Bismuth nano-powder electrode for trace analysis of heavy metals using anodic stripping voltammetry

In the present work, a more sensitive and conveniently usable electrode sensor for a trace analysis of heavy metal was developed by using Bi nanopowder synthesized by levitational gas condensation (LGC) method. It was observed from the TEM image that the Bi nanopowder is spherical in shape with a size of nearly 50 nm. The XRD pattern revealed intense peaks which can be indexed as a rhombohedral structure of Bi without any other diffraction peaks corresponding to an oxide or an impurity. This indicates that the resulting nanopowder synthesized by the LGC method is a highly crystallized Bi with a high purity. The square wave anodic stripping voltammograms (SWASV), experimentally measured for the Bi nanopowder electrode, showed well-defined and highly reproducible electrochemical responses relating to the stripping of Cd and Pb. The detection limit of the electrode was estimated to be 0.15 μg/l and 0.07 μg/l for Cd and Zn, respectively, on the basis of the signal-to-noise characteristics (S/N = 3) of the response for the 1.0 μg/l solution under a 10 min accumulation.     

Studying the oxygen reduction and hydrogen oxidation reactions under realistic fuel cell conditions

A new approach to test fuel cell catalysts under conditions of high mass transport and variable temperature is described. This approach relies upon utilising a 5 μm thick gold grid to act as a catalyst support in contact with a perfluorsulfonic acid (PFSA) membrane in a true three electrode electrochemical configuration. The gold grid has 20 μm × 20 μm sized holes in it which allow the reactant gas to reach the catalyst layer. The high electrical conductivity and low profile of the grid ensure that electrical and mass transport losses are minimal. We have used this configuration to look at the oxygen reduction reaction (orr) and the hydrogen oxidation reaction (hor) on a platinum-black and platinum on carbon catalyst at a loading of about 10 μg cm⁻². We find that for the orr we can measure kinetic currents over the entire range of relevant fuel cell operating potentials (0.55–1 V). Although platinum-black shows higher specific catalytic activity towards the orr than platinum on carbon at high potentials, this performance benefit is reduced at lower potentials. For the hor we measure exchange current densities of 0.022 A cm⁻² and 0.026 A cm⁻² respectively on the Pt-Black and Pt/C. These values indicate that there does not appear to be a size effect for the hor, unlike the orr.     

Effects of disordered hemispherical micropatterns on Staphylococcus epidermidis biofilm formation

Surfaces which have physical patterns in the scale of bacteria cells have been shown to influence the microorganism's adhesion and biofilm formation characteristics. Layer-by-layer self-assembly was utilized to create disordered hemispherical patterns on poly(dimethylsiloxane) with a feature size of 0.5 μm, 1.0 μm and 2.0 μm. The effects of pattern size on the retention and biofilm formation of Staphylococcus epidermidis were examined as a function of culture time. The 1.0 μm pattern significantly reduced biofilm surface coverage by ～30% after 5 h of culture in comparison to that on an unpatterned surface while the effect of the 0.5 and 2.0 μm patterns was negligible. On the 1.0 μm surface, bacteria initially adhered on the unpatterned areas of the disordered surface and subsequently developed into biofilms by spreading across the unpatterned areas while avoiding those covered by the pattern. The results suggest that the size of surface patterns is an important factor in altering bacteria adhesion and biofilm formation characteristics.     

Direct determination of arsenate based on its electrocatalytic reduction at the poly(aniline-co-o-aminophenol) electrode

It was found that the copolymer poly(aniline-co-o-aminophenol) (PANOA) can strongly catalyze the reduction of arsenate in a NaCl solution, which was proved by cyclic voltammetry and the determination of activation energy. On the basis of the electrocatalytic reduction of arsenate, the PANOA copolymer was used as a probe to determine directly arsenate. The electrocatalytic activity of the PANOA electrode toward As(V) reduction strongly depended on the pH and the applied potential. Under the optimal conditions, the PANOA electrode can be used to determine directly As(V) concentration in a wide linear range (n = 19) of 0.949 and 495 μM with a correlation coefficient of 0.995 and a limit of detection of 0.495 μM. The sensitivity of the electrode was 0.192 μA μM^?1 cm^?2. The PANOA electrode had the good storage stability and a less negative operation potential of ?0.15 V (vs. SCE).     

