Low Double Layer Research Articles

High-efficient of graphene nanocomposite: Application to rapidly simultaneous identification and quantitation of fat-soluble vitamins in different matric samples

An alternative approach for rapid, highly sensitive and specific analytical sensor for the simultaneous determination of fat-soluble vitamins (A, D, E and K) in different matric samples was demonstrated using our developed sensor by graphene nanocomposite. The adsorptive square wave voltammetry was used to determine the amounts of vitamin A, D, E and K in infant milk, yogurt and parsley. Various analytical conditions were investigated to enhance the best performance of the proposed method. Under optimal conditions, a good linear relationship was obtained between the anodic current and the concentration of vitamins within the range from 0.02 μg mL −1 to 1 μg mL −1 . The limits of detection were found to be 0.0086, 0.0063, 0.0075 and 0.0071 μg mL −1 for vitamin A, D, E and K, respectively. The accuracy of the proposed sensor has been validated with the standard AOAC guideline. The reproducibility has also been demonstrated by repeating the experiments between sensor-to-sensor. Compared to conventional chromatographic methods, the electrochemical sensor outlined here shows a comparable performance yet faster, simpler, and cheaper approach that enables the continuous monitoring of the total quantity of vitamin A, D, E and K in various samples with good reliability, sensitivity, selectivity and accuracy. • A sensitive electroanalysis for the simultaneous determination of fat-soluble vitamins was presented. • Greatly enhanced in S/B ratio and low double layer capacitance were achieved from using proposed material. • The usual fouling effect from fat-soluble vitamins analysis was not observed in the developed sensor. • The selectivity was achieved without prior sample preparation and can be applied for various samples.

Nanostructured boron-doped diamond electrode for seawater salinity detection

Electrodes with high response and stability are urgently required to reach a steady and accurate measurement of seawater salinity. Herein, boron-doped diamond (BDD) is for the first time considered as a promising alternative to commercial platinum black in seawater salinity detection due to their considerable conductivity and outstanding stability. However, the intrinsical low double layer capacitance (DLC) of planar BDD film (BDDF) electrodes affect their response in the detection. To solve these problems, boron-doped diamond nanorod forest (BDDNF) electrodes are fabricated via hot filament chemical vapor deposition. Noted, four orders of magnitude larger of DLC (2820 μF/cm2) than BDDF (0.35 μF/cm2) is achieved on BDDNF due to a much enhanced electroactive surface area which is calculated to be 1.47 times larger than BDDF. Benefited from the enhanced DLC and accelerating diffusion resulted by the nanostructure, the response of BDDNF exhibits an enhancement by a factor of 1.5 compared to BDDF at the salinity of 40 ‰. Moreover, in striking contrast to commercial platinum black electrode, the obtained BDDNF electrodes exhibit outstanding stability thanks to the increased amount of carbon oxygen functional groups on BDDNF surface. This work greatly promises the potential applications of BDDNF electrodes in seawater salinity detection.

Zn Wetted CeO2 Based Composite Galvanization: An Effective Route To Combat Biofouling.

The present paper reports for the first time the development and application of novel Zn wetted CeO2 (Zn/CeO2) composite galvanic zinc coating to combat microbial induced corrosion (MIC). Zinc metal-metal interaction causes the effective incorporation of composite into the galvanic coating and accordingly increases the active sites for antibiofouling activity. The developed coatings are explored for their anticorrosion/antibiofouling characteristics toward MIC induced by cultured seawater consortia. Enhanced antibiofouling activity of the composite galvanic coating is achieved due to the tuned content of 28 wt % Zn and 34 wt % of Ce. High charge transfer resistance as high as 4.0 × 1014 Ω cm2 and low double layer capacitance as low as 3.99 × 10-8 F are achieved by tuning the structure and composition of the coating. The synergistic effect of Zn and Ce ensures the stability and corrosion resistance of the coatings in a corrosive bacterial environment. Evident decreases in the bacterial attachment and biofilm formation are illustrated using antibiofouling assay. The antibiofouling activity is attributed to the effective reduction of Ce4+ to Ce3+ and the shuttling characteristics of oxidation state of CeO2. This impairs the cellular respiration and results in bacterial death. Thus, it can be used as an effective coating to protect the steel based equipment in corrosive marine environments to combat marine microorganisms and their interactions. The present study also paves the scope for exploration of similar effective protective systems.

