Kurt Kalcher

Structural and spectroelectrochemical investigations of sol-gel derived electrochromic spinel Co{sub 3}O{sub 4} films

Thin films of the cubic spinel Co{sub 3}O{sub 4} were prepared by the sol-gel route from a Co(II) sulfate precursor using a dip-coating technique. The films (50 to 60 nm thick) were deposited on indium-tin oxide glass substrates with a single dipping. The electrochromic properties of the films were studied in an aqueous alkaline electrolyte (0.1 M LiOH) using cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. The intermediate oxide products that appeared during cycling at current peak potentials were analyzed by x-ray diffraction (XRD) and ex situ Fourier transform infrared (FTIR) reflection-absorption spectroscopy performed at near-grazing incidence angle conditions (NGIA). High hydration of the spinel structure enables complex redox processes to take place inside the structure or on the surface of the film when potential cycling is performed. Vibrational bands characteristic of the formation of CoO, Co(OH){sub 2}, and hydrated Co{sub 3}O{sub 4} phases have been assigned and discussed according to the results obtained from ex situ NGIA FTIR, CV, and XRD studies. The change in transmittance ({lambda} = 634 nm) between bleached and colored states for single-dipped films was 25%, and for electrochromic efficiency ({eta}) was approximately 25 cm{sup 2}/C.

Carbon paste electrodes in the new millennium

In this review (with 500 refs), both electrochemistry and electroanalysis with carbon paste-based electrodes, sensors, and detectors are of interest, when attention is focused on the research activities in the years of new millennium. Concerned are all important aspects of the field, from fundamental investigations with carbon paste as the electrode material, via laboratory examination of the first electrode prototypes, basic and advanced studies of various electrode processes and other phenomena, up to practical applications to the determination of inorganic ions, complexes, and molecules. The latter is presented in a series of extensive tables, offering a nearly complete survey of methods published within the period of 2001–2008. Finally, the latest trends and outstanding achievements are also outlined and future prospects given.

Bismuth-film-plated carbon paste electrodes

Abstract In this preliminary note, carbon paste electrodes (CPEs) plated with a bismuth film are presented. The bismuth film can be generated onto the carbon paste surface either from an external plating solution or in situ; the latter being performed in two ways: (i) as a spike of the Bi 3+ ions to the solution or (ii) via modifying the carbon paste with solid bismuth oxide (5% m/m). As shown on selected examples, bismuth-film-plated CPEs exhibit a good performance in voltammetric stripping analysis of some heavy metals such as Pb, Cd, and Zn.

A chemiluminescence sensor for the determination of hydrogen peroxide

A chemiluminescence one-shot sensor for hydrogen peroxide is described. It is prepared by immobilization of cobalt chloride and sodium lauryl sulphate in hydroxyethyl cellulose matrix cast on a microscope cover glass. Luminol, sodium phosphate and the sample are mixed before use and applied on the membrane by a micropipette. The calibration graph is linear in the range 20-1600mug/L, and the detection limit of the method (3sigma) is 9mug/L. A relative standard deviation of 4.5% was obtained for 100mug/L H(2)O(2) (n=11). The sensor has been applied successfully to the determination of hydrogen peroxide in rainwater.

Amperometric Determination of Hydrogen Peroxide With a ManganeseDioxide-modified Carbon Paste Electrode Using Flow InjectionAnalysis

A carbon paste electrode bulk modified with MnO 2 was investigated as an amperometric detector for hydrogen peroxide in flow injection analysis (FIA). With an operating potential of +0.46 V versus Ag/AgCl, H 2 O 2 produces catalytic oxidation currents which can be exploited for quantitative determinations. Factors influencing the analytical performance of the electrode, such as paste composition and pH, were studied both for batch voltammetry and for FIA. For the flow system the influence of the injection volume and flow rate were examined. The amperometric signals are linearly proportional to H 2 O 2 concentrations in the range 0.5–350 mg l - 1 , showing a detection limit (three times the signal-to-noise ratio) of 45 µg l - 1 .

An improved voltammetric method for the determination of trace amounts of uric acid with electrochemically pretreated carbon paste electrodes.

