Atomic-Scale Deformation in N-Doped Carbon Nanotubes

Highly selective adsorption of Hg (II) from aqueous solution by three-dimensional porous N-doped starch-based carbon

For the first time, N-doped carbon materials with 3D porous-layered skeleton structure was synthesized through a one-step co-pyrolysis method, which was fabricated by co-pyrolysis of natural corn starch and melamine using metal catalysts (Ni (II) and Mn (II)). The 3D-NC possessed a heterogeneously meso-macroporous surface with a hierarchically connected sheet structure inside. Batch adsorption experiments suggested that highly selective adsorption of Hg (II) by the 3D-NC could be completed within 90 min and had maximum adsorption capacities as high as 403.24 mg/g at 293 K, pH = 5. The adsorption mechanism for Hg (II) was carefully evaluated and followed the physical adsorption, electrostatic attraction, chelation, and ion exchange. Besides, thermodynamic study demonstrated that the Hg (II) adsorption procedure was spontaneous, endothermic, and randomness. More importantly, the 3D-NC could be regenerated and recovered well after adsorption-desorption cycles, showing a promising prospect in the remediation of Hg (II)-contaminated wastewater.

Amorphous Nitrogen-Doped Carbon Nanocages with Excellent SERS Sensitivity and Stability for Accurate Identification of Tumor Cells

The surface-enhanced Raman scattering (SERS) bioprobe's strategy for identifying tumor cells always depended on the intensity difference of the Raman signal compared with that of normal cells. Hence, exploring novel SERS nanostructure with excellent spectra stability, a high enhancement factor (EF), and good biocompatibility is a primary premise for boosting SERS signal reliability and accuracy of tumor cells. Here, high SERS EF (5.52 × 10⁶) is acquired by developing novel amorphous nitrogen-doped carbon (NDC) nanocages (NCs), whose EF value was in a leading position among carbon-based SERS substrates. In addition, a uniform SERS signal was obtained on NDC NCs due to homogeneous morphology and size. The delocalized carbon-conjugated systems of graphitic-N, pyrrole-N, and pyridine-N with lone pair electrons increase the electronic density of states and reduce the electron localization function of NDC NCs, thereby promoting the charge transfer process. The electron-donor platform of the NDC NCs facilitates the thermodynamic process of charge transfer, resulting in multimode vibrational coupling in the surface complexes, which greatly amplifies the molecular polarizability. Importantly, the good biocompatibility and signal stability endow these NDC NC SERS bioprobes unique superiority in distinguishing tumor cells, and quantitative recognition of two triple-negative breast cancer cells based on SERS detection mode has been successfully realized.

Electronic structure modulation of multi-walled carbon nanotubes using azo dye for inducing non-radical reaction: Effect of graphitic nitrogen and structural defect

Multiwalled carbon nanotube (MWCNT) have a great potential for advanced oxidation process as a metal free catalyst. However, there catalytic activity is very low and needs to be appropriately tuned. Herein, we demonstrate a novel synthesis method for tuning the defect and surface functionality of MWCNT using azo dyes and the catalytic performance was tested for the degradation of different organic contaminates using PMS as an oxidant. The content, type of heteroatom functional groups, and the defect parameters were optimized by varying the pH and concentration of the organic dye. The quenching effect showed that singlet oxygen (¹O₂) is the primary reactive species generated by graphitic nitrogen, which can be boosted by the degree of graphitic structure disruption in MWCNT. The Linear sweep voltammetry (LSV) also confirmed that extrinsic doping enhanced the non-radical degradation by increasing the direct charge transfer rate from MB to PMS. Moreover, the designed catalyst showed a fast degradation performance with 35.1 kJ/mol activation energy and achieved the highest dye degradation rate and even surpassed some state-of-the-art metal-based and metal-free catalysts. The effect of inorganic anions study has also confirmed its industrial applicability.

Porous Carbon Nanofibers Derived from Silk Fibroin through Electrospinning as N-Doped Metal-Free Catalysts for Hydrogen Evolution Reaction in Acidic and Alkaline Solutions

Water electrolysis is considered as one promising strategy for hydrogen production, and thus, preparing electrocatalysts of superior efficiency and low cost for a hydrogen evolution reaction (HER) in a wide pH range is of paramount importance. In this research, N-doped porous carbon nanofibers derived from silk fibroin by KCl chemical activation are successfully synthesized as the metal-free catalyst for the HER under both acidic and alkaline conditions. After chemical activation of KCl, hierarchical porous structures are formed. Besides, it is found that the concentration of KCl in the electrospun membrane will affect the maintenance of the fibrous morphology for the carbonized samples due to the destruction of β-sheets in silk fibroin induced by KCl. The specific surface area of the optimized sample, 4%-SPCNF, increased by nearly nine times compared with that without activation because of the hierarchical pores and large through pores between fibers. Meanwhile, the porosity increases from 59.87 to 80.28% due to the existence of through pores. Moreover, the 4%-SPCNF has remarkable stability and durability since the carbon substrate is resistant against the corrosion of the electrolyte. Our work provides insights into the design and engineering of silk fibroin-derived carbon nanofibers for metal-free catalysts of the HER under acidic and alkaline conditions.