Towards a Deeper Understanding of the Anticorrosive Properties of Hydrazine Derivatives in Acid Medium: Experimental, DFT and MD Simulation Assessment

The corrosion inhibition properties of two compounds namely, 1,2-dibenzylidenehydrazine (C1) and 1,2-bis(1-phenylethylidene)hydrazine (C2) for mild steel (MS) in 1.0 M HCl were studied by using weight loss, electrochemical techniques, density functional theory (DFT), and molecular dynamic (MD) simulations. Experimental results show that both C1 and C2 behave as mixed-type inhibitors. Both inhibitors showed efficient binding with metal surface. With C1 exhibiting the highest inhibition efficiency, resulting in low double layer capacitance and a high polarization resistance. The mechanism of inhibition action of the studied compounds was discussed in the light of the DFT and MD simulations studies. MD simulation revealed a nearly flat configuration for the C1 molecule on the metal surface, with more negative interaction energy in comparison to C2. Theoretical results are in line with the experimental results.

Большепролетные металлические купольные покрытия и их возведение

The article presents the main types of geometrical and structural systems of steel frameworks of metal dome roofs. Based on the geometrical system, three main types of metal domes can be specified: ribbed domes, ribbed domes with rings, and lattice domes. Lattice domes can be cyclically symmetrical with repeating sectorial patterns, or geodesic, that are based on geodesic polyhedrons, inscribed in a sphere. Based on the structural system, the frameworks of ribbed domes can have single chord or dou- ble chord ribs. Geometric system of the framework of a large-span metal dome governs the method of its erection which in its turn defines the structural solutions for the elements of the framework and the sequence of their assembly. The paper describes the following methods of erection of large-span domes: erection by crane from the ground with temporary supports, placement of the complete structure or large elements of the dome, and cantilever erection. The examples of large-span metal domes built in different countries of the world are reviewed with respect to the method of construction used. General characteristics of the structural system of the framework of each dome are presented. The examples are used to demonstrate that the method of construction of a large-span metal dome roof is dependent on the geometric system of its framework. It is noted that metal domes are widely used as structural solutions for roofs of buildings of different types. It is noted that erection with temporary supports of different types, or ground assembly are mostly used for the construction of relatively low double layer domes, or high single-layer domes. For large-span double-layer metal domes of considerable high the method of cantilever erection is usually preferred.

Robust Diamond Electrodes for Electrochemical Applications

With one of the widest potential windows of any solid electrode material, boron doped diamond (BDD) has proven excellence as an electrochemical tool. From water treatment and chemical synthesis to electrochemical analysis and sensing, BDD has applications in a variety of sample media. This combined with its’ stability, low background current, and low double layer capacitance make BDD specifically useful in trace detection, such as the determination of toxic heavy metals and polycyclic aromatic hydrocarbons (PAHs) in water. We have developed several BDD electrode technologies, each tailored to a specific electroanalytical application. With a Nafion coated BDD optically transparent electrode (OTE) we engineered a fluorescence based spectroelectrochemical sensor for a common PAH, 1-hydroxypyrene, achieving a detection limit of 80 nM (17 ppb). With this, we fabricated BDD microelectrode arrays (MEAs) for the detection of toxic heavy metal ions where we obtained parts-per-trillion (ppt) detection limits for lead (Pb) using measurements taking no longer than 2 minutes. We also designed and produced BDD rod electrodes for general electroanalytical applications. These BDD rod electrodes exhibit superb electrochemical redox processes where we observed peak separations of 65 mV or less in cyclic voltammetry (CV) of potassium ferricyanide, K3Fe(CN)6. Lastly, we developed BDD electrode stacks for electrochemical oxidation processes including, general TOC/COD reduction, perfluoroalkyl substance (PFAS) degradation, and ammonia (NH3) removal. Near complete removal of PFAS and NH3 from wastewater samples­ was observed. This work further exemplifies BDD as an excellent electrode material while broadening its’ sensing applications and electrochemical capability. Figure 1

Polymer lead pencil graphite as electrode material: Voltammetric, XPS and Raman study

Mechanical pencil leads were studied as disposable, low-cost electrodes. Lateral surfaces of mechanical pencil leads branded as “polymer” show high electron transfer rates for hexaamineruthenium chloride, potassium ferricyanide, ascorbate, ferric chloride and dopamine electrochemical probes, and are significantly better electrode materials than either classic woodcase clay–graphite pencil compositions or non-polymer mechanical pencil leads. Best polymer leads outperform glassy carbon, basal and edge graphite and boron-doped diamond electrodes. In addition to electrochemical experiments, the studied pencil leads were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy. High content of sp3 hybridized carbon (up to 80%) with a low degree of surface oxidation and occurrence of silicon monoxide (SiO) on the surfaces of the polymer pencil leads were found using X-ray photoelectron spectroscopy. Low double layer capacitance values of similar magnitude as that found for boron-doped diamond electrodes are at the origin of favourably low background currents on the polymer pencil lead electrodes. SiO containing polymer pencil lead electrodes allow electrochemical analysis that is more sensitive than common carbon electrodes, as demonstrated by voltammetry of adenine and xanthine.

Influence of Fluoride Ion on the Performance of Pb-Ag Anode During Long-Term Galvanostatic Electrolysis

Anodic potential, morphology and phase composition of the anodic layer, corrosion morphology of the metallic substrate, and oxygen evolution behavior of Pb-Ag anode in H2SO4 solution without/with fluoride ion were investigated and compared. The results showed that the presence of fluoride ions contributed to a smoother anodic layer with lower PbO2 concentration, which resulted in lower double layer capacity and higher charge transfer resistance for the oxygen evolution reaction. Consequently, the Pb-Ag anode showed a higher anodic potential (about 35 mV) in the fluoride-containing electrolyte. In addition, the fluoride ions accelerated the detachment of loose flakes on the anodic layer. It was demonstrated that the anodic layer formed in the fluoride-containing H2SO4 solution was thinner. Furthermore, fluoride ions aggravated the corrosion of the metallic substrate at interdendritic boundary regions. Hence, the presence of fluoride ions is detrimental to oxygen evolution reactivity and increases the corrosion of the Pb-Ag anode, which may further increase the energy consumption and capital cost of zinc plants.

Electrochemical impedance spectroscopy study of CuO and Cu coating systems

Purpose This paper aims to analyse the coating behaviour in corrosion environment as well as to evaluate the best percentage amount of copper oxide and copper needed for organic coating in order to prevent the corrosion degradation. Electrochemical impedance spectroscopy (EIS) studies have been conducted in order to evaluate the corrosion performance of polyester-epoxy-copper oxide and polyester-epoxy-copper coating systems. Design/methodology/approach The availability of this modem instruments is used to obtain impedance data as well as computer programs to interpret the results that made the technique popular. In addition, EIS is well suited to the study of polymer-coated metals. Findings The results showed that samples containing 25 weight per cent of copper oxide and copper (90P25CuO and 90P25Cu) obtained the excellent corrosion properties from the first day up to 30 days of NaCl immersion. The highest corrosion resistance values obtained by 90P25CuO and 90P25Cu on the 30th day were 7.107 × 108 O and 5.701 × 108 O, respectively, with lower double layer capacitance of 1.407 × 10−9 Farad and 3.935 × 10−9 Farad, respectively. Moreover, the water uptake gained by these two coating samples was the lowest at the end of immersion, which was 0.0084 for 90P25CuO and 0.1592 for 90P25Cu, showing that the sample has good corrosion performance. Originality/value This paper discussed on the highest corrosion resistance, double layer capacitance and the water uptake of the copper (Cu) and copper oxide (CuO) coating system obtained from the EIS measurements.

Effect of Triton X-100 on the double layer capacitance and conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films

Among conducting polymers, PEDOT:PSS is a promising electrode material for supercapacitors, due to stability and simple processability of the polymer. However, a thin film of spin coated PEDOT:PSS shows a compact structure with relatively low double layer capacitance. In order to enhance the film porosity, a surfactant (Triton X-100) has been added to the polymer solution before spin coating. In this work, the effect of concentration of Triton X-100 on the double layer capacitance and conductivity of the PEDOT:PSS film has been studied. Different electrodes were fabricated with PEDOT:PSS samples that were prepared with different levels of Triton X-100. A peak specific double layer capacitance of 20F/g was achieved in the electrode with 3.0wt% of Triton X-100 which was ∼10 times larger than the capacitance in the electrodes with 0.0 and 5.0wt% surfactant. Additionally, the conductivity of the PEDOT:PSS films were enhanced with application of Triton X-100 by at least 20 times. The SEM (scanning electron microscopy) images of the electrodes show correlation that the increase in capacitance with 3.0wt% surfactant was due to the augmentation of porosity of the films structure.

Boosting the electrochemical properties of diamond electrodes using carbon nanotube scaffolds

Diamond is a very attractive electrode material for analytical measurements including for instance bio-sensing. However, it suffers from a relatively low double layer capacitance and high impedance when it comes to the development of supercapacitors or neural interfaces, applications for which it could also be extremely promising. One way to increase the double layer capacitance of the material is to increase its specific surface area. Here we propose here to use vertically aligned carbon nanotubes (VACNTs) with high surface areas as a template onto which boron doped diamond is grown. The resulting composite was found to exhibit a double layer capacitance as high as 0.58mFcm−2 and very low impedance when compared to planar diamond electrodes in phosphate buffer saline solution. The influence of the VACNT length as well as of the thickness of the diamond coatings on the electrode performances were also investigated and are discussed in this paper.

