3D Self-Supported Nitrogen-Doped Carbon Nanofiber Electrodes Incorporated Co/CoOx Nanoparticles: Application to Dyes Degradation by Electro-Fenton-Based Process

We developed free-standing nitrogen-doped carbon nanofiber (CNF) electrodes incorporating Co/CoOx nanoparticles (NPs) as a new cathode material for removing Acid Orange 7 (AO7; a dye for wool) from wastewater by the heterogeneous electro-Fenton reaction. We produced the free-standing N-doped CNF electrodes by electrospinning a polyacrylonitrile (PAN) and cobalt acetate solution followed by thermal carbonation of the cobalt acetate/PAN nanofibers under a nitrogen atmosphere. We then investigated electro-Fenton-based removal of AO7 from wastewater with the free-standing N-doped-CNFs-Co/CoOx electrodes, in the presence or not of Fe2+ ions as a co-catalyst. The electrochemical analysis showed the high stability of the prepared N-doped-CNF-Co/CoOx electrodes in electrochemical oxidation experiments with excellent degradation of AO7 (20 mM) at acidic to near neutral pH values (3 and 6). Electro-Fenton oxidation at 10 mA/cm2 direct current for 40 min using the N-doped-CNF-Co/CoOx electrodes loaded with 25 wt% of Co/CoOx NPs led to complete AO7 solution decolorization with total organic carbon (TOC) removal values of 92.4% at pH 3 and 93.3% at pH 6. The newly developed N-doped-CNF-Co/CoOx electrodes are an effective alternative technique for wastewater pre-treatment before the biological treatment.

In Situ-Formed Cobalt Nanoparticles Embedded Within Carbonaceous Matrix as Highly Efficient and Selective Catalysts for the Hydrogenation of Nitroarenes

Inhibiting the side reactions (such as dehalogenation) while promoting both/transfer hydrogenation are the main target for the production of functional anilines from nitroarenes; consequently, the preparation of an ideal catalyst to improve reaction selectivity stays as the fundamental direction for this field. In this work, we provided an easy-to-prepared heterogeneous catalyst with multilayered graphene shells where cobalt nanoparticles were encapsulated inside and distributed uniformly. This as-prepared catalysts were fabricated via one-pot pyrolysis by using mixture of citrate acid and cobalt acetate as C source and Co source, respectively. First of all, structural features of catalyst were characterized by a series of analytic techniques involving XPS, SEM/EDS, TEM as well as elemental mapping, to reveal its unique properties in relation to the catalytic mechanisms; in simple terms, the outer graphitic shell could be activated by the electronic interaction between the inner metallic nanoparticles and the outer graphene layer. Subsequently, the catalytic performance was tested in hydrogenation of nitrobenezene by using H2 as hydrogen source, so as to optimize the preparation process as well as the reaction conditions. Other nitro aromatics with functional groups such as halogen atoms, methyl or hydroxyl were also tolerated under very mild industrially viable and scalable conditions (60 °C, 2 h, and 2 MPa H2). More surprisingly, this catalyst could still exhibit excellent yields over 96 % in gram-scale test for the selected substrates, and could also be easily separated from the aqueous system due to its magnetic properties. The determined yields of target products were not decreased even after eight cycles, suggesting a potential for future industrial application in the selective hydrogenation of nitroarenes to the corresponding amines.

In Situ-Formed Cobalt Nanoparticles Embedded Within Carbonaceous Matrix as Highly Efficient and Selective Catalysts for the Hydrogenation of Nitroarenes

Inhibiting the side reactions (such as dehalogenation) while promoting both/transfer hydrogenation are the main target for the production of functional anilines from nitroarenes; consequently, the preparation of an ideal catalyst to improve reaction selectivity stays as the fundamental direction for this field. In this work, we provided an easy-to-prepared heterogeneous catalyst with multilayered graphene shells where cobalt nanoparticles were encapsulated inside and distributed uniformly. This as-prepared catalysts were fabricated via one-pot pyrolysis by using mixture of citrate acid and cobalt acetate as C source and Co source, respectively. First of all, structural features of catalyst were characterized by a series of analytic techniques involving XPS, SEM/EDS, TEM as well as elemental mapping, to reveal its unique properties in relation to the catalytic mechanisms; in simple terms, the outer graphitic shell could be activated by the electronic interaction between the inner metallic nanoparticles and the outer graphene layer. Subsequently, the catalytic performance was tested in hydrogenation of nitrobenezene by using H2 as hydrogen source, so as to optimize the preparation process as well as the reaction conditions. Other nitro aromatics with functional groups such as halogen atoms, methyl or hydroxyl were also tolerated under very mild industrially viable and scalable conditions (60 °C, 2 h, and 2 MPa H2). More surprisingly, this catalyst could still exhibit excellent yields over 96 % in gram-scale test for the selected substrates, and could also be easily separated from the aqueous system due to its magnetic properties. The determined yields of target products were not decreased even after eight cycles, suggesting a potential for future industrial application in the selective hydrogenation of nitroarenes to the corresponding amines.

