal length of the BPLC microlens array can be tuned from ∞ to 12.05 mm while keep a low operating voltage (~35V_rms). Besides, the driving mode (simplification driving) and fabrication process (using printing method or mold-pressing method) of the BPLC microlens array is very simple. The simulation results show that the BPLC microlens array is insensitive to the polarisation of incident light while keeping parabolic-like phase profile.     

An analysis of the kinetics of oxidation of ascorbate at poly(aniline)-poly(styrene sulfonate) modified microelectrodes

A detailed kinetic study is provided for the oxidation of ascorbate at poly(aniline)-poly(styrene sulfonate) coated microelectrodes. Flat films with a low degree of polymer spillover and a thickness much lower than the microelectrode radius were produced by controlled potentiodynamic electrodeposition. The currents for ascorbate oxidation are found to be independent of the polymer thickness, indicating that the reaction occurs at the outer surface of the polymer film. At low ascorbate concentrations, below around 40 mM, the currents are found to be mass transport limited. At higher ascorbate concentrations the currents became kinetically limited. The experimental data for measurements at a range of potentials are fitted to a consistent kinetic model and the results summarized in a case diagram. The results obtained for the poly(aniline)-(polystyrene sulfonate) coated microelectrode are compared to those for a poly(aniline)-poly(vinyl sulfonate) coated microelectrode and to the results of an earlier study of the reaction at poly(aniline)-poly(vinyl sulfonate) coated rotating disc electrodes. For poly(aniline)-poly(styrene sulfonate) the oxidation of ascorbate is found to proceed by one electron reaction whereas for poly(aniline)-poly(vinyl sulfonate) the reaction is found to be a two electron oxidation.     

Facile Nonenzymatic Glucose Electrode Composed of Commercial CuO Powder and Ionic Liquid Binder

Commercially available micro-sized CuO powder was dispersed in the mixture of ethanol and protonated betaine bis((trifluoromethyl)sulfonyl)amide ([Hbet][TFSA]), a hydrophobic amide-type protic ionic liquid (IL), to prepare a composite paste for the modification of screen-printed carbon electrode (SPCE) via spin-coating. The fabricated SPCE\CuO−IL composite-based electrode showed a comparable activity as that of the nanonized metal-oxide based electrodes towards the electrochemical oxidation of glucose in alkaline solutions. Hydrodynamic chronoamperometry tests performed at +0.55 V showed a linear dynamic response of the electrode over the concentration range of 1 μM–2.8 mM with a sensor-sensitivity of 0.16 μA μM⁻¹ in 0.1 M NaOH. The data also showed a linear dynamic response over the concentration range of 1 μM–4.6 mM with a sensor-sensitivity of 0.10 μA μM⁻¹ in 0.1 M NaOH with 0.1 M NaCl, indicating that the major interferant Cl⁻ had negligible effects on glucose detection . Ascorbic acid (AA) (in the physiological level) and ethanol also did not interfere with the detection. Detection of glucose in real samples showed the recovery ratios higher than 95 %. This study has clearly demonstrated that commercial CuO powder without nanostructure can provide sufficient reactivity to the electrocatalytic oxidation of glucose by using IL as the organic binder. Facile preparation of the micro-sized metal oxide-modified electrodes can be accordingly pursued.     

New insights into the Belousov-Zhabotinskii reaction derived from EQCM measurements at a gold electrode

Electrochemical quartz crystal microbalance experiments were used to study the classical Belousov-Zhabotinskii (BZ) homogeneous oscillating system. This system involves 2 × 10(-3) M Ce(III), 0.28 M malonic acid and 0.063 M bromate as the main initial components in 1 M sulfuric acid solution. The gold-evaporated electrodes on a 10 MHz AT-cut quartz crystal were used for potentiometric and amperometric studies while the changes in crystal frequency provided mass data. Under open-circuit conditions, during the BZ reaction, oscillations of the gold electrode potential in the range ca. 0.8 to 1.07 V (SCE) with a period about 80 s occurred. They were accompanied by periodic 10-15 ng [i.e. ca. 45-70 ng cm(-2)] changes in the electrode mass. At more positive potentials a decrease in electrode mass occurred, while the mass increased at more negative potentials. At a constant applied electrode potential, corresponding to either the upper or the lower potential limit attained under open-circuit conditions, periodic pulses of cathodic current occurred and were accompanied by mass changes. A continuous decrease in the electrode mass occurred at 1.06 V. A detailed examination of the gold electrode behavior in the solutions containing individual components of the system using cyclic voltammetry and quartz crystal microgravimetry provided the information needed to interpret the mass changes that occur in the complete system. No significant changes in the electrode mass occurred in sulfuric acid solution in the potential range where current and mass oscillations take place in the full BZ reaction solution. The same result was found in sulfuric acid solutions containing either Ce(III) or malonic acid. Dissolution of gold occurred in a sulfuric acid solution containing bromate or bromide ions. Adsorption of bromide ions on gold electrode occurred in Br(-)-containing sulfuric acid solution at more negative potentials. In the BZ system, dissolution of gold in the presence of oxidizing (bromate) and complexing (bromide) species causes the decrease in the electrode mass that accompanies the positive potential jump under open-circuit conditions, or the current pulse that occurs at more negative applied constant potentials. Cathodic current pulses occurring at a constant electrode potential (either 0.8 or 1.06 V) are associated with the reduction of Ce(IV) formed as a result of periodic homogeneous oxidation of Ce(III) by bromate. Bromide ions formed in the course of the BZ reaction appear to play a significant role in electrode mass changes, causing a mass decrease at more positive potentials due to dissolution of gold, and a subsequent mass increase at more negative potentials due to adsorption processes.     

Fabrication of Self-Oscillating Micelles with a Built-In Oxidizing Agent

Various biological behaviors are fueled by “respiration”, which is an example of catabolism. So far, we have reported various self-oscillating soft materials exhibiting bioinspired dynamic movements. These autonomous polymer systems are driven by the Belousov–Zhabotinsky (BZ) reaction, which is analogous to the tricarboxylic acid (TCA) cycle that is an integral part of respiration. However, in the BZ reaction, the external addition of an oxidizing agent is necessary to initiate the oxidation process, which is realized by intracellular moieties such as ubiquinone in living systems. Herein, we realized self-oscillating micelles that are driven without the external addition of an oxidizing agent. This was achieved by embedding the oxidizing source into the structure of the self-oscillating AB diblock copolymers. This strategy introduces a new function equivalent to intracellular oxidizing moieties, and is useful for the design of completely autonomous bioinspired materials.     

Advantages of using a mercury coated, micro-wire, electrode in adsorptive cathodic stripping voltammetry

A mercury coated, gold, micro-wire electrode is used here for the determination of iron in seawater by catalytic cathodic stripping voltammetry (CSV) with a limit of detection of 0.1 nM Fe at a 60 s adsorption time. It was found that the electrode surface is stable for extended periods of analyses (at least five days) and that it is reactivated by briefly (2 s) applying a negative potential prior to each scan. Advantages of this electrode over mercury drop electrodes are that metallic mercury use is eliminated and that it can be readily used for flow analysis. This is demonstrated here by the determination of iron in seawater by continuous flow analysis. It is likely that this method can be extended to other elements. Experiments using bismuth coated, carbon fibre, electrodes showed that the bismuth catalyses the oxidation of the important oxidants bromate and hydrogen peroxide, which makes it impossible to use bismuth based electrodes for catalytic CSV involving these oxidants. For this reason mercury coated electrodes retain a major advantage for catalytic voltammetric analyses.     

Fabrication of Self‐Oscillating Micelles with a Built‐In Oxidizing Agent

Various biological behaviors are fueled by “respiration”, which is an example of catabolism. So far, we have reported various self‐oscillating soft materials exhibiting bioinspired dynamic movements. These autonomous polymer systems are driven by the Belousov–Zhabotinsky (BZ) reaction, which is analogous to the tricarboxylic acid (TCA) cycle that is an integral part of respiration. However, in the BZ reaction, the external addition of an oxidizing agent is necessary to initiate the oxidation process, which is realized by intracellular moieties such as ubiquinone in living systems. Herein, we realized self‐oscillating micelles that are driven without the external addition of an oxidizing agent. This was achieved by embedding the oxidizing source into the structure of the self‐oscillating AB diblock copolymers. This strategy introduces a new function equivalent to intracellular oxidizing moieties, and is useful for the design of completely autonomous bioinspired materials.     

Recent progress in electrochemical oxidation of saccharides at gold and copper electrodes in alkaline solutions

This article reviews the progress made in the past 10 years, on electrochemical oxidation of saccharides in alkaline media for gold and copper electrodes. The mechanism and processes associated with the electrochemical oxidation of saccharides at native and surface coated electrodes continues to be of great interest. Despite the effort and various mechanisms proposed, still the need for an electrochemically active material that understands the complexity associated with saccharides continues to increase as their detection poses a challenge for bioanalytical chemistry and liquid chromatography.     

