Cobalt Atoms Research Articles

Nanoparticles and single atoms of cobalt synergistically enabled low-temperature reductive amination of carbonyl compounds.

Low-temperature and selective reductive amination of carbonyl compounds is a highly promising approach to access primary amines. However, it remains a great challenge to conduct this attractive route efficiently over earth-abundant metal-based catalysts. Herein, we designed several Co-based catalysts (denoted as Co@C–N(x), where x represents the pyrolysis temperature) by the pyrolysis of the metal–organic framework ZIF-67 at different temperatures. Very interestingly, the prepared Co@C–N(800) could efficiently catalyze the reductive amination of various aldehydes/ketones to synthesize the corresponding primary amines with high yields at 35 °C. Besides non-noble metal and mild temperature, the other unique advantage of the catalyst was that the substrates with different reduction-sensitive groups could be converted into primary amines selectively because the Co-based catalyst was not active for these groups at low temperature. Systematic analysis revealed that the catalyst was composed of graphene encapsulated Co nanoparticles and atomically dispersed Co–Nx sites. The Co particles promoted the hydrogenation step, while the Co–Nx sites acted as acidic sites to activate the intermediate (Schiff base). The synergistic effect of metallic Co particles and Co–Nx sites is crucial for the excellent performance of the catalyst Co@C–N(800). To the best of our knowledge, this is the first study on efficient synthesis of primary amines via reductive amination of carbonyl compounds over earth-abundant metal-based catalysts at low temperature (35 °C).

Features of polymorphic transformation during heating and cooling of cobalt

Differential scanning calorimetry was used to study the regularities of polymorphic α↔β-transformation in polycrystalline cobalt. The value of the activation energy of the α->β-transformation during heating of cobalt (290-50 kJ/mol), enthalpy and entropy, depending on the thermal history of the metal, is determined. It is shown that the mechanisms of recrystallization under heating are closer to the first-order I phase transformations. When cooling under conditions of limited diffusion mobility of cobalt atoms, recrystallization is apparently carried out due to the passage of several diffusion-free mechanisms of phase transformation, implemented in close temperature ranges. Keywords: activation energy, cobalt, calorimetry, polymorphism, enthalpy, entropy.

Effect of fullerene on the anisotropy, domain size and relaxation of a perpendicularly magnetized Pt/Co/C60/Pt system

(a) Spinterface formation on a single C60 unit. The surface cobalt atom Co2 is bonded to the C2 carbon atom of C60. (b)- (e) Domain images near the coercive field for samples Pt/Co/C60/Pt having C60 thickness 0, 0.5, 1.6 and 3.2 nm, respectively.

Cobalt Atom Sites Anchored on Sulfydryl Decorated Uio-66 to Activate Peroxymonosulfate for Norfloxacin Degradation

Cobalt Atom Sites Anchored on Sulfydryl Decorated Uio-66 to Activate Peroxymonosulfate for Norfloxacin Degradation

Особенности полиморфного превращения при нагреве и охлаждении кобальта

Differential scanning calorimetry was used to study the regularities of polymorphic αβ transformation in polycrystalline cobalt. The value of the activation energy of the αβ transformation during heating of cobalt (29050 kJ/mol), enthalpy and entropy, depending on the thermal history of the metal, is determined. It is shown that the mechanisms of recrystallization under heating are closer to the first-order I phase transformations. When cooling under conditions of limited diffusion mobility of cobalt atoms, recrystallization is apparently carried out due to the passage of several diffusion-free mechanisms of phase transformation, implemented in close temperature ranges.