Fischer-Tropsch Synthesis: The Characterization and Testing of Pt-Co/SiO2 Catalysts Prepared with Alternative Cobalt Precursors

Different low-cost cobalt precursors (acetate, chloride) and thermal treatments (air calcination/H2 reduction versus direct H2-activation) were investigated to alter the interaction between cobalt and silica. H2-activated catalysts prepared from cobalt chloride had large Co0 particles (XRD, chemisorption) formed by weak interactions between cobalt chloride and silica (temperature programmed reduction (TPR), TPR with mass spectrometry (TPR-MS), TPR with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge spectroscopy (XANES) techniques) and retained Cl-blocked active sites, resulting in poor activity. In contrast, unpromoted Co/SiO2 catalysts derived from cobalt acetate had strong interactions between Co species and silica (TPR/TPR-MS, TPR-EXAFS/XANES); adding Pt increased the extent of the Co reduction. For these Pt-promoted catalysts, the reduction of uncalcined catalysts was faster, resulting in larger Co0 clusters (19.5 nm) in comparison with the air-calcined/H2-activated catalyst (7.8 nm). Both catalysts had CO conversions 25% higher than that of the Pt-promoted catalyst prepared in the traditional manner (air calcination/H2 reduction using cobalt nitrate) and three times higher than that of the traditional unpromoted Co/silica catalyst. The retention of residual cobalt carbide (observed in XANES) from cobalt acetate decomposition impacted performance, resulting in a higher C1–C4 selectivity (32.2% for air-calcined and 38.7% for uncalcined) than that of traditional catalysts (17.5–18.6%). The residual carbide also lowered the α-value and olefin/paraffin ratio. Future work will focus on improving selectivity through oxidation–reduction cycles.

Improving safety and thermal decomposition performance by the in situ synthesis of core–shell structured ammonium perchlorate/cobalt acetate hydroxide composites

The AP/Co3(CH3COO)5(OH) composites of the core–shell structure were prepared, the safety and thermal decomposition properties of AP were improved simultaneously, and the possible catalytic mechanism was analyzed.

Measuring the Electrical and Photonic Properties of Cobalt Oxide-Containing Composite Carbon Fibers

In this work, cobalt acetate was incorporated into polyacrylonitrile (PAN) polymer through electrospinning as the cobalt oxide source. After oxidization and pyrolysis, a PAN-derived composite carbon fiber containing cobalt oxide was obtained. Measuring the electrical and photonic properties of the composite fiber under visible light irradiation was performed to evaluate the photoelectric behavior of the composite fiber. The p-type semiconducting behavior of the composite fiber was confirmed by measuring the open circuit voltage of a photochemical fuel cell consisting of the photosensitive electrode made from the composite fiber. The application of the composite fiber for glucose sensing was demonstrated.

Improvement of the Pseudocapacitive Performance of Cobalt Oxide-Based Electrodes for Electrochemical Capacitors

Cobalt oxide nanopowders are synthesized by the pyrolysis of aerosol particles of water solution of cobalt acetate. Cobalt nanopowder is obtained by subsequent reduction of obtained cobalt oxide by annealing under a hydrogen atmosphere. The average crystallite size of the synthesized porous particles ranged from 7 to 30 nm, depending on the synthesis temperature. The electrochemical characteristics of electrodes based on synthesized cobalt oxide and reduced cobalt oxide are investigated in an electrochemical cell using a 3.5 M KOH solution as the electrolyte. The results of electrochemical measurements show that the electrode based on reduced cobalt oxide (Re-Co3O4) exhibits significantly higher capacity, and lower Faradaic charge–transfer and ion diffusion resistances when compared to the electrodes based on the initial cobalt oxide Co3O4. This observed effect is mainly due to a wide range of reversible redox transitions such as Co(II) ↔ Co(III) and Co(III) ↔ Co(IV) associated with different cobalt oxide/hydroxide species formed on the surface of metal particles during the cell operation; the small thickness of the oxide/hydroxide layer providing a high reaction rate, and also the presence of a metal skeleton leading to a low series resistance of the electrode.