How the electrolyte limits fast discharge in nanostructured batteries and supercapacitors

Solid state and interfacial processes are not necessarily the principal rate limiting process during fast discharge of LiFePO₄ composite electrodes with particle size less than 1 μm. A simple model based on salt diffusion to a sharp discharge front explains the observed dependence of discharge rate on electrode thickness, electrolyte concentration, lithium transference number, and dilution of the active material. The effect of changing the electrolyte is dramatic, e.g. discharge to 25% capacity was obtained on a 40 μm thick electrode after only 4 s in an optimised electrolyte, aqueous Li₂SO₄, showing a rate of 900 C as compared with less than 10 C for a similar cell with an ionic liquid as the electrolyte.     

Characterization of the 3-dimensional microstructure of a graphite negative electrode from a Li-ion battery

The 3-dimensional microstructure of a porous electrode from a lithium-ion battery has been characterized for the first time. We use X-ray tomography to reconstruct a 43 × 348 × 478 μm sample volume with voxel dimensions of 480 nm, subsequent division of the reconstructed volumes into sub-volumes of different sizes allow us to determine microstructural parameters as a function of sub-division size. We show that the minimum size for a representative volume element is about 43 × 60 × 60 μm for volume-specific surface area, but as large as the full sample volume for porosity and tortuosity.     

Mesoporous silica thin films for molecular sieving and electrode surface protection against biofouling

Electrode fouling is a major challenge for the long term use of sensors in real samples as it leads to the decay of the electroanalytical signal and is often caused by the formation of an inhibiting layer formed by biomolecules. We demonstrate here that ordered and vertically aligned mesoporous silica generated at the surface of an indium tin oxide electrode by electrochemically assisted self-assembly act as a molecular sieve and a protective layer for the electrode surface. They indeed prevent the adsorption of size excluded large undesired molecules (e.g. haemoglobin) while allowing the detection of small redox active molecules likely to reach the electrode surface through the film (e.g. propranolol) with almost no loss of sensitivity. At a bare electrode, the oxidation of propranolol is completely inhibited in the presence of 5 μM haemoglobin. At a modified electrode, the sensitivity for propranolol in the absence of haemoglobin is (72.8 ± 2.9) mA mol^− 1 (R² = 0.992, N = 7) and it remains similar in the presence of 5 μM haemoglobin with a value of (67.4 ± 7.2) mA mol^− 1 (R² = 0.992, N = 7).     

Electrochemical detection of perchloroethylene using differential pulse voltammetry

We demonstrate the application of differential pulse voltammetry (DPV) for the electrochemical detection of perchloroethylene (PCE) on an unmodified glassy carbon electrode surface. Detection sensitivity was substantially improved using DPV, in which dechlorination was denoted by a cathodic peak observed at approximately − 0.6 V (vs Ag/AgCl). Peak current intensity was found to correlate linearly with concentration over a tested range of 0 to 10 μM. The utility of this technique was subsequently evaluated for PCE-spiked environmental samples containing either Methylobacterium adhaesivum (1 × 10⁶ cells/mL) or creek water (10% v/v). In all environmental samples, a linear dynamic range was also observed from approximately 0 to 10 μM. The limit of detection was determined to be 0.3 μM in blank buffer, 0.4 μM in bacteria-containing samples and 1.2 μM in creek water samples.     