Development of Silica Glass Coatings on 316L SS and Evaluation of its Corrosion Resistance Behavior in Ringer’s Solution

Sol-gel derived silica glasses have many promising features, including low-temperature preparation as well as chemical and physical stability. Two silica glasses with Si100 and Si80 composition were prepared to understand the factors contributing to the rate of bioactivity. The effects of pH, solution aging temperature, and molar ratio of H2O/tetraethyl orthosilicate (TEOS) were studied, and the obtained powder sample was characterized by Fourier transform infrared spectroscopy, X-ray diffraction studies, and scanning electron microscopy. The synthesized silica glasses were deposited on 316L SS by the spin coating method at the optimized speed of 2000 revolutions per minute. The corrosion resistance behavior of the coatings was determined by (1) open-circuit potential vs time of exposure, (2) electrochemical impedance spectroscopy, and (3) cyclic polarization in Ringer’s solution. A higher breakdown potential (E b) and repassivation potential (E p) value with lower current density was obtained from cyclic polarization. Similar results were observed from impedance analysis with higher charge transfer resistance (R ct) and lower double layer capacitance (C dl) indicating the corrosion resistance behavior of the coatings compared with the uncoated 316L stainless steel. From the results, it was observed that both Si100 and Si80 glass coatings had a positive effect on the corrosion resistance behavior. An adhesive strength of 46 MPa and 45 MPa was obtained for the Si100 and Si80 coatings, respectively. An accelerated leach out study was carried out by impressing the potential at their breakdown potential to determine the effect of glass coating for long-term contact between the implant and a normal biological medium.

Poly( o-phenylenediamine) coatings on mild steel: Electrosynthesis, characterization and its corrosion protection ability in acid medium

Strong adherent electroactive conductive polymer films of poly( o-phenylenediamine) (PoPD) have been electrodeposited on mild steel (MS) by potentiodynamic method using 0.1 M oxalic acid solution in 0.05 M of o-phenylenediamine ( o-PD) monomer. Thin, adherent and transparent layers of PoPD contains ladder conductive polymer structure with phenazine skeleton were confirmed by Fourier Transform Infra Red (FT-IR) and Ultra Violet visible (UV–vis) spectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analysis. The corrosion protection performance of the PoPD coatings on MS in 0.5 M hydrochloric acid (HCl) was investigated using Open Circuit Potential (OCP), potentiodynamic polarization and Electrochemical Impedance Spectroscopic (EIS) measurements. OCP and polarization measurements have shown that the MS coated with PoPD maintain the potential in the passive state whereas the uncoated MS exhibit potentials in the active state indicating that significant protection is achieved by the polymer coating. High charge transfer resistance (R ct) and low double layer capacitance (C dl) values from EIS suggest that the PoPD film exhibits excellent corrosion inhibition behavior on MS in acid environment.

Electrochemical analysis of the adsorption and desorption behaviors of carboxylic acid and anhydride monomers onto zinc surfaces

The interfacial bondings formed between succinic acid and myristic acid, as well as succinic anhydride molecules with a set of differently treated zinc substrates have been investigated using infrared reflection absorption spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The compounds were selected to model typically used carboxylic-based adhesives and coatings. Moreover, the adsorption kinetic has been evaluated by means of chronoamperometry (CA) and chronovoltammetry measurements. XPS results showed a relation between the amount of carboxylates formed by adsorption of succinic acid/myristic acid and the hydroxyl fraction presented on the surfaces as proved by a higher electron transfer in CA. On the other hand a set of oxidative/reductive interactions was detected during the adsorption of succinic anhydride, in turn proving a spontaneous ring opening and adsorption mechanism. A clear relationship between the amount of adsorbents and surface hydroxyls/carbonates was detected for the adsorption of succinic anhydride. The extent to which the formed carboxylates resisted negative potentials was also investigated by cyclic voltammetry (CV) in an aqueous solution. The coordinative bonding of a bifunctional carboxylic acid group to the oxide surface was found to be not stable in the presence of a negative potential, while a monofunctional carboxylic acid group could resist displacement by water for a prolonged period of time. On the other hand, a low double layer capacitance was obtained after the adsorption of succinic anhydride, which was related to a change in potential of zero charge (PZC) upon the adsorption.

