In-Situ Nanoarchitectonics of Fe/Co LDH over Cobalt-Enriched N-Doped Carbon Cookies as Facile Oxygen Redox Electrocatalysts for High-Rate Rechargeable Zinc-Air Batteries

The reality of long-term rechargeable and high-performance zinc-air batteries relies majorly on cost-effective and eminent bifunctional electrocatalysts, which can perform both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Herein, we demonstrate a new approach for the synthesis of in-situ-grown layered double hydroxide of iron and cobalt over a cobalt nanoparticle-enriched nitrogen-doped carbon frame (CoL 2:1) by a simple coprecipitation reaction with facile scale-up and explore its electrocatalytic ORR and OER activity for an electrically rechargeable zinc-air battery. Consequently, the developed composite displays excellent ORR and OER activity with an ORR half-wave potential of 0.84 V, a limiting current density of 5.85 mA/cm2, and an OER overpotential of 320 mV with exceptional stability. The outstanding bifunctionality index of the catalyst (ΔE = 0.72 V) inspired us to utilize it as a cathode catalyst in an in-house developed prototype zinc-air battery. The battery could easily supply a specific capacity of 804 mAh/g with a maximum peak power density of 161 mW/cm2. The battery exhibits an attractive charge-discharge profile with a lesser voltage gap of 0.76 V at 10 mA/cm2 with durability for a period of 200 h and a voltage efficiency of 97%, which surpassed the corresponding Pt/C + RuO2-based zinc-air battery. Further, a maximum load of 50 mA/cm2 could easily be sustained during cycling, revealing its outstanding stability. A series-connected two CoL 2:1-based zinc-air batteries effortlessly enlighten a pinwheel fan and LED panel simultaneously, revealing its practicality. The high electrical conductivity and greater specific surface area of Co/N-C and its robust attachment with Fe/Co LDH preserves both active sites, thereby resulting in exceptional performance. Our method is capable of being flexible enough to create various bifunctional Co/N-C-based composite electrodes, opening up a feasible pathway to rechargeable zinc-air batteries with maximum energy density.

Comparative Bioactivity Analysis of Green-Synthesized Metal (Cobalt, Copper, and Selenium) Nanoparticles

Aim This study involves synthesizing metal nanoparticles (NPs) via the green synthesis method using Millettia pinnata leaf, Acacia auriculiformis bark, and Citrus sinensis peel and comparatively evaluating their antibacterial activity in vitro through the analysis of cobalt oxide NPs (CoNPs), copper NPs (CuNPs), and selenium NPs (SeNPs). This research contributes to eco-friendly approaches for producing functional nanomaterials with potential applications in medicine and environmental remediation. Materials and methods The metal NPs were synthesized using M. pinnata leaf, A. auriculiformis bark, and C. sinensis peel. These leaf extracts act as self-reducing and stabilizing agents. The antibacterial activity was assessed by the well diffusion method. Cultures of pathogenic bacteria species such as Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa were prepared. NPs were applied to the culture, and zones of inhibition (ZOIs) were measured. The data were statistically analyzed to compare the antibacterial efficacy of the different NPs. Results The successfully synthesized CoNPs, CuNPs, and SeNPs showed distinctive phytochemical properties. CoNPs exhibited the highest ZOI against most bacterial strains, with CuNPs and SeNPs following. CoNPs consistently showed superior performance compared to CuNPs and SeNPs. Conclusion Our study analyzed the bioactivity of metal NPs produced using green synthesis with plant extracts. CoNPs have shown superior antibacterial effectiveness against both Gram-positive and Gram-negative bacteria when compared to CuNPs and SeNPs. This may be due to their larger surface area, smaller size, unique electrical, magnetic, and catalytic properties, as well as their improved contact with the bacterial cell wall and membrane.

Selenium Nanoparticles Attenuate Cobalt Nanoparticle-Induced Skeletal Muscle Injury: A Study Based on Myoblasts and Zebrafish

Cobalt alloys have numerous applications, especially as critical components in orthopedic biomedical implants. However, recent investigations have revealed potential hazards associated with the release of nanoparticles from cobalt-based implants during implantation. This can lead to their accumulation and migration within the body, resulting in adverse reactions such as organ toxicity. Despite being a primary interface for cobalt nanoparticle (CoNP) exposure, skeletal muscle lacks comprehensive long-term impact studies. This study evaluated whether selenium nanoparticles (SeNPs) could mitigate CoNP toxicity in muscle cells and zebrafish models. CoNPs dose-dependently reduced C2C12 viability while elevating reactive oxygen species (ROS) and apoptosis. However, low-dose SeNPs attenuated these adverse effects. CoNPs downregulated myogenic genes and α-smooth muscle actin (α-SMA) expression in C2C12 cells; this effect was attenuated by SeNP cotreatment. Zebrafish studies confirmed CoNP toxicity, as it decreased locomotor performance while inducing muscle injury, ROS generation, malformations, and mortality. However, SeNPs alleviated these detrimental effects. Overall, SeNPs mitigated CoNP-mediated cytotoxicity in muscle cells and tissue through antioxidative and antiapoptotic mechanisms. This suggests that SeNP-coated implants could be developed to eliminate cobalt nanoparticle toxicity and enhance the safety of metallic implants.

Enhanced Photoelectrochemical Performance Using Cobalt-Catalyst-Loaded PVD/RF-Engineered WO3 Photoelectrodes

Critical to boosting photoelectrochemical (PEC) performance is improving visible light absorption, accelerating carrier separation, and reducing electron-hole pair recombination. In this investigation, the PVD/RF method was employed to fabricate WO3 thin films that were subsequently treated using the surface treatment process, and the film surface was modified by introducing varying concentrations of cobalt nanoparticles, a non-noble metal, as an effective Co catalyst. The results show that the impact of loaded cobalt nanoparticles on the film surface can explain the extended absorption spectrum of visible light, efficiently capturing photogenerated electrons. This leads to an increased concentration of charge carriers, promoting a faster rate of carrier separation and enhancing interface charge transfer efficiency. Compared with a pristine WO3 thin film photoanode, the photocurrent of the as-prepared Co/WO3 films shows a higher PEC activity, with more than a one-fold increase in photocurrent density from 1.020 mA/cm2 to 1.485 mA/cm2 under simulated solar radiation. The phase, crystallinity, and surface of the prepared films were analysed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The PVD/RF method, scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM) were employed to assess the surface morphology of the fabricated film electrode. Optical properties were studied using UV-vis absorbance spectroscopy. Simultaneously, the photoelectrochemical properties of both films were evaluated using linear sweep voltammetry and electrochemical impedance spectroscopy (EIS). These results offer a valuable reference for designing high-performance photoanodes on a large scale for photoelectrochemical (PEC) applications.

Cobalt/Nitrogen Co-Doped Carbon Materials Enhance the Reaction Rate of Sodium-Potassium Alloy Electrodes

Sodium-potassium (NaK) alloy electrodes are ideal for next-generation dendrite-free alkali metal electrodes due to their dendrite-free nature. However, issues such as slow diffusion kinetics due to the large K+ radius and the loss of active potassium during the reaction severely limit its application. Here a novel cobalt/nitrogen-doped carbon material is designed and it is applied to the construction of a NaK alloy electrode. The experimental and theoretical results indicate that the confining effect of the nitrogen-doped graphitic carbon layer can protect the cobalt nanoparticles from corrosion leaching, while the presence of Co─Nx bonds and cobalt nanoparticles provides more active sites for the reaction, realizing the synergistic effect of adsorption-catalytic modulation, lowering the K+ diffusion energy barrier and promoting charge transfer and ion diffusion. The application of this electrode to a symmetrical battery can achieve more than 1800 stable cycles under a current density of 0.4 mA cm-2 and a charge/discharge specific capacity of 122.64 mAh g-1 under a current of 0.5C in a full battery. This finding provides a new idea to realize a fast, stable, and efficient application of NaK alloy electrodes.