Factors affecting membrane fouling reduction by surface modification and backpulsing

Several factors affecting microfiltration membrane fouling and cleaning, including backpulsing, crossflushing, backwashing, particle size, membrane surface chemistry, and ionic strength, were investigated with suspensions of latex beads. Approximately two-fold permeate volume enhancements over 1 h of filtration were obtained by using water or gas backpulsing, and 50% enhancement was obtained with crossflushing, for filtration of 1.0 μm diameter carboxylate modified latex (CML) particles using unmodified polypropylene (PP) membranes of 0.3 μm nominal pore diameter. When 0.2 μm diameter CML particles or mixtures of 1.0 and 0.2 μm CML particles were used, however, the average flux decreased 60% compared with using 1.0 μm CML particles for experiments with or without backpulsing.PP membranes were rendered hydrophilic with neutral or positively on negatively charged surfaces by grafting monomers of poly(ethylene glycol 200) monomethacrylate (PEG200MA), dimethyl aminoethyl methacrylate (DMAEMA), or acrylic acid (AA), respectively, to the base PP membranes. Filtration experiments show that fouling is not strongly dependent on membrane surface chemistry for filtration of 1.0 μm CML particles without backpulsing. With backpulsing, however, a 10% increase and a 20% decrease of permeate volumes collected in 1 h were observed when the CML particles and the membranes had like charges and opposite charges, respectively, compared to the permeate collected with the unmodified membrane. Using the PP membranes modified with AA, permeate volumes with backpulsing decreased 30 and 40% when NaCl concentrations of 0.01 and 0.1 M, respectively, were added to the feed. However, the permeate volumes did not vary significantly with changing ionic strength for filtration without backpulsing.     

A study on solution deposited CuSCN thin films: Structural,electrochemical, optical properties

A cost-effective successive ionic layer adsorption and reaction (SILAR) method was used to deposit copper (I) thiocyanate (CuSCN) thin films on glass and steel substrates for this study. The deposited thin films were characterized for their structural, morphological, optical and electrochemical properties using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and VersaSTAT potentiostat. A direct band gap of 3.88 eV and 3.6 eV with film thickness of 0.7 μm and 0.9 μm was obtained at 20 and 30 deposition cycles respectively. The band gap, microstrain, dislocation density and crystal size were observed to be thickness dependent. The specific capacitance of the CuSCN thin film electrode at 20 mV/s was 760 F g⁻¹ for deposition 20 cycles and 729 F g⁻¹ for deposition 30 cycles.     

Amperometric enzyme biosensor for hydrogen peroxide via Ugi multicomponent reaction

A novel strategy based on the Ugi multicomponent reaction was employed for immobilizing horseradish peroxidase on sodium alginate-coated gold electrode. The electrode was employed for constructing an amperometric biosensor device using 1 mM hydroquinone as electrochemical mediator. The electrode showed linear response (poised at −300 mV vs Ag/AgCl) toward H₂O₂ concentration between 70 μM and 8.8 mM at pH 7.0. The biosensor reached 95% of steady-state current in about 12 s and its sensitivity was 33.8 mA/M cm². The electrode retained full initial activity after 30 days of storage at 4 °C in 50 mM sodium phosphate buffer, pH 7.0.     

Functionalization of multi-walled carbon nanotubes with poly(amidoamine) dendrimer for mediator-free glucose biosensor

By grafting with poly(amidoamine) (PAMAM) dendrimer, novel carbon nanotube (CNT) nano-composites have been successfully prepared. The novel functionalized matrix with plenty amino groups circumvents the troublesome solubility problem of CNTs in solvents, especially in water, greatly expanding the scope of the application of carbon nanotubes. The GO_x and HRP immobilized CNT-PAMAM based on the functional CNTs was synthesized. The bi-enzymatic CNT-PAMAM nano-composites are highly dispersible in water and show very promising applications in the fabrication of mediator-free bi-enzymatic biosensors for sensitive detection of glucose. The cooperation of nano-composite between CNT and high dense GO_x and HRP results in very high sensitivity to glucose with a current response of 2200 nA mM⁻¹ and fast response (∼1 s). The modified electrode exhibits a wide linear response range for glucose from 4.0 μM to 1.2 mM (R = 0.9971, N = 15), with a detection limit of 2.5 μM. The negative electrode potential of −0.34 V is favorable for glucose detection in real samples without interference caused by other biomolecules.     