Single Atom Cobalt Catalyst Derived from Co-Pyrolysis of Vitamin B12 and Graphitic Carbon Nitride for Pms Activation to Degrade Emerging Pollutants

Single Atom Cobalt Catalyst Derived from Co-Pyrolysis of Vitamin B12 and Graphitic Carbon Nitride for Pms Activation to Degrade Emerging Pollutants

Manufacturing of carbon-supported single atomic cobalt materials with N/O coordination for 3D printable lithium sulfur batteries

Carbon-supported single atomic metals have been proven to be very useful in different energy storage and conversion fields. Compared with the micro/nano-scale metal species, the unique local atomic structure of atomic metal sites brings about superior catalytic effects, enhanced binding energy and other positive influences toward different electrochemical reactions. By varying the non-metal atoms on the carbon substrate, the interactions between metal and substrate renders modified electronic structure and unexpected effects towards electrochemical reactions. Here, carbon-supported N, O-coordinated single atomic Co (Co-N3O2) was successfully synthesized by utilizing the oxygen species from the graphene oxide and N species from organic compounds. The atomic structure was characterized by synchrotron radiation. To further adopted as the host of Li metal to deliver high performance Li metal batteries, the artificial three-dimensional (3D) hierarchical porous microgrid aerogel can be designed by the carbon-supported structure and fabricated by a direct-ink writing (DIW) 3D printing technology.

The cobalt atom protection layers in-situ anchored titanium carbide with controllable interlayer spacing towards stable and fast lithium ions storage

MXenes are the typical ions insertion-type two-dimensional (2D) nanomaterials, have attracted extensive attention in the Li+ storage field. However, the self-stacking of layered structure and the consumption of electrolyte during the process of charge/discharge will limit the Li+ diffusion dynamics, rate capability and capacity of MXenes. Herein, a Co atom protection layers with electrochemical nonreactivity were anchored on/in the surface/interlayer of titanium carbide (Ti3C2) by in-situ thermal anchoring (x-Co/m-Ti3C2, x = 45, 65 and 85), which can not only avoid the self-stacking and expand the interlayer spacing of Ti3C2 but also reduce the consumption of Li+ and electrolyte by forming the thin solid electrolyte interphase (SEI) film. The interlayer spacing of Ti3C2 can be expanded from 0.98 to 1.21, 1.36 and 1.33 nm when the anchoring temperatures are 45, 65 and 85 °C due to the pillaring effects of Co atom layers, in where the 65-Co/m-Ti3C2 can achieve the best specific capacity and rate capability attributed to its superior diffusion coefficient of 8.8 × 10-7 cm2 s−1 in Li+ storage process. Furthermore, the 45, 65 and 85-Co/m-Ti3C2 exhibit lower SEI resistances (RSEI) as 1.45 ± 0.01, 1.26 ± 0.01 and 1.83 ± 0.01 Ω compared with the RSEI of Ti3C2 (5.18 ± 0.01 Ω), suggesting the x-Co/m-Ti3C2 demonstrates a thin SEI film due to the protection of Co atom layers. The findings propose a Co atom protection layers with electrochemical nonreactivity, not only giving an approach to expand the interlayer spacing, but also providing a protection strategy for 2D nanomaterials.

Paramagnetic 7Li NMR Shifts and Magnetic Properties of Divalent Transition Metal Silylamide Ate Complexes [LiM{N(SiMe3)2}3] (M2+ = Mn, Fe, Co).

7Li NMR shifts and magnetic properties have been determined for three so-called ate complexes [LiM{N(SiMe3)2}3] (M2+ = Mn, Fe, Co; e.g., named lithium-tris(bis(trimethylsilylamide))-manganate(II) in accordance with a formally negative charge assigned to the complex fragment [M{N(SiMe3)2}3]-, which comprises the transition metal). They are formed by addition reactions of LiN(SiMe3)2 and [M{N(SiMe3)2}2] and stabilized by Lewis base/Lewis acid interactions. The results are compared to those of the related "ion-separated" complexes [Li(15-crown-5)][M{N(SiMe3)2}3]. The ate complexes with the lithium atoms connected to the 3d metal atoms manganese, iron, or cobalt via μ2 nitrogen bridges reveal strong 7Li NMR paramagnetic shifts of about -75, 125, and 171 ppm, respectively, whereas the shifts for the lithium ions coordinated by the 15-crown-5 ether are close to zero. The observed trends of the 7Li NMR shifts are confirmed by density-functional theory calculations. The magnetic dc and ac properties display distinct differences for the six compounds under investigation. Both manganese compounds, [LiMn{N(SiMe3)2}3] and [Li(15-crown-5)][Mn{N(SiMe3)2}3], display almost pure and ideal spin-only paramagnetic behavior of a 3d5 high-spin complex. In this respect slightly unexpected, both complexes show slow relaxation behavior at low temperatures under applied dc fields, which is especially pronounced for the ate complex [LiMn{N(SiMe3)2}3]. Dc magnetic properties of the iron complexes reveal moderate g-factor anisotropies with small values of the axial magnetic anisotropy parameter D and a larger E (transversal anisotropy). Both complexes display at low temperatures and, under external dc fields of up to 5000 Oe, only weak ac signals with no maxima in the frequency range from 1 to 1500 s-1. In contrast, the two cobalt complexes display strong g-factor anisotropies with large values of D and E. In addition, in both cases, the ac measurements at low temperatures and applied dc fields reveal two, in terms of their frequency range, well separated relaxation processes with maxima lying for the most part outside of the measurement range between 1 and 1500 s-1.