Evaluation of neurotoxicity and the role of oxidative stress of cobalt nanoparticles, titanium dioxide nanoparticles, and multiwall carbon nanotubes in Caenorhabditis elegans

The widespread use of nanomaterials in daily life has led to increased concern about their potential neurotoxicity. Therefore, it is particularly important to establish a simple and reproducible assessment system. Representative nanomaterials, including cobalt nanoparticles (CoNPs), titanium dioxide nanoparticles (TiO2-NPs), and multiwall carbon nanotubes (MWCNTs), were compared in terms of their neurotoxicity and underlying mechanisms. In 0, 25, 50, and 75 μg/ml of these nanomaterials, the survival, locomotion behaviors, acetylcholinesterase (AchE) activity, reactive oxygen species production, and glutathione-S transferase 4 (Gst-4) activation in wildtype and transgenic Caenorhabditis elegans (C. elegans) were evaluated. All nanomaterials induced an imbalance in oxidative stress, decreased the ratio of survival, impaired locomotion behaviors, as well as reduced the activity of AchE in C. elegans. Interestingly, CoNPs and MWCNTs activated Gst-4, but not TiO2-NPs. The reactive oxygen species scavenger, N-acetyl-l-cysteine, alleviated oxidative stress and Gst-4 upregulation upon exposure to CoNPs and MWCNTs, and rescued the locomotion behaviors. MWCNTs caused the most severe damage, followed by CoNPs and TiO2-NPs. Furthermore, oxidative stress and subsequent activation of Gst-4 were involved in nanomaterials-induced neurotoxicity. Our study provides a comprehensive comparison of the neurotoxicity and mechanisms of typical nanomaterials, which could serve as a model for hazard assessment of environmental pollutants using C. elegans as an experimental model system.

Prevalence of Cobalt in the Environment and Its Role in Biological Processes

Cobalt (Co) is an essential trace element for humans and other animals, but high doses can be harmful to human health. It is present in some foods such as green vegetables, various spices, meat, milk products, seafood, and eggs, and in drinking water. Co is necessary for the metabolism of human beings and animals due to its key role in the formation of vitamin B12, also known as cobalamin, the biological reservoir of Co. In high concentrations, Co may cause some health issues such as vomiting, nausea, diarrhea, bleeding, low blood pressure, heart diseases, thyroid damage, hair loss, bone defects, and the inhibition of some enzyme activities. Conversely, Co deficiency can lead to anorexia, chronic swelling, and detrimental anemia. Co nanoparticles have different and various biomedical applications thanks to their antioxidant, antimicrobial, anticancer, and antidiabetic properties. In addition, Co and cobalt oxide nanoparticles can be used in lithium-ion batteries, as a catalyst, a carrier for targeted drug delivery, a gas sensor, an electronic thin film, and in energy storage. Accumulation of Co in agriculture and humans, due to natural and anthropogenic factors, represents a global problem affecting water quality and human and animal health. Besides the common chelating agents used for Co intoxication, phytoremediation is an interesting environmental technology for cleaning up soil contaminated with Co. The occurrence of Co in the environment is discussed and its involvement in biological processes is underlined. Toxicological aspects related to Co are also examined in this review.

Textile Waste-Derived Cobalt Nanoparticles Embedded in Active Carbon Fiber for Efficient Activation of Peroxymonosulfate to Remove Organic Pollutants

Burning and dumping textile wastes have caused serious damage to the environment and are a huge waste of resources. In this work, cobalt nanoparticles embedded in active carbon fiber (Co/ACF) were prepared from bio-based fabric wastes, including cotton, flax and viscose. The obtained Co/ACF was applied as a catalyst for the heterogeneous activation of peroxymonosulfate (PMS) to remove bisphenol A (BPA) from an aqueous solution. The results showed that cotton-, flax- and viscose-derived Co/ACF all exhibited excellent performance for BPA degradation; over ~97.0% of BPA was removed within 8 min. The Co/ACF/PMS system exhibited a wide operating pH range, with a low consumption of the catalyst (0.1 g L-1) and PMS (0.14 g L-1). The high specific surface area (342 m2/g) and mesoporous structure of Co/ACF allowed the efficient adsorption of pollutants as well as provided more accessible active sites for PMS activation. This study provided an example of using textile wastes to produce a valuable and recyclable catalyst for environmental remediation.

Direct Evidence of Dynamic Metal Support Interactions in Co/TiO2 Catalysts by Near-Ambient Pressure X-ray Photoelectron Spectroscopy

The interaction between metal particles and the oxide support, the so-called metal-support interaction, plays a critical role in the performance of heterogenous catalysts. Probing the dynamic evolution of these interactions under reactive gas atmospheres is crucial to comprehending the structure-performance relationship and eventually designing new catalysts with enhanced properties. Cobalt supported on TiO2 (Co/TiO2) is an industrially relevant catalyst applied in Fischer-Tropsch synthesis. Although it is widely acknowledged that Co/TiO2 is restructured during the reaction process, little is known about the impact of the specific gas phase environment at the material's surface. The combination of soft and hard X-ray photoemission spectroscopies are used to investigate in situ Co particles supported on pure and NaBH4-modified TiO2 under H2, O2, and CO2:H2 gas atmospheres. The combination of soft and hard X-ray photoemission methods, which allows for simultaneous probing of the chemical composition of surface and subsurface layers, is one of the study's unique features. It is shown that under H2, cobalt particles are encapsulated below a stoichiometric TiO2 layer. This arrangement is preserved under CO2 hydrogenation conditions (i.e., CO2:H2), but changes rapidly upon exposure to O2. The pretreatment of the TiO2 support with NaBH4 affects the surface mobility and prevents TiO2 spillover onto Co particles.

A Hyperbranched Polyol Process for Designing and Manufacturing Nontoxic Cobalt Nanocomposite

A method for the design and synthesis of a metallopolymer composite (CoNP) based on cobalt nanoparticles using the hyperbranched polyol process was developed. It was shown that hyperbranched polyester polyols in a melted state can be both a reducing agent and a stabilizer of metal nanoparticles at the same time. The mechanism of oxidation of hyperbranched polyol was studied using diffuse reflectance IR spectroscopy. The process of oxidation of OH groups in G4-OH started from 90 °C and finished with the oxidation of aldehyde groups. The composition and properties of nanomaterials were determined with FT-IR and UV-Vis spectroscopy, Nanoparticle Tracking Analysis (NTA), thermogravimetric analysis (TG), powder X-ray diffraction (XRD), NMR relaxation, and in vitro biological tests. The cobalt-containing nanocomposite (CoNP) had a high colloidal stability and contained spheroid polymer aggregates with a diameter of 35-50 nm with immobilized cobalt nanoparticles of 5-7 nm. The values of R2 and R1 according to the NMR relaxation method for CoNPs were 6.77 mM·ms-1 × 10-5 and 4.14 mM·ms-1 × 10-5 for, respectively. The ratio R2/R1 = 0.61 defines the cobalt-containing nanocomposite as a T1 contrast agent. The synthesized CoNPs were nonhemotoxic (HC50 > 8 g/mL) multifunctional reagents and exhibited the properties of synthetic modulators of the enzymatic activity of chymosin aspartic proteinase and exhibited antimycotic activity against Aspergillus fumigatus. The results of the study show the unique prospects of the developed two-component method of the hyperbranched polyol process for the creation of colloidal multifunctional metal-polymer nanocomposites for theranostics.

as a novel antimicrobials and antioxidants

Trianthema portulacastrum is a dietary and medicinal plant that has gained substantial importance due to its pharmacological properties. This plant was used for its various healing properties since the ancient period in ayurvedic system of medicine. The green synthesis technique is an eco-friendly as well as cost effective technique which can produce more biocompatible nanoparticles when compared with those fabricated by physio-chemical methods. Therefore, nanoparticles produced by green synthesis are credible alternatives to those which are produced by conventional synthesis techniques. This research mainly aims to produce nanoparticles with the methanolic leaf extract of T. portulacastrum. The optimized nanoparticles were further analyzed for anti-fungal, anti-bacterial and antioxidant properties. Disk diffusion assay was used for the determination of the antimicrobial property and on the other hand, DPPH radical scavenging assay as well as hydrogen peroxide scavenging activity proved the antioxidant property of the formulation. The study revealed that Escherichia coli (gram negative strain) shows greater zone of inhibition when compared with Bacillus subtilis (gram positive bacteria). The nanoparticles have also been reported to show significant anti-fungal activity against the strains of Aspergillus niger and Fusarium oxysporum which proves its desirability for its further use against both bacterial as well as fungal infections. The novel formulation can be explored dually as antimicrobial and antioxidant agent.

