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[en] Two nano structures of cobalt oxyhydroxide (CoOOH) and Zinc-(Zn-) doped CoOOH (1–4% Zn) are prepared from Co(NO_3)_2 solution via microtitration with NaOH and oxidation in air. The X-ray diffraction (XRD) analysis results show that a pure state of nano-CoOOH can be obtained at an alkalinity (OH−/Co"+) of 5 with 40°C heat treatment after 6 h. The Zn ions preferentially substitute Co ions in the CoOOH structure, resulting in a decrease of its crystallinity. The disc-like CoOOH nano structure exhibits good sensitivity to carbon monoxide (CO) in a temperature range of 40–110°C with maximum sensitivity to CO at around 70–80°C. When CoOOH nano structure is doped with 1% Zn, its sensitivity and selectivity for CO gas are improved at 70–80°C; further Zn doping to 2% degraded the CO sensing properties of nano-CoOOH. The results of a cross-sensitivity investigation of the sensor to various gases coexisting at early stages of a fire show that the sensitivity of Zn-doped nano-CoOOH is the highest toward CO. Zn-doped nano-CoOOH film exhibits a high sensitivity to CO at room temperature, making it a promising sensor for early-stage fire detection.
[en] Voltametry and open circuit measurements of coprecipitated (nickel+cobalt) hydroxide electrodes, cobalt hydroxide+nickel hydroxide electrodes and nickel hydroxide+cobalt hydroxide electrodes in 0.1 M KOH at 250C were made. Coprecipitated electrodes exhibit an overpotential decrease for the Ni(II)/Ni(III) redox reactions and an overpotential increase for the oxygen evolution reaction. The behaviour of the different electrodes is interpreted in terms of a catalytic effect of the Co(II)/Co(III) reaction on the Ni(II)/Ni(III) reaction through hydroxide ions inserted into the metal hydroxide layer. (C.L.B.)
[pt]Foram feitas medidas voltametricas e de circuito aberto, de: eletrodos de hidroxido de (niquel+cobalto) coprecipitado, eletrodos de hidroxido de cobalto+hidroxido de niquel e eletrodos de hidroxido de niquel+hidroxido de cobalto, em 0,1M de KOH a 250C. Os eletrodos coprecipitados apresentam um decrescimo de potencial para as reacoes de oxirreducao Ni(II)/Ni(III) e um aumento de potencial para a reacao com evolucao de oxigenio. O comportamento dos diferentes eletrodos e interpretado em termos do efeito catalitico da reacao Co(II)/Co(III) sobre a reacao Ni(II)/Ni(III) atraves da insercao dos ions hidroxido na camada do hidroxido metalico. (C.L.B.)
[en] First aqueous non-silica foams, solely stabilized by CoOOH nanoparticles, were prepared by a new colloidal strategy. Highly water-soluble CoOOH nanoparticles with size of 1.5 nm were produced from the reaction between Co(OH)2 nanosheets and ammonia. The foams were formed through the hand-shaking of the high-concentration colloid formed by the redisolving of CoOOH nanoparticles in water. The stability of the foams was attributed to the reduction of surface tension induced by the hydrophilic CoOOH particles and the support of particulate network in the void between bubbles. These two factors also provided resistance for the bubble collapse during the evaporation of solvent, resulting in the keeping of the original foam morphology after drying and the formation of a hierarchically hollow structure of CoOOH. Herein, we proved that the highly hydrophilic nanoparticles also can stabilize liquid foams. This conclusion is different from the classic theory on foams, which may provide new insight for foams and also a pathway for the preparation of inorganic hollow structure
[en] A turn-on fluorometric method is described for the determination of adenosine-5′-triphosphate (ATP). It is based on the displacement of a dye-labeled oligonucleotide from a cobalt(II) based layered double hydroxide (LDH). Due to the electrostatic and ligand exchange interaction, the FAM-labeled DNA is readily adsorbed on the LDH. This leads to complete and fast quenching of the green fluorescence of the label. However, on addition of ATP, the DNA is detached from the LDH because of the stronger affinity of ATP for LDH. This results in the restoration of the green fluorescence. The effect was used to design a sensitive assay that has a linear response in the 0.5–100 μM ATP concentration range and a 0.23 μM lower detection limit. It was applied to the determination of ATP in spiked serum samples. .
[en] The isothermal decomposition of cobalt hydroxide and cobalt hydroxynitrate at different intervals of temperature leads to the formation of Co3O4. The phase evolution during the decomposition process was monitored using powder X-ray diffraction. The transformation of cobalt hydroxide to cobalt oxide occurs via three phase mixture while cobalt hydroxynitrate to cobalt oxide occurs through a two phase mixture. The nature of the sample and its preparation method controls the decomposition mechanism. The comparison of topotactical relationship between the precursors to the decomposed product has been reported in relation to polytypism. - Graphical abstract: Isothermal thermal decomposition studies of cobalt hydroxide and cobalt hydroxynitrate at different intervals of temperature show the metastable phase formed prior to Co3O4 phase.
[en] Hollow and hollowed-out Co3O4 nanoboxes (denoted as Co3O4-HHNBs) that assembled by porous ultrathin nanosheets (∼2 nm) have been synthesized through a morphology-conserved transformations of metal-organic framework (MOF) based precursors strategy and then applied to gas sensors. The switching process used a facile two-step approach, including the formation of box-shaped Co(OH)2 followed by thermal conversion to Co3O4-HHNBs. The sensors based on Co3O4-HHNBs exhibit high response with the value of 56.6 to 100 ppm of toluene at 200 °C and 15.9 for ethanol at 220 °C, respectively. The response/recovery time to 50 ppm toluene and ethanol are as short as 10 s/9 s and 0.4 s/0.5 s at 200 °C, respectively. The formation mechanism of Co3O4-HHNBs and the gas sensing mechanism are discussed in detail. Benefiting from the unique structural features, it exhibit high response and ultra-fast response/recovery speed. This synthesis concept of Co3O4-HHNBs may open new avenues to fabricate high performance gas sensor by carefully controlling the morphology of sensitive nanomaterials. (paper)
[en] Transition metal oxide nanostructures and conducting polymers like polyaniline have specific capacitance orders of magnitude higher than those of carbon based nanomaterials. In the present study nanoflowers of Cobalt Hydroxide, Polyaniline and Carbon Nanotubes were combined on a conventional Polymeric sponge to develop by using facile wet chemical techniques. High surface area of Cobalt Hydroxide nanoflowers when combined with Polyaniline showed enhanced capacitance values and stability. The carbon nanotubes enhanced the conductivity of the composite while the double porous structure of polyurethane sponge enhances the electrolyte flow, surface area, and reduces current density which leads to good reversibility and greater capacitance. Samples were characterized by cyclic voltammetry technique against Ag/AgCl reference electrode in three electrode setup. (author)