Homogeneous Cobalt Research Articles

Hydroxylation of an ultrathin Co3O4(111) film on Ir(100) studied by in situ ambient pressure XPS and DFT

In the present work, we have studied the interaction of water with spinel cobalt oxide (Co3O4), an effect which has been considered a major cause of its catalytic deactivation. Employing a Co3O4(111) model thin film grown on Ir(100) in (ultra)high vacuum, and ambient pressure X-ray photoelectron spectroscopy (APXPS), hydroxylation in 0.5 mbar H2O vapor at room temperature was monitored in real time. The surface hydroxyl (OH) coverage was determined via two different models based (i) on the termination of a pristine and OH-covered Co3O4(111) surface as derived from density functional theory (DFT) calculations, and (ii) on a homogeneous cobalt oxyhydroxide (CoO(OH)) overlayer. Langmuir pseudo-second-order kinetics were applied to characterize the OH evolution with time, suggesting two regimes of chemisorption at the mosaic-like Co3O4(111) film: (i) plateaus, which were quickly saturated by OH, followed by (ii) slow hydroxylation in the “cracks” of the thin film. H2O dissociation and OH formation, blocking exposed Co2+ ions and additionally consuming surface lattice oxygen, respectively, may thus account for catalyst deactivation by H2O traces in reactive feeds.

Ni-CoSe2 heterojunction coated by N-doped carbon for modified separators of high-performance Li-sulfur batteries.

Functional separators modified by transition metal compounds have been proven to be effective in suppressing the shuttle effect of polysulfides and accelerating sluggish electrode dynamics in lithium-sulfur batteries (LSBs). However, the behaviors of heterojunctions composed of transition metals and their compounds in LSBs are still rarely studied. Herein, we report a novel Ni-CoSe2 heterostructure coated with nitrogen-doped carbon. Compared to homogeneous cobalt diselenide, it exhibits much stronger adsorption and catalytic conversion abilities towards polysulfides. With the modified separators, the lithium-sulfur batteries exhibit significantly improved capacity retention and reduced polarization during cycling.

A homogeneous cobalt complex mediated electro and photocatalytic O2/H2O interconversion in neutral water

The O2/H2O redox couple is vital in various renewable energy conversion strategies. This work delves into the Co(L-histidine)2 complex, a functional mimic of oxygen-carrying metalloproteins, and its electrochemical behavior driving the bidirectional oxygen reduction (ORR) and oxygen evolution (OER) activity in neutral water. This complex electrocatalyzes O2 via two distinct pathways: a two-electron O2/H2O2 reduction (catalytic rate= 250 s-1) and a four-electron O2 to H2O production (catalytic rate= 66 s-1). The formation of the key trans-μ-1,2-Co(III)-peroxo intermediate expedites this process. Additionally, this complex effectively oxidizes water to O2 (catalytic rate= 15606 s-1) at anodic potentials via a Co(IV)-oxo species. Additionally, this complex executes the ORR and OER under photocatalytic conditions in neutral water in the presence of appropriate photosensitizer (Eosin-Y) and redox mediators (triethanolamine/ORR and Na2S2O8/OER) at an appreciable rate. These results highlight one of the early examples of both electro- and photoactive bidirectional ORR/OER catalysts operational in neutral water.

Alcohol Dehydrogenation-Triggered Selective C3-Alkylation of Indoles by Homogeneous Azo-aromatic Cobalt Catalysts.