Spectroscopic study of Co-doped CaCu3Ti4O12

Calcium-copper titanate has been thoroughly studied by scientists around the world for several decades due to the manifestation of colossal dielectric permeability values (ε ~104 –105) in wide frequency ranges (102 –106 Hz) and temperature ranges (100 – 600 K), showing neither ferroelectric nor relaxor properties. Due to the unique dielectric characteristics of calcium-copper titanate (CCTO), materials based on it are promising for the manufacture of multilayer capacitors and microwave devices. Restrictions on the practical use of CCTO are caused by high dielectric losses. Electrophysical characteristics are optimized by modifying the CCTO composition, partially replacing copper, titanium and calcium cations. Good dielectric properties are demonstrated by the CCTO ceramics doped with cobalt atoms. Co-doped CaCu3Ti4O12 was obtained by solid phase synthesis method. The samples are characterized by a grain microstructure; a thin layer of CuO is fixed in the intergranular space. From the interpretation of the obtained XPS- and NEXAFS 2p-spectra of Co-doped CaCu3Ti4O12 and the corresponding oxides it can be concluded that in the Co-doped ССТО atoms of copper and calcium have a charge state of +2, atoms of titanium — +(4 − δ), and cobalt atoms mainly +2 with some fraction of Co (III) in the high spin state. The Co-doped sample FTIR spectrum clearly captures the absorption bands in the fingerprint area at ≈408, 488, 539 cm−1, which are typical for ССТО.

Cobalt Catalysts for [2+2+2] Cycloaddition Reactions: Isolated Precatalysts and in situ Generated Catalysts.

[2+2+2] Cycloaddition reactions belong to the not even large class of reactions, which can be catalyzed or mediated by a significant number of different transition metals. Cobalt complexes belong to the catalysts that paved the way for the extensive use and profound mechanistic knowledge on this particular transformation. Beside the established role, cyclopentadienyl (Cp) cobalt complexes inherit in synthetic applications of the cyclotrimerization reaction, modification of the precatalysts opened up novel reactivities and versatility for such catalytic initiators. At the same time the development of in situ generated cobalt catalysts allowed the conversion of novel substrates as well as novel reaction modes to be realized. In this personal account recent developments will be presented and the possibilities of catalysts containing cobalt atoms in different oxidation states be discussed.

Iodine-Doping-Induced Electronic Structure Tuning of Atomic Cobalt for Enhanced Hydrogen Evolution Electrocatalysis

The development of strategies for tuning the electronic structure of the metal sites in single-atom catalysts (SACs) is the key to optimizing their activity. Herein, we report that iodine doping within the carbon matrix of a cobalt-nitrogen-carbon (Co-N-C) catalyst can effectively modulate its electronic structure and catalytic activity toward the hydrogen evolution reaction (HER). The iodine-doped Co-N-C catalyst shows exceptional HER activity in acid with an overpotential of merely 52 mV at 10 mA cm-2, a small Tafel slope of 56.1 mV dec-1, making it among the best SACs based on both precious and nonprecious metals. Moreover, this catalyst possesses a high turnover frequency (TOF) value of 1.88 s-1 (η = 100 mV), which is about 1 order of magnitude larger than that (0.2 s-1) of the iodine-free counterpart. Experimental and theoretical studies demonstrate that the introduction of iodine dopants lowers the chemical oxidation state of the Co sites, resulting in the optimized hydrogen adsorption and facilitated HER kinetics. This work provides an alternative strategy to regulate the electronic structure of SACs for improved performance.