Biosynthesis and characterization of cobalt nanoparticles using combination of different plants and their antimicrobial activity

It has become crucial to biosynthesize efficient, secure, and affordable nanoparticles that we use for the treatment of various infections, including surgical site infection and wound infection, due to the rapid development of microbial resistance to numerous antibiotic drugs. The objective of the present study is to biosynthesize cobalt nanoparticles using an extract from the combined peels of garlic (Allium sativum) and onion (Allium cepa). Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction were used to confirm the synthesis of cobalt nanoparticle (XRD). Well diffusion was used to measure antimicrobial activity. Escherichia coli, Proteus, Staphylococcus aureus, Staphylococcus cohnii, and Klebsiella pneumonia were the bacterial strains employed Both the crude prepared extract and the biosynthesized cobalt nanoparticles demonstrated efficacy against all strains of bacteria, but the crude prepared extract displayed a low zone of inhibition ranging from 10 to 13 mm, while the biosynthesized cobalt nanoparticles displayed a high zone of inhibition ranging from 20 to 24 mm.

Simulation and Synthesis of Cobalt (Co) Nanoparticles by Gamma Radiation Technique

Cobalt nanoparticles were synthesized using the gamma radiolytic technique, and the particle size was found to be reduced from 12±1 to 7±1 nm by increasing the dose from 10 to 60 kGy. The UV-visible absorption spectra were measured and exhibited a steady absorption maxima at 517 nm in the UV region, which blue-shifted toward a lower wavelength with a decrease in particle size. By taking the conduction electrons of an isolated particle that are not entirely free but are instead bound to their respective quantum levels, the optical absorption of the cobalt nanoparticles can be calculated and simulated via intra-band quantum excitation for particle sizes comparable to the measured ones. We found that the simulated absorption maxima of electronic excitations corresponded to the measured absorption maxima. Moreover, the structural characterizations were performed utilizing dynamic light scattering (DLS), transmission electron microscopy (TEM), and X-ray diffraction (XRD).

Co-Doped Zeolite-GO Nanocomposite as a High-Performance ORR Catalyst for Sustainable Bioelectricity Generation in Air-Cathode Single-Chambered Microbial Fuel Cells

High-performance cobalt (Co) nanoparticles supported on a zeolite-graphene oxide (1:2) matrix (catalyst Z2) are synthesized through a facile reduction method. In multipoint Brunauer-Emmett-Teller (MBET) surface area analysis, catalyst Z2 demonstrates a higher surface area compared with other synthesized catalysts, indicating the presence of a larger number of catalytic active sites, and supports outstanding ORR performance due to an improved electron-transfer rate and a higher number of redox-active sites. Furthermore, it is observed that catalyst Z2 is an excellent electrocatalytic material due to its low charge-transfer resistance and higher oxygen reduction reaction (ORR) activity. Herein, the electrocatalytic investigation suggests that catalyst Z2 at a potential of 483 mV and a reduction current of -0.382 mA displays a higher electrocatalytic performance and higher stability toward ORR compared with other synthesized catalysts and even the standard Pt/C catalyst. Also, when catalyst Z2 is applied as an air-cathode ORR electrocatalyst for a single-chambered microbial fuel cell (SC-MFC), the SC-MFC coated with catalyst Z2 generates the maximum power density of 416.78 mW/m2, which is 306% higher than that of SC-MFC coated with Pt/C (102.67 mW/m2). In fact, the longer stability and electronic conductivity have contributed to an outstanding ORR activity of the nanocomposite due to its porous surface morphology and the presence of the functional groups in the zeolite-GO support matrix. In brief, Co (cobalt) nanoparticles doped on a zeolite-GO (1:2) support matrix are promising cathode electrocatalysts in the practical application of MFCs and other related devices.

Dielectric Properties of Hybrid Polyethylene Composites Containing Cobalt Nanoparticles and Carbon Nanotubes

Polymer composites with electrically conductive inclusions are intensively developed for microwave shielding applications, where lightweight and elastic coatings are necessary. In this paper, dielectric properties of hybrid polyethylene composites containing cobalt nanoparticles and multi-wall carbon nanotubes (MWCNT) were investigated in the wide frequency range of 20–40 GHz for electromagnetic shielding applications. The percolation threshold in the hybrid system is close to 6.95 wt% MWCNT and 0.56 Co wt%. Cobalt nanoparticles (up to highest investigated concentration 4.8 wt%) had no impact on the percolation threshold, and for the fixed total concentration of fillers, the complex dielectric permittivity is higher for composites with bigger MWCNT concentrations. Moreover, the microwave complex dielectric permittivity of composites with high concentration of fillers is quite high (for composites with 13.4 wt% MWCNT and 1.1 wt% Co ε′ ≈ ε″ ≈ 20 at 30 GHz, it corresponds to microwave absorption 50% of 1 mm thickness plate); therefore, these composites are suitable for electromagnetic shielding applications.

A Multiscale Strategy to Construct Cobalt Nanoparticles Confined within Hierarchical Carbon Nanofibers for Efficient CO2 Electroreduction

The efficiency of CO₂ electroreduction has been largely limited by the activity of the catalysts as well as the three-phase interface. Herein, a multiscale strategy is proposed to synthesize hierarchical nanofibers covered by carbon nanotubes and embedded with cobalt nanoparticles (Co/CNT/HCNF). The confinement effect of carbon nanotubes can restrict the diameter of the cobalt particles down to several nanometers and prevent the easy corrosion of these nanoparticles. The three-dimensional carbon nanofibers, in size range of several hundred nanometers, improve the electrochemically active surface area, facilitate electron transfer, and accelerate CO₂ transportation. These cross-linked carbon nanofibers eventually form a freestanding Co/CNT/HCNF membrane of dozens of square centimeters. Consequently, Co/CNT/HCNF produces CO with 97% faradaic efficiency at only -0.4 V_RHE cathode potential in an H-type cell. From the regulation of catalyst nanostructure to the design of macrography devices, Co/CNT/HCNF membrane can be directly used as the gas-diffusion compartment in a flow cell device. Co/CNT/HCNF membrane generates CO with faradaic efficiencies higher than 90% and partial current densities greater than 300 mA cm^-2 for at least 100-h stability. This strategy provides a successful example of efficient catalysts for CO₂ electroreduction and also has the feasibility in other self-standing energy conversion devices.

Carbon Dioxide Reduction with Hydrogen on Fe, Co Supported Alumina and Carbon Catalysts under Supercritical Conditions

Reduction of CO₂ with hydrogen into CO was studied for the first time on alumina-supported Co and Fe catalysts under supercritical conditions with the goal to produce either CO or CH₄ as the target products. The extremely high selectivity towards methanation close to 100% was found for the Co/Al₂O₃ catalyst, whereas the Fe/Al₂O₃ system demonstrates a predominance of hydrogenation to CO with noticeable formation of ethane (up to 15%). The space–time yield can be increased by an order of magnitude by using the supercritical conditions as compared to the gas-phase reactions. Differences in the crystallographic phase features of Fe-containing catalysts cause the reverse water gas shift reaction to form carbon monoxide, whereas the reduced iron phases initiate the Fischer–Tropsch reaction to produce a mixture of hydrocarbons. Direct methanation occurs selectively on Co catalysts. No methanol formation was observed on the studied Fe- and Co-containing catalysts.