Amperometric biosensing of glutamate using carbon nanotube based electrode

Amperometric biosensing of glutamate using nanobiocomposite derived from multiwall carbon nanotube (CNT), biopolymer chitosan (CHIT), redox mediator meldola’s blue (MDB) and glutamate dehydrogenase (GlDH) is described. The CNT composite electrode shows a reversible voltammetric response for the redox reaction of MDB at −0.15 V; the composite electrode efficiently mediates the oxidation of NADH at −0.07 V, which is 630 mV less positive than that on an unmodified glassy carbon (GC) electrode. The CNTs in the composite electrode facilitates the mediated electron transfer for the oxidation of NADH. The CNT composite electrode is highly sensitive (5.9 ± 1.52 nA/μM) towards NADH and it could detect as low as 0.5 μM of NADH in neutral pH. The CNT composite electrode is highly stable and does not undergo deactivation by the oxidation products. The electrode does not suffer from the interference due to other anionic electroactive compounds such as ascorbate (AA) and urate (UA). Separate voltammetric peaks have been observed for NADH, AA and UA, allowing the individual or simultaneous determination of these bioanalytes. The glutamate biosensor was developed by combining the electrocatalytic activity of the composite film and GlDH. The enzymatically generated NADH was electrocatalytically detected using the biocomposite electrode. Glutamate has been successfully detected at −0.1 V without any interference. The biosensor is highly sensitive, stable and shows linear response. The sensitivity and the limit of detection of the biosensor was 0.71 ± 0.08 nA/μM and 2 μM, respectively.     

Carbon black as successful screen-printed electrode modifier for phenolic compound detection

We report a miniaturized and disposable electrochemical sensor for phenolic compound detection. The sensor was constructed by modifying the working electrode surface of screen-printed electrode (SPE) with carbon black (CB) dispersion. This new probe showed higher sensitivity and better resistance to fouling than the bare SPE, displaying the suitability of CB as an excellent nanomodifier of SPE for phenolic compound detection. Catechol, gallic acid, caffeic acid, and tyrosol were detected by square wave voltammetry with a detection limit of 0.1 μM, 1 μM, 0.8 μM, and 2 μM, respectively. The sensor was able to selectively discriminate the mono-phenols and ortho-diphenols with rapid and easy measurement, paving the way to use a cost-effective device for quality control of foods and beverages containing phenolic compounds.     

Photocurrent generated on a carotenoid-sensitized TiO2 nanocrystalline mesoporous electrode

Photocurrent was observed upon monochromatic illumination of an ITO electrode coated with a TiO₂ nanocrystalline mesoporous membrane with carotenoid 8′-apo-β-caroten-8′-oic acid (ACOA) deposited as a sensitizer (illuminated area 0.25 cm²) and immersed in an aqueous 10 mM hydroquinone (H₂Q), 0.1 M NaH₂PO₄ solution (pH = 7.4) purged with argon, using a platinum flag counter electrode (area 3.3 cm²) and a SCE reference electrode. The carotenoid-sensitized short-circuit photocurrent reached 4.6 μA/cm² upon a 40 μW/cm² incident light beam at 426 nm, with an IPCE (%, incident monochromatic photon-to-photocurrent conversion efficiency) as high as 34%. The short-circuit photocurrent was stable during 1 h of continuous illumination with only a 10% decrease. An open-circuit voltage of 0.15 V was obtained (upon 426 nm, 40 μW/cm² illumination) which remained at a constant value for hours. The observed open-circuit voltage is close to the theoretical value (0.22 V) expected in such a system. The action spectrum resembled the absorption spectrum of ACOA bound on the TiO₂ membrane with a maximum near 426 nm. No decay of the ACOA on the TiO₂ surface was observed after 12 h, presumably because of rapid regeneration of ACOA from ACOA⁺ at the surface by electron transfer from H₂Q.     