Engineering the low-coordinated single cobalt atom to boost persulfate activation for enhanced organic pollutant oxidation

Two atomically dispersed cobalt catalysts with different nitrogen coordination numbers (denoted as CoSA-Nx-C) were synthesized and firstly compared to activate peroxydisulfate (PDS) for bisphenol A (BPA) degradation. Theoretical calculations unveiled that lowering the CoN coordination number from four to three can apparently increase the electron density of the single Co atom in CoSA-N3-C to enhance PDS conversion. The low-coordinated CoSA-N3-C with CoN3 coordination structure displays a high specific activity of 0.067 L min1 m2, which is 1.31 times greater than that of CoSA-N4-C with normal CoN4 configuration (0.051 L min1 m2) in PDS activation. Electron paramagnetic resonance (EPR) measurements and quenching tests confirmed the primary role of sulfate radical (SO4•−) in BPA oxidation over CoSA-N3-C with PDS. Moreover, CoSA-N3-C delivers favorable durability for PDS activation and potential practicability for realistic wastewater remediation. These findings provide a novel and useful avenue to coordination number modulation of SACs for wider environmental applications.

Spectral studies of bismuth-containing pyrochlores

Thermal stable solid solutions of titanates, niobates, and tantalates of bismuth with a pyrochlore structure doped with 3d-metal atoms were studied using XPS and NEXAFS spectroscopy. Based on spectral studies, it was shown that the manganese, cobalt, nickel and copper atoms in these solid solutions have mainly charge state +2 and iron atoms – charge state +3.

Electronics and coordination engineering of atomic cobalt trapped by oxygen-driven defects for efficient cathode in solar cells

A rational design and the metal coordination environment regulating of single-atom catalysts (SACs) in specific catalytic reaction remain great challenges. The oxygen defective support can be employed as traps to capture metal species, which provides an effective pathway to synthesize SACs. Here, we propose a counterions-assisted oxygen-driven defect capture (CODC) strategy to fabricate a series of atomically dispersed Co-based catalysts with different electronic and coordination environments. When serving as cathode for dye-sensitized solar cells (DSCs), the triiodine reduction reaction (IRR) activity is very sensitive to the coordination structure. Density functional theory (DFT) calculations reveal that the intrinsic electronic distributions, electron-donating ability, and energy level position determine the coordination behavior and catalytic performance of SACs. Our findings not only define an efficient synthetic strategy to a broad class of M-N x C y based SACs for highly-efficient IRR, but also provide an insight for exploring coordination-sensitive reaction from the atomic view. • An electronic and coordination environment control for accelerating the IRR process was developed. • The atomically dispersed Co-based catalysts were synthesized by a counterions-assisted oxygen-driven defect capture strategy. • The IRR catalytic activity was sensitive to the coordination structure of atomic cobalt. • The electron-donating ability and energy level position determined the coordination behavior of SACs by DFT study.

Unraveling Site Selective Magnetic Properties of Cobalt Sites in Critical Elements Lean RE(TM)5 Magnet Materials

We report here our discovery of crystallographic and interstitial sites and onsite electron correlation propelled intrinsic and derived permanent magnetic properties of critical elements lean RE(TM)5 (RE = La, Ce and TM = Fe, Co) magnet materials. A full potential linearized augmented plane wave (FP-LAPW) method within the local density approximation (LDA) is used to investigate and analyze the electronic structure and magnetism of these RE(TM)5 type structures. To better correlate the experimental results, the effective Coulomb (U) and exchange (J) interactions (Hubbard parameters) are crucial at the transition metal sites. Results show that the main propeller of magnetic anisotropy in these compounds is the cobalt atoms at the 2c sites not the 3g sites. This site-specific property and site preference energetics are used to replace 3g sites with non-critical elements such as iron that exhibits a larger magnetic moment. Based on this strategic replacement, we predict two new compounds that have a larger hardness parameter with a relatively large energy product due to the atomic dilution caused by interstitial addition of nitrogen in the compounds: CeCo2Fe3N2 and LaCo2Fe3N2.