Selenomethionine protects hematopoietic stem/progenitor cells against cobalt nanoparticles by stimulating antioxidant actions and DNA repair functions

Hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) can differentiate into all blood lineages to maintain hematopoiesis, wound healing, and immune functions. Recently, cobalt-chromium alloy casting implants have been used extensively in total hip replacements; however, cobalt nanoparticles (CoNPs) released from the alloy were toxic to HSCs and HPCs. We aimed to investigate the mechanism underlying the toxic effect of CoNPs on HSCs/HPCs and to determine the protective effect of selenomethionine (SeMet) against CoNPs in vitro and in vivo. Human and rat CD34+ HSCs/HPCs were isolated from cord blood and bone marrow, respectively. CoNPs decreased the viability of CD34+ HSCs/HPCs and increased apoptosis. SeMet attenuated the toxicity of CoNPs by enhancing the antioxidant ability of cells. The protective effect of SeMet was not completely abolished after adding H2O2 to abrogate the improvement of the antioxidant capacity by SeMet. SeMet and CoNPs stimulated ATM/ATR DNA damage response signals and inhibited cell proliferation. Unlike CoNPs, SeMet did not damage the DNA, and cell proliferation recovered after removing SeMet. SeMet inhibited the CoNP-induced upregulation of hypoxia inducible factor (HIF)-1α, thereby disrupting the inhibitory effect of HIF-1α on breast cancer type 1 susceptibility protein (BRCA1). Moreover, SeMet promoted BRCA1-mediated ubiquitination of cyclin B by upregulating UBE2K. Thus, SeMet enhanced cell cycle arrest and DNA repair post-CoNP exposure. Overall, SeMet protected CD34+ HSCs/HPCs against CoNPs by stimulating antioxidant activity and DNA repair.

Kinetically Stable Nonequilibrium Gold-Cobalt Alloy Nanoparticles with Magnetic and Plasmonic Properties Obtained by Laser Ablation in Liquid

Nonequilibrium nanoalloys are metastable solids obtained at the nanoscale under nonequilibrium conditions that allow the study of kinetically frozen atoms and the discovery of new physical and chemical properties. However, the stabilization of metastable phases in the nanometric size regime is challenging and the synthetic route should be easy and sustainable, for the nonequilibrium nanoalloys to be practically available. Here we report on the one-step laser ablation synthesis in solution (LASiS) of nonequilibrium Au-Co alloy nanoparticles (NPs) and their characterization on ensembles and at the single nanoparticle level. The NPs are obtained as a polycrystalline solid solution stable in air and water, although surface cobalt atoms undergo oxidation to Co(II). Since gold is a renowned plasmonic material and metallic cobalt is ferromagnetic at room temperature, these properties are both found in the NPs. Besides, surface conjugation with thiolated molecules is possible and it was exploited to obtain colloidally stable solutions in water. Taking advantage of these features, an array of magnetic-plasmonic dots was obtained and used for surface-enhanced Raman scattering experiments. Overall, this study confirms that LASiS is an effective method for the formation of kinetically stable nonequilibrium nanoalloys and shows that Au-Co alloy NPs are appealing magnetically responsive plasmonic building blocks for several nanotechnological applications.

A new and efficient methodology for olefin epoxidation catalyzed by supported cobalt nanoparticles

A new heterogeneous catalytic system consisting of cobalt nanoparticles (CoNPs) supported on MgO and tert-butyl hydroperoxide (TBHP) as oxidant is presented. This CoNPs@MgO/t-BuOOH catalytic combination allowed the epoxidation of a variety of olefins with good to excellent yield and high selectivity. The catalyst preparation is simple and straightforward from commercially available starting materials and it could be recovered and reused maintaining its unaltered high activity.

Metal Organic Framework (MOF)/Wood Derived Multi-cylinders High-Power 3D Reactor

3D monolithic reactor has shown great promise for varied heterogeneous catalysis reactions including water treatment, energy generation and storage, and clean fuel production. As a natural porous material, macroporous wood is regarded as an excellent support for inorganic catalyst due to its abundant polar functional groups and channels. On the other hand, a metal organic framework (MOF) has been widely used as heterogeneous catalyst due to its high specific surface area and large amount of microporosities. Combining macroporous wood and a microporous MOF is expected to produce a high-performance 3D reactor and is demonstrated here for Fischer-Tropsch synthesis. The carbonized MOF/wood reactor retains the original cellular structure with over 180 000 channels/cm². When being decorated with hexagonal-shaped core-shell Co@C nanoparticles aggregates derived from Co-MOF, the MOF/wood reactor resembles a multi-cylinders reactor for Fischer-Tropsch synthesis. Because of the unique combination of macro- and microporous hierarchical structure, the 3D MOF/wood reactor demonstrates exceptional performance under high gas hourly space velocity (81.2% CO conversion and 48.5% C₅₊ selectivity at 50 L·h^-1·g_cat^-1 GHSV). This validates that MOF/wood can serve as a multi-cylinders and high-power reactor for catalytic reactions, which is expected to be applicable for environmental and energy applications.

Green fabrication of Co and Co3O4 nanoparticles and their biomedical applications: A review

Nanotechnology is the fabrication, characterization, and potential application of various materials at the nanoscale. Over the past few decades, nanomaterials have attracted researchers from different fields because of their high surface-to-volume ratio and other unique and remarkable properties. Cobalt and cobalt oxide nanoparticles (NPs) have various biomedical applications because of their distinctive antioxidant, antimicrobial, antifungal, anticancer, larvicidal, antileishmanial, anticholinergic, wound healing, and antidiabetic properties. In addition to biomedical applications, cobalt and cobalt oxide NPs have been widely used in lithium-ion batteries, pigments and dyes, electronic thin film, capacitors, gas sensors, heterogeneous catalysis, and for environmental remediation purposes. Different chemical and physical approaches have been used to synthesize cobalt and cobalt oxide NPs; however, these methods could be associated with eco-toxicity, cost-effectiveness, high energy, and time consumption. Recently, an eco-friendly, safe, easy, and simple method has been developed by researchers, which uses biotic resources such as plant extract, microorganisms, algae, and other biomolecules such as starch and gelatin. Such biogenic cobalt and cobalt oxide NPs offer more advantages over other physicochemically synthesized methods. In this review, we have summarized the recent literature for the understanding of green synthesis of cobalt and cobalt oxide NPs, their characterization, and various biomedical applications.

In Situ Self-Polymerization to Form Hollow Graphitized Carbon Nanocages with Embedded Cobalt Nanoparticles for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries, owing to the multi-electron participation in the redox reaction, possess enormous energy density, which has aroused much attention. Nevertheless, the detrimental shuttle effect, volume expansion, and electrical insulation of sulfur, have hindered their application. To improve the cyclability, a functional host, consisting of Co nanoparticles and N-doped hollow graphitized carbon (Co-NHGC) material, is elaborated, which has the advantages of: 1) the graphitized carbon material working as an electronic matrix to improve the utilization rate of sulfur; 2) the hollow structure relieving the stress change caused by volume expansion; 3) the rich active sites catalyze the electrochemical reaction of sulfur and entrap polysulfides. These advantages significantly improve the performance of the lithium-sulfur batteries. Accordingly, the S@Co-NHGC cathode exhibits excellent initial specific capacity, high coulombic efficiency, and excellent rate performance. This work utilizes a novel method of dopamine in situ etching of a metal-organic framework to synthetize the Co-NHGC host of sulfur, which will hopefully provide inspiration for other energy materials.

Assessing Cobalt Metal Nanoparticles Uptake by Cancer Cells Using Live Raman Spectroscopy

Purpose

Nanotechnology applied to cancer treatment is a growing area of research in nanomedicine with magnetic nanoparticle-mediated anti-cancer drug delivery systems offering least possible side effects. To that end, both structural and chemical properties of commercial cobalt metal nanoparticles were studied using label-free confocal Raman spectroscopy.

Materials and Methods

Crystal structure and morphology of cobalt nanoparticles were studied by XRD and TEM. Magnetic properties were studied with SQUID and PPMS. Confocal Raman microscopy has high spatial resolution and compositional sensitivity. It, therefore, serves as a label-free tool to trace nanoparticles within cells and investigate the interaction between coating-free cobalt metal nanoparticles and cancer cells. The toxicity of cobalt nanoparticles against human cells was assessed by MTT assay.

Results

Superparamagnetic Co metal nanoparticle uptake by MCF7 and HCT116 cancer cells and DPSC mesenchymal stem cells was investigated by confocal Raman microscopy. The Raman nanoparticle signature also allowed accurate detection of the nanoparticle within the cell without labelling. A rapid uptake of the cobalt nanoparticles followed by rapid apoptosis was observed. Their low cytotoxicity, assessed by means of MTT assay against human embryonic kidney (HEK) cells, makes them promising candidates for the development of targeted therapies. Moreover, under a laser irradiation of 20mW with a wavelength of 532nm, it is possible to bring about local heating leading to combustion of the cobalt metal nanoparticles within cells, whereupon opening new routes for cancer phototherapy.