Synthesis and electrical properties of (LiCo3/5Fe1/5Mn1/5)VO4 ceramics

(LiCo_3/5Fe_1/5Mn_1/5)VO₄ ceramic was synthesized via solution-based chemical method. X-ray diffraction analysis was carried out on the synthesized powder sample at room temperature, which confirms the orthorhombic structure with the lattice parameters of a = 10.3646 (20) Å, b = 3.7926 (20) Å, c = 9.2131 (20) Å. Field emission scanning electron microscopic analysis was carried out on the sintered pellet sample that indicates grains of unequal sizes (～0.1 to 2 μm) presents average grains size with polydisperse distribution on the surface of the ceramic. Complex impedance spectroscopy (CIS) technique is used for the study of electrical properties. CIS analysis identifies: (i) grain interior, grain boundary and electrode–material interface contributions to electrical response (ii) the presence of temperature dependent electrical relaxation phenomena in the ceramics. Detailed conductivity study indicates that electrical conduction in the material is a thermally activated process. The variation of A.C. conductivity with frequency at different temperatures obeys Jonscher's universal law.     

Field emission investigation of single Fe-doped SnO2 wire

Tin oxide submicronwires doped with Fe element were prepared by the thermal evaporation method. Morphological and structural characterizations revealed wires with sub micron size and crystalline in nature. The field electron emission from the single Fe:SnO₂ wire was carried out in conventional field emission microscope. The Fowler–Nordheim plot obtained from I–V characteristics of the wire showed a linear behavior typical that of metal. The field enhancement factor estimated from the slope of the F–N plot is 7455 cm^?1, indicating that the field emission is from nanometric features of the emitter. A current density of 10 A/cm² has been obtained at an applied field of 4.845 × 10³ V/μm. The field emission current–time record at a current level of 1 μA for more than 3 h duration is promising for various field emissions based applications.     

Preliminary study for producing higher harmonic hard X-rays from weakly ionized nickel plasma

In the plasma flash X-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash X-rays are produced by the discharging. The X-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of nickel ions and electrons, around the fine target, and intense Kα lines are left using a 15-μm-thick cobalt filter. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 18 kA. The K-series characteristic X-rays were clean and intense, and higher harmonic X-rays were observed. The X-ray pulse widths were approximately 300 ns, and the time-integrated X-ray intensity had a value of approximately 1.0 mGy at 1.0 m from the X-ray source with a charging voltage of 50 kV.     

Novel poly (neutral red) nanowires as a sensitive electrochemical biosensing platform for hydrogen peroxide determination

Poly (neutral red) nanowires (PNRNWs) have been synthesized for the first time by the method of cyclic voltammetric electrodeposition using porous anodic aluminum oxide (AAO) template and were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Moreover, horseradish peroxidase (HRP) was encapsulated in situ in PNRNWs (denoted as PNRNWs–HRP) by electrochemical copolymerization for potential biosensor applications. The PNRNWs showed excellent efficiency of electron transfer between the HRP and the glassy carbon (GC) electrode for the reduction of H₂O₂ and the PNRNWs–HRP modified GC electrode showed to be excellent amperometric sensors for H₂O₂ at −0.1 V with a linear response range of 1 μM to 8 mM with a correlation coefficient of 0.996. The detection limit (S/N = 3) and the response time were determined to be 1 μM and <5 s and the high sensitivity is up to 318 μA mM⁻¹ cm⁻².     

New ceramic microfiltration membranes from mineral coal fly ash

This work aims to develop a new mineral porous tubular membrane based on mineral coal fly ash. Finely ground mineral coal powder was calcinated at 700 °C for about 3 h. The elaboration of the mesoporous layer was performed by the slip casting method using a suspension made of the mixture of fly ash powder, water and PVA. The obtained membrane was submitted to a thermal treatment which consists in drying at room temperature for 24 h then a sintering at 800 °C. SEM photographs indicated that the membrane surface was homogeneous and did not present any macro defects (cracks, etc.). The average pore diameter of the active layer was 0.25 μm and the thickness was around 20 μm. The membrane permeability was 475 l/h m² bar.This membrane was applied to the treatment of the dying effluents generated by the washing baths in the textile industry. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 l/h m²). The quality of permeate was almost the same with the two membranes: the COD and color removal was 75% and 90%, respectively.