Peak overlap in voltammetry poses challenges for the quantitative analysis of electroactive species. Dopamine and uric acid are typically challenging to determine voltammetrically because of their very similar oxidation peak potentials. We report preliminary results of the use of a screen-printed carbon electrode for the determination of dopamine and uric acid in an electrolyte solution maintained above ambient temperatures. Higher temperatures resulted in dramatic shifting of the dopamine oxidation peak toward lower potentials, while the uric acid peak was essentially stationary. Ascorbic acid, an interference in voltammetric uric acid determinations, is effectively suppressed at higher temperatures. This resulted in a greater peak separation of dopamine from uric acid at higher temperatures, which is desirable for better peak integration. In addition, greater current responses for both species were recorded at higher temperatures. The cause for such an increase in peak current is unraveled using ac impedance measurements. Presented are preliminary results for determining dopamine and uric acid at temperatures higher than ambient. Much improved voltammetric peak separation and sensitivity is obtained at these higher temperatures compared to ambient.
Presented is a surfactant-mediated extraction procedure that uses an ionic surfactant and corresponding homologues. These surfactants contain the quaternary methylammonium functional group, which absorbs minimally at commonly used ultraviolet (UV)/visible wavelengths. Most surfactant-mediated extraction procedures for highperformance liquid chromatography are limited to applications requiring a detector other than the most commonly used UV/visible detector. Other detectors are necessary because most surfactants used in surfactantmediated extraction methodologies are nonionic in nature and contain chromophores that strongly absorb in the UV/ visible region. The high background created by the injected surfactant-rich aliquot extract makes trace analysis impossible. The utility of the presented procedure is demonstrated through the application of determining selected chlorophenols in river water. Quantitative and qualitative data are readily obtained with this procedure, because of minimal background interference, compared to nonionic surfactant-mediated extractions. Recoveries of greater than 95% and detection limits lower than 62 parts-per-billion for the selected chlorophenols are obtained with this procedure.
Iron cobalt oxides, such as typical FeCo 2 O 4 and CoFe 2 O 4 , are two spinel structured transitional metal oxide materials with excellent electrochemical performance. As the electrodes, they have been widely applied in the current energy storage and conversion processes such as supercapacitors, Lithium-ion batteries and fuel cells. Based on synthesis approaches and controlled conditions, these two materials exhibited broad morphologies and nanostructures and thus distinct electrochemical performance. Some of them have shown promising applications as electrodes in energy storage and conversion. The incorporation with other materials to form composites further improved their performance. This review briefly summarized the recent applications of FeCo 2 O 4 and CoFe 2 O 4 in energy storage and conversion, current understandings on mechanisms and especially the relevance of morphologies and structures and composites to electrochemical performance. Some recommendations were finally put forward addressing current issues and future prospects on electrodes of FeCo 2 O 4 and CoFe 2 O 4 based materials in energy storage and conversion, implying there was still space to further optimize their performance.
We report a promising simple strategy for improving the performance of the photoanode for photoelectrochemical (PEC) water splitting. ZnO nanorods on an indium tin oxide glass substrate were synthesized by a hydrothermal method following calcinations in air at 500 °C for 2 h and pure ambient hydrogen at atmospheric pressure at 400 °C for 30 min. The hydrogenated ZnO (H:ZnO) sample shows an enhanced photocurrent in comparison to that of ZnO nanorods. To enhance the absorption in the visible light and near-infrared regions, H:ZnO nanorods were sensitized by cadmium sulfide (CdS) nanoparticles and carbon quantum dots (CQDs). The H:ZnO nanorod film sensitized in this way exhibited significantly improved PEC properties after treatment with ambient nitrogen at 400 °C for 30 min. The optimized H:ZnO nanorod sample sensitized by CdS and CQDs yields a photocurrent density of ∼12.82 mA/cm 2 at 0 V (vs saturated calomel electrode (SCE)) in 0.25 M Na 2 S and 0.35 M Na 2 SO 3 solution under the illumination of simulated solar light (100 mW/cm 2 from a 150 W xenon Arc lamp source). The optimal structure shows a solarto-hydrogen conversion efficiency of ∼3.85% (at −0.67 V vs SCE). The H 2 gas generation obtained using this optimal structure consisting of H:ZnO nanorods sensitized by CdS and CQDs was 7.04 mL/cm 2 in 1 h. The morphology and properties of the samples were examined by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, ultraviolet−visible absorption, and electrical measurements.
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