Cobalt Crystals Research Articles

Ruthenium-doped dual-phase cobalt catalysts for enhanced electrocatalytic hydrogen evolution

Controlling the structural sensitivity and selectivity of metal catalysts in reactions, such as the hydrogen evolution reaction (HER) on cobalt crystals, remains a challenging issue in heterogeneous catalysis. In this study, we introduced a straightforward approach to tuning the phase composition of hexagonal close-packed cobalt (HCP-Co) and face-centered cubic cobalt (FCC-Co) in a core–shell Co/C catalyst through the incorporation of Ru atoms. The HER performance was evaluated by controlling the contents of HCP-Co and FCC-Co phases in the catalysts. Single-atom Ru-doped cobalt catalysts containing dual-phase HCP and FCC were prepared by a mechanical ball-milling zeolitic imidazolate framework (ZIF-67) with appropriate ruthenium chloride, followed by a pyrolysis process. The doping of Ru resulted in changes in the contents of the HCP-Co and FCC-Co phases, which significantly boosted the HER activity of the catalysts. The obtained biphasic Ru-Co/C catalyst demonstrated ultra-low HER overpotential and promising stability in alkaline and acidic media, outperforming single-phase cobalt and commercial Pt/C catalysts. Theoretical calculations revealed the synergistic catalysis effect of biphasic cobalt on HER. These findings, which indicated that significant activity dependence on the crystallographic structure, may inspire new design concepts for efficient metal electrocatalysts.

Adsorption/desorption of H2O and phase transition in crystals of cobalt(II) bis(tolylterpyridine) nitrate

Adsorption/desorption of H2O and phase transition in crystals of cobalt(II) bis(tolylterpyridine) nitrate

Interaction of Valine with Biometal Chlorides in an Aqueous Environment at 25°C

Research in medical biology and pharmacology can expand understanding of the interactions of biometals with amino acids, which are key components of biological systems. This may lead to the development of new complexes that can be used in medicine, for example, to develop new drugs with antimicrobial activity or to maintain metabolic balance in the body. Research purpose:obtaining complex compounds of biometals, cobalt chloride, nickel chloride and manganese chloride with the amino acid valine, as well as the study of their physicochemical and biological properties. For the analysis, the Kjeldahl method was used to determine the nitrogen content. The composition of the formed crystals was analyzed by IR spectroscopy. The structure and shape of cobalt, nickel and manganese crystals were determined using a microscope. The identity of the obtained compounds was confirmed by IR spectroscopy and microscopic analyses. We can conclude that valine in the complex is coordinated to metal ions through the oxygen atoms of the carboxyl and nitrogen groups of the amine groups.

Interaction of Threonine with Biometal Chlorides in an Aqueous Environment at 25°C

The method for the synthesis of complexes with transition group biometal salts with the amino acid threonine includes improvement of reaction conditions, selection of reagents and analytical methods to confirm the formation of complexes. Research purpose: obtaining complex compounds of biometals, cobalt chloride, nickel chloride and manganese chloride with the amino acid threonine, as well as the study of their physicochemical and biological properties. In the synthesis of complex compounds, the preparative method was used. Compositions of the formed crystals were analyzed by IR spectroscopy. The structure and shape of cobalt, nickel and manganese crystals were determined using a microscope. The identity of the obtained compounds was confirmed by IR spectroscopy and microscopic analyses. We can conclude that threonine in the complex is coordinated to metal ions through the oxygen atoms of the carboxyl and nitrogen groups of the amine groups.

Electrodeposition of nanocrystalline cobalt from sulfate baths containing butynediol ethoxylate

Cobalt electrodeposit is a potential ideal matrix for precision diamond tools. In this work, cobalt electrodeposition was conducted in sulfate baths and the effects of butynediol ethoxylate (BEO) on the surface morphology, crystal structure, surface roughness and microhardness of cobalt deposits were investigated. Experimental results revealed that BEO had a strong inhibitory effect on the cobalt deposition process due to its high adsorption ability on cobalt; the addition of BEO favored the formation of smooth deposits of hexagonal close packed structure with [0002] preferred orientation, whose morphology was characterized by tiny granular structures, but it had trivial effects on their microhardness and average crystallite size. The changes in the properties of cobalt deposits could be related to the adsorption of BEO on (0002) plane of cobalt crystals, since the adsorption energy of BEO on this plane is much lower than that on other planes according to the results of molecular dynamics simulation.

Unravelling the effects of short pore on Fischer-Tropsch synthesis and its role as selectivity controller

Ordered mesoporous silica with different pore lengths were synthesized and used as supports for cobalt catalysts in the Fischer-Tropsch (FT) synthesis. The effects of pore length on the product distribution and activity were meticulously investigated, while keeping the cobalt crystal size and pore diameter almost identical. Especially, the catalysts with short pore exhibited significantly increased CO conversion, increased C2–C4 paraffin ratio, and decreased C5+ hydrocarbon selectivity. The short pore was found to provide much faster access rate to reactants, whereas it significantly decreased reaction time due to the shortened residence time in the pore. In situ diffuse reflectance infrared Fourier transform (DRIFT) study revealed that the bridge-type CO adsorption mode was less favored than the linear adsorption mode. This feature reflected decreased propagation probability, and lower selectivity for long-chain hydrocarbons than the Anderson–Schulz–Flory (ASF) distribution predicted. Therefore, catalysts with controlled pore length can be utilized as a selective FT catalyst, exhibiting non-ASF feature. In addition, ordered mesoporous aluminosilicate supports having relatively large mesopore were prepared to see the effects of pore confinement and pore length as well.

CoCl2·6H2O crystal growth and its spectral characteristics

For the first time, a crystal of cobalt (II) chloride hexahydrate has been obtained, the size and quality of which have made it possible to study its faceting and spectral characteristics. The temperature dependence of the cobalt chloride solubility has been determined in the temperature range 29–44 °C. The temperature range of the transition area of change in the composition of equilibrium crystalline hydrates of cobalt chloride from CoCl2·6H2O to CoCl2·2H2O has been established. A CoCl2·6H2O crystal has been grown from a water solution, and its main transmission bands in the wavelength range of λ = 200–1400 nm and thermal stability have been estimated.

Single crystal structure of cobalt and nickel complexes constructed by imidazole ligand and their polycrystalline thin films for nonlinear optical refraction properties

The single crystals of new cobalt and nickel complexes constructed by the imidazole ligand: hexakis(imidazole)-cobalt(II) dichloride tetrahydrate ((C18H24N12Co)Cl2•4(H2O), HICDCTH) and hexakis(imidazole)-nickel(II) acetate dihydrate ((C18H24N12Ni)(CH3COO)2•2(H2O), HINADH) have been obtained and their single crystal structure were determined by X-ray single crystal diffraction. Their polycrystalline thin films on quartz substrates were prepared using in-situ crystallization methods. The surface morphology of the polycrystalline thin films were studied by atomic force microscopy. The nonlinear optical refraction properties of the polycrystalline thin films were investigated by using closed aperture Z-scan technique with 20 picosecond pulses at wavelength 532 nm. Time-dependent density-functional theory with the basis set LanL2DZ were used in theoretically computing their maximum absorption wavelengths, frontier molecular orbitals and molecule′s second hyperpolarizability γ values.

Growth and characterizations of pure and co doped piperazinium L-tartrate single crystals (PPLT) single crystals: Optical and NLO properties

Single crystal of pure and cobalt (Co) doped piperazinium l-tartrate (PPLT) was grown by slow evaporation solution growth method. The effects of Co-doping on the growth, structural, optical, dielectric and NLO properties of PPLT crystals have been investigated. Powder XRD results demonstrate that both pure and Co doped PPLT crystals have crystal belongs to monoclinic system with non-centrosymmetric space group P21. The PPLT crystal has a large transmission window with a low near-UV cut-off wavelength of 231 nm, according to a UV–vis–NIR study. The incorporated Co ion could significantly improve the optical, mechanical, dielectric, conductivity and activation energy of PPLT crystal. The etching experiments were carried out to determine the crystal development pattern. The addition of Co to PPLT crystals improves optical transmittance, energy band gap, second and third order nonlinear optical efficiency, as well as the laser damage threshold. Density functional theory computations of equilibrium geometry and the first order hyperpolarizability of the crystal were calculated. The optimized geometric bond lengths and bond angles obtained by using DFT (B3LYP/6-31G (d,p)) show good agreement with the experimental data.

Hydromechanics for crystal growth from water-salt solutions

This paper presents an overview of the current state of technological problem solving related to controlling of hydrodynamics and mass transfer in crystallizers of complex design (continuous-flowing and non-flowing) during the growth of crystals with technologically important properties (potassium dihydrogen phosphate - KDP and a mixed crystal of nickel and cobalt - KCNSH) from special water-salt solutions. Unlike crystallizers of standard designs for crystal growth from a melt (by Czochralski, Bridgman, etc.), there are also crystallizers of different design for crystal growth from water-salt solutions. According to the designers, the necessary crystal growth conditions are maintained in these crystallizers by creating the best characteristics of the flow, i.e., by controlling its velocity and direction, as well saline saturation solution and temperature. In this work, hydromechanical problems are solved for continuous-flowing and non-flowing crystallizers. The flow visualization through its physical model reveals a multi-vortex and unsteady flow structure due to mixer action, three-dimensional solution inflow and outflow and spatial crystal placement. For this reason, primary attention is given to the studies devoted to the development and application of the mathematical models for hydromechanics and heat and mass transfer based on the complete Navier-Stokes equations in the Boussinesq’s approximation for laminar regimes, as well as to the standard (k-ε)-turbulence model for turbulent regimes. The hydromechanical features associated with the three-dimensional flow complexity are discussed for continuous-flow crystallizers. The possibilities of maintaining the required saline saturation near the growing crystal over a long period of time are analyzed for non-flowing crystallizers. Mathematical models of convective mass transfer are considered in a "solution-crystal" conjugate formulation. The local features of hydrodynamics and mass transfer conditions in solution (saline solution saturation near growing crystal) are analyzed.

Crystallographic, spectroscopic, thermal and computational studies of polymeric cobalt(II)–mellitate complex with 2,2′-bipyridine

Orange single crystals of new polymeric cobalt(II) complex {[Co(bipy)(H2O)4]2[Co(μ-mell)(H2O)2]·10H2O}n, 1, were synthesized by slow evaporation method at room temperature (bipy = 2,2′-bipyridine, mell = hexaanion of mellitic acid) and its crystal structure was determined by single-crystal X-ray diffraction. The complex 1 was characterized based on elemental analysis, FTIR spectroscopy and thermal (TG/DTA) analysis followed by computational analysis of noncovalent interactions and quantum chemical calculations of interaction energies. In 1, two crystallographically different Co(II) atoms adopt a deformed octahedral geometry, while bridging mell acts as a tetrakis monodentate ligand allowing the development of wavy-like anionic chains running along [100] direction. The 3D supramolecular network of 1 is composed of alternating supramolecular and water layers connected by hydrogen bonds. The supramolecular layer is formed of ionic interactions between complex cations and polymeric complex anions, established mainly through O–H···O hydrogen bonds, as well as stacking interactions between bipy ligands, while the water layers are comprised of hydrogen bonded lattice water molecules. Upon heating up to 1200 °C in nitrogen and air atmosphere, complex 1 showed multiple-step degradation that resulted in the formation of Co and Co3O4, respectively. Computed Hirshfeld surfaces and 2D fingerprint plots indicated that O–H···O hydrogen bonds are the most dominant in the crystal structure, while the shape index and curvedness mapped on the Hirshfeld surfaces of 1 revealed that stacking interactions have an important role in the stabilization of the crystal packing. Quantum chemical calculations showed that, aside from ionic hydrogen-bonded interaction between cation and anionic polymer, the important role in the stability of supramolecular structure of 1 is played by hydrogen bonds of cation and anionic polymer with lattice water, as well as by stacking interactions between bipy ligands.

Comprehensive studies on amino acid based organometallic L-threoninum cobalt (II) sulfate (LTCS) single crystal and its antibacterial and antifungal properties

Highly transparent superior quality nonlinear single crystals of L-Threoninum Cobalt (II) Sulfate Heptahydrate were prepared by simple novel slow evaporation solution growth method. The space group, lattice parameters, crystal structure and crystalline nature of L-Threoninum Cobalt (II) Sulfate (LTCS) materials assessed through diffraction analysis (PXRD and SXRD). The optical behavior of LTCS crystals were checked via UV–Vis analysis and it confirms optical parameters often depend on photon energy with optical band gap Eg = 5.6 eV and LTCS material can be acceptable for optoelectronic devices. The hardness and work hardening coefficient of LTCS crystal were investigated using Vickers microhardness testing and the work hardening value 1.94 point out soft nature of the grown material. By use of Kurtz and Perry technique the nonlinear second harmonic generation (SHG) efficiency of prepared LTCS crystals was assessed. The LTCS material developed here is used to treat bacterial and fungal infections and is detected by an antimicrobial assay.

Wide spectral range ultrafast pump-probe magneto-optical spectrometer at low temperature, high-magnetic and electric fields.

We developed a table-top setup to perform magneto-optical pump-probe measurements with the possibility to independently tune the photon-energy of both pump and probe beams in the 0.5 eV-3.5 eV range. Our apparatus relies on a commercial turn-key amplified laser system, able to generate light pulses with duration shorter than or comparable to 100 fs throughout the whole spectral range. The repetition rate of the source can be modified via the computer in the 1 kHz to 1 MHz range. A commercial balanced detector is connected to a high-frequency digitizer, allowing for a highly-sensitive detection scheme: rotations of the probe polarization as small as 70 μdeg can be measured. Additionally, a DC magnetic field as high as 9 T and voltages in the kV regime can be applied on the sample. A cryostat allows us to precisely set the temperature of the specimen in the 4 K-420 K interval. We prove the performance of our setup by measuring the ultrafast demagnetization of a cobalt crystal as a function of a wide variety of experimental parameters.

Structural Changes of Co Caused a Change of the Solution pH During Chemical Deposition

The phase transformations of the Co lattice are discussed, which determine the anomalous changes in the magnetic properties of chemically deposited Co-P films obtained at various pH values. The coercivity of the Hc films obtained at low pH values exceeds 1 kOe and decreases to several units Oe in the films obtained at high pH values. It is shown that the observed changes in the magnetic properties of Co-P films are caused by the transition of the cobalt crystal lattice to the nanocrystalline state

Controllable synthesis of core-shell Co@C@SiO2 catalysts for enhancing product selectivity in Fischer-Tropsch synthesis by tuning the mass transfer resistance

Fischer-Tropsch synthesis (FTS) is the key step in converting syngas into clean fuels. Traditional supported catalysts for FTS are problematic because the active metal crystalline size is positively related to metal loading. Therefore, increasing active metal loading may reduce the cobalt time yield (CTY) since a high CTY is usually obtained when the Co size is 8 nm. Here, a ZIF-67 (Zeolitic imidazolate framework-67) with a MOF (Metal organic framework) structure is used as a precursor to prepare the [email protected] catalyst with not only high cobalt loading (55.6 wt%) but also with a small cobalt crystal size (as small as 8.6 nm). Core-shell [email protected]@SiO2-X catalysts with different SiO2 shell thicknesses were successfully prepared by coating different amounts of TEOS on the outer surface of [email protected] to modify product selectivity. Compared with 40 wt% Co/SiO2 catalyst, core-shell [email protected]@SiO2-X catalysts exhibited improved FTS performance. Furthermore, different gaseous hourly space velocities (GHSVs) were used to obtain CO conversion at similar levels to compare CTY and the turnover frequency (TOF). Among the catalysts, the [email protected]@SiO2-1 catalyst, with its better mass transfer ability and suitable hydrophilic property, presented the highest TOF (9.75 × 10−3 s−1) and lowest CH4 selectivity (9.75%). In addition, heavy hydrocarbons were effectively suppressed with the increase in shell thickness due to the increased mass transfer resistance.

The synergism of nanoplates with habit-tuned crystal and substitution of cobalt with titanium in Ni-rich LiNi0.80Co0.15Al0.05O2 cathode for lithium-ion batteries

LiNi0.80Co0.15Al0.05O2 (NCA), as a kind of commercial Ni-rich cathode material, draws significant attention due to its outstanding advantage of high capacity. Here, we synthesize layer LiNi0.80Co0.15-xTixAl0.05O2 (x = 0, 0.03, 0.06, 0.09) nanoplates with {010} electrochemical planes through a facile and versatile approach to improve their cycling life and rate capability. Among all the samples, LiNi0.80Co0.09Ti0.06Al0.05O2 nanoplates (NCA-T2) has the most {010} planes exposure. As cathode for Li-ion batteries, NCA-T2 displays the largest discharge capacity of 190.2 mAh g−1 corresponding to the capacity retention of 92.9% after 100 charge/discharge cycles at 0.1 C between 2.7 and 4.3 V. The capacity retention of NCA-T2 is much larger than 80.8% of the pristine NCA nanoplates with no Ti-substitution (NCA-T0). The Ti-substituted NCA-T2 sample displays the capacity retention of 90.6% at 5 C during 500 charge/discharge cycles. It suggests that the synergism of nanoplates with {010} electrochemical active planes and Ti in the Co sites can stabilize the structure and improve the rate capability. In addition, the density functional theory (DFT) calculation illustrates Ti doping can suppress the structure variation of NCA-T2.