Clinical implications of vitamin B12 as redox-active cofactor.

Vitamin B12 is a redox-active compound containing a cobalt atom that cycles between oxidation states. Superoxide scavenging induces its oxidation, disabling activation of the enzymes methionine synthase and methylmalonyl-CoA mutase, disrupting gene expression and energy production. High-dosed vitamin B12 may be clinically used to reduce oxidative stress and preserve cofactor functions.

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Comparison of biodiesel production using a novel porous Zn/Al/Co complex oxide prepared from different methods: Physicochemical properties, reaction kinetic and thermodynamic studies

The use of heterogeneous catalysts in the transesterification reaction is an eco-friendly and cost-effective approach for biodiesel production as compared to the homogeneous catalyst-based processes. In this study, a heterogeneous cobalt doping Zn/Al complex oxide was prepared by a simple birch-templating method, and successfully applied to the transesterification of jatropha oil with methanol. The catalyst had strong diffraction peaks of ZnAl2O4 spinel crystal with substitutional doping of amorphous cobalt atom. It had a tendency to achieve a high base strength whilst increasing the specific surface area in the presence of cobalt. By contrast to the impregnation and coprecipitation methods, the crystalline particles from templating method were uniformly distributed on the catalyst surface, thus forming a well-defined tiled network with large amounts of grain-free pores. The exposure of available activity sites resulted in a biodiesel yield of 91.4%. After used several times and recycled, the regenerated catalyst also exhibited good catalytic potency without obvious deactivation. The transesterification kinetics satisfied the Pseudo first order model that controlled by the reaction temperature and catalyst dosage. The thermodynamic parameters of ΔH of 16.7 kJ/mol, ΔS of −284.6 J/mol/K, and ΔG of 140.0 kJ/mol suggested an endothermic, endergonic, and non-spontaneous nature of the reaction.

Construction of Two Stable Co(II)-Based Hydrogen-Bonded Organic Frameworks as a Luminescent Probe for Recognition of Fe3+ and Cr2O72- in H2O.

A pair of cobalt(II)-based hydrogen-bonded organic frameworks (HOFs), [Co(pca)2(bmimb)]n (1) and [Co2(pca)4(bimb)2] (2), where Hpca = p-chlorobenzoic acid, bmimb = 1,3-bis((2-methylimidazol-1-yl)methyl)benzene, and bimb = 1,4-bis(imidazol-1-ylmethyl)benzene were hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. X-ray diffraction structural analysis revealed that 1 has a one-dimensional (1D) infinite chain network through the deprotonated pca− monodentate chelation and with a μ2-bmimb bridge Co(II) atom, and 2 is a binuclear Co(II) complex construction with a pair of symmetry-related pca− and bimb ligands. For both 1 and 2, each cobalt atom has four coordinated twisted tetrahedral configurations with a N2O2 donor set. Then, 1 and 2 are further extended into three-dimensional (3D) or two-dimensional (2D) hydrogen-bonded organic frameworks through C–H···Cl interactions. Topologically, HOFs 1 and 2 can be simplified as a 4-connected qtz topology with a Schläfli symbol {64·82} and a 4-connected sql topology with a Schläfli symbol {44·62}, respectively. The fluorescent sensing application of 1 was investigated; 1 exhibits high sensitivity recognition for Fe3+ (Ksv: 10970 M−1 and detection limit: 19 μM) and Cr2O72− (Ksv: 12960 M−1 and detection limit: 20 μM). This work provides a feasible detection platform of HOFs for highly sensitive discrimination of Fe3+ and Cr2O72− in aqueous media.