Conclusion

Label-free confocal Raman spectroscopy enables accurately localizing the Co metal nanoparticles in cellular environments. The interaction between the surfactant-free cobalt metal nanoparticles and cancer cells was investigated. The facile endocytosis in cancer cells shows that these nanoparticles have potential in engendering their apoptosis. This preliminary study demonstrates the feasibility and relevance of cobalt nanomaterials for applications in nanomedicine such as phototherapy, hyperthermia or stem cell delivery.

Conversion of Co Nanoparticles to CoS in Metal-Organic Framework-Derived Porous Carbon during Cycling Facilitates Na2S Reactivity in a Na-S Battery

Room-temperature sodium-sulfur batteries have attracted wide interest due to their high energy density and high natural abundance. Polysulfide dissolution and irreversible Na₂S conversion are challenges to achieving high battery performance. Herein, we utilize a metal-organic framework-derived Co-containing nitrogen-doped porous carbon (CoNC) as a catalytic sulfur cathode host. A concentrated sodium electrolyte based on sodium bis(fluorosulfonyl)imide, dimethoxyethane, and bis(2,2,2-trifluoroethyl) ether is used to mitigate polysulfide dissolution. We tune the amount of Co present in the CoNC carbon host by acid washing. Significant improvement in reversible sulfur conversion and capacity retention is observed with a higher Co content in CoNC, with 600 mAh g^-1 and 77% capacity retention for CoNC and 261 mAh g^-1 and 56% capacity retention for acid-washed CoNC at cycle 50 at 80 mAh g^-1. Post-mortem X-ray photoelectron spectroscopy, transmission electron microscopy, and selected area electron diffraction suggest that CoS is formed during cycling in place of Co nanoparticles and CoN₄ sites. Raman spectroscopy suggests that CoS exhibits a catalytic effect on the oxidation of Na₂S. Our findings provide insights into understanding the role Co-based catalysts play in sulfur batteries.

Tunable Syngas Production through CO2 Electroreduction on Cobalt-Carbon Composite Electrocatalyst

Controllable concomitant production of CO and H₂ (syngas) during electrochemical CO₂ reduction reactions (CO₂RR) is expected to improve the commercial feasibility of the technology to mitigate CO₂ emissions as the generated syngas can be converted into useful chemicals using the commercial Fischer-Tropsch (FT) process. Herein, we demonstrate the ability of a Co single-atom-decorated N-doped graphitic carbon shell-encapsulated cobalt nanoparticle electrocatalyst (referred as Co@CoNC-900) to controllably produce syngas at low overpotentials during CO₂RR. Through the engineering and modulation of dual active sites for CO₂RR (modified carbon shell with encapsulated Co) and hydrogen evolution reaction (Co-N₄ moieties) within Co@CoNC by varying the annealing temperature, we are able to tune the H₂: CO ratio from 1: 2 to 1: 1 to 3: 2 over a wide range of applied potentials (-0.5 V to -0.8 V versus reversible hydrogen electrode, RHE). This versatile control of H₂: CO ratio in CO₂RR reaction brings up significant opportunity of using CO₂ and H₂O and renewable energy for producing a range of chemicals.

Cobalt Nanoparticles on Plasma-Controlled Nitrogen-Doped Carbon as High-Performance ORR Electrocatalyst for Primary Zn-Air Battery

Metal-air batteries and fuel cells have attracted much attention as powerful candidates for a renewable energy conversion system for the last few decades. However, the high cost and low durability of platinum-based catalysts used to enhance sluggish oxygen reduction reaction (ORR) at air electrodes prevents its wide application to industry. In this work, we applied a plasma process to synthesize cobalt nanoparticles catalysts on nitrogen-doped carbon support with controllable quaternary-N and amino-N structure. In the electrochemical test, the quaternary-N and amino-N-doped carbon (Q-A)/Co catalyst with dominant quaternary-N and amino-N showed the best onset potential (0.87 V vs. RHE) and highest limiting current density (-6.39 mA/cm2). Moreover, Q-A/Co was employed as the air catalyst of a primary zinc-air battery with comparable peak power density to a commercial 20 wt.% Pt/C catalyst with the same loading, as well as a stable galvanostatic discharge at -20 mA/cm2 for over 30,000 s. With this result, we proposed the synergetic effect of transitional metal nanoparticles with controllable nitrogen-bonding can improve the catalytic activity of the catalyst, which provides a new strategy to develop a Pt-free ORR electrocatalyst.

Selective Electrocatalytic H2 O2 Generation by Cobalt@N-Doped Graphitic Carbon Core-Shell Nanohybrids

Electrocatalytic oxygen reduction (ORR) is an emerging synthetic strategy to prepare H₂ O₂ in a sustainable fashion. N-doped graphitic carbon with embedded cobalt nanoparticles was selected as an advanced material able to selectively trigger the ORR to form H₂ O₂ with a faradaic efficiency of almost 100 % at very positive applied potentials. The production of H₂ O₂ proceeded with high rates as calculated by bulk electrolysis (49 mmol g^-1  h^-1 ) and excellent current densities (≈-0.8 mA cm^-2 at 0.5 V vs. reversible hydrogen electrode). The totally selective behavior depended on the combination of concomitant material features, such as the textural properties, the nature of the metal, the distribution of N moieties, the acidic environment, and the applied potential.

Nitrogen-Doped Carbon Nanotube Confined Co-Nx Sites for Selective Hydrogenation of Biomass-Derived Compounds

Biomass is the most abundant renewable resource on earth and developing high-performance nonprecious selective hydrogenation (SH) catalysts will enable the use of biomass to replace rapidly diminishing fossil resources. This work utilizes ZIF-67-derived nitrogen-doped carbon nanotubes to confine Co nanoparticles (NPs) with Co-N_x active sites as a high-performance SH catalyst. The confined Co NPs with Co-N_x exhibit excellent catalytic activity, selectivity, and stability toward a wide range of biomass-derived compounds. Such active sites can selectively hydrogenate aldehyde, ketone, carboxyl, and nitro groups of biomass-derived compounds into value-added fine chemicals with 100% selectivity. The reported approach could be adopted to create other forms of catalytically active sites from other nonprecious metals.

High-Density Cobalt Nanoparticles Encapsulated with Nitrogen-Doped Carbon Nanoshells as a Bifunctional Catalyst for Rechargeable Zinc-Air Battery

High efficient electrocatalytic activity and strong stability to both oxygen reduction reaction (ORR) and oxygen evolution (OER) are very critical to rechargeable Zn-air battery and other renewable energy technologies. As a class of promising catalysts, the nanocoposites of transition metal nanoparticles that are encapsulated with nitrogen-doped carbon nanoshells are considered as promising substitutes to expensive precious metal based catalysts. In this work, we demonstrate the successful preparation of high-density cobalt nanoparticles encapsulated in very thin N-doped carbon nanoshells by the pyrolysis of solid state cyclen-Co-dicyandiamide complex. The morphologies and properties of products can be conveniently tuned by adjusting the pyrolysis temperature. Owing to the synergetic effect of hybrid nanostructure, the optimized Co@N-C-800 sample possesses outstanding bifunctional activity for both ORR and OER in alkaline electrolyte. Meanwhile, the corresponding rechargeable zinc-air battery that is based on Co@N-C-800 air cathode also has excellent current density, low charge-discharge voltage gap, high power density, and strong cycle stability, making it a suitable alternative to take the place of precious metal catalysts for practical utilization.

Synthesis of Polystyrene-Coated Superparamagnetic and Ferromagnetic Cobalt Nanoparticles

Polystyrene-coated cobalt nanoparticles (NPs) were synthesized through a dual-stage thermolysis of cobalt carbonyl (Co₂(CO)₈). The amine end-functionalized polystyrene surfactants with varying molecular weight were prepared via atom-transfer radical polymerization technique. By changing the concentration of these polymeric surfactants, Co NPs with different size, size distribution, and magnetic properties were obtained. Transmission electron microscopy characterization showed that the size of Co NPs stabilized with lower molecular weight polystyrene surfactants (M_n = 2300 g/mol) varied from 12–22 nm, while the size of Co NPs coated with polystyrene of middle (M_n = 4500 g/mol) and higher molecular weight (M_n = 10,500 g/mol) showed little change around 20 nm. Magnetic measurements revealed that the small cobalt particles were superparamagnetic, while larger particles were ferromagnetic and self-assembled into 1-D chain structures. Thermogravimetric analysis revealed that the grafting density of polystyrene with lower molecular weight is high. To the best of our knowledge, this is the first study to obtain both superparamagnetic and ferromagnetic Co NPs by changing the molecular weight and concentration of polystyrene through the dual-stage decomposition method.