Carbon paste electrodes, preanodized in alkaline medium at 1.4 V vs SCE for a short period of time, exhibit a great shift of the oxidation potential of uric acid in cathodic direction and a marked enhancement of its current response, compared to unpretreated electrodes. These effects are dependent on the preanodization potential and the time imposed on the electrodes as well as on the alkalinity of the supporting electrolyte. The enhanced voltammetric response can be used to determine uric acid in the concentration range of 5.0-4.0 x 10(4) mug/1 (3.0 x 10(-8)-2.4 x 10(-4)M) with a detection limit (3sigma) of 2.0 mug/1 (1.2 x 10(-8)M). Ascorbic acid in less than 30-fold excess does not interfere. For multiple determinations (5 runs), the relative standard deviation is 2.1% at a concentration of 1 mg/1 uric acid. The proposed procedure can be used to determine uric acid in human urine and serum without any preliminary treatment of the samples in an accurate, rapid and simple way.

Optical and electrochemical properties of CeO2 and CeO2TiO2 coatings

Thin solid films of CeO2 and mixed CeO2TiO2 were prepared by the sol-gel route via the dip-coating technique. Particulate sols of ceria were made from inorganic ((NH4)2Ce(NO3)6) precursor which were used for preparation of CeO2 thin solid films while CeO2TiO2 coatings have been made by using mixed organic-inorganic (Ti(OiPr)4 and CeCl3·7H2O) precursors. The solar transmission values (Ts) of both coatings are in the range 0.6–0.8 and depend on coating thickness. Cyclic voltammetric (CV) measurements show that the CeO2/LiOH system exhibits higher overall electrochemical reversibility when compared to the CeO2TiO2/LiOH system. The CeO2/LiOH system is also less sensitive with regard to the coating thickness. Coulometric measurements show that CeO2 exhibits a larger storage capability which was determined as a function of the coating thickness. “In situ” UV-VIS spectroelectrochemical measurements which have been performed on CeO2 and CeO2TiO2 coatings revealed that both types of samples exhibit electrochromic effect in the spectral range 500 < λ < 330 nm but remain unchanged in the visible spectral range.

Electrochemical sensors for the simultaneous determination of zinc, cadmium and lead using a Nafion/ionic liquid/graphene composite modified screen-printed carbon electrode.

A simple, low cost, and highly sensitive electrochemical sensor, based on a Nafion/ionic liquid/graphene composite modified screen-printed carbon electrode (N/IL/G/SPCE) was developed to determine zinc (Zn(II)), cadmium (Cd(II)), and lead (Pb(II)) simultaneously. This disposable electrode shows excellent conductivity and fast electron transfer kinetics. By in situ plating with a bismuth film (BiF), the developed electrode exhibited well-defined and separate peaks for Zn(II), Cd(II), and Pb(II) by square wave anodic stripping voltammetry (SWASV). Analytical characteristics of the BiF/N/IL/G/SPCE were explored with calibration curves which were found to be linear for Zn(II), Cd(II), and Pb(II) concentrations over the range from 0.1 to 100.0 ng L(-1). With an accumulation period of 120 s detection limits of 0.09 ng mL(-1), 0.06 ng L(-1) and 0.08 ng L(-1) were obtained for Zn(II), Cd(II) and Pb(II), respectively using the BiF/N/IL/G/SPCE sensor, calculated as 3σ value of the blank. In addition, the developed electrode displayed a good repeatability and reproducibility. The interference from other common ions associated with Zn(II), Cd(II) and Pb(II) detection could be effectively avoided. Finally, the proposed analytical procedure was applied to detect the trace metal ions in drinking water samples with satisfactory results which demonstrates the suitability of the BiF/N/IL/G/SPCE to detect heavy metals in water samples and the results agreed well with those obtained by inductively coupled plasma mass spectrometry.

(Bio)sensors based on manganese dioxide-modified carbon substrates: retrospections, further improvements and applications

An overview is presented which summarizes our accomplishment in the development of sensors and biosensors based on heterogenous carbon electrodes modified with manganese dioxide. Brief account of each sensor and biosensor has been given and example of real sample applications provided where appropriate.

Voltammetric determination of trace amounts of gold with a chemically modified carbon paste electrode

Abstract A carbon paste electrode chemically modified with anion-exchangers is used for the voltammetric determination of gold(III). Tetrachloro- or tetrabromo-aurate(III) is preconcentrated on the electrode surface, modified with Amberlite LA2, and the electrode is transferred to an electrochemical cell for voltammetric measurements by cathodic stripping. The response depends on the concentration of gold in the bulk solution, preconcentration time, and other parameters. Detection limits are 100–300 μg l −1 depending on the conditions. Many elements forming stable halo complex anions interfere.