Herein, we report azo-benzimidazole containing cobalt complexes (1-3) for alcohol dehydrogenation-triggered C3-alkylation of indoles. In complexes 1-3, ligands are redox noninnocent and showed facile irreversible L/L• reduction followed by Co(II)/Co(I) reduction in close-lying potentials. Taking advantage of facile redox events in 1-3, the first aerial dehydrogenation of alcohols to their corresponding carbonyl compounds is explored. Subsequently, C3-alkylation of indole was studied using alcohols as the alkylating agents. The developed catalytic protocol was found to be efficient and very selective. It has a broad substrate scope and good functional group tolerance. As far as we are aware, it is the first homogeneous cobalt catalyst for C3-alkylation of indole using alcohol as the alkylating agent. Detailed mechanistic studies, including a deuterium labeling experiment, have suggested a borrowing hydrogen method for the C3-alkylation of indole. The coordinated ligand, cooperatively with the Co(II)/Co(I) redox couple, oxidized the coordinated alkoxide in a radical pathway to result in the carbonyl compound (Scheme 1), which on subsequent condensation with indole generates the alkylideneindolenine intermediate "X". Reduction of "X" by an azo-anion radical Co(I) catalyst intermediate resulted in the C3-alkylated indole.

The Transfer Hydrogenation of Cinnamaldehyde Using Homogeneous Cobalt(II) and Nickel(II) (E)-1-(Pyridin-2-yl)-N-(3-(triethoxysilyl)propyl)methanimine and the Complexes Anchored on Fe3O4 Support as Pre-Catalysts: An Experimental and In Silico Approach

The imino pyridine Schiff base cobalt(II) and nickel(II) complexes (C1 and C2) and their functionalised γ-Fe3O4 counterparts (Fe3O4@C1 and Fe3O4@C2) were synthesised and characterised using IR, elemental analysis, and ESI-MS for C1 and C2, and single crystal X-ray diffraction for C1, while the functionalised materials Fe3O4@C1 and Fe3O4@C2 were characterized using IR, XRD, SEM, TEM, EDS, ICP-OES, XPS and TGA. Complexes C1, C2 and the functionalised materials Fe3O4@C1 and Fe3O4@C2 were tested as catalysts for the selective transfer hydrogenation of cinnamaldehyde and all four pre-catalysts showed excellent catalytic activity. Complexes C1 and C2 acted as homogeneous catalysts with high selectivity towards the formation of hydrocinnamaldehyde (88.7% and 92.6%, respectively) while Fe3O4@C1 and Fe3O4@C2 acted as heterogeneous catalysts with high selectivity towards cinnamyl alcohol (89.7% and 87.7%, respectively). Through in silico studies of the adsorption energies, we were able to account for the different products formed using the homogeneous and the heterogeneous catalysts which we attribute to the preferred interaction of the C=C moiety in the substrate with the Ni centre in C2 (-0.79 eV) rather than the C=O (-0.58 eV).

Advance of Dehydrogenation and Transfer Hydrogenation of Ammonia-Borane Catalyzed by Homogeneous Cobalt Complexes

Advance of Dehydrogenation and Transfer Hydrogenation of Ammonia-Borane Catalyzed by Homogeneous Cobalt Complexes

Design and synthesis of a covalent organic framework bridging CdS nanoparticles and a homogeneous cobalt–bipyridine cocatalyst for a highly efficient photocatalytic CO2reduction

A 2,2′-bipyridine based ketoenamine COF (TpBpy), which can be synthesized by a facile and eco-friendly hydrothermal method, is used to promote CO2photoreduction processes by bridging CdS nanoparticles and a homogeneous [Co(bpy)3]2+cocatalyst.

Translating aqueous CO2 hydrogenation activity to electrocatalytic reduction with a homogeneous cobalt catalyst.

A molecular cobalt CO2 hydrogenation catalyst was explored for electrocatalytic CO2 reduction under aqueous conditions. The resulting pH-dependent selectivity between H2 and HCO2- is rationalized with thermodynamic analysis and stoichiometric experiments.