Ferromagnetic-like behavior of Co doped TiO2 flexible thin films fabricated via co-sputtering for spintronic applications

TiO2:Co thin films on ITO (Indium-tin-oxide)/PET (Poly Ethylene Terephthalate) flexible and glass substrates were fabricated via DC magnetron co-sputtering at room temperature. The samples deposited on glass substrates were subjected to annealing processes at 473 K for 2 h to improve the crystallization of the material. Both TiO2:Co/ITO/PET and TiO2:Co/glass thin films exhibited excellent optical properties with more than 80% transmission in the visible region. An increase on ITO/PET surface temperature was detected during the synthesis of the samples; this variation in the ITO substrate (∼ 2 K) was associated to impact energetic of ion or atoms bombarded during the deposition process. X-ray diffraction measurements evidenced local phases to growth on the flexible substrate; the random distributions of Cobalt crystals into the rutile and anatase phases were associated to a crystalline lattice embedded with magnetic ions. A configuration of small grains and absence of cluster formation on the surface of thin films was observed through SEM and AFM measurements. From this topographic study and MFM measurements evidenced that surface grains were not constituted magnetic domains formation in the thin films. The ferromagnetic-like behavior was observed in a magnetization as function of field measurement by PPMS. M vs H curves at room temperature for TiO2:Co/ITO/PET thin films, showed the hysteresis loop. The dipolar interaction between Cobalt ions without formation of domains were correlated to the magnetic behavior in the material, as the doping concentration is lower than 12%.

Preparation of cobalt crystals with various morphologies and the catalytic performance of platinum-on-cobalt crystal for the selective hydrogenation of nitrobenzene

The Pt/Co-No catalyst exhibited the best catalytic property (yield to aniline-95.8%) due to high Pt dispersion and nano-synergy effect between Pt- and Co-related species.

Spatial confinement of cobalt crystals in carbon nanofibers with oxygen vacancies as a high-efficiency catalyst for organics degradation.

Catalytic activation of peroxymonosulfate (PMS) to generate radicals has received considerable and increasing attention in the environmental catalysis for treatment of recalcitrant pollutants. In the current study, a series of highly porous, cobalt-loaded activated carbon nanofibers (Co/CNFs) were prepared by one-pot electrospinning followed by thermal treatment. Observations showed that the limited addition of Co (≤8%) had no obvious effect on the morphology of the resulted CNFs, but it did affect the surface area and porosity of the CNFs as well as the carbon graphitic process during the carbonization. The applicability of this confined nanoreactor used in sulfate-radical based advanced oxidation processes (SR-AOPs) was systematically investigated. The effect of pH on the radical generation and organics removal was examined. The oxygen species on the CNFs played an important role in the activation of PMS. The carbon layer encapsulated on the Co crystal surface inhibited the Co leaching during the reaction and increased the catalytic efficiency due to the enhanced interfacial charge transfer. Meanwhile, the carbon layer could synchronously function as the adsorptive active sites during the degradation of organics. Results showed that the Co/CNFs possessed the highest catalytic efficiency under neutral pH, corresponding to the sulfate radical generation. The Co leaching and XPS results showed that the Co served as the main active site in PMS activation.

Determination of cathode current efficiency for electrodeposition of ferromagnetic cobalt nanowire arrays in nanochannels with extremely large aspect ratio

Cathode current efficiency for the electrodeposition of cobalt from an acidic aqueous solution, which took place in anodized aluminum oxide (AAO) nanochannels with an average diameter of ca. 25 nm, was determined by Faraday’s first law of electrolysis. The electrodeposited metallic cobalt crystals were grown as an array of nanowires embedded in the nanochannels. The amount of charge consumed for the electrochemical reduction in the nanochannels was estimated considering the time dependence of the cathode current during the electrodeposition of the cobalt nanowires. Meanwhile, the volume of electrodeposition on the cobalt nanowires was determined from the saturated magnetic moment of the nanowires, which was obtained from the magnetization curves. The cathode current efficiency for the electrodeposition of the cobalt nanowire arrays remained at a high level (over 75%) in the cathode potential ranging from −0.70 V to −0.85 V vs. Ag/AgCl. At the cathode potential of −0.80 V, the cathode current efficiency reached 97%. The texture coefficient TC(0 0 2) of the cobalt nanowire arrays increased as the cathodic overpotential for the electrodeposition of cobalt decreased. Due to the extremely large aspect ratio (more than 1000), the cobalt nanowire arrays were spontaneously magnetized in the direction parallel to the long axis of the nanowires. With increasing TC(0 0 2), the coercivity and squareness of the cobalt nanowire arrays also increased up to ca. 1.6 kOe and 0.8, respectively, at room temperature.