Highly Stable COF-Supported Co/Co(OH)2 Nanoparticles Heterogeneous Catalyst for Reduction of Nitrile/Nitro Compounds under Mild Conditions

Ordered nanoporosity in covalent organic framework (COF) offers excellent opportunity for property development. Loading nanoparticles (nPs) onto them is one approach to introducing tailor-made properties into a COF. Here, a COF-Co/Co(OH)₂ composite containing about 16 wt% of <6 nm sized Co/Co(OH)₂ nPs is prepared on a N-rich COF support that catalyzes the release of theoretical equivalence of H₂ from readily available, safe, and cheap NaBH₄ . Furthermore, the released H₂ is utilized for the hydrogenation of nitrile and nitro compounds to amines under ambient conditions in a facile one-pot reaction. The COF "by choice" is built from "methoxy" functionalized dialdehydes which is crucial in enabling the complete retention of the COF structure under the conditions of the catalysis, where the regular Schiff bonds would have hydrolyzed. The N-rich binding pockets in the COF ensure strong nP-COF interactions, which provides stability and enables catalyst recycling. Modeling studies reveal the crucial role played by the COF in exposing the active facets and thereby in controlling the activation of the reducing agent. Additionally, via density functional theory, we provide a rational explanation for how these COFs can stabilize nanoparticles which grow beyond the limiting pore size of the COF and yet result in a truly stable heterogeneous catalyst - a ubiquitous observation. The study underscores the versatility of COF as a heterogeneous support for developing cheap and highly active nonnoble metal catalysts.

Cobalt Nanoparticles/Black Phosphorus Nanosheets: An Efficient Catalyst for Electrochemical Oxygen Evolution

Black phosphorus (BP) nanosheet (NS) is an emerging oxygen evolution reaction (OER) electrocatalyst with both high conductivity and abundant active sites. However, its ultrathin structure suffers instability because of the lone pair electrons exposed at the surface, which badly restricts durability for achieving long-term OER catalysis. Herein, a facile solvothermal reduction route is designed to fabricate Co/BP NSs hybrid electrocatalyst by in situ growth of cobalt nanoparticles on BP NSs. Notably, electronic structure engineering of Co/BP NSs catalyst is observed by electron migration from BP to Co due to the higher Fermi level of BP than that of Co. Because of the preferential migration of the active lone pairs from the defect of BP NSs, the stability and high hole mobility can be effectively retained. Consequently, Co/BP NSs electrocatalyst exhibits outstanding OER performance, with an overpotential of 310 mV at 10 mA cm-2, and excellent stability in alkaline media, indicating the potential for the alternatives of commercial IrO2. This study provides insightful understanding into engineering electronic structure of BP NSs by fully utilizing defect and provides a new idea to design hybrid electrocatalysts.

Metal/Carbon Hybrid Nanostructures Produced from Plasma-Enhanced Chemical Vapor Deposition over Nafion-Supported Electrochemically Deposited Cobalt Nanoparticles

In this work, we report development of hybrid nanostructures of metal nanoparticles (NP) and carbon nanostructures with strong potential for catalysis, sensing, and energy applications. First, the etched silicon wafer substrates were passivated for subsequent electrochemical (EC) processing through grafting of nitro phenyl groups using para-nitrobenzene diazonium (PNBT). The X-ray photoelectron spectroscope (XPS) and atomic force microscope (AFM) studies confirmed presence of few layers. Cobalt-based nanoparticles were produced over dip or spin coated Nafion films under different EC reduction conditions, namely CoSO₄ salt concentration (0.1 M, 1 mM), reduction time (5, 20 s), and indirect or direct EC reduction route. Extensive AFM examination revealed NP formation with different attributes (size, distribution) depending on electrochemistry conditions. While relatively large NP with >100 nm size and bimodal distribution were obtained after 20 s EC reduction in H₃BO₃ following Co²⁺ ion uptake, ultrafine NP (<10 nm) could be produced from EC reduction in CoSO₄ and H₃BO₃ mixed solution with some tendency to form oxides. Different carbon nanostructures including few-walled or multiwalled carbon nanotubes (CNT) and carbon nanosheets were grown in a C₂H₂/NH₃ plasma using the plasma-enhanced chemical vapor deposition technique. The devised processing routes enable size controlled synthesis of cobalt nanoparticles and metal/carbon hybrid nanostructures with unique microstructural features.

Molybdenum Carbide-Decorated Metallic Cobalt@Nitrogen-Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) based on water splitting holds great promise for clean energy technologies, in which the key issue is exploring cost-effective materials to replace noble metal catalysts. Here, a sequential chemical etching and pyrolysis strategy are developed to prepare molybdenum carbide-decorated metallic cobalt@nitrogen-doped porous carbon polyhedrons (denoted as Mo/Co@N-C) hybrids for enhanced electrocatalytic hydrogen evolution. The obtained metallic Co nanoparticles are coated by N-doped carbon thin layers while the formed molybdenum carbide nanoparticles are well-dispersed in the whole Co@N-C frames. Benefiting from the additionally implanted molybdenum carbide active sites, the HER performance of Mo/Co@N-C hybrids is significantly promoted compared with the single Co@N-C that is derived from the pristine ZIF-67 both in alkaline and acidic media. As a result, the as-synthesized Mo/Co@N-C hybrids exhibit superior HER electrocatalytic activity, and only very low overpotentials of 157 and 187 mV are needed at 10 mA cm^-2 in 1 m KOH and 0.5 m H₂ SO₄ , respectively, opening a door for rational design and fabrication of novel low-cost electrocatalysts with hierarchical structures toward electrochemical energy storage and conversion.

Electrochemical Hydrogen Storage in Facile Synthesized Co@N-Doped Carbon Nanoparticle Composites

A Co@nitrogen-doped carbon nanoparticle composite was synthesized via a facile molecular self-assembling procedure. The material was used as the host for the electrochemical storage of hydrogen. The hydrogen storage capacity of the material was over 300 mAh g^-1 at a rate of 100 mAg^-1. It also exhibited superior stability for storage of hydrogen, high rate capability, and good cyclic life. Hybridizing metallic cobalt nanoparticle with nitrogen-doped mesoporous carbon is found to be a good approach for the electrochemical storage of hydrogen.

Co Nanoparticles Encapsulated in N-Doped Carbon Nanosheets: Enhancing Oxygen Reduction Catalysis without Metal-Nitrogen Bonding

It is known that introducing metal nanoparticles (e.g., Fe and Co) into N-doped carbons can enhance the activity of N-doped carbons toward the oxygen reduction reaction (ORR). However, introducing metals into N-doped carbons inevitably causes the formation of multiple active sites. Thus, it is challenging to identify the active sites and unravel mechanisms responsible for enhanced ORR activity. Herein, by developing a new N-heterocyclic carbene (NHC)-Co complex as the nitrogen- and metal-containing precursor, we report the synthesis of N-doped carbon nanosheets embedded with Co nanoparticles as highly active ORR catalysts without direct metal-nitrogen bonding. Electrochemical measurements and X-ray absorption spectroscopy indicate that the carbon-nitrogen sites surrounding Co nanoparticles are responsible for the observed ORR activity and stability. Density functional theory calculations further reveal that Co nanoparticles could facilitate the protonation of O₂ and thus promote the ORR activity. These results provide new prospects in the rational design and synthesis of heteroatom-doped carbon materials as non-precious-metal catalysts for various electrochemical reactions.