Dual Metal-Loaded Porous Carbon Materials Derived from Silk Fibroin as Bifunctional Electrocatalysts for Hydrogen Evolution Reaction and Oxygen Evolution Reaction

Developing electrocatalysts with high efficiency and long-term stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is significant to massively generate hydrogen energy by water splitting. In this work, cobalt and tungsten dual metal-loaded N-doped porous carbon electrocatalysts derived from silk fibroin were successfully prepared through facile carbonization and chemical activation by KCl and applied as efficient electrocatalysts for HER and OER. After chemical activation, the resulting catalysts present a unique hierarchical porous structure with micro-, meso-, and macropores, which is able to expose more implantation sites for catalytic active metals and will in turn promote the efficient diffusion of the electrolyte. The catalyst under the optimized condition (CoW@ACSF) has a specific area of 326.01 m² g^-1. The overpotential at a current density of 10 mA cm ^-2 of CoW@ACSF is 138.42 ± 10.39 mV toward HER and 492.05 ± 19.04 mV toward OER. Furthermore, the overpotential only increases 101.2 mV toward HER and 66.00 mV toward OER after the long-term stability test of chronopotentiometric test over 10 h, which confirms the excellent stability of the CoW@ACSF, owing to its unique carbon shell structure. This work gives an insight into the design and engineering of silk fibroin-derived carbon materials for electrocatalysis toward HER and OER.

A C-S-C Linkage-Triggered Ultrahigh Nitrogen-Doped Carbon and the Identification of Active Site in Triiodide Reduction

An efficient chemical synthesis route, with an aim of reaching an ultrahigh nitrogen (N)-doping level in carbon materials can provide a platform where the type and amount of N dopant can be tuned over a wide range. We propose a C-S-C linkage-triggered confined-pyrolysis strategy for the high-efficiency in situ N-doping into carbon matrix and an ultrahigh doping level up to 13.5 at %, which is close to the theoretical upper limit (15.2 at %) is realized at a high carbonization temperature of 1000 °C. The pyridinic N is dominant with a maximum percent of 48.7 %. By using I₃ ^- reduction as an example, the resultant NCM-5 exhibits the best activity with a power conversion efficiency of 8.77 %. A pyridinic N site-dependent activity is demonstrated in which the amount of active sites increases with the increase of pyridinic N, and the carbon atom adjacent to electron-withdrawing pyridinic N at the armchair edge acts as the most favorable site for the adsorption of I₂ .

A carbonized porous aromatic framework to achieve customized nitrogen atoms for enhanced supercapacitor performance

A porous aromatic framework serving as a precursor preserves the customized nitrogen atoms in the porous carbons, which endows improved electrochemical properties for high-performance supercapacitor applications.

Microwave-Assisted Synthesis of Boron and Nitrogen co-doped Reduced Graphene Oxide for the Protection of Electromagnetic Radiation in Ku-Band

The electromagnetic interference (EMI) shielding of reduced graphene oxide (MRG), B-doped MRG (B-MRG), N-doped MRG (N-MRG), and B-N co-doped MRG (B-N-MRG) have been studied in the Ku-band frequency range (12.8-18 GHz). We have developed a green, fast, and cost-effective microwave assisted route for synthesis of doped MRG. B-N-MRG shows high electrical conductivity in comparison to MRG, B-MRG and N-MRG, which results better electromagnetic interference (EMI) shielding ability. The co-doping of B and N significantly enhances the electrical conductivity of MRG from 21.4 to 124.4 Sm(-1) because N introduces electrons and B provides holes in the system and may form a nanojunction inside the material. Their temperature-dependent electrical conductivity follows 2D-variable range hopping (2D-VRH) and Efros-Shklovskii-VRH (ES-VRH) conduction model in a low temperature range (T<50 K). The spatial configuration of MRG after doping of B and N enhances the space charge polarization, natural resonance, dielectric polarization, and trapping of EM waves by internal reflection leading to a high EMI shielding of -42 dB (∼99.99% attenuation) compared to undoped MRG (-28 dB) at a critical thickness of 1.2 mm. Results suggest that the B-N-MRG has great potential as a candidate for a new type of EMI shielding material useful in aircraft, defense industries, communication systems, and stealth technology.

An accurate benchmark description of the interactions between carbon dioxide and polyheterocyclic aromatic compounds containing nitrogen

We assessed the performance of a large variety of modern density functional theory approaches for the adsorption of carbon dioxide on molecular models of pyridinic N-doped graphene.

Controlling the doping level of double-walled carbon nanotubes by using aromatic hydrocarbon complexes

The level of potassium doping in double-walled carbon nanotubes has been tailored by the combination of potassium and aromatic hydrocarbons in a polar solvent.

One-pot microbial method to synthesize dual-doped graphene and its use as high-performance electrocatalyst

A novel strategy to synthesize nitrogen (N) and sulfur (S)-doped graphene (G) is developed through sulfate-reducing bacteria treating graphene oxide (GO). The N, S-doped G demonstrates significantly improved electrocatalytic properties and electrochemical sensing performances in comparison with single-doped graphene due to the synergistic effects of dual dopants on the properties of graphene.

Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes

The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.

A COMPARATIVE STUDY OF OPTICAL PROPERTIES OF C3N AND CN3 SYSTEMS THROUGH DENSITY FUNCTIONAL THEORY (DFT)

The optical properties of (8,0) single wall carbon nanotubes (SWCNTs) alloyed with nitrogen ( N ) are computed using ab initio density functional theory (DFT). Both the real as well as imaginary dielectric constant in the long wavelength limit depends essentially on the nature of electromagnetic field. It is observed that for CN 3 systems, the reflectivity vanishes at 3.45, 6.95, and 8.20 eV, respectively for parallel, perpendicular polarization, and unpolarized light with incidence (1,0,0), while for C 3 N the vanishing reflectivity occurs only for parallel polarization at 8.05 eV. Although the magnitude of the significant peaks of loss function of CN 3 systems are comparable to C 3 N in perpendicular and unpolarized situation, however, they are significantly one order of magnitude higher in CN 3 for parallel polarization.

Spontaneous Synthesis and Electrochