Covalent Carbon Research Articles

Metal-free disinfection effects induced by graphitic carbon nitride polymers under visible light illumination

Covalent carbon nitride polymers were applied as metal-free robust catalysts for the inactivation of Escherichia coli K-12 (E. coli), a common Gram-negative bacterium, under visible light illumination. The results demonstrated that the creation of antibacterial function on the surface of conjugated polymers has now become possible.

Conversion of multilayer graphene into continuous ultrathin sp3-bonded carbon films on metal surfaces

The conversion of multilayer graphenes into sp3-bonded carbon films on metal surfaces (through hydrogenation or fluorination of the outer surface of the top graphene layer) is indicated through first-principles computations. The main driving force for this conversion is the hybridization between sp3 orbitals and metal surface dz2 orbitals. The induced electronic gap states and spin moments in the carbon layers are confined in a region within 0.5 nm of the metal surface. Whether the conversion occurs depend on the fraction of hydrogenated (fluorinated) C atoms at the outer surface and on the number of stacked graphene layers. In the analysis of the Eliashberg spectral functions for the sp3 carbon films on a metal surface that is diamagnetic, the strong covalent metal-sp3 carbon bonds induce soft phonon modes that predominantly contribute to large electron-phonon couplings, suggesting the possibility of phonon-mediated superconductivity. Our computational results suggest a route to experimental realization of large-area ultrathin sp3-bonded carbon films on metal surfaces.

Thermal conductivity of one-, two- and three-dimensional sp2 carbon

Carbon atoms can form structures in one, two and three dimensions due to their unique chemical versatility. In terms of thermal conductivity, carbon polymorphs cover a wide range from very low values with amorphous carbon to very high values with diamond, carbon nanotubes and graphene. Schwarzites are a class of three-dimensional fully covalent sp2-bonded carbon polymorphs, with the same local chemical environment as graphene and carbon nanotubes, but negative Gaussian curvature. We calculate the thermal conductivity of a (10,0) carbon nanotube, graphene and two schwarzites with different curvature, by molecular dynamics simulations based on the Tersoff empirical potential. We find that schwarzites present a thermal conductivity two orders of magnitude smaller than nanotubes and graphene. The reason for such large difference is explained by anharmonic lattice dynamics calculations, which show that phonon group velocities and mean free paths are much smaller in schwarzites than in nanotubes and graphene. Their reduced thermal conductivity, in addition to tunable electronic properties, indicate that schwarzites could pave the way towards all-carbon thermoelectric technology with high conversion efficiency.

Extremely high wear resistance and ultra-low friction behaviour of oxygen-plasma-treated nanocrystalline diamond films

The diamond nanowire (DNW) film was deposited by N2-enriched microwave plasma-enhanced chemical vapour deposition (MPECVD) process. As-deposited DNW film was treated in O2 plasma which resulted in chemical and microstructural modification. Sheath of the DNW film is chemically constituted by amorphous carbon (a-C)- and graphite (sp2C=C)-like bonding. However, nanowires transformed into ultra-small spherical grains after the O2-plasma treatments. In this condition, a-C and sp2C=C bonding significantly reduced due to plasma etching caused by oxygen atoms. After the O2-plasma treatment, formation of functional groups such as C=O, C–O–C, O–H, O–CH3 and H2O was observed on the surface and inside the wear track as evident from the micro FTIR analysis. H2O is hydrogen bonded to oxygen-containing groups such as –OH and –H. The O2-plasma-exposed DNW film exhibits surface charging and causes formation of dangling bonds and electron trapping centres. This results in significant decrease in contact angle, hence superhydrophilic behaviour. The friction coefficient of O2-plasma-treated film showed super low value ∼0.002 with high wear resistance 2 × 10−12 mm3 N−1 m−1. In the reciprocating ball-on-disc tribology test, only ∼80 nm wear loss was observed after the 1 km of sliding distance at 10 N loads. Such an advance in tribological properties is explained by passivation of covalent carbon bonding and transformation of sliding surfaces by weak van der Waals and hydrogen bondings. High surface energy and the consequent superhydrophilic behaviour of film is attributed to the formation of the above-mentioned functional groups on the surface. This protects against deformation of the wear track leading to extremely high wear resistance.

A facile synthesis of covalent carbon nitride photocatalysts by Co-polymerization of urea and phenylurea for hydrogen evolution

Phenylurea has been integrated into the traditional polymerization route of carbon nitride (CN) precursors (e.g., urea, thiourea, dicyandiamide, and ammonium thiocyanide) in a facile one-pot approach, to modify the chemical composition, electronic structure, and catalytic performance of graphitic CN (g-CN). Results revealed that the co-polymerization of phenylurea with urea dramatically modifies the optical and electronic properties of g-CN, leading to a remarkable improvement by a factor of 9 in the photocatalytic activity of g-CN (when coupled with Pt as a co-catalyst) in an assay of hydrogen evolution reaction, while still keeping a high catalytic stability during pre-longed operations. The active catalyst is eventually a hybrid organocatalyst that is a heterogeneous Pt catalyst supported on a urea-based polymer. The promotional effect of phenylurea as the co-monomer for urea on the activity and stability of Pt/g-CN could be related to the extension of delocalized π-conjugated system of CN heterocycles, as a result of the fusion of phenyl motifs in the CN framework. The thus created surface dyadic structure favors the separation and migration of charge-carriers photoexcited upon light illumination. This work highlights a wide accessibility of chemical protocols for the design and synthesis of functional CN photocatalysts at molecular levels by applying suitable CN precursors and co-monomers.

Synthesis of carbon doped ZnO with a porous structure and its solar-light photocatalytic properties

Carbon (C) doped Zinc oxide (ZnO) with a porous structure is obtained by calcination of the powders prepared by hydrothermal reaction of zinc gluconate. The prepared ZnO powders are characterized by X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, ultraviolet–visible (UV–vis) diffuse reflectance spectra. The visible-light photocatalytic activity is evaluated by photocatalytic decomposition of the dye Rhodamine B (RhB) in aqueous solution. Results show that the covalent carbon incorporated into the O site of ZnO lattice causes the lattice compression. The porous C-doped ZnO consisted of many oblong nanocrystals. The photo-response of the C-doped ZnO expands to the visible region up to 800nm with lower band gap energy. The C-doped ZnO exhibit a significantly enhanced photocatalytic activity due to the improved absorption in the UV and visible-light region.

Improvement in Tribological Properties by Modification of Grain Boundary and Microstructure of Ultrananocrystalline Diamond Films

Grain boundaries and microstructures of ultrananocrystalline diamond (UNCD) films are engineered at nanoscale by controlling the substrate temperature (TS) and/or by introducing H2 in the commonly used Ar/CH4 deposition plasma in a microwave plasma enhanced chemical vapor deposition system. A model for the grain growth is proposed. The films deposited at low TS consist of random/spherical shaped UNCD grains with well-defined grain boundaries. On increasing TS, the adhering efficiency of CH radical onto diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nanosize diamond clusters break due to hydrogen abstraction activated, rendering the diamond phase less passivated. This leads to the C2 radical further attaching to the diamond lattice, resulting in the modification of grain boundaries and promoting larger sized clustered grains with a complicated defect structure. Introduction of H2 in the plasma at low TS gives rise to elongated clustered grains that is attributed to the presence of atomic hydrogen in the plasma, preferentially etching out the t-PA attached to nanosized diamond clusters. On the basis of this model a technologically important functional property, namely tribology of UNCD films, is studied. A low friction of 0.015 is measured for the film when ultranano grains are formed, which consist of large fractions of grain boundary components of sp(2)/a-C and t-PA phases. The grain boundary component consists of large amounts of hydroxylic and carboxylic functional groups which passivates the covalent carbon dangling bonds, hence low friction coefficient. The improved tribological properties of films can make it a promising candidate for various applications, mainly in micro/nanoelectro mechanical system (M/NEMS), where low friction is required for high efficiency operation of devices.

An Optimized and General Synthetic Strategy for Fabrication of Polymeric Carbon Nitride Nanoarchitectures

AbstractNanostructured covalent carbon nitride (CN) holds great promise for artificial photosynthesis, but its nanotexturation using templating methods is restricted by the weak binding affinities of neutral silica templates towards basic precursors that are kinetically difficult to diffuse into the nanopores of the templates. This weak affinity leads to an incomplete inclusion of the CN precursors into the nanostructured silica templates, and consequently, yields a defective replica of the parent porous structures. Here, this issue is addressed through the development of an innovative synthetic strategy to facilitate the sufficient inclusion of CN precursors in silica templates, by taking advantage of the surface acidification of silica and sonication‐promoted insertion. The ordered mesoporous CN (ompg‐CN) fabricated using SBA‐15 mesozeolite as the template has been demonstrated to show a better 2D mesoporous hexagonal framework, larger surface area, and higher photocatalytic activity than that synthesized by the traditional method. This innovative strategy can in general be expanded to other silica templates with various nanostructures, enabling the creation of stable polymeric CN nanostructures with maximized material and structure functions.

New Frontiers in Nanocarbons

Carbon is an extraordinary element. Its ability to covalently bond with different orbital hybridizations leads to a uniquely rich array of molecular structures that form the vast subject of organic chemistry. Approximately 20 million organic compounds containing carbon and other elements have been characterized, and it is estimated that than more than 90% of all recognized chemical compounds include carbon. By contrast, for millennia only two known substances were composed exclusively of carbon atoms: the elemental allotropes graphite and diamond. This situation changed dramatically in 1985 with the discovery of a new molecular allotrope, the soccer-ball shaped cage molecule C60, also known as Buckminsterfullerene. The discovery of C60 marked the dawn of carbon nanostructure research. In this field the focus is on all-carbon materials whose properties are determined by their specific covalent bonding geometries and the resulting well defined nanoscale structures. Activity in nanocarbon research grew explosively after the 1991 report of a method for making bulk quantities of fullerenes, and two years later a Fullerenes Group was formed within The Electrochemical Society to serve this new research community. With dimensions of approximately 1 nm, C60 and related larger fullerenes such as C70, C76, C84, etc. are studied using the experimental methods and concepts of chemistry. The scientific literature currently contains approximately 28,000 papers dealing with fullerenes. A second category of carbon nanostructure emerged in the early 1990s: nanotubes. Like fullerenes, these ordered cage structures are composed entirely of 5and 6-membered covalently bonded carbon rings, but nanotubes are highly elongated and contain 5-membered rings only at their caps. Carbon nanotubes also exist in far more structural varieties than fullerenes. With their large aspect ratios and crystalline order along the tube axis, nanotubes must be studied from an interdisciplinary viewpoint that combines concepts from chemistry and condensed matter physics. Carbon nanotubes display remarkable properties that have attracted great interest among basic and applied researchers working in chemistry, physics, materials science, chemical engineering, electrical engineering, and biomedicine. More than 85,000 papers have been published to date on carbon nanotubes. In 2004, a technique was demonstrated for removing and studying single atomic layers of carbon from graphite. These graphene sheets represent a third category of carbon nanostructures, with particularly unusual electrical properties arising from the semi-metallic pielectron band structure. As is true for nanotubes, the network of covalent carbon–carbon bonds linking the entire structure also gives graphene very high strength and suggests novel mechanical New Frontiers in Nanocarbons

Direct Mechanistic Transformations from Isotactic or Syndiotactic Living Anionic Polymerizations of Methyl Methacrylate into Metal-Catalyzed Living Radical Polymerizations.

The mechanistic transformations from living anionic polymerizations into living radical polymerizations were examined after halogenating the growing terminal during the stereospecific living anionic polymerization of methyl methacrylate (MMA), directly forming a macroinitiator with a covalent carbon-halogen terminal for subsequent transition metal-catalyzed living radical polymerizations. The quantitative halogenation of the living isotactic or syndiotactic PMMA anion, prepared using tBuMgBr in toluene or diphenylhexyllithium (DPHLi) in THF, respectively, was achieved using CCl3Br or CCl4 as a halogen source in the presence of strong Lewis bases, such as 1,8-diazabicyclo[5.4.0]undec-7-ene, to generate stereoregular PMMA with a C-X (X = Br or Cl) bond. The halogenated terminal was then transformed into the radical species through a one-electron redox reaction of the ruthenium catalysts to allow the living radical polymerization of styrene or MMA, resulting in block copolymers that consisted of stereoregular PMMA and polystyrene segments or stereoblock PMMAs.

Light harvesting with non covalent carbon nanotube/porphyrin compounds

We present recent developments in the synthesis and in the functional study of non covalently bound porphyrin/carbon nanotube compounds. The issue of the chemical stability of non covalent compounds is tackled by means of micelle assisted chemistry. The non covalent functionalization allows to preserve the electronic integrity of the nanotubes that display bright NIR luminescence. In the same time, the coupling between the subunits is very strong and leads to efficient energy transfer and PL quenching of the chromophore. This transfer occurs on a subpicosecond time-scale and leads to a near 100% efficiency. It allows to uniformly excite a whole set of chiral species with a single wavelength excitation. Insight into the transfer mechanism is gained by means of transient absorption spectroscopy.

ChemInform Abstract: Advances in the Chemical Modification of Epitaxial Graphene

AbstractReview: 118 refs.

Improving the Degree of Functionalization and Solubility of Single-Walled Carbon Nanotubes via Covalent Multiple Functionalization

The synthesis of covalent multi-functionalized single-walled carbon nanotubes (SWNT) via the combination of two diazonium salt addition reactions with tetrabutylammonium hydroxide to form carbon nanotube salts was carried out. The formation of carbon nanotube salts allows SWNT to be easily dissolved in common solvents, which increases the processing capability of the SWNT. The dissolutions of some of the obtained products can be increased three-fold through multi-functionalization. Thus tetrabutylammonium cation plays an extraordinarily important role; i.e., balancing the charges on the functionalized SWNT surface and de-bundling of the functionalized SWNT. This approach provides a useful way of preparing some SWNT-containing biomaterials. The multi-functionalized SWNT were confirmed by standard techniques used for carbon nanotube characterization.

Advances in the chemical modification of epitaxial graphene

Chemistry will play an increasingly important role in the realization of graphene applications. The chemical formation of covalent carbon–carbon bonds involving the basal plane carbon atoms offers an alternative approach to the control of the electronic properties of graphene, and potentially allows the generation of insulating and semiconducting regions in graphene wafers. This review summarizes recent progress in the covalent modification of epitaxial graphene and the effect that chemistry has on the electronic and magnetic properties of the material.

Electrochemical Coupling Layer-by-layer (ECC-LbL) Assembly in Patterning Mode

Abstract Functional building blocks (fullerene and fluorene) were integrated into multilayers by utilizing electrochemical coupling layer-by-layer (ECC-LbL) assembly driven by the covalent carbon–carbon coupling reaction of pendant alkylcarbazoyl groups. The ECC-LbL assembly in patterning mode can be used to locally immobilize functional units and has been demonstrated here in a patterned fluorescent display. ECC-LbL is a versatile method for surface fabrication with promising potential in many applications.