Plasma-Assisted Synthesis of Self-Supporting Porous CoNPs@C Nanosheet as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

The utilization of a highly active and robust bifunctional catalyst for simultaneously producing H₂ and O₂ is still a major challenging issue, which is vital for improving the efficiency of overall water splitting. Herein, we employ a novel plasma-assisted strategy to rapidly and conveniently synthesize the three-dimensional (3D) porous composite nanosheets assembled on monodispersed Co nanoparticles encapsulated in a carbon framework (CoNPs@C) on a carbon cloth. Such a novel 3D hierarchical porous nanosheet improves the exposure and accessibility of active sites as well as ensures high electroconductibility. Moreover, the coating of a few graphene layers on the surface of catalysts favors improvement of the catalytic activity. Benefited from these multiple merits, the CoNPs@C composite nanosheets enable a low overpotential of 153 mV at -10 mA cm^-2 for hydrogen evolution reaction. Furthermore, they are also capable of catalyzing the oxygen evolution reaction with high efficiency to achieve current density of 10 mA cm^-2 at the overpotential of 270 mV. Remarkably, when assembled as an alkaline water electrolyzer, the bifunctional CoNPs@C composite nanosheets can afford a water-splitting current density of 10 mA cm^-2 at a cell voltage of 1.65 V.

Evidence of Structure Sensitivity in the Fischer-Tropsch Reaction on Model Cobalt Nanoparticles by Time-Resolved Chemical Transient Kinetics

The Fischer-Tropsch process, or the catalytic hydrogenation of carbon monoxide (CO), produces long chain hydrocarbons and offers an alternative to the use of crude oil for chemical feedstocks. The observed size dependence of cobalt (Co) catalysts for the Fischer-Tropsch reaction was studied with colloidally prepared Co nanoparticles and a chemical transient kinetics reactor capable of measurements under non-steady-state conditions. Co nanoparticles of 4.3 nm and 9.5 nm diameters were synthesized and tested under atmospheric pressure conditions and H₂ /CO=2. Large differences in carbon coverage (Θ_C ) were observed for the two catalysts: the 4.3 nm Co catalyst has a Θ_C less than one while the 9.5 nm Co catalyst supports a Θ_C greater than two. The monomer units present on the surface during reaction are identified as single carbon species for both sizes of Co nanoparticles, and the major CO dissociation site is identified as the B₅ -B geometry. The difference in activity of Co nanoparticles was found to be a result of the structure sensitivity caused by the loss of these specific types of sites at smaller nanoparticle sizes.

Effect of the Polymeric Stabilizer in the Aqueous Phase Fischer-Tropsch Synthesis Catalyzed by Colloidal Cobalt Nanocatalysts

A series of small and well defined cobalt nanoparticles were synthesized by the chemical reduction of cobalt salts in water using NaBH4 as a reducing agent and using various polymeric stabilizers. The obtained nanocatalysts of similar mean diameters (ca. 2.6 nm) were fully characterized and tested in the aqueous phase Fischer-Tropsch Synthesis (AFTS). Interestingly, the nature and structure of the stabilizers used during the synthesis of the CoNPs affected the reduction degree of cobalt and the B-doping of these NPs and consequently, influenced the performance of these nanocatalysts in AFTS.

Electrocatalytic Cobalt Nanoparticles Interacting with Nitrogen-Doped Carbon Nanotube in Situ Generated from a Metal-Organic Framework for the Oxygen Reduction Reaction

A metal organic framework (MOF), synthesized from cobalt salt, melamine (mela), and 1,4-dicarboxybezene (BDC), was used as precursor to prepare Co/CoN_x/N-CNT/C electrocatalyst via heat treatment at different temperature (700-900 °C) under nitrogen atmosphere. Crystallites size and microstrain in the 800 °C heat-treated sample (MOFs-800) were the lowest, whereas the stacking fault value was the highest among the rest of the homemade samples, as attested to by the Williamson-Hall analysis, hence assessing that the structural or/and surface modification of Co nanoparticles (NPs), found in MOFs-800, was different from that in other samples. CNTs in MOFs-800, interacting with Co NPs, were formed on the surface of the support, keeping the hexagonal shape of the initial MOF. Among the three homemade samples, the MOF-800 sample, with the best electrocatalytic performance toward oxygen reduction reaction (ORR) in 0.1 M KOH solution, showed the highest density of CNTs skin on the support, the lowest I_D/I_G ratio, and the largest N atomic content in form of pyridinic-N, CoN_x, pyrrolic-N, graphitic-N, and oxidized-N species. Based on the binding energy shift toward lower energies, a strong interaction between the active site and the support was identified for MOFs-800 sample. The number of electron transfer was 3.8 on MOFs-800, close to the value of 4.0 determined on the Pt/C benchmark, thus implying a fast and efficient multielectron reduction of molecular oxygen on CoN_x active sites. In addition, the chronoamperometric response within 24 000 s showed a more stable current density at 0.69 V/RHE on MOFs-800 as compared with that of Pt/C.

Ultrafine Co-based Nanoparticle@Mesoporous Carbon Nanospheres toward High-Performance Supercapacitors

A general synthetic methodology is reported to grow ultrafine cobalt-based nanoparticles (NPs, 2-7 nm) within high-surface-area mesoporous carbon (MC) frameworks. Our design strategy is based on colloidal amphiphile (CAM) templated oxidative self-polymerization of dopamine. The CAM templates consisting of a hydrophobic silica-like core and a hydrophilic PEO shell can coassemble with dopamine and template its self-polymerization to form polydopamine (PDA) nanospheres. Given that PDA has rich binding sites such as catechol and amine to coordinate metal ions (e.g., Co²⁺), PDA nanospheres containing Co²⁺ ions can be converted into hierarchical porous carbon frameworks containing ultrafine metallic Co NPs (Co@MC) using high-temperature pyrolysis. The CAM templates offer strong "nanoconfinements" to prevent the overgrowth of Co NPs within carbon frameworks. The yielded ultrafine Co NPs have an average size of <7 nm even at a very high loading of 65 wt %. Co@MC can be further converted into various oxides and sulfides, e.g., CoO, Co₃O₄, CoS₂ and transition-metal doped bimetallic Co_xM_1-xS₂, without significantly changing the size of NPs. As a proof-of-concept application, the porous Co-based NPs@MC hybrids were used as electrode materials for supercapacitors, which exhibit excellent supercapacitive performance with outstanding long-term cycling stability, due to the features such as ultrafine size, controllable chemical compositions, hierarchical porous structures, and full coverage of conductive carbons.

Covalent versus Charge Transfer Modification of Graphene/Carbon-Nanotubes with Vitamin B1: Co/N/S-C Catalyst toward Excellent Oxygen Reduction

High-performance nonprecious cathodic catalysts for oxygen reduction are highly demanded for low-temperature polymer electrolyte membrane fuel cells (PEMFCs). Here, we report a noble-meta- free, nitrogen and sulfur codoped graphene(G)/carbon-nanotube(CNT) material decorated with Co nanoparticles (NPs), which serve as catalytic sites for excellent oxygen reduction reaction (ORR) in basic and acidic media. Out of the cathodic catalysts synthesized by either covalent (cov) or charge transfer (CT) modification of graphen oxide (GO) with thiamine (Th: Vitamin B1), ThG/CNT/Co-cov shows more promising ORR properties than ThG/CNT/Co-CT. Catalyst ThG/CNT/Co-cov exhibits onset/halfwave potentials of 0.95/0.86 V in 0.1 M KOH and 0.92/0.83 V in 0.1 M HClO4, which are comparable to those of commercial catalyst Pt/C (0.95/0.86 V). As compared to Pt/C, our catalyst shows higher current densities of 6.72 mA cm(-2) in basic medium and 7.08 mA cm(-2) in acidic medium at 0.55 V (vs reversible hydrogen electrode (RHE)). It also exhibits better catalytic stability and methanol tolerance. High catalytic efficiency and stability of ThG/CNT/Co-cov show a promising prospect of materialization of PEMFCs for clean energy production.

