Synthesis and photocatalytic activity of doped zinc oxide nanoparticles

In this study, we have investigated the effect of doping with cobalt and manganese oxide on the photocatalytic activity of nanoparticulate zinc oxide. Zinc oxide powders with controlled particle size, minimal agglomeration, and controlled chemical composition were manufactured by mechanochemical processing. The photocatalytic activity of the powders was measured using the spin trapping technique with electron paramagnetic resonance spectroscopy. It was found that the addition of cobalt oxide decreased the yield of photogenerated hydroxyl radicals. In contrast, doping with manganese oxide was found to substantially increase the rate of radical production.

Extraction of copper(II) ions from aqueous solutions with a methimazole-based ionic liquid

The recently synthesized ionic liquid (IL) 2-butylthiolonium bis(trifluoromethanesulfonyl)amide, [mimSBu][NTf2], has been used for the extraction of copper(II) from aqueous solution. The pH of the aqueous phase decreases upon addition of [mimSBu]+, which is attributed to partial release of the hydrogen attached to the N(3) nitrogen atom of the imidazolium ring. The presence of sparingly soluble water in [mimSBu][NTf2] also is required in solvent extraction studies to promote the incorporation of Cu(II) into the [mimSBu][NTf2] ionic liquid phase. The labile copper(II) system formed by interacting with both the water and the IL cation component has been characterized by cyclic voltammetry as well as UV−vis, Raman, and 1H, 13C, and 15N NMR spectroscopies. The extraction process does not require the addition of a complexing agent or pH control of the aqueous phase. [mimSBu][NTf2] can be recovered from the labile copper−water−IL interacting system by washing with a strong acid. High selectivity of copper(II) extraction is achieved relative to that of other divalent cobalt(II), iron(II), and nickel(II) transition-metal cations. The course of microextraction of Cu2+ from aqueous media into the [mimSBu][NTf2] IL phase was monitored in situ by cyclic voltammetry using a well-defined process in which specific interaction with copper is believed to switch from the ionic liquid cation component, [mimSBu], to the [NTf2] anion during the course of electrochemical reduction from Cu(II) to Cu(I). The microextraction−voltammetry technique provides a fast and convenient method to determine whether an IL is able to extract electroactive metal ions from an aqueous solution.

Novel B-site ordered double perovskite Ba2Bi0.1Sc0.2Co1.7O6-x for highly efficient oxygen reduction reaction

Double perovskite Ba₂Bi_0.1Sc_0.2Co_1.7O_6-x (BBSC) demonstrates low polarization resistance between 600 and 750 °C due to the high oxygen reduction rate of BBSC as reflected by its large D_V and k values, which are derived from the face centered cubic structure and high cobalt content.

Blood mineral, trace-element and vitamin concentrations in Huacaya alpacas and Merino sheep grazing the same pasture

We aimed to determine whether the concentration of minerals and trace constituents in blood of Merino sheep and Huacaya alpacas grazing the same pasture differed with species and time of sampling. Blood samples and pasture samples were collected at frequent intervals over a period of 2 years for mineral and trace-nutrient assay. The concentration of the minerals and trace nutrients in the grazed pasture usually met the dietary needs of sheep at maintenance, apart from potassium, sulfur, cobalt and Vitamin E in occasional samples. Restricted maximum likelihood mixed model analysis indicated a significant (P < 0.001) species by month by year interaction for all blood constituents assayed, a significant (P < 0.05) species by coat shade interaction for plasma Vitamin D, E and B12 and a significant (P < 0.001) species by month by Vitamin D interaction for plasma phosphorus concentrations. In general, plasma calcium concentrations were greater in sheep than in alpacas but plasma magnesium concentrations were greater in alpacas than in sheep. There was no consistent difference between the two species in plasma phosphorus concentrations although low values were recorded in individual sheep and alpacas. Plasma Vitamin D concentrations were more responsive to increasing hours of sunlight in alpacas than they were in sheep. Sheep had consistently higher concentrations of plasma copper, zinc and Vitamin B12 and higher concentrations of blood selenium but lower concentrations of plasma selenium and Vitamin A, than did alpacas. No consistent difference was observed between the two species in plasma Vitamin E concentrations.

Deactivation and regeneration of oxygen reduction reactivity on double perovskite Ba2Bi0.1Sc0.2Co1.7O6−x cathode for intermediate-temperature solid oxide fuel cells

in situ high-temperature X-ray diffraction and thermal gravimetric- differential thermal analysis on room-temperature powder, as well as X-ray diffraction, Raman spectroscopy, and transmission electron microscopy on quenched powder, were applied to study crystal structure and phase transformations in Ba₂Bi_0.1Sc_0.2Co _1.7O_6-x (BBSC). Heating BBSC in air to over 800 °C produces a pure cubic phase with space group Fm3m (no. 225), and cooling down below 800 °C leads to a mixture of three noncubic phases including an unknown phase between 200 and 650 °C, a 2H hexagonal BaCoO3 with space group P63/mmc (no. 194) between 600 and 800 °C, and an intermediate phase at 800 °C. These three phases exist concurrently with the major cubic phase. The weight gain and loss between 300 and 900 °C suggest the occurrence of cobalt reduction, oxidation, and disproportion reactions with dominant reduction reaction at above 600 °C. The thermal expansion of BBSC was also examined by dilatometry. BBSC has a highly temperature-dependent thermal expansion coefficient which relates well with its structure evolution. Furthermore, the oxygen reduction reaction (ORR) of BBSC was probed by symmetrical cell and three-electrode configurations. The presence of hexagonal phase at 700 °C rarely affects the ORR performance of BBSC as evidenced by a slight increase of its area-specific resistance (ASR) value following 48 h of testing in this three-electrode configuration. This observation is in contrast to the commonly held point of view that noncubic phase deteriorates performance of perovskite compounds (especially in oxygen transport applications). Moreover, cathodic polarization treatment, for example, current discharge from BBSC (tested in three-electrode configuration), can be utilized to recover the original ORR performance. The cubic structure seems to be retained on the cathodic polarization - the normal cathode operating mode in fuel cells. Stable 72-h performance of BBSC in cathodic polarization mode further confirms that despite the presence of phase impurities, BBSC still demonstrates good performance between 500 and 700 °C, the desired intermediate operating temperature in solid oxide fuel cells.

Oxygen reduction reaction activity of La-based perovskite oxides in alkaline medium : a thin-film rotating ring-disk electrode study

In this work, LaMO₃ and LaNi_0.5M_0.5O₃ (M = Ni, Co, Fe, Mn and Cr) perovskite oxide electrocatalysts were synthesized by a combined ethylenediaminetetraacetic acid-citrate complexation technique and subsequent calcinations at 1000 °C in air. Their powder X-ray diffraction patterns demonstrate the formation of a specific crystalline structure for each composition. The catalytic property of these materials toward the oxygen reduction reaction (ORR) was studied in alkaline potassium hydroxide solution using the rotating disk and rotating ring-disk electrode techniques. Carbon is considered to be a crucial additive component because its addition into perovskite oxide leads to optimized ORR current density. For LaMO₃ (M = Ni, Co, Fe, Mn and Cr)), in terms of the ORR current densities, the performance is enhanced in the order of LaCrO₃, LaFeO₃, LaNiO₃, LaMnO₃, and LaCoO3. For LaNi_0.5M_0.5O₃, the ORR current performance is enhanced in the order of LaNi_0.5Fe_0.5O₃, LaNi_0.5Co_0.5O₃, LaNi_0.5Cr_0.5O₃, and LaNi_0.5Mn_0.5O₃. Overall, LaCoO₃ demonstrates the best performance. Most notably, substituting half of the nickel with cobalt, iron, manganese, or chromium translates the ORR to a more positive onset potential, suggesting the beneficial catalytic effect of two transition metal cations with Mn as the most promising candidate. Koutecky–Levich analysis on the ORR current densities of all compositions indicates that the four-electron pathway is favored on these oxides, which are consistent with hydroperoxide ion formation of <2%.

Reduction of the photocatalytic activity of ZnO nanoparticles for UV protection applications

The detrimental effects of UV radiation are having a significant impact on our life and environment. The development of effective UV shielding agents is therefore of great importance to our society. ZnO nanoparticles are considered to be one of the most effective UV blocking agents. However, the development of ZnO-based UV shielding products is currently hindered due to the adverse effects of the inherent photocatalytic activity exhibited by ZnO. This paper reports our recent study on the possibility of reducing the photoactivity of ZnO nanoparticles via surface modification and impurity doping. It was found that the photoactivity was drastically reduced by SiO2-coatings that were applied to ZnO quantum dots using the Stöber method and a microemulsion technique. The effect of transition metal doping on the photoactivity was also studied using mechanochemical processing and a co-precipitation method. Cobalt doping reduced the photoactivity, while manganese doping led to mixed results, possibly due to the difference in the location of dopant ions derived from the difference in the synthesis methods.