Development and Evaluation of Gold 3D Cylindrical Nanoelectrode Ensembles

AbstractGold 3D cylindrical nanoelectrode ensembles (NEEs), 100 nm in diameter and 500 nm in length were prepared by electroless template synthesis in polycarbonate filter membranes, followed by selective controlled chemical etching. The morphology of the nanowires and cylindrical NEEs was imaged by scanning electron microscopy. The protruding nanoelectrodes were in good parallel order. EDX study showed that the nanoelectrode elements consisted of pure gold. The electrochemical evaluation of the 3D electrodes was conducted using the well known [Fe(CN)6]3−/[Fe(CN)6]4− couple. Cyclic voltammgrams (CV) show a very low double layer charging current and a higher ratio of signal to background current than 2D disc NEEs. Electrochemical impedance spectroscopy (EIS) indicates that the 3D cylindrical NEEs effectively accelerate the charge transfer process, which is in consistent with the results of CV. The linear relationship with a slope of 0.5 between lg Ipc and lg v shows that linear diffusion is dominant on the 3D cylindrical NEEs at conventional scan rates.

Adsorption Behaviour of Laprol 2402 C on a Tin Electrode

SUMMARYVoltammetry and EIS were used to study the adsorption behaviour of laprol 2402 C (the copolymer of ethene and propene oxides) on a Sn electrode in strongly acid Sn(II) sulphate solutions. At least two states of adsorption layers were found to exist depending on cathodic polarisation. Adsorption of laprol, observed at low or sufficiently high cathodic polarisations, results in a moderate decrease in the double layer capacitance (from 100 to 18 μF cm2) and is accompanied by 100-fold reduction in the exchange current density. A pronounced inhibition of Sn(II) reduction takes place in the vicinity of-0.3 V where voltammograms acquire a negative slope. High negative charge transfer resistance ranging from -2.3 to -4.5 kΩ cm2 and low (7–9 μF cm 2) double layer capacitances are indicative of the formation of a more compact surface layer.

Nanocrystalline carbon film electrodes generated and patterned by UV-laser ablation of polystyrene

A carbon conductive film consisting of nanometer sized domains has been patterned by scanning photoablation of polystyrene. The film formation involves the photoablation of a highly insulating polymer, and the redeposition of conductive carbon fragments. This film has been investigated by scanning electron microscopy, atomic force microscopy, microRaman spectroscopy, electrical conductivity and standard electrochemical measurements. Film deposition under different gas flow conditions has revealed major differences in the electrical and electrochemical properties of the material. Cyclic voltammetry and double layer capacitance measurements have indicated the formation of a conductive layer with a high specific area when generated in ambient atmosphere. Inert atmospheres like nitrogen and argon lead to conducting films with low double layer capacitance values (10 µF cm-2), whereas an air atmosphere leads to conducting films with supercapacitance values (5 mF cm-2). This large difference in capacitances is discussed in terms of the photochemical effects of the ambient atmosphere during the polymer treatment.

EIS of cathodically deposited wet paint films prior to the stoving process

Cathodic deposition of paint is industrially exploited for the application of the polymer primer to metal mass ware surfaces. EIS was systematically employed for the first time for the characterization of the wet paint film prior to stoving on Al and Fe. A distinct advantage is the lower impedance in comparison to stoved paints. The Bode diagrams show two well-separated processes in most cases. The low frequency part is attributed to the electrochemical impedance at the metal surface. A low double layer capacity of 0.1–1 μF/cm −2 was found due to the very low ion concentration. The charge transfer resistance was as high as about 1–5 MΩcm 2. The high frequency part is due to the layer impedance. Inter-layers such as AlOOH from cathodic corrosion of Al and lead deposits from lead silicate in the pigment systems are the origin of characteristic features in the impedance spectra. Surface treatments as zinc phosphatation are also of some influence on the EIS results. A quantitative fitting of the Bode plots was possible after the introduction of constant phase elements ( cpe).

The electrochemical activity of boron-doped polycrystalline diamond thin film electrodes

The electrochemical activity of [open quotes]as grown[close quotes] boron-doped polycrystalline diamond thin film electrodes has been studied using cyclic voltammetry, chronoamperometry, and ac impedance without external illumination. The resistivity of these materials after doping is ca. 10 ohm-cm. The diamond electrodes possess a low double layer capacitance and a relatively high polarization resistance toward surface oxidation. Slow electrode kinetics are observed for Fe(CN)[sub 6][sup 3[minus]/4[minus]] at the [open quotes]as grown[close quotes] surface; however, the electrode response was observed to be extremely stable over a 2-month period as compared with freshly polished glassy carbon. The results suggest that diamond electrodes may have suitable properties as an electrode material for use in electroanalysis. 30 refs., 8 figs., 4 tabs.