Synthesis of Co3O4 nanoparticles with block and sphere morphology, and investigation into the influence of morphology on biological toxicity

In the present study, cobalt oxide (Co₃O₄) magnetic nanoparticles with block and sphere morphologies were synthesized using various surfactants, and the toxicity of the particles was analyzed by monitoring biomarkers of nanoparticle toxicity in zebrafish. The use of tartarate as a surfactant produced highly crystalline blocks of Co₃O₄ nanoparticles with pores on the sides, whereas citrate lead to the formation of nanoparticles with a spherical morphology. Co₃O₄ structure, crystallinity, size and morphology were studied using X-ray diffractogram and field emission scanning electron microscopy. Following an increase in nanoparticle concentration from 1 to 200 ppm, there was a corresponding increase in nitric oxide (NO) generation, induced by both types of nanoparticles [Co₃O₄-NP-B (block), r=0.953; Co₃O₄-NP-S (sphere), r=1.140]. Comparative analyses indicated that both types of nanoparticle produced significant stimulation at ≥5 ppm (P<0.05) compared with a control. Upon analyzing the effect of nanoparticle morphology on NO generation, it was observed that Co₃O₄-NP-S was more effective compared with Co₃O₄-NP-B (5 and 100 ppm, P<0.05; 200 ppm, P<0.01). Exposure to both types of nanoparticles produced reduction in liver glutathione (GSH) activity with corresponding increase in dose (Co₃O₄-NP-B, r=-0.359; Co₃O₄-NP-S, r=-0.429). However, subsequent analyses indicated that Co₃O₄-NP-B was more potent in inhibiting liver GSH activity compared with Co₃O₄-NP-S. Co₃O₄-NP-B proved to be toxic at 5 ppm (P<0.05) and GSH activity was almost completely inhibited at 200 ppm. A similar toxicity was observed with both types of Co₃O₄-NPs against brain levels of acetylcholinesterase (AChE; Co₃O₄-NP-B, r=-0.180; Co₃O₄-NP-S, r=-0.230), indicating the ability of synthesized Co₃O₄-NPs to cross the blood-brain barrier and produce neuronal toxicity. Co₃O₄-NP-B showed increased inhibition of brain AChE activity compared with Co₃O₄-NP-S (1,5, and 10 ppm, P<0.05; 50, 100 and 200 ppm, P<0.01). These results suggested that the morphology of nanoparticle and surface area contribute to toxicity, which may have implications for their biological application.

Cobalt nanoparticles embedded in nitrogen-doped carbon for the hydrogen evolution reaction

There is great interest in renewable and sustainable energy research to develop low-cost, highly efficient, and stable electrocatalysts as alternatives to replace Pt-based catalysts for the hydrogen evolution reaction (HER). Though nanoparticles encapsulated in carbon shells have been widely used to improve the electrode performances in energy storage devices (e.g., lithium ion batteries), they have attracted less attention in energy-related electrocatalysis. Here we report the synthesis of nitrogen-enriched core-shell structured cobalt-carbon nanoparticles dispersed on graphene sheets and we investigate their HER performances in both acidic and basic media. These catalysts exhibit excellent durability and HER activities with onset overpotentials as low as ∼70 mV in both acidic (0.5 M H2SO4) and alkaline (0.1 M NaOH) electrolytes, and the overpotentials needed to deliver 10 mA cm(-2) are determined to be 265 mV in acid and 337 mV in base, further demonstrating their potential to replace Pt-based catalysts. Control experiments reveal that the active sites for HER might come from the synergistic effects between the cobalt nanoparticles and nitrogen-doped carbon.

Importance of the HIF pathway in cobalt nanoparticle-induced cytotoxicity and inflammation in human macrophages

Recent, unexpected high failure rates of metal-on-metal hip implants have reintroduced the issue of cobalt toxicity. An adverse reaction to cobalt ions and cobalt-induced lung injury occurs during environmental exposure and is now strictly controlled. Currently adverse reaction occurs to cobalt nanoparticles during wear and tear of metal-on-metal hip implants of which the underlying mechanism is not fully understood. The putative role of the hypoxia-inducible factor (HIF) pathway in the mechanism of cobalt nanoparticle (Co-NPs) toxicity was examined using the U937 cell line, human alveolar macrophages and monocyte-derived macrophages. Co-NPs (5-20 μg/ml)-induced cytotoxicity (viability ranged from 75% to <20% of control, respectively) and reactive oxygen species (ROS), whereas a comparable concentration of cobalt ions (Co(II); up to 350 μM) did not. Co-NPs induced HIF-1α stabilization. Addition of ascorbic acid (100 µM) and glutathione (1 mM) both prevented the increased ROS. However, only treatment with ascorbic acid reduced HIF-1α levels and prevented cell death, indicating that a ROS-independent pathway is involved in Co-NPs-induced cytotoxicity. Replenishing intracellular ascorbate, which is crucial in preventing HIF pathway activation, modified Co-induced HIF target gene expression and the inflammatory response, by decreasing interleukin-1 beta (IL-1β) mRNA and protein expression. Addition of glutathione had no effect on Co-NPs-induced HIF target gene expression or inflammatory response. Thus, Co-NPs induce the HIF pathway by depleting intracellular ascorbate, leading to HIF stabilization and pathway activation. This suggests a strong, ROS-independent role for HIF activation in Co-NPs-induced cytotoxicity and a possible role for HIF in metal-on-metal hip implant pathology.

Cobalt-embedded nitrogen-rich carbon nanotubes efficiently catalyze hydrogen evolution reaction at all pH values

Despite being technically possible, splitting water to generate hydrogen is still practically unfeasible due mainly to the lack of sustainable and efficient catalysts for the half reactions involved. Herein we report the synthesis of cobalt-embedded nitrogen-rich carbon nanotubes (NRCNTs) that 1) can efficiently electrocatalyze the hydrogen evolution reaction (HER) with activities close to that of Pt and 2) function well under acidic, neutral or basic media alike, allowing them to be coupled with the best available oxygen-evolving catalysts-which also play crucial roles in the overall water-splitting reaction. The materials are synthesized by a simple, easily scalable synthetic route involving thermal treatment of Co(2+) -embedded graphitic carbon nitride derived from inexpensive starting materials (dicyandiamide and CoCl2 ). The materials' efficient catalytic activity is mainly attributed to their nitrogen dopants and concomitant structural defects.

Lung toxicities of core-shell nanoparticles composed of carbon, cobalt, and silica

We present here comparative assessments of murine lung toxicity (biocompatibility) after in vitro and in vivo exposures to carbon (C–SiO₂-etched), carbon–silica (C–SiO₂), carbon–cobalt–silica (C–Co–SiO₂), and carbon–cobalt oxide–silica (C–Co₃O₄–SiO₂) nanoparticles. These nanoparticles have potential applications in clinical medicine and bioimaging, and thus their possible adverse events require thorough investigation. The primary aim of this work was to explore whether the nanoparticles are biocompatible with pneumatocyte bioenergetics (cellular respiration and adenosine triphosphate content). Other objectives included assessments of caspase activity, lung structure, and cellular organelles. Pneumatocyte bioenergetics of murine lung remained preserved after treatment with C–SiO₂-etched or C–SiO₂ nanoparticles. C–SiO₂-etched nanoparticles, however, increased caspase activity and altered lung structure more than C–SiO₂ did. Consistent with the known mitochondrial toxicity of cobalt, both C–Co–SiO₂ and C–Co₃O₄–SiO₂ impaired lung tissue bioenergetics. C–Co–SiO₂, however, increased caspase activity and altered lung structure more than C–Co₃O₄–SiO₂. The results indicate that silica shell is essential for biocompatibility. Furthermore, cobalt oxide is the preferred phase over the zerovalent Co(0) phase to impart biocompatibility to cobalt-based nanoparticles.

Improvement of the oxidation stability of cobalt nanoparticles

In order to enhance the resistance of cobalt nanoparticles to oxidation in air, the impact of different stabilization strategies on the isothermal oxidation of particle dispersions and powders was kinetically investigated and compared to as-prepared particle preparations. A post-synthesis treatment with different alcohols was employed, and we also investigate the influence of two different polymer shells on the oxidation process. We found a parabolic decrease of the magnetization for all particle charges, indicating that the process is dominated by a diffusion of oxygen to the cobalt core and a radial growth of the oxide layer from the particle surface to the core. A significant deceleration of the oxidation process was observed for all alcohol-passivated particle preparations, and this resulted finally in a stagnation effect. The stabilizing effect increases in the sequence Co@OA/MeOH < Co@OA/EtOH < Co@OA/iPrOH. For polymer-coated particle preparations Co@PCL and Co@PS, the deceleration was even more pronounced. The results demonstrate that cobalt nanoparticles can effectively be protected against oxidation in order to improve their mid- to longterm stability.