Ultra-trace level determinations of benzidine and dichlorobenzidine residues in surface water by liquid chromatography-electrospray ionization tandem mass spectrometry

A liquid chromatography-electrospray ionization tandem mass spectrometric method (LC-ESI-MS/MS) has been developed for the determination of benzidine (BZ) and 3, 3′-dichlorobenzidine (DCBZ) from surface water. Parent ion of DCBZ gave strong signal with ESI by dissolving with 15?mM ammonium formate, which is also used as mobile phase. Deuterated BZ (d8-BZ) was chosen as the internal standard (IS). BZ and DCBZ were extracted by solid-phase extraction on Oasis hydrophilic-lipophilic balance (HLB) from water at pH 8.0. The coefficients of variation of BZ and DCBZ were less than 13.1% and the detection limits were 0.004?ng?L^?1 for BZ and 0.7?ng?L^?1 for DCBZ using 0.5?L surface water. The detection limit shows fair lower value than the water quality criteria for BZ and DCBZ established by the US EPA. When the proposed method was used to analyze the target compounds in sixteen surface water samples, BZ was detected in a concentration range of 0.15–2.33?ng?L^?1 in four of sixteen surface water samples     

A blue-phase liquid crystal lens array based on dual square ring-patterned electrodes

We propose a blue-phase liquid crystal (BPLC) lens array based on dual square ring-patterned electrodes. A high dielectric constant layer is used to smoothen out the horizontal electric field and reduce the operating voltage. By creating a potential difference between the dual square ring-patterned electrodes, gradient electric fields are generated and lens-like phase profile is obtained. Besides, the focal length of the BPLC lens is adjustable with voltage changes and all simulation results indicate that the BPLC lens array is polarisation-insensitive.     

Effects of poly-(p-phenylene terephthamide) powder coated with polydopamine on ethylene-propylene-diene-terpolymer grafted maleic anhydride

In this paper, we reported a technique for the surface modification of poly-(p-phenylene terephthamide) (PPTA) powder coated with polydopamine (PDOPA). We used air oxidation to self-polymerize dopamine (DOPA) to ensure that the PPTA powder was coated. Our results indicate that the modified surface of PPTA powder enhances compatibility with the polymer matrix without damaging its structure. Additionally, it is possible to control the coating thickness of PDOPA by regulating the reaction time. The modified PPTA powder improved the comprehensive property of ethylene-propylene-diene-terpolymer grafted maleic anhydride (EPDM-g-MAH), and it proved that this method can enhance the strength and electric insulativity of EPDM-g-MAH.     

Amperometric detection of glucose using self-catalytic carbon paste electrodes

The analytical detection of d-glucose by means of self-catalytic carbon paste electrodes is described. In the construction of these electrodes, carbon powder has been modified with the redox liquid n-butylferrocene, which simultaneously serves both to help bind the paste together whilst also acting as a mediator in the enzymatic oxidation of d-glucose by glucose oxidase. The sensor then functions by monitoring the electrochemical oxidation of the constituent n-butylferrocene itself. Through testing in model glucose solutions, the electrodes were found to yield a linear response over a d-glucose concentration range of 2-20 mM. They were also successfully employed in the determination of d-glucose levels in a spiked blood sample, giving a detection limit of 0.8 mM (based on the 3sigma criterion).     

Hydrophobic silica sol-gel films for biphasic electrodes and porotrodes

Hydrophobic sol-gel films from methyltrimethoxysilane (MTMOS) are deposited onto glass and tin-doped indium oxide (ITO) coated glass substrates. Uniform and microporous films of ca. 200 nm thickness are obtained and investigated by scanning electron microscopy and by electrochemical techniques. From cyclic voltammograms for the oxidation of ferrocenedimethanol in aqueous 0.1 M KNO3 apparent diffusion coefficients and free volume data for processes within the film are derived and it is demonstrated that the film morphology can be controlled by the deposition timing. Two novel types of biphasic electrodes for observing liquid/liquid ion transfer reactions are introduced: (i) an ITO electrode coated with a hydrophobic sol-gel film and (ii) a hydrophobic sol-gel film on glass sputter-coated with 20 nm porous gold (porotrode). For the t-butylferrocene redox system deposited in the form of an organic liquid, very low and morphology dependent current responses are observed on modified ITO electrodes. However, the porotrode system allows biphasic electrode reactions to be driven with high efficiency and with no significant morphology effect of the hydrophobic sol-gel film. This type of nanofilm-modified electrode system will be of interest for biphasic sensor developments.