Functional characterization of the twin ZIP/SLC39 metal transporters, NpunF3111 and NpunF2202 in Nostoc punctiforme

The ZIP family of metal transporters is involved in the transport of Zn2+ and other metal cations from the extracellular environment and/or organelles into the cytoplasm of prokaryotes, eukaryotes and archaeotes. In the present study, we identified twin ZIP transporters, Zip11 (Npun_F3111) and Zip63 (Npun_F2202) encoded within the genome of the filamentous cyanobacterium, Nostoc punctiforme PCC73120. Sequence-based analyses and structural predictions confirmed that these cyanobacterial transporters belong to the SLC39 subfamily of metal transporters. Quantitative real-time (QRT)-PCR analyses suggested that the enzymes encoded by zip11 and zip63 have a broad allocrite range that includes zinc as well as cadmium, cobalt, copper, manganese and nickel. Inactivation of either zip11 or zip63 via insertional mutagenesis in N. punctiforme resulted in reduced expression of both genes, highlighting a possible co-regulation mechanism. Uptake experiments using 65Zn demonstrated that both zip mutants had diminished zinc uptake capacity, with the deletion of zip11 resulting in the greatest overall reduction in 65Zn uptake. Over-expression of Zip11 and Zip63 in an E. coli mutant strain (ZupT736::kan) restored divalent metal cation uptake, providing further evidence that these transporters are involved in Zn uptake in N. punctiforme. Our findings show the functional role of these twin metal uptake transporters in N. punctiforme, which are independently expressed in the presence of an array of metals. Both Zip11 and Zip63 are required for the maintenance of homeostatic levels of intracellular zinc N. punctiforme, although Zip11 appears to be the primary zinc transporter in this cyanobacterium, both ZIP's may be part of a larger metal uptake system with shared regulatory elements.

Electrochemical investigation of sodium reactivity with nanostructured Co3O4 for sodium-ion batteries

The electrochemical behaviour of Co3O4 with sodium is reported here. Upon cycling in the voltage window of 0.01–3.0 V, Co3O4 undergoes a conversion reaction and exhibits a reversible capacity of 447 mA h g−1 after 50 cycles. Therefore, nanostructured Co3O4 presents feasible electrochemical sodium storage, offering possibilities to develop new anode materials for sodium-ion batteries.

Silver nanoparticles prepared by gamma irradiation across metal-organic framework templates

In this study, we demonstrate for the first time the successful fabrication of well-dispersed ultrafine silver nanoparticles inside metal-organic frameworks through a single step gamma irradiation at room temperature. HKUST-1 crystals are soaked in silver nitrate aqueous solution and irradiated with a Cobalt 60 source across a range of irradiation doses to synthesize highly uniformly distributed silver nano-particles. The average size of the silver nanoparticles across the Ag@HKUST-1 materials is found to vary between 1.4 and 3 nm for dose exposures between 1 and 200 kGy, respectively. The Ag@HKUST-1 hybrid crystals exhibit strong surface plasmon resonance and are highly durable and efficient catalytic materials for the reduction of 4-nitrophenol to 4-aminophenol (up to 14.46 × 10-3 s-1 for 1 kGy Ag@HKUST-1). The crystals can be easily recycled for at least five successive cycles of reaction with a conversion efficiency higher than 99.9%. The gamma irradiation is demonstrated to be an effective and environmental friendly process for the synthesis of nano-particles across confined metal-organic frameworks at room temperature with potential applications in environmental science.

Evaluation of electrochemical methods for determination of the seebeck coefficient of redox electrolytes

Recent advances in thermoelectrochemical cells, which are being developed for harvesting low grade waste heat, have shown the promise of cobalt bipyridyl salts as the active redox couple. The Seebeck coefficient, Se, of a redox couple determines the open circuit voltage achievable, for a given temperature gradient, across the thermoelectrochemical cell. Thus, the accurate determination of this thermodynamic parameter is key to the development and study of new redox electrolytes. Further, techniques for accurate determination of Se using only one half of the redox couple reduces the synthetic requirements. Here, we compare three different experimental techniques for measuring Se of a cobalt tris(bipyridyl) redox couple in ionic liquid electrolytes. The use of temperature dependent cyclic voltammetry (CV) in isothermal and non-isothermal cells was investigated in depth, and the Se values compared to those from thermo-electromotive force measurements. Within experimental error, the Se values derived from CV methods were found to be in accordance with those obtained from electromotive force (emf) measurements. The applicability of cyclic voltammetry techniques for determining Se when employing only one part of the redox couple was demonstrated.