A High Catalytic Activity Nanozyme Based on Cobalt-Doped Carbon Dots for Biosensor and Anticancer Cell Effect

Nanozyme technology as an emerging field has been successfully applied to chemical sensing, biomedicine, and environmental monitoring. It is very significant for the advance of this field to construct nanozymes with high catalytic activity by a simple method and to develop their multifunctional applications. Here, a new type of cobalt-doped carbon dots (Co-CDs) nanozymes was designed using vitamin B12 and citric acid as the precursors. The homogeneous cobalt doping at carbon nuclear led the Co-CDs to show significant peroxidase-like activity resembling natural metalloenzymes. Based on the high affinity of Co-CDs to H2O2 (Km = 0.0598 mM), a colorimetric sensor for glucose detection was constructed by combining Co-CDs with glucose oxidase. On account of the high catalytic activity of nanozymes and the cascade strategy, a good linear relationship was obtained from 0.500 to 200 μM, with a detection limit of 0.145 μM. The biosensor has realized the accurate detection of glucose in human serum samples. Moreover, Co-CDs could specifically catalyze H2O2 in cancer cells to generate a variety of reactive oxygen species, leading to the death of cancer cells, which has useful application potential in tumor catalytic therapy. In this work, the catalytic activity of Co-CDs has been adequately exploited, which extends the application of carbon dots in multiple biotechnologies, including biosensing, disease diagnosis, and treatment.

Homogeneous cobalt catalyzed reductive formylation of N-heteroarenes with formic acid

Herein, we report a cobalt N,N-bidentate complex catalyzed reductive formylation of N-heteroarenes for the generation of N-formyltetrahydroquinoline (FTHQ) derivatives, formic acid was employed as a transfer hydrogenation reagent that was safe, abundant and easy to handle. This work represented the first homogeneous system for reductive formylation of N-heteroarenes, the metal ligand cooperated dehydrogenation was the key to the success of this transformation. Deuteration labelling experiments and Hammet analysis were conducted and a plausible mechanism was suggested.

Synthesis of Cobalt-Nickel Aluminate Spinels Using the Laser-Induced Thermionic Vacuum Arc Method and Thermal Annealing Processes.

To obtain highly homogeneous cobalt-nickel aluminate spinels with small crystallite sizes, CoNiAl alloy thin films were primarily deposited using Laser-induced Thermionic Vacuum Arc (LTVA) as a versatile method for performing processing of multiple materials, such as alloy/composite thin films, at a nanometric scale. Following thermal annealing in air, the CoNiAl metallic thin films were transformed into ceramic oxidic (Co,Ni)Al2O4 with controlled composition and crystallinity suitable for thermal stability and chemical resistance devices. Structural analysis revealed the formation of (Co,Ni)Al2O4 from the amorphous CoNiAl alloys. The mean crystallite size of the spinels was around 15 nm. Thermal annealing induces a densification process, increasing the film thickness together with the migration process of the aluminum toward the surface of the samples. The sheet resistance changed drastically from 200-240 Ω/sq to more than 106 Ω/sq, revealing a step-by-step conversion of the metallic character of the thin film to a dielectric oxidic structure. These cermet materials can be used as inert anodes for the solid oxide fuel cells (SOFCs), which require not only high stability with respect to oxidizing gases such as oxygen, but also good electrical conductivity. These combination metal-ceramics are known as bi-layer anodes. By controlling the crystallite size and the interplay between the oxide/metal composite, a balance between stability and electrical conductivity can be achieved.

A counter-current flow micro-packed-bed DBD plasmatron for the synthesis of a methylated cobaloxime

An atmospheric, dielectric-barrier discharge µ-plasmatron was designed, fabricated, and applied to synthesize a methylated organometallic complex. The design comprises counter-current flow to packed-bed microstructures to facilitate gas–liquid and plasma–liquid mixing. Micropillars arranged in a staggered configuration served as a porous media for the optimum 2D mixing of components that replenish plasma-liquid interfaces. Longitudinal dispersion was characterized through residence time distribution (RTD) measurements. The experimental RTD data were then described by an axial dispersion model with a time delay parameter. Levenspiel number (lv) indicating the intensity of axial dispersion was estimated in the range of 20.1–374, indicating that a dispersion model should be accounted for in plasma-assisted reaction kinetics development. Stable plasma excitation of methane-helium gas mixtures was observed within the 2D porous media, by in-situ optical emission spectra, while applying an alternating high voltage across the dielectric barrier. This novel technique made it possible to confirm in-situ formations of methyl radicals. Interestingly, the porous media served as a static mixer as no discrete plasma streamers were observed. To investigate its utility, an example homogeneous cobalt catalyst was injected into the µ-plasmatron and methylated. Our findings potentially introduce a new plasma-assisted reactor design and methodology for the synthesis of methylated cobaloxime.

