Core-shell Carbon Research Articles

All-around coating of CoNi nanoalloy using a hierarchically porous carbon derived from bimetallic MOFs for highly efficient hydrolytic dehydrogenation of ammonia-borane

In situ synthesis of core–shell carbon enclosed CoNi alloys achieves efficient heterogeneous catalysis.

Nonradical degradation of microorganic pollutants by magnetic N-doped graphitic carbon: A complement to the unactivated peroxymonosulfate

Abstract N-doped carbonaceous materials are highly promising for efficient removal of microorganic contaminants from aqueous solutions by simultaneously serving as adsorbents and catalysts. However, their recollection from aqueous solutions for repeated use is challenging. Here, we designed a magnetic N-doped graphitic carbon core–shell structure (MN-GCCS) for oxidative degradation of various microorganic contaminants via the activation of environmentally friendly peroxymonosulfate (PMS). The magnetic Co3O4 core ensured the easily recollection of MN-GCCS via magnetic separation. Meanwhile, the graphitic carbon ideally prevented the Co3O4 from leaching. MN-GCCS showed great reactivity for pollutant degradation at a wide range of pH values and was particularly active under circumneutral conditions (pH 6–8). MN-GCCS outperformed the commonly known activators of PMS; Under identical conditions, near 100% of atrazine was removed with MN-GCCS, while only 36%, 21%, and 14% of the atrazine were removed with multi-walled carbon nanotubes, CuFe2O4, and Co3O4, respectively. In contrast to the known radical processes, the degradation of contaminants by MN-GCCS–PMS was not mediated by radicals. Instead, a mechanism involving a transition oxidation state of MN-GCCS as the major oxidizing intermediate was proposed. The results from this study suggest a novel and highly efficient nonradical process for oxidative degradation of organic contaminants.

Iron oxide@graphitic carbon core-shell nanoparticles embedded in ordered mesoporous N-doped carbon matrix as an efficient cathode catalyst for PEMFC

Developing electrocatalysts with high activity and long-term stability towards oxygen reduction reaction (ORR) in acidic media is still an important topic. However, most of the already reported non-precious-metal catalysts (NPMCs) for ORR exhibit excellent performance in basic media.In the present work, we report a newly designed FeOx@graphitic carbon core-shell structured nanoparticles implanted in N-doped carbon matrix, with ordered and mesoporous structure (FeOx@GC-NOMC), which i) exhibits a better electrocatalytic activity in acidic media, ii) follows a four-electron ORR process, and iii) shows superior stability and inertness to methanol when compared with commercial Pt/C (20 wt %). These features are mostly attributed to the following two points: i) the ordered mesoporous carbon matrix can not only be favorable for the rapid transfer and active sites exposure, but also limit the embedded nanoparticles size and avoid its agglomeration, and ii) the high content of “Fe-N” active sites, and the core-shell structure of embedded nanoparticles (FeOx@GC) can protect the active sites from the corrosion of harsh conditions and ensure the long-term durability.It is found that the as-prepared FeOx@GC-NOMC shows one of the best H2-O2 PEMFC single-cell performances, among all thetested and currently reported NPMCs, as well as a long-term durability. More precisely, at an open circuit potential of ca. 1 V, the peak power density reaches up to 350 W g−1 (1050 mW cm-2 based on active area). A slight current decay is observed after a chronoamperometric test of 120 h. The above features make FeOx@GC-NOMC a promising potential alternative to Pt/C for ORR electrocatalysis in practical fuel cell applications.

Carbon nanotube@silicon carbide coaxial heterojunction nanotubes as metal-free photocatalysts for enhanced hydrogen evolution

Considerable research efforts have been devoted to developing novel photocatalysts with increased performances by hybridizing inorganic nanomaterials with carbon nanotubes. In this work, one-dimensional coaxial core-shell carbon nanotubes@SiC nanotubes were successfully synthesized via in situ growth of SiC coatings on carbon nanotubes by a vapor-solid reaction between silicon vapor and carbon nanotubes. High-resolution transmission electron microscope images show that SiC and carbon nanotubes link to form a robust heterojunction with intrinsic atomic contact, which results in efficient separation of the photogenerated electron-hole pairs on SiC and electron transfer from SiC to carbon nanotubes. Compared with those of similar materials such as pure SiC nanocrystals and SiC nanotubes, the metal-free carbon nanotubes@SiC exhibits an enhanced photocatalytic activity for hydrogen evolution, which is attributed to the enhanced light absorption and the efficient interfacial charge transfer/separation brought about by their one-dimensional coaxial nanoheterostructures. Moreover, the photocatalytic stability of the metal-free carbon nanotubes@SiC was tested for over 20 h without any obvious decay.

Prolonged antimicrobial activity of silver core-carbon shell nanoparticles

Ag nanoparticles present good antimicrobial activity but with a potential toxicity to the cell, which limits the application. To address this issue, in this work, carbon-encapsulated sliver nanocapsules (Ag@C nanocapsules) were prepared by evaporating pure Ag ingot with the modified arc-discharge technique, and the Ag@C nanocapsules were acidified with nitric acid subsequently to facilitate the silver ion to release. Finally, Ag@C nanocapsules displayed a good and sustained antimicrobial activity against E. coli as a model of Gram-negative bacteria, due to the long-term release of sliver ions from Ag@C nanocapsules. The results obtained in this work indicate that the Ag@C nanocapsules may be a suitable nanomaterial for the bactericidal application.

A microfluidic study to investigate the effect of magnetic iron core-carbon shell nanoparticles on displacement mechanisms of crude oil for chemical enhanced oil recovery

The main objective of this work is to evaluate the effect of the simultaneous use of a surfactant mixture and magnetic iron core-carbon shell nanoparticles on oil recovery via a microfluidic study based on the rock-on-a-chip technology. The surfactant solution used for all experiments was prepared based on a field formulation and consisted of a mixture of a hydrophilic and a lipophilic surfactant. Magnetic iron core-carbon shell nanoparticles with a mean particle size of 60 nm and a surface area of 123 m2 g−1 were employed. The displacement experiments consisted of waterflooding, surfactant flooding and nanoparticle-surfactant flooding and were performed using PDMS (polydimethylsiloxane)-glass microdevices type random network. The characteristics and design of the microfluidic device allowed to emulate a mixed wettability of a porous medium. Then, the oil was displaced by injecting the solution at a constant injection rate, until steady-state conditions were obtained. Furthermore, the effect of three injection rates corresponding to 0.1 ft day−1, 1 ft day−1, and 10 ft day−1 was investigated. The increase in the injection rate favored the oil recovery percentage. In addition, for all injection rates, the oil recovery decreased in the following order: nanoparticle-surfactant flooding > surfactant flooding > waterflooding. The nanoparticle-surfactant system at the injection rate of 1.9 μL min−1 presented the highest oil recovery (i.e., 84%). Likewise, nanoparticle-surfactant flooding showed a more stable displacement front and consequently, the highest capillary number among the injection fluids. Oil recovery by waterflooding was the lowest among the evaluated systems due to the viscous fingering phenomena under different injection rates. In addition, it can be observed that for all injection rates, the presence of the surfactant mixture and nanoparticles reduce the viscous fingering effect. The results can be used to visually and quantitatively analyze the role of the simultaneous use of nanoparticles with surfactants in enhanced oil recovery processes.

Design and Synthesis of Core-Shell Carbon Polymer Dots with Highly Stable Fluorescence in Polymeric Materials.

In recent years, fluorescent carbon dots have attracted great attention due to their good luminescence and low toxicity. Here, blue fluorescent core-shell structured carbon polymer dots (CPDs) with high stability under a wide range of pH values, long storage time and excellent fluorescence in various solvents and even in solid state were prepared by hydrothermal synthesis of dendritic tris(2-aminoethyl)amine (TAEA) and citric acid. The CPDs core structure provides strong fluorescent luminescence, a shell structure of the core possesses high amount of dendritic primary amino groups connected by ethylene groups to the core. This unique structure prevents aggregation of the cores and self-quenching effect of CPDs. As a result, the CPDs have high fluorescence in both aqueous and hydrophobic solutions and even as pure solid-state powder. In addition, the CPDs are also insensitive to pH of solutions, and the fluorescence intensity of the solution was stable in the pH range of 4-14. The CPDs embedded polymer films and fibers revealed excellent fluorescent properties.

Importance of the Nanofluid Preparation for Ultra-Low Interfacial Tension in Enhanced Oil Recovery Based on Surfactant–Nanoparticle–Brine System Interaction

The main objective of this study is to evaluate the effect of the preparation of the nanofluids based on the interactions between the surfactants, nanoparticles, and brine for being applied in ultra-low interfacial tension (IFT) for an enhanced oil recovery process. Three methodologies for the addition of the salt–surfactant–nanoparticle components for the formulation of an efficient injection fluid were evaluated: order of addition (i) salts, nanoparticles, and surfactants, (ii) salts, surfactants, and then nanoparticles, (iii) surfactants, nanoparticles, and then salts. Also, the effects of the total dissolved solids and the surfactant concentration were evaluated in the interfacial tension for selecting the better formulation of the surfactant solution. Three nanoparticles of different chemical natures were studied: silica gel (SiO2), alumina (γ-Al2O3), and magnetic iron core–carbon shell nanoparticles. The nanoparticles were characterized using dynamic light scattering, zeta-potential, N2 physisorption at −196 °C, and Fourier transform infrared spectroscopy. In addition, the interactions between the surfactant, different types of nanoparticles, and brine were investigated through adsorption isotherms for the three methodologies. The nanofluids based on the different nanoparticles were evaluated through IFT measurements using the spinning drop method. The adsorbed amount of surfactant mixture on nanoparticles decreased in the order of alumina > silica gel > magnetic iron core–carbon shell nanoparticles. The minimum IFT achieved was 1 × 10–4 mN m–1 following the methodology II at a core–shell nanoparticle dosage of 100 mg L–1.

CoO/CoFe2O4 core/shell nanoparticles assembled in carbon sheets as anode materials for lithium ion battery

We demonstrate a facile method to prepare monodisperse CoO–CoFe2O4 core-shell nanoparticles and a NaCl-assisted thermal sintering route to the generation of monodisperse core-shell structure of CoO–CoFe2O4 nanoparticles embedded in carbon sheet. Owing to the unique core-shell nanostructure, CoO–Co2FeO4 carbon nanosheets show excellent electrochemical performance as the anode material in lithium ion batteries. The discharge capacity can still maintain 1127 mAh g−1 thoughout 50 cycles at current density of 100 mA g−1. This synthetic strategy is inexpensive, facile and easily for large-scale production. The developed CoO–CoFe2O4 core-shell carbon nanosheets can be considered as promising battery materials.

Ultrafine Co@nitrogen-doped carbon core-shell nanostructures anchored on carbon nanotubes for highly efficient oxygen reduction

The rational design of non-noble-metal electrocatalysts for oxygen reduction reaction (ORR) with both excellent activity and robust stability still remains a key challenge nowadays. Herein, N-doped carbon wrapped Co nanoparticles core-shell nanostructures grafted on carbon nanotubes (Co@NC@CNTs) were achieved by a simple pyrolysis process using ZIF-67 and CNTs as precursors. Most importantly, this unique structure of Co@NC@CNTs is beneficial to increase the contact area of N-doped carbon and Co, inhibit the aggregation of Co@NC core-shell nanoparticles and protect the Co from dissolution, thus improving the electrocatalytic performance and stability for ORR. As a result, the well-defined Co@NC@CNTs electrocatalyst exhibits excellent ORR activity with a high onset potential, half-wave potential and limited current density, comparable to the commercial Pt/C in alkaline electrolyte. Furthermore, the Co@NC@CNTs electrocatalyst presents outstanding electrochemical durability and methanol tolerance in comparison with Pt/C. This strategy will open a new avenue toward the development of nonprecious high-performance ORR catalysts.

Hierarchical hollow dual Core–Shell carbon nanowall-encapsulated p–n SnO/SnO2 heterostructured anode for high-performance lithium-ion-based energy storage

A hierarchical hollow SnO/SnO2 heterostructure anode surrounded by a dual carbon layer (DCL@SnO/SnO2), inner (host) and outer carbon layers, was successfully designed via a simple hydrothermal method with a single Sn precursor to achieving high-performance Li-ion batteries (LIBs) and Li-ion capacitors (LICs). The carbon nanotube (CNT)-based inner carbon host and an ultrathin outer amorphous carbon layer introduced at the SnO/SnO2 heterostructure had good elasticity and high electrical properties to prevent volume change and ensure fast Li-ion transport during cycling, respectively. Meanwhile, the SnO/SnO2 heterostructure comprising p-type SnO and n-type SnO2 facilitated further fast interfacial Li-ion transfer within the p–n SnO/SnO2 heterojunction anode via the acceleration effect induced by the built-in electric field (BEF). The resulting half cells LIBs consisting DCL@SnO/SnO2 anode shows a high reversible specific capacity of 902.1 mAh g−1 after 500 cycles at a current density of 1400 mA g−1. The specific capacity of 347.04 mAh g−1 was still maintained even at a high current density of 10 000 mA g−1. Moreover, the maximum energy and power density of 125 W kg−1 and 200 Wh kg−1, respectively, were achieved from the half cells LIC comprising DCL@SnO/SnO2 anode (LIC-DCL@SnO/SnO2).

In situ synthesis of core-shell carbon nanowires as a potent targeted anticoagulant

We have developed a one-pot synthesis of bio-carbon nanowires from the natural product sodium alginate at low temperature, without using any catalyst, for anticoagulation applications. Sodium alginate is carbonized and sulfated/sulfonated in situ by solid state heating of a mixture of sodium alginate and ammonium sulfite. By regulating the heating temperature and the ratio of ammonium sulfite to sodium alginate, we modulated the degree of sulfation/sulfonation and carbonization, as well as the morphology of the carbon nanomaterials. The core-shell sulfated/sulfonated bio-carbon nanowires (CNWsAlg@SOx) made by the reaction of a mixture of ammonium sulfite and sodium alginate with a mass ratio of 5 (ammonium sulfite to sodium alginate) at 165 °C for 3 h, exhibit strong inhibition of thrombin activity due to their ultrahigh binding affinity towards it (dissociation constant (Kd) = 8.7 × 10−11 M). The possible formation mechanism of the carbon nanowires has been proposed. The thrombin-clotting time delay caused by CNWsAlg@SOx is ∼ 170 times longer than that caused by sodium alginate. Hemolysis and cytotoxicity assays demonstrated the high biocompatibility of CNWsAlg@SOx. Furthermore, the thromboelastography of whole-blood coagulation and rat-tail bleeding assays further reveal that CNWsAlg@SOx have a much stronger anticoagulation activity than sodium alginate and naturally sulfated polysaccharides (e.g., fucoidan). Our results suggest that the low-temperature prepared, cost-effective, and highly biocompatible CNWsAlg@SOx show great potential as an efficient anticoagulant for the prevention and treatment of diseases associated with thrombosis.

N, S doped hollow core-shell carbon microspheres to enhance catalytic activity in solar cell

The development of the metal-free materials with hollow core-shell construction as higher efficient catalysts in related energy conversion field is still a great challenge. This structure usually possesses a larger specific surface area. However, the catalytic activity of dye-sensitized solar cells (DSSCs) is weakened due to its fewer active edge sites. Here, a novel strategy is described by building a category of N, S doped hollow core-shell carbon microspheres (N, S-HCCS) in the process of simple easy operation. The electrochemical measurements include electrochemical impedance spectroscopy, Tafel polarization measurements and cyclic voltammetry, which unravel the outstanding electrocatalytic activities of N, S-HCCS as counter electrode (CE) for iodine ion. The photoelectric conversion efficiency (PCE) value of the whole cell reaches 8.03%, which is far larger than Pt’s value (7.52%).

Metal-free core-shell structured N-doped carbon/carbon heterojunction for efficient CO2 capture

N-doped carbon/carbon heterojunction holds huge potential for efficient CO2 capture. Here, a series of site-specific N-doped core-shell carbon spheres with carbon/carbon heterojunction were successfully prepared by carbonization of polypyrrole coated hypercrosslinked polystyrene spheres, followed by chemical activation with KOH. These activated carbon spheres possessed large specific surface area (2080 m2 g−1) and abundant micropores (0.45 cm3 g−1). Despite their low nitrogen content (0.96 wt%), the CO2 adsorption capacities of activated samples reached 3.69 and 5.80 mmol g−1 measured at 298 and 273 K, respectively, under atmospheric pressure (1 bar). More significantly, the N-doped carbon/carbon heterojunction contributes to a stronger and denser CO2 packing in this system.

Hierarchical Carbon Nanofiber/Birnessite-MnO2 Nanosheets Cathode for High Performance and Low-Cost Aqueous Rechargeable Zinc Ion Battery

Abundant and safe charge carrying feedstock with high energy density have made aqueous zinc-ion batteries (ZIBs), specifically the Zn/MnO2 system, a highly promising candidate for large-scale energy storage device. The traditional alkaline Zn/MnO2 batteries have become dominant in primary battery chemistry. Great efforts have been devoted to developing rechargeable alkaline Zn/MnO2 batteries, however, they are plagued by poor cycling stability. Very recently, the Zn/MnO2 systems in near neutral electrolyte have emerged to demonstrate improved capacities, cyclability and rechargeability. However, the commonly used tunnel-type MnO2 cathode with low conductivity usually undergoes phase transition to layered structure upon discharge-charge cycles, leading to collapse of framework and thus poor cycling and rate performance. To address these issues, it is proposed that directly using birnessite-MnO2 with layered structure as a cathode may minimize the “sacrificial capacity” induced by phase transition and integrating birnessite-MnO2 with a conductive substrate may enhance the conductivity. In this work, the hierarchical core-shell carbon nanofiber@MnO2 (CNF@MnO2) cathode was prepared by a facile wet-chemistry method, where vertically aligned birnessite-MnO2 nanosheets were in situ grown on the surface of carbon nanofibers. The self-supported CNF@MnO2 cathode showed excellent electrochemical performance for Zn-ion batteries in a near neutral electrolyte due to its structural stability and enhanced conductivity. A high discharge capacity of 306 mA h g−1 has been reached after 100 cycles at current density of 300 mA g−1. Even at a high rate of 1.5 A g−1, CNF@MnO2 still maintained a high capacity of 258 mA h g-1 upon 100 cycles. Such remarkable performance is attributed to the unique core-shell structure and intimate contact between CNF and layered MnO2, in which the conductive CNF core facilitates the electron transfer and layered MnO2 minimizes the structural collapse and promotes the kinetics for co-insertion and extraction of Zn2+/H+ ions. Given the simplicity of preparation, exceptional electrochemical performance and low cost, CNF@MnO2 cathode holds substantial promise for aqueous rechargeable Zn-ion batteries. Figure 1. Scanning electron microscopy image of carbon nanofiber@MnO2 (CNF@MnO2) cathode for aqueous rechargeable Zn-ion batteries in near neutral electrolyte. Figure 1

Effect of Magnetic Iron Core–Carbon Shell Nanoparticles in Chemical Enhanced Oil Recovery for Ultralow Interfacial Tension Region

Some of the advantages of the simultaneous use of surfactants and nanoparticles in enhanced oil recovery (EOR) processes are the increase in the efficiency of injection fluid for sweeping, the redu...

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.

High-efficiency enhancement on thermal and electrical properties of epoxy nanocomposites with core-shell carbon foam template-coated graphene

Recently, three-dimensional graphene foam has received considerable attention and displayed excellent properties as reinforcement for polymer composites. However, the brittleness and poor controllability limited its application in resin to form conducting pathways for phonons and electrons. This study developed a facile method with compressible and constitutionally stable commercial melamine foam (MF) as template to prepare a core-shell composite with carbon skeleton structure. The core carbon structure was fabricated by carbonization of MF, while the shell carbon structure was the in-situ self-assembled coating of graphene. Vacuum-impregnated method was employed to fabricate epoxy resin composites. The thermal and electrical conductivities of epoxy composites were significantly increased to 0.92 W/(m·K) and 0.70 S/cm, which was 318% and 13 orders of magnitude higher than that of pure epoxy. Herein, we provide a highly efficient, green, high-quality method for building a double-layer heat conduction path, which facilitates the utilization of graphene. The proposed method proves to be efficient in enhancing the multifunctionality of epoxy resin composites. Furthermore, we explored the thermal and electrical conductive mechanisms of the three-dimensional core-shell structure in resin matrix.

Polymerization-dissolution strategy to prepare Fe, N, S tri-doped carbon nanostructures for Zn-Air batteries

Heteroatom doped carbon based hierarchical nanostructures are one of most interesting electrode materials for boosting oxygen reduction reaction (ORR) owing to the active electronic structure and appealing structural stability. Herein we demonstrated a ‘polymerization-dissolution’ method to prepare a highly stable Fe, N, S tri-heteroatom doped core-shell carbon (HCSC) nanostructural ORR catalyst. The unique advantages, including the uniformly dispersed N, S and Fe–N active sites, and the special leaf-like core-shell nanostructure, endow the optimized HCSC catalyst (HCSC-IV-H) owning high-efficient ORR activity. Moreover, a Zn–air battery assembled with HCSC-IV-H exhibits a higher open potential (1.430 V) and lower discharge overpotential, comparing with the commercial IrO2 + 20% Pt/C catalyst. The present work highlights a novel strategy to construct highly efficient heteroatom doped nano-carbon materials for renewable energy storage and conversion devices.

Fe3O4@C Core-Shell Carbon Hybrid Materials as Magnetically Separable Adsorbents for the Removal of Dibenzothiophene in Fuels.

Herein, we demonstrate a new class of core–shell magnetic carbon hybrid materials (Fe3O4@C) for remarkable adsorptive desulfurization of dibenzothiophene (DBT), which have been successfully prepared through hydrocarbonization of glucose on the surface of Fe3O4 and the subsequent pyrolyzation process. The as-obtained Fe3O4@C retains amorphous nature of carbon shells with a large surface area and displays an increase of iron atoms as active sites under elevated pyrolyzation temperature which is favorable in the adsorption of sulfur-containing species through physical and chemical adsorption, respectively. We investigate the adsorption capacity and efficiency of Fe3O4@C as a magnetically adsorbent for the removal of DBT in model oils under various experimental conditions including the adsorbent obtained at different temperatures, the amount of adsorbents, the DBT initial concentration, the regeneration approach, as well as the interference species. Our results demonstrated that the as-obtained Fe3O4@C at 650 °C (Fe3O4@C-650) displays a remarkable estimated adsorption performance (57.5 mg DBT/g for 200 ppmw), extraordinary high desulfurization efficiency (99% for 200 ppmw), and a high selectivity for DBT compared with its derivatives. Moreover, Fe3O4@C can be recovered in a quite easy, economical, and eco-friendly manner by an external magnet after five cycles without significant weight loss, which significantly simplifies the operation procedure and favors the recycle of Fe3O4@C. Combined with the economic and eco-friendly merits, Fe3O4@C offers a new avenue to employ the magnetic carbon materials for industrial applications and provides a promising substitute for adsorptive desulfurization in view of academic, industrial, and environmental aspects.