Computational study of linear carbon chains on gold and silver surfaces

Density-functional-theory calculations were carried out for hydrogen capped linear carbon chains, polyynes and cumulenes, adsorbed dissociatively on the (111) and (211) surfaces of gold and silver. In the studied adsorption reactions, carbon–hydrogen bonds are broken and covalent carbon–metal bonds are created. The adsorption of cumulenes is highly endothermic, whereas the adsorption of polyynes is near thermoneutral. Also, the hydrogenation of adsorbed polyynyl radicals (·CnH) into adsorbed cumulene carbenes (:CnH2) was investigated, which was found to be exothermic on both metals. Vibrational calculations were conducted on the adsorption systems, and the results were compared with experimental surface enhanced Raman scattering spectra. An interpretation is proposed for the spectra of polyyne–silver solutions, and features of polyyne–gold spectra are predicted.

Influence of Periodic Nitrogen Functionality on the Selective Oxidation of Alcohols

An enhancement in catalytic alcohol oxidation activity is attributed to the presence of nitrogen heteroatoms on the external surface of a support material. The same Pd particles (3.1-3.2 nm) were supported on polymeric carbon-nitrogen supports and used as catalysts to selectively oxidize benzyl alcohol. The polymeric carbon-nitrogen materials include covalent triazine frameworks (CTF) and carbon nitride (C(3)N(4)) materials with nitrogen content varying from 9 to 58 atomic percent. With comparable metal exposure, estimated by X-ray photoelectron spectroscopy, the activity of these catalysts correlates with the concentration of nitrogen species on the surface. Because the catalysts showed comparable acidic/basic properties, this enhancement cannot be ascribed to the Lewis basicity but most probably to the nature of N-containing groups that govern the adsorption sites of the Pd nanoparticles.

Graphene Actuators: Quantum-Mechanical and Electrostatic Double-Layer Effects

The electrochemical actuation of covalent carbon materials, such as graphene, immersed in liquid electrolytes has shown immense promise for a myriad of applications. To realize this potential, an intimate understanding of the physics behind the actuation is essential. With the use of ab initio density functional calculations, it is shown that the strain induced in monolayer graphene by the formation of an electrostatic double-layer (DL) is the dominant actuation mechanism. The DL-induced strain (~1%) is found to exceed the quantum-mechanical strain (~0.2%) due to charge injection only, for charges and electric potentials of greater than -0.08 e/C-atom and 1 V, respectively. Various methods of calculating the graphene atomic charges based on first principle charge densities are compared and contrasted. The electrochemical charge-strain and potential-strain relationships for monolayer graphene are shown to be parabolic in nature. This study proves that the origin of the high electrochemical strains in covalent carbon materials is the electrostatic DL potential, and demonstrates the true viability of using monolayer graphene for nanoelectromechanical systems (NEMS) actuators.

Thermographic studies of a dynamic synthesis product in the C-N system

The results have been considered of the research into an ultradispersed product synthesized in a hyperspeed flow of a carbon electric-discharge plasma in the nitrogen atmosphere using electron scanning and transmission microscopies, thermography, and IR- Fourier spectroscopy. The aim of the studies has been to remove the impurity carbon phases from the product and to estimate the thermostability of covalent carbon nitride.

Amine-linker length dependent electron transfer between porphyrins and covalent amino-modified single-walled carbon nanotubes

Single-walled carbon nanotube (SWNT)-porphyrin hybrid materials have received much attention due to their promising applications in photovoltaic devices, photodynamic therapy and energy conversion. Herein, three covalent amine-modified single-walled carbon nanotubes with different alkyl chain lengths have been synthesized and characterized by FT-IR, 1H NMR, XPS, and TGA-DTA methods. The electron transfer (ET) between SWNTs and porphyrins has been studied and the important influencing ET factors, such as linker length, solvent polarity, pH and ionic strength, and central metal of porphyrin, are discussed in detail in this report. Our results indicate that shorter alkyl chain length, higher polarity of the solvent, lower pH and ionic strength are all favorable for ET, the central metal coordinated to the porphyrin macrocycle is not essential for ET.