Carbon Core Research Articles

Mixed-Mode Liquid Chromatography on Core Shell Stationary Phases based on Layer-By-Layer Nanodiamond/Polyamine Architecture

Background: The use of diamond as a chromatographic stationary phase has been studied for more than 45 years now. Detonation nanodiamonds (DND) have been regularly used to increase the low specific surface area of these non-porous stationary phases. Recently, core-shell particles with multiple layers of polyallylamine (PAAm) and DND have been reported for liquid chromatographic separations and solid phase extractions. However, retention mechanisms and selectivity of such core-shell particles are not well -understood due to their complex architecture. Objective: The objective of this work was to perform a detailed evaluation of the mixed mode behavior of three structural analogues of new nanodiamond (ND)/polyamine based core-shell stationary phases. Method: Particles were composed of a glassy carbon core coated with poly(allylamine) (PAAm) and ND, deposited using a layer-by-layer (LbL) approach, with the outer PAAm layer treated with a mixture of a hydrophobic cross-linker and modifier to introduce C8/C18 functional groups. Three types of the core-shell stationary phases having different shell thicknesses and purity of NDs were investigated. Type II was prepared with fewer PAAm/ND bilayers as compared to Type I, whereas Type III was prepared with a same number of bilayers but with an additionally purified form of ND as compared to Type II. Ion-exchange interactions of the phases were tested with a set of model anionic, cationic and ampholytic analytes at different eluent pHs. The relative degree of anionexchange and hydrophobic interactions was also evaluated using a set of dansylated amino acids (Dns-AAs) at varied mobile phase buffer concentrations and organic solvent contents. Results: Anion-exchange properties were noted for all phases at low pH, with the Type I phase exhibiting stronger retention of anionic analytes due to higher PAAm content in its shell. Typical reversed-phase behaviour was observed for the hydrophobic Dns-AAs (Phe, Ile, Leu, Trp, Val and Pro), while the retention selectivity for hydrophilic Dns-AAs (Gln, Asn, Thr, Ser) indicated mixed mode mechanism. Values of methylene selectivity obtained for homologues of carboxylic acids indicated relatively low hydrophobicity for all studied phases. Conclusion: All three columns demonstrated low to medium hydrophobicity, and the solute selectivity was dominated by their ion-exchange property. These nanodiamond columns result in lower performance as compared to conventional analytical columns, however, the inherently stable nanodiamond platform ascertains that nanodiamond columns offer better stability at extreme conditions.

A facile in-situ etching route to hollow C@SnO2 nanocomposites and their gas-sensing properties

A novel hollow carbon@SnO2 nanocomposite has been developed via a high cost-effective and facile in-situ etching technique. The as-prepared C@SnO2 product has a high surface area of about 115 m2 g−1 and a hollow carbon core, where a lot of SnO2 nanosheets grow onto the carbon shell. Particularly, the silica core as the sacrificial template can be fully removed by hydrofluoric acid (HF) byproduct during the reaction process. Moreover, the deposition of SnO2 sheets and the removal of the silica template can be synchronously performed by a simple one-step process. When applied as the gas-sensing material, the C@SnO2 product manifests highly sensitive and selective to n-butanol. The large surface area, hollow nanostructure and the perfect combination of SnO2 nanosheets and carbon layer contribute to the enhanced gas-sensing performances. The method described in our work can also be employed to design other hollow metal oxides@carbon hybrids for energy storage and catalysis.

Controlled Synthesis of Noble Metal@Mesoporous Carbon Colloids as Highly Active Nanocatalysts

The key concept to simplify the synthesis steps of core–shell nanocomposites is to synthesize the core and shell components together without tedious separation and purification steps. In addition, the sintering problems of carbon spheres during the high-temperature carbonization process need to be addressed with the aim of obtaining monodisperse carbon nanospheres. Through extension of our reported silica-assisted strategy, a facile one-pot strategy is reported here to synthesize noble metal@mesoporous carbon (NM@MC) core–shell colloids in which the formation and encapsulation processes of noble metal nanoparticles happen simultaneously through a series of synergetic reactions. The resulting NM@MC colloidal nanospheres show uniform and highly dispersed morphology, tunable size, high surface area, and clear core–shell structure with abundant mesopores. In particular, the Au@MC colloid shows significantly high catalytic activity in the reduction of 4-nitrophenol to 4-aminopheol thanks to the excellent catal...

A facile hydrothermal synthesis of novel hollow triple-shell CuNiFe2O4 nanospheres with robust catalytic performance in the Suzuki–Miyaura coupling reaction

Triple-shell hollow spheres of crystalline copper–nickel ferrite have been synthesized in a simple one-pot procedure using carbon spheres as templates via a hydrothermal approach. Ferric nitrate, copper nitrate, and nickel nitrate were dissolved in water together with glucose, and the mixture was heated to 180 °C in an autoclave. Finally, the carbon core was removed by calcination at 550 °C. The triple-shell hollow spheres of CuNiFe2O4 were characterized by XRD, TEM, FE-SEM, and EDS. High catalytic activity for the Suzuki reaction was obtained for this new triple-shell hollow sphere of CuNiFe2O4. This also reveals obvious advantages such as the recyclability of the catalyst, simple experimental operation, and excellent yields.

Preparation of hollow mesoporous carbon spheres and their performances for electrochemical applications

Hollow carbon materials have received intensive attention for energy storage/conversion applications due to their attractive properties of high conductivity, high surface area, large void and short diffusion pathway. In this work, a novel hollow mesoporous material based on carbide-derived carbon (CDC) is presented. CDC is a new class of carbon material synthesized by the selective extraction of metals from metal carbides. With a two-stage extraction procedure of carbides with chlorine, firstly hybrid core-shell carbon particles were synthesized, i.e. mesoporous/graphitic carbon shells covering microporous/amorphous carbon cores. The amorphous cores were then selectively removed from particles by a careful oxidative treatment utilizing its low thermal characters while the more stable carbon shells remained, thus resulting hollow particles. The characterization methods (e.g. N2 sorption, Raman spectroscopy, temperature-programmed oxidation and SEM) proved the successful synthesis of the aspired material. In electric double-layer capacitor (EDLC) testing, this novel hollow core material showed a remarkable enhancement of EDLC’s rate handling ability (75% at a high scan rate) with respect to an entirely solid-mesoporous material. Furthermore, as a fuel cell catalyst support the material showed higher Pt mass activity (a factor of 1.8) compared to a conventional carbon support for methanol oxidation without noticeably decreasing activity in a long-term testing. Therefore, this carbon nanostructure shows great promises as efficient electrode materials for energy storage and conversion systems.

Exploring the Emissive States of Heteroatom-Doped Graphene Quantum Dots

The photoluminescence (PL) emission states of heteroatom-doped graphene quantum dots (GQDs) remain unknown, particularly the assignment of the low-energy excitation band (more than 330 nm). To address these issues, this work synthesized three different types of GQDs: undoped GQDs (UGQDs), nitrogen-doped GQDs (NGQDs), and boron-doped GQDs (BGQDs), with similar sizes, chemical compositions (types and compositions of surface functional groups), and defects using a constant potential electrolysis method. The PL emissive states in these GQDs and the effects of the dopant heteroatom on the PL were revealed based on the combination of spectroscopic methods and theoretical calculations. The results indicated that the GQDs exhibit multiemissive centers for the PL emission mechanism. An excitation-independent PL emission band (band I) results from a high-energy transition originating from the quantum confinement of the carbon core (carbon π–π* transitions in sp2 domain), and an excitation-dependent PL emission band...

Yolk–shell structured Co-C/Void/Co9S8 composites with a tunable cavity for ultrabroadband and efficient low-frequency microwave absorption

A yolk–shell structured Co-C/Void/Co9S8 ternary composite composed of a Co nanoparticle-embedded porous carbon core and Co9S8 shell was synthesized by the sulfidation of a Co-based zeolitic imidazolate framework and subsequent pyrolysis. The composition and interior cavity of the Co-C/Void/Co9S8 composite could be precisely modulated by controlling the sulfidation reaction. Due to the abundant heterointerfaces, well-controlled cavity, and magnetic–dielectric synergistic effects, the Co-C/Void/Co9S8 exhibited excellent and tunable microwave-absorbing properties. The optimized Co-C/Void/Co9S8, having a loading of 25 wt.% and thickness only 2.2 mm, displayed an ultrabroad absorption bandwidth of 8.2 GHz at high frequencies. Moreover, the composite could achieve an extremely high reflection loss of–54.02 dB at low frequencies by adjusting its loading to 30 wt.%. This study provides a new insight into promising lightweight microwave-absorbing materials with ultrabroad absorption bandwidths and strong low-frequency absorption.

Yolk-shell structured composite for fast and selective lithium ion sieving

Yolk-shell structured C@Li4Ti5O12 microspheres composed of carbon core (ca. 500 nm) and sea urchin-like Li4Ti5O12 shell (ca. 400–500 nm) are formed by hydrothermally treating the core–shell structured C@TiO2 in the EtOH/H2O solution of LiOH and calcining it in N2 atmosphere. Yolk-shell structured TiO2-type lithium ion sieve is further transformed from C@Li4Ti5O12 through the acid treatment, which have a high specific surface area of 201.74 m2/g. The composite shows adsorption capacity towards Li+ proportional to the pH value in the range of 7–13. The adsorption reaches equilibrium within 2 h with a high equilibrium adsorption capacity of 28.46 mg/g under alkaline conditions, which is ca. 8 times the value of ordinary TiO2 lithium ion sieve with comparable size and surface area, demonstrating the enhanced adsorption is attributed to the generation of more accessible surficial voids by replacing internal part with light carbon core. The adsorption follows Freundlich and pseudo-second-order kinetic models with a high rate constant of 0.015 g/(mg·min). The selective adsorption to Li+ is verified in the presence of K+, Na+, Ca2+ and Mg2+.

Sub-Chandrasekhar-mass White Dwarf Detonations Revisited

Abstract The detonation of a sub-Chandrasekhar-mass white dwarf (WD) has emerged as one of the most promising Type Ia supernova (SN Ia) progenitor scenarios. Recent studies have suggested that the rapid transfer of a very small amount of helium from one WD to another is sufficient to ignite a helium shell detonation that subsequently triggers a carbon core detonation, yielding a “dynamically driven double-degenerate double-detonation” SN Ia. Because the helium shell that surrounds the core explosion is so minimal, this scenario approaches the limiting case of a bare C/O WD detonation. Motivated by discrepancies in previous literature and by a recent need for detailed nucleosynthetic data, we revisit simulations of naked C/O WD detonations in this paper. We disagree to some extent with the nucleosynthetic results of previous work on sub-Chandrasekhar-mass bare C/O WD detonations; for example, we find that a median-brightness SN Ia is produced by the detonation of a 1.0 WD instead of a more massive and rarer 1.1 WD. The neutron-rich nucleosynthesis in our simulations agrees broadly with some observational constraints, although tensions remain with others. There are also discrepancies related to the velocities of the outer ejecta and light curve shapes, but overall our synthetic light curves and spectra are roughly consistent with observations. We are hopeful that future multidimensional simulations will resolve these issues and further bolster the dynamically driven double-degenerate double-detonation scenario’s potential to explain most SNe Ia.

In Situ Time‐Dependent and Progressive Oxidation of Reduced State Functionalities at the Nanoscale of Carbon Nanoparticles for Polarity‐Driven Multiscale Near‐Infrared Imaging

AbstractSurface abundant oxidize‐able functionalities at the nanoscale of carbon dots are prone to undergo sequential aerial oxidation leading to polarity‐driven wavelength tuning of their photoluminescence and consequently boost their quantum yields. With the progression of time, aerial oxidation is gradually increased from 1 to 6 h; consequently, a remarkable shift in the emission peak is observed, likely due to a gradual decrease in their respective band gaps leading to red shift of their photoluminescence. These bands are found to be dependent on the time of hydrothermal treatment of the model small molecules, i.e., benzophenone imine, and not on the size of the carbon core, as is the typical case for semiconductor quantum dots. Due to their high quantum yield (≈31%), it is demonstrated that these wavelength‐tuned carbon nanoparticles can be efficiently used for multiscale bioimaging, i.e., intracellular, deep tissue ex vivo and in vivo fluorescence bioimaging.

Bond characteristics of SFRP composites containing FRP core/anchors coated on geopolymer mortar

The present study investigates the bending bond characteristics of novel hybrid sprayed fiber-reinforced polymer (SFRP) composites containing fiber core/anchors. Carbon or basalt fiber cores were embedded in SFRP composites as core reinforcements, and of which their ends were inserted into the beams to act as anchors. Four-point bending bond tests were conducted to characterize the bonding behavior of these hybrid SFRP composites in terms of enhancement of the ultimate bond strength (τu). The effects of the type and number of FRP core/anchors on τu of SFRP-coated geopolymer mortar were investigated. Furthermore, geopolymer mortar was reinforced with 0.5 and 1.5 wt% of short steel fibers to study the effects of fibers on τu, and their results were compared with the efficiency of hybrid SFRP composites. The test results revealed that the hybrid SFRP composites had significant effects on the bond strength, and their bonding performance was relatively better than the fiber-reinforcement in geopolymer mortar. About 46% and 37% increments were observed in τu through the use of hybrid SFRP composites and steel fiber-reinforcement, respectively. The effective bond length (Le) of hybrid SFRP composites was approximately 39 mm.

Photoluminescence of carbon quantum dots: coarsely adjusted by quantum confinement effects and finely by surface trap states

Photoluminescence (PL) mechanism of carbon quantum dots (CQDs) remains controversial up to now even though a lot of approaches have been made. In order to do that, herein a PL color ladder from blue to near infrared of CQDs with the absolute quantum yields higher than 70% were prepared via a one-pot hydrothermal synthesis route and separated by silica gel column. Time-correlated single photon counting measurements suggest that the electron transition takes in effect in the PL progress of the crystalline core-shell structured CQDs, and the PL properties could be coarsely adjusted by tuning the size of the crystalline carbon core owing to quantum confinement effects, and finely adjusted by changing the surface functional groups consisted shell owing to surface trap states, respectively. Both coarse and fine adjustments of PL, as optical and photoelectrical characterizations and density-functional theory (DFT) calculations have demonstrated, make it possible for top-level design and precise synthesis of new CQDs with specific optical properties.

Polymer dots grafted TiO2 nanohybrids as high performance visible light photocatalysts

As a new member of carbon dots (CDs), Polymer dots (PDs) prepared by hydrothermal treatment of polymers, usually consist of the carbon core and the connected partially degraded polymer chains. This type of CDs might possess aqueous solubility, non-toxicity, excellent stability against photo-bleaching and high visible light activity. In this research, PDs were prepared by a moderate hydrothermal treatment of polyvinyl alcohol, and PDs grafted TiO2 (PDs-TiO2) nanohybrids with TiOC bonds were prepared by a facile in-situ hydrothermal treatment of PDs and Ti (SO4)2. Under visible light irradiation, the PDs-TiO2 demonstrate excellent photocatalytic activity for methyl orange degradation, and the photocatalytic rate constant of PDs-TiO2 is 3.6 and 9.5 times higher than that of pure TiO2 and commercial P25, respectively. In addition, the PDs-TiO2 exhibit good recycle stability under UV–Vis light irradiation. The interfacial TiOC bonds and the π-conjugated structures in PDs-TiO2 can act as the pathways to quickly transfer the excited electrons between PDs and TiO2, therefore contribute to the excellent photocatalytic activity.

Biomimetic Bipolar Microcapsules Derived from Staphylococcus aureus for Enhanced Properties of Lithium–Sulfur Battery Cathodes

AbstractLithium–sulfur (Li–S) batteries suffer from some serious issues, such as volume expansion, polysulfide migration, and so on, which lead to inferior rate properties, low Coulombic efficiency, and poor cycling stability. To a great extent, the significantly changing polarities, conductivities, and solubilities of sulfur species complicate these issues and make them hard to deal with. In this study, a biomimetic bipolar microcapsule is developed via bacteria fermentation and chemical modification. The biomimetic hierarchical microcapsule has a nonpolar core to load active materials and a polar shell to “selectively” control mass transport in and out. Each capsule acts as a microreactor, which adsorbs sulfur with the porous carbon core, retards polysulfide migration with the polar TiO2 shell, and only facilitates lithium ion diffusion through the shell. The advantages of bipolar microcapsules are able to concurrently address S hosting, electron conducting, and polysulfide migration issues in particle scales instead of electrode scales. Because the resulting sulfur cathodes effectively interact with all sulfur species and confine them inside microcapsules, those intractable issues that lead to poor cycling properties are significantly managed. Thus, a high specific capacity and excellent cycling stability are achieved by using this novel structure design.

Fluorescent carbon dots with two absorption bands: luminescence mechanism and ion detection

Herein, we report the synthesis of carbon dots (CDs) with two characterized absorption bands but without excitation wavelength-dependent fluorescence via a one-step hydrothermal method. The structure of CDs was characterized using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared, and UV–Vis spectroscopy. The structure and photoluminescence of CDs vary significantly with different raw materials and preparation methods, and the mechanism of luminescence is not clear yet. Hence, we studied the luminescence mechanism behind two characterized absorption bands of CDs using fluorescence quenching method with ninhydrin and several ions as quenchers. The influence of the surface groups of CDs on its photoluminescence properties was also discussed. Ninhydrin and a variety of other ions exhibited different quenching effects on the fluorescence emissions which obtained at the two absorption bands of CDs. Combining with the structure characterization results, it can be concluded that the emission wavelength is mainly determined by the carbon core, while the excitation wavelength is determined by the surface nitrogen-containing groups. (The excitation at 234 nm might be due to the Schiff base structure, while the excitation at 345 nm was mainly due to the amide structure.) Furthermore, based on the interaction of NO2− with the surface nitrogen-containing groups of CDs, a quantitative detection method of NO2− using CDs was proposed in our study. CDs exhibited high selectivity for NO2− at pH 1.6 with good linearity to NO2− concentration in the range of 1–10 μM.