Hydrothermal Preparation of Homogeneous Cobalt Oxide Nanomaterials as Stable Anodes for Superior Lithium Ion Batteries

In this study, uniform Co3O4 nanoparticles are prepared via a simple and facile hydrothermal synthesis without calcination treatment. When the Co3O4 nanomaterials are investigated as anodes for lithium ion batteries, a good electrochemical property is achieved. Particularly, the reversible capacity of the as-synthesized Co3O4 nanoparticle has a significant growth from 383 mAh g−1 of the initial cycle to 471 mAh g−1 of the 300th cycle at 2 A g−1. Moreover, when it recovers to 50 mA g−1 after different current densities, a superior reversible capacity of 695 mAh g−1 can be reached. Such favorable electrochemical properties will make the as-obtained Co3O4 have a good application prospect as anode material for lithium ion batteries.

α-Alkylation of Nitriles with Primary Alcohols by a Well-Defined Molecular Cobalt Catalyst.

The α-alkylation of nitriles with primary alcohols to selectively synthesize nitriles by a well-defined molecular homogeneous cobalt catalyst is presented. Thirty-two examples with up to 95% yield are reported. Remarkably, this transformation is environmentally friendly and atom economical with water as the only byproduct.

Metal-Organic Framework@Carbon Hybrid Magnetic Material as an Efficient Adsorbent for Pollutant Extraction.

The preparation of a hybrid magnetic metal-organic framework (MOF)@carbon from a MOF-derived porous carbon is reported. MOF-74(Co) is used as a precursor for the synthesis of a magnetic carbon with homogeneous cobalt particle distribution (C-MOF-74) by a direct carbonization step. The cobalt particles present in the carbon are partially converted to zeolitic imidazolate framework (ZIF)-67 by reaction with 2-methylimidazole to obtain a core-shell ZIF-67@C-MOF-74. The effect of the reaction time and 2-methylimidazole concentration in the conversion procedure is studied by X-ray diffraction and scanning microscopy. Because of its high surface area, dual porosity, and magnetic properties, ZIF-67@C-MOF-74 exhibits high extraction capacity (180 mg g-1), fast adsorption rate, and excellent recyclability for Congo red adsorption. In addition, the prepared material shows high efficiency in the extraction of different phenolic compounds. The developed procedure can be easily adapted to different carbons and MOFs, thus potentially enabling the preparation of a wide number of new hybrid materials.

Homogeneous cobalt and iron oxide hollow nanocages derived from ZIF-67 etched by Fe species for enhanced water oxidation

To develop highly efficient non-noble-metal electrocatalysts for oxygen evolution reaction is still a great challenge. Herein, cobalt and iron oxide with hollow structure has been fabricated using ZIF-67 as template, via reflux process followed by calcination. The simultaneous structural and electronic modulation are achieved due to the homogenous Fe incorporation. The Co sites in higher oxidation states and Fe sites with higher electron density can enhance the adsorption of H2O molecules and OOH species, and thus promote the water oxidation. The unique hollow structure also facilitates the mass transfer at the interface of electrolyte and active atoms. The optimal cobalt and iron oxide hollow nanocages exhibit superior OER performance, delivering an ultralow overpotential of 274 mV at 10 mA cm−2 and a very small Tafel slope of 31 mV dec−1 in alkaline media, which outperform the state-of-the-art RuO2. This work provides an efficient approach to design and explore non-precious electrocatalysts for electrochemical energy conversion and storage.

Cobalt-doped g-C3N4 as a heterogeneous catalyst for photo-assisted activation of peroxymonosulfate for the degradation of organic contaminants

Cobalt-mediated peroxymonosulfate (PMS) activation is an effective way to generate sulfate radicals for the degradation of pollutants. Herein, a heterogeneous Co-based catalyst was prepared by integrating the cobalt species to the cavities of g-C3N4 via the CoN bonds through the methods of impregnation and calcination, which was applied to activate PMS for the degradation of organic contaminates under visible light. The cobalt species were atomically dispersed on g-C3N4, which could provide more reactive sites for PMS activation. The catalytic efficiency of cobalt-doped g-C3N4 was greater than that of pure g-C3N4 or even slightly higher than that of the homogeneous cobalt ions during the photo-assisted PMS activation catalytic processes. The optimum Co loading is 1.0% in weight. In 25 min, the dye of rhodamine B was almost completely degraded with a 70.5% of total organic carbon (TOC) removal under its natural pH value in the presence of such catalytic system. The enhanced catalytic activity of Co-doped g-C3N4 was due to the effective separation of the photo-generated charges as well as the sufficient accessible reactive sites for PMS activation. And the synergistic interaction between the photocatalytic and PMS activation processes facilitated the generation of active species for the removal of pollutants.

Interfacial CoOx Layers on TiO2 as an Efficient Catalyst for Solvent-Free Aerobic Oxidation of Hydrocarbons.

Construction of efficient interfaces to improve the performance of supported metal catalysts is a challenging but effective technique. A newly synthesized catalyst with layered cobalt oxide on the surface of titania (layer-CoOx /TiO2 ) is highly selective towards the aerobic oxidation of C-H bonds in a series of hydrocarbons under sustainable conditions. The layer-CoOx /TiO2 easily outperforms the state-of-the-art noble metal catalysts and homogeneous cobalt salts used in industry. In-depth structural and functional characterization reveal that the layer-CoOx /TiO2 readily reacts with O2 for the adsorption and activation of C-H bonds. The layered structure of CoOx can maximize the interfacial effect of CoOx /TiO2 leading to a good performance for the oxidation of C-H bonds.

Cobalt iron selenide/sulfide porous nanocubes as high-performance electrocatalysts for efficient dye-sensitized solar cells

A novel series of ternary compounds, namely cobalt iron selenide/sulfide nanocubes, are successfully synthesized as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs), which deliver excellent performances. Homogeneous cobalt iron Prussian-blue-analog (PBA) nanocubes are prepared as the templates and are subsequently dealt with selenation/sulfidation processes via hydrothermal methods. Owing to their unique morphology, porous structure, high surface area, small charge transfer resistance and high diffusion coefficient, the Co-Fe-Se/S nanocubes possess high catalytic activity and excellent conductivity, which are tested and verified by electrochemical measurements. Meanwhile, cobalt iron selenide/sulfide nanocubes CEs achieve high efficiencies of 9.58% and 9.06%, respectively, which are both higher than that of Pt CE (8.16%). All these prominent merits make them outstanding and promising participants among Pt-free CE materials of DSSCs with lower production costs and higher power conversion efficiency.

ELECTRODEPOSITION OF COBALT NANOCLUSTERS FROM AMMONICAL CHLORIDE SOLUTIONS ONTO HOPG ELECTRODES. A KINETICAL AND MORPHOLOGICAL STUDY

A kinetical study about the Co electrodeposition onto Highly Oriented Pyrolytic Graphite electrodes from an aqueous solution containing 0.01 M CoCl2 + 1 M NH4CI (pH = 7) was conducted at overpotential conditions through potentiostatic studies. The entire chronoamperograms were adequately predicted, consider­ing the contribution to the total current of three different processes: a Langmuir-type adsorption process, a three-dimensional nucleation and growth and a proton reduction process. In all cases, the nucleation rate and the number of active nucleation sites are potential dependent. The Atomic Force Microscopy study revealed the presence of homogeneous cobalt clusters of less of 100 nm in height and 50 nm in diameter at different potential values.