Carbon-coated Cobalt Nanoparticles Research Articles

Tailoring the physical parameters of nematogen using non-mesogenic ferromagnetic unit: dielectric and photoluminescence study

Liquid crystals are self-organized anisotropic fluids which exhibit ordered states ranging from nematics to smectics/hexatics. Hybridized liquid crystals with nanoparticles broaden the research area in finding the novel functional devices. Reported herein, the study of highly stable room temperature nematic liquid crystal E7 and carbon-coated cobalt (Co) nanoparticles. Dispersion of 0.50 wt.% Co into E7 has been introduced to tailor the physical parameters of host E7. Dielectric studies have been performed in planar as well as homeotropic cells in the frequency range of 20 Hz–10MHz while photoluminescence spectra have been recorded at excitation wavelength of 325 nm in planar cells. Dielectric studies reveal the change in phase transition temperature and molecular dynamics associated with magnetic nanoparticles doped liquid crystals. Quenching in photoluminescence intensity has been observed with the inclusion of Co nanoparticles due to the formation of non-radiative channels in the composite system. The intercalation of Co nanoparticles into E7 studies manifests the strong correlation between liquid crystals and nanoparticles. Allocation of magnetic attributes onto liquid crystal molecules finds potential applications in advanced magnetic materials, information devices and optical devices.

Rational Design of N-doped Carbon Coated Cobalt Nanoparticles for Highly Efficient and Durable Photothermal CO2 Conversion.

The photothermal CO2 hydrogenation to high value-added chemicals and fuels is an appealing approach to alleviate the energy and environmental concerns. However, it still relies on the development of earth-abundant, efficient and durable catalysts. Here, we report the design of N-doped carbon coated Co nanoparticles (NPs) as a photothermal catalyst, synthesized through a two-step pyrolysis of Co-based ZIF-67 precursor. Consequently, the catalyst exhibits remarkable activity and stability for photothermal CO2 hydrogenation to CO with a 0.75mol gcat -1 h-1 CO production rate under the full spectrum of light illumination. The high activity and durability of this Co NPs are mainly attributed to the synergy of the attuned size of Co NPs, the thickness of carbon layers and the N doping species. Impressively, the experimental characterizations and theoretical simulations show that such a simple N-doped carbon coating strategy can effectively facilitate the desorption of generated CO and activation of reactants due to the strong photothermal effect. This work provides a simple and efficient route for the preparation of highly active and durable nonprecious metal catalysts for promising photothermal catalytic reactions. This article is protected by copyright. All rights reserved.

The Developed Wave Cancellation Theory Contributing to Understand Wave Absorption Mechanism of ZIF Derivatives with Controllable Electromagnetic Parameters.

How to better understand the influence of electromagnetic parameters on the absorbing properties of electromagnetic wave absorbers (EMAs) is an essential prerequisite for further synthesis and development of high-performance EMAs. In this work, an improved wave cancellation theory is used as a guiding principle to prepare N-doped carbon-coated cobalt nanoparticles (Co@NC) using ZIF-8@ZIF-67 as the precursor, thus enabling controllable electromagnetic parameters by regulating the conduction loss and dipole polarization ability. The Co@NC generated by pyrolysis at 700 °C under H2 atmosphere presents an optimized absorption performance. Benefiting from developed wave cancellation theory, the thickness of the film can be accurately adjusted so that the difference between the amplitude of the reflected and transmitted electromagnetic waves is only 0.001 and the phase difference is 180.05°, thus achieving a minimum reflection loss (RLmin (dB)) of -64.0dB. Meanwhile, a maximum effective absorption bandwidth of 5.4GHz is achieved simultaneously attributing to its most suitable electromagnetic parameters. Accordingly, the current research based on wave cancellation theory significantly contributes to understand the relationships between electromagnetic parameters and wave absorption properties, therefore providing a theoretical insight into the further development of high-performance EMAs.

Targeted Large-Volume Lymphocyte Removal Using Magnetic Nanoparticles in Blood Samples of Patients with Chronic Lymphocytic Leukemia: A Proof-of-Concept Study.

In the past, our research group was able to successfully remove circulating tumor cells with magnetic nanoparticles. While these cancer cells are typically present in low numbers, we hypothesized that magnetic nanoparticles, besides catching single cells, are also capable of eliminating a large number of tumor cells from the blood ex vivo. This approach was tested in a small pilot study in blood samples of patients suffering from chronic lymphocytic leukemia (CLL), a mature B-cell neoplasm. Cluster of differentiation (CD) 52 is a ubiquitously expressed surface antigen on mature lymphocytes. Alemtuzumab (MabCampath®) is a humanized, IgG1κ, monoclonal antibody directed against CD52, which was formerly clinically approved for treating chronic lymphocytic leukemia (CLL) and therefore regarded as an ideal candidate for further tests to develop new treatment options. Alemtuzumab was bound onto carbon-coated cobalt nanoparticles. The particles were added to blood samples of CLL patients and finally removed, ideally with bound B lymphocytes, using a magnetic column. Flow cytometry quantified lymphocyte counts before, after the first, and after the second flow across the column. A mixed effects analysis was performed to evaluate removal efficiency. p < 0.05 was defined as significant. In the first patient cohort (n = 10), using a fixed nanoparticle concentration, CD19-positive B lymphocytes were reduced by 38% and by 53% after the first and the second purification steps (p = 0.002 and p = 0.005), respectively. In a second patient cohort (n = 11), the nanoparticle concentration was increased, and CD19-positive B lymphocytes were reduced by 44% (p < 0.001) with no further removal after the second purification step. In patients with a high lymphocyte count (>20 G/L), an improved efficiency of approximately 20% was observed using higher nanoparticle concentrations. A 40 to 50% reduction of B lymphocyte count using alemtuzumab-coupled carbon-coated cobalt nanoparticles is feasible, also in patients with a high lymphocyte count. A second purification step did not further increase removal. This proof-of-concept study demonstrates that such particles allow for the targeted extraction of larger amounts of cellular blood components and might offer new treatment options in the far future.

Removal of Circulating Tumor Cells from Blood Samples of Cancer Patients Using Highly Magnetic Nanoparticles: A Translational Research Project.

The count of circulating tumor cells (CTCs) has been associated with a worse prognosis in different types of cancer. Perioperatively, CTCs detach due to mechanical forces. Diagnostic tools exist to detect and isolate CTCs, but no therapeutic technique is currently available to remove CTCs in vivo from unprocessed blood. The aim of this study was to design and test new magnetic nanoparticles to purify whole blood from CTCs. Novel magnetic carbon-coated cobalt (C/Co) nanoparticles conjugated with anti-epithelial cell adhesion molecule (EpCAM) antibodies were synthesized, and their antifouling and separation properties were determined. The newly developed C/Co nanoparticles showed excellent separation and antifouling properties. They efficiently removed tumor cells that were added to healthy subjects’ blood samples, through an anti-EpCAM antibody interaction. The nanoparticles did not interact with other blood components, such as lymphocytes or the coagulation system. In blood samples of carcinoma patients suffering from metastatic disease, on average, ≥68% of CTCs were removed. These nanoparticles could prompt the development of a blood purification technology, such as a dialysis-like device, to perioperatively remove CTCs from the blood of cancer patients in vivo and potentially improve their prognosis.

Preparation of Functionalized Carbon-Coated Cobalt Nanoparticles with Sulfonated Arene Derivatives, a Study on Surface Functionalization and Stability.

The functionalization of magnetic nanoparticles has been an important field in the last decade due to the versatile applications in catalysis and biomedicine. Generally, a high degree of functionalities on the surface of the nanoparticles is desired. In this study, covalent functionalization of various aromatic sulfonic acids on carbon-coated cobalt nanoparticles are investigated on surface functionalization yield and stability. The nanoparticles are prepared via covalent linkage of an in situ generated diazonium on the graphene-like surface. Adsorption and wash experiments were performed to confirm a covalent bonding of the naphthalene derivatives on the nanoparticle surface. With an increased number of sulfonic acid groups on the aromatic compound a significantly lower loading is observed on the corresponding functionalized nanoparticles. This can be counteracted by a change of nitrite species. With this method, nanoparticles with a high number of sulfonic acid groups can be produced.

Transfer Hydrogenation of Nitroarenes on Carbon-Coated Cobalt Nanoparticles

Key words heterogeneous catalysis - cobalt catalysis - nanoparticles - transfer hydrogenation - nitroarenes

Nitrogen-doped carbon nanotubes decorated with cobalt nanoparticles derived from zeolitic imidazolate framework-67 for highly efficient oxygen reduction reaction electrocatalysis

Nitrogen-doped carbon nanotubes decorated with carbon-coated cobalt nanoparticles (Co@C-NCNTs) are constructed from the zeolitic imidazolate framework ZIF-67. Electrostatic force-induced preadsorption of coordination center ions on the surface of halloysite nanotubes leads to confined nucleation and in situ growth of a thin layer of ZIF-67. Subsequent carbonization and template removal give rise to NCNTs with open end and large inner cavity, thin wall moderate graphitization, and decoration with carbon-coated Co nanoparticles. The synthetic strategy can be easily extended to the preparation of various NCNTs with tunable graphitization and metal decoration from different ZIFs. Benefited from one-dimensional nanotubes with more exposed active surface area and convenient channels for the transport of electrons and reactants, the resulting Co@C-NCNTs exhibit enhanced catalytic performance in oxygen reduction reaction with an onset potential of −0.1 V vs Ag/AgCl, high current density (−4.42 mA/cm2 at −0.6 V), and approximate 4e− transfer process in O2-saturated 0.1 M KOH. The Co@C-NCNTs have higher durability and remarkable methanol tolerance capability both in alkaline and acidic solutions superior to the commercial Pt/C. The present strategy for structure-control electrocatalysts creates a new pathway for the fabrication of promising cathode catalyst for fuel cell applications.

Activating Cobalt Nanoparticles via the Mott-Schottky Effect in Nitrogen-Rich Carbon Shells for Base-Free Aerobic Oxidation of Alcohols to Esters.

Heterogeneous catalysts of inexpensive and reusable transition-metal are attractive alternatives to homogeneous catalysts; the relatively low activity of transition-metal nanoparticles has become the main hurdle for their practical applications. Here, the de novo design of a Mott-Schottky-type heterogeneous catalyst is reported to boost the activity of a transition-metal nanocatalyst through electron transfer at the metal/nitrogen-doped carbon interface. The Mott-Schottky catalyst of nitrogen-rich carbon-coated cobalt nanoparticles (Co@NC) was prepared through direct polycondensation of simple organic molecules and inorganic metal salts in the presence of g-C3N4 powder. The Co@NC with controllable nitrogen content and thus tunable Fermi energy and catalytic activity exhibited a high turnover frequency (TOF) value (8.12 mol methyl benzoate mol-1 Co h-1) for the direct, base-free, aerobic oxidation of benzyl alcohols to methyl benzoate; this TOF is 30-fold higher than those of the state-of-the-art transition-metal-based nanocatalysts reported in the literature. The presented efficient Mott-Schottky catalyst can trigger the synthesis of a series of alkyl esters and even diesters in high yields.

A Layer-Structured Metal-Organic Framework-Derived Mesoporous Carbon for Efficient Oxygen Reduction Reaction

Developing highly active and durable electrocatalysts for the oxygen reduction reaction (ORR) is crucial to large-scale commercialization of fuel cells and metal-air batteries. Here we report a facile approach for the synthesis of nitrogen and oxygen dual-doped mesoporous layer-structured carbon electrocatalyst embedded with graphitic carbon coated cobalt nanoparticles by direct pyrolysis of a layer-structured metal-organic framework. The electrocatalyst prepared at 800 °C exhibits comparable ORR performance to Pt/C catalysts but possesses superior stability to Pt/C catalysts. This synthetic approach provides new prospects in developing sustainable carbon-based electrocatalysts for electrochemical energy conversion devices.

Synthesis and Application of Magnetic Noyori-Type Ruthenium Catalysts for Asymmetric Transfer Hydrogenation Reactions in Water

A Noyori-type ruthenium catalyst was immobilized on magnetic platforms consisting of carbon-coated cobalt nanoparticles and different polymers. Both reactivity and enantioselectivity of these catalysts were benchmarked in the asymmetric transfer hydrogenation of acetophenone in an aqueous medium. The best catalyst, having connected the ruthenium catalyst to the nanoparticle by a poly(styrene) matrix, was characterized by infrared (IR) spectroscopy and via a superconducting quantum interference device (SQUID) to determine the saturation magnetization of the magnetic material as well as by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). A variety of aryl methyl ketones could be reduced to their corresponding alcohols with good yields (81–100%) and selectivity (91–99% ee), and catalyst recovery and reuse was evaluated over 10 runs with ruthenium leaching into the product of <10 ppm, meeting the pharmaceutical requirements for ruthenium impurities of orally available drugs.

ChemInform Abstract: Hierarchically Structured MnO2‐Co/C Nanocomposites: Highly Efficient and Magnetically Recyclable Catalysts for the Aerobic Oxidation of Alcohols.

Porous MnO2 microspheres distributed around magnetic carbon-coated cobalt nanoparticles were developed. The performance of these nanoparticles rivals that of Pd-based catalysts for the selective oxidation of alcohols. Excellent recyclability was conveniently achieved by magnetic decantation and is demonstrated in ten consecutive cycles with no apparent material or performance losses.

Hierarchically Structured MnO2-Co/C Nanocomposites: Highly Efficient and Magnetically Recyclable Catalysts for the Aerobic Oxidation of Alcohols

Porous MnO2 microspheres distributed around magnetic carbon-coated cobalt nanoparticles were developed. The performance of these nanoparticles rivals that of Pd-based catalysts for the selective oxidation of alcohols. Excellent recyclability was conveniently achieved by magnetic decantation and is demonstrated in ten consecutive cycles with no apparent material or performance losses.

ChemInform Abstract: A Palladium Catalyst Supported on Carbon‐Coated Cobalt Nanoparticles — Preparation of Palladium‐Free Biaryls by Suzuki‐Miyaura Reactions in Ethanol.

The preparation of a heterogeneous Pd catalyst supported on carbon-coated magnetic nanoparticles (NPs) bearing 4-(diphenylphosphinomethyl)phenyl groups is discussed. These NPs were initially prepared by chemical vapour deposition (CVD) of carbon on preformed Co NPs; however, the particles prepared in one step by reducing flame synthesis were more appropriate for functionalization. The Pd catalyst was then prepared by three simple steps. We show that Suzuki–Miyaura couplings can be efficiently performed in the presence of very low amounts of supported Pd, usually 50 μequiv. Finally, the Pd leaching was very low: in most cases only 1 μequiv. of Pd is found in the reaction medium (which amounts to less than 1 ppm of the product). Compared to other catalysts supported on magnetic particles, this catalyst is very simple to prepare even in large quantities and is easy to recover completely owing to the high magnetic saturation of the Co nucleus. To the best of our knowledge, it is the simplest and the most-active Pd catalyst supported on carbon-coated Co nanoparticles for Suzuki–Miyaura reactions. The reusability of the catalyst was also ascertained.

Electrocatalytic H2 production from seawater over Co, N-codoped nanocarbons.

One of the main barriers blocking sustainable hydrogen production is the use of expensive platinum-based catalysts to produce hydrogen from water. Herein we report the cost-effective synthesis of catalytically active, nitrogen-doped, cobalt-encased carbon nanotubes using inexpensive starting materials-urea and cobalt chloride hexahydrate (CoCl2·6H2O). Moreover, we show that the as-obtained nanocarbon material exhibits a remarkable electrocatalytic activity toward the hydrogen evolution reaction (HER); and thus it can be deemed as a potential alternative to noble metal HER catalysts. In particular, the urea-derived carbon nanotubes synthesized at 900 °C (denoted as U-CNT-900) show a superior catalytic activity for HER with low overpotential and high current density in our study. Notably also, U-CNT-900 has the ability to operate stably at all pH values (pH 0-14), and even in buffered seawater (pH 7). The possible synergistic effects between carbon-coated cobalt nanoparticles and the nitrogen dopants can be proposed to account for the HER catalytic activity of U-CNT-900. Given the high natural abundance, ease of synthesis, and high catalytic activity and durability in seawater, this U-CNT-900 material is promising for hydrogen production from water in industrial applications.

Reversible magnetic mercury extraction from water

Magnetic carbon-coated cobalt nanoparticles functionalized with polyethyleneimine proved to be highly effective and selective for the detoxification of mercury ions from aqueous solutions.

Polymer- and Dendrimer-Coated Magnetic Nanoparticles as Versatile Supports for Catalysts, Scavengers, and Reagents

The work-up of chemical reactions by standard techniques is often time consuming and energy demanding, especially when chemists have to guarantee low levels of metal contamination in the products. Therefore, scientists need new ideas to rapidly purify reaction mixtures that are both economically and environmentally benign. One intriguing approach is to tether functionalities that are required to perform organic reactions to magnetic nanoparticles, for example, catalysts, reagents, scavengers, or chelators. This strategy allows researchers to quickly separate active agents from reaction mixtures by exploiting the magnetic properties of the support. In this Account, we discuss the main attributes of magnetic supports and describe how we can make the different nanomagnets accessible by surface functionalization. Arguably the most prominent magnetic nanoparticles are superparamagnetic iron oxide nanoparticles (SPIONs) due to their biologically well-accepted constituents, their established size-selective synthesis methods, and their diminished agglomeration (no residual magnetic attraction in the absence of an external magnetic field). However, nanoparticles made of pure metal have a considerably higher magnetization level that is useful in applications where high loadings are needed. A few layers of carbon can efficiently shield such highly reactive metal nanoparticles and, equally important, enable facile covalent functionalization via diazonium chemistry or non-covalent functionalization through π-π interactions. We highlight carbon-coated cobalt (Co/C) and iron (Fe/C) nanoparticles in this Account and compare them to SPIONs stabilized with surfactants or silica shells. The graphene-like coating of these nanoparticles offers only low loadings with functional groups via direct surface modification, and the resulting nanomagnets are prone to agglomeration without effective steric stabilization. To overcome these restrictions and to tune the dispersibility of the magnetic supports in different solvents, we can introduce dendrimers and polymers on Co/C and Fe/C platforms by various synthetic strategies. While dendrimers have the advantage of being able to array all functional groups on the surface, polymers need fewer synthetic steps and higher molecular weight analogues are easily accessible. We present the application of these promising hybrid materials for the extraction of analytes or contaminates from complex aqueous solutions (e.g. waste water treatments or blood analytics), for metal-, organo-, and biocatalysis, and in organic synthesis. In addition, we describe advanced concepts like magnetic protecting groups, a multistep synthesis solely applying magnetic reagents and scavengers, and thermoresponsive self-separating magnetic catalysts. We also discuss the first examples of the use of magnetic scaffolds manipulated by external magnetic fields in flow reactors on the laboratory scale. These hold promise for future applications of magnetic hybrid materials in continuous flow or highly parallelized syntheses with rapid magnetic separation of the applied resins.

Synthesis of functionalized, dispersible carbon-coated cobalt nanoparticles for potential biomedical applications.

Ferromagnetic carbon-coated cobalt nanoparticles have been ligated by a covalent or non-covalent strategy with dendrons or polymers bearing amino-, hydroxy- or polyether-functionalities, aiming at synthesizing materials that are dispersible in aqueous solutions, being a prerequisite for applications in biomedicine. Most efficiently for this purpose proved to be a covalently anchored polyethyleneimine (PEI) with a loading of approximately 10 mmol of amino groups per gram of hybrid nanomaterial, resulting in dispersions that are stable in water for several days.

Rapid Surface–Biostructure Interaction Analysis Using Strong Metal-Based Nanomagnets

Nanomaterials are increasingly suggested for the selective adsorption and extraction of complex compounds in biomedicine. Binding of the latter requires specific surface modifications of the nanostructures. However, even complicated macromolecules such as proteins can afford affinities toward basic surface characteristics such as hydrophobicity, topology, and electrostatic charge. In this study, we address these more basic physical interactions. In a model system, the interaction of bovine serum albumin and amyloid β 42 fibrillar aggregates with carbon-coated cobalt nanoparticles, functionalized with various polymers differing in character, was studied. The possibility of rapid magnetic separation upon binding to the surface represents a valuable tool for studying surface interactions and selectivities. We find that the surface interaction of Aβ 42 fibrillar aggregates is mostly hydrophobic in nature. Because bovine serum albumin (BSA) is conformationally adaptive, it is known to bind surfaces with widely differing properties (charge, topology, and hydrophobicity). However, the rate of tight binding (no desorption upon washing) can vary largely depending on the extent of necessary conformational changes for a specific surface. We found that BSA can only bind slowly to polyethylenimine-coated nanomagnets. Under competitive conditions (high excess BSA compared to that for β 42 fibrillar aggregates), this effect is beneficial for targeting the fibrillar species. These findings highlight the possibility of selective extractions from complex media when advantageous basic physical surface properties are chosen.

In vivo visualization of single native pancreatic islets in the mouse

The purpose of this study was to investigate the potential of a novel targeted contrast agent (CA) for the in vivo visualization of single native pancreatic islets, the sites of insulin production, in the pancreas of mice using magnetic resonance imaging (MRI). The CA for intravenous administration was composed of the β-cell-specific single-chain antibody fragment, SCA B1, and ferromagnetic carbon-coated cobalt nanoparticles. MRI experiments were performed at 7, 9.4 and 16.4 T in excised organs (pancreas, liver, kidney, spleen), at 7 T in mice fixed in formalin and at 9.4 and 16.4 T in living mice. Image contrast in untreated control animals was compared with images from mice treated with unspecific and specific CA. For the validation of MRI results, selected pancreases were subjected to immunohistochemical staining and numerical contrast simulations were performed. Ex vivo results and the outcome of immunohistochemistry suggest that islets are marked only by the CA containing SCA B1. Strong accumulation of particles was found also in other investigated organs owing to the uptake by the reticuloendothelial system, but the contrast in the MR images is clearly distinguishable from the islet specific contrast in pancreases and numerical predictions. In vivo experiments based on averaged dynamic sampling with 66 × 66 × 100 µm³ and triggered acquisition with 90 × 90 × 200 µm³ nominal resolution resulted in similar particle contrast to in in vitro measurements. The newly developed CA and MRI strategies have the potential to be used for studying mouse diabetes models by visualizing single native pancreatic islets.