Correlative Light-Electron Microscopy of Lipid-Encapsulated Fluorescent Nanodiamonds for Nanometric Localization of Cell Surface Antigens.

Containing an ensemble of nitrogen-vacancy centers in crystal matrices, fluorescent nanodiamonds (FNDs) are a new type of photostable markers that have found wide applications in light microscopy. The nanomaterial also has a dense carbon core, making it visible to electron microscopy. Here, we show that FNDs encapsulated in biotinylated lipids (bLs) are useful for subdiffraction imaging of antigens on cell surface with correlative light-electron microscopy (CLEM). The lipid encapsulation enables not only good dispersion of the particles in biological buffers but also high specific labeling of live cells. By employing the bL-encapsulated FNDs to target CD44 on HeLa cell surface through biotin-mediated immunostaining, we obtained the spatial distribution of these antigens by CLEM with a localization accuracy of ∼50 nm in routine operations. A comparative study with dual-color imaging, in which CD44 was labeled with FND and MICA/MICB was labeled with Alexa Fluor 488, demonstrated the superior performance of FNDs as fluorescent fiducial markers for CLEM of cell surface antigens.

Co9S8@N,S-codoped carbon core–shell structured nanowires: constructing a fluffy surface for high-density active sites

Co9S8 nanowires are coated with a fluffy surface layer constructed of N,S-codoped carbon nanotubes to form high-density active sites.

Graphitic carbon-wrapped NiO embedded three dimensional nitrogen doped aligned carbon nanotube arrays with long cycle life for lithium ion batteries.

In this work, a three-dimensional nitrogen doped aligned carbon nanotube array (NACNTs)@NiO@graphitic carbon composite was fabricated by an effective strategy involving nebulized ethanol assisted infiltration, In this structure, the NiO nanoparticles were wrapped by graphitic carbon layers and NiO@graphitic carbon core–shell nanoparticles adhered strictly to the surface of NACNTs to form a highly ordered 3D structure. When this composite was used as an anode for lithium ion batteries, the well-ordered pore of its NACNTs can facilitate the electrolyte to penetrate and improve electronic conductivity. At the same time, the graphitic layers can promote the stability of a solid electrolyte interface film. Therefore, the NACNTs@NiO@graphitic carbon composite containing 68.1 wt% NiO delivers excellent capacity retention of 91.6% after 200 cycles at 0.2C.

Experimental and theoretical calculation investigation of 2,4-dichlorophenoxyacetic acid adsorption onto core-shell carbon microspheres@layered double hydroxide composites.

Layered double hydroxides (LDHs) usually aggregate irregularly and hardly redisperse in water. Moreover, the affinity of LDHs is poor for organic compounds. In this study, three different core–shell composites, i.e. CMS@MgAl–LDH, CMS@NiAl–LDH, and CMS@ZnAl–LDH, were synthesized by direct fabrication of LDH nanoplatelets onto carbon microspheres (CMS) for the removal of the adsorbed 2,4-dichlorophenoxyacetic acid (2,4-D). The CMS@LDH composites show good water-dispersity due to the 3D hierarchical sphere structure and high affinity for 2,4-D due to the organic carbon cores that possess abundant hydrophobic compounds. It was found that the adsorption process was rapid, and the time required to reach the sorption equilibrium was within 100 min. The theoretical DFT calculation analysis suggested that the adsorption of 2,4-D on the CMS@LDH composites was dominated by π–π interactions, ion-exchange, and hydrogen bonding. The core–shell CMS@LDH composites can serve as a promising adsorbent that offers a rapid and effective adsorption capacity for the removal of 2,4-D in an aqueous solution.

A self-assembled silicon/phenolic resin-based carbon core-shell nanocomposite as an anode material for lithium-ion batteries.

Silicon, with advantages such as high theoretical capacity and relatively low working potential, has been regarded as promising when it is used for lithium-ion battery anodes. However, its practical application is impeded by the intrinsic low electrical conductivity and the dramatic volume change during the lithiation/delithiation process, which leads to a rapid capacity fading of the electrode. In this regard, we design silicon nanoparticles homogeneously coated with a phenolic resin-based carbon layer as a core–shell nanocomposite via a facile self-assembly method followed by carbonization. The surrounding carbon shell, confirmed by transmission electron microscopy and Raman spectroscopy, is not only beneficial to the formation of a stable solid electrolyte interface film, but the electrical conductivity of the electrode is also enhanced. A high and stable specific capacity of nearly 1000 mA h g−1 is achieved at C/3 after 200 cycles with a coulombic efficiency of >99.6%. The entire synthesis process is quite simple and easy to scale up, thus having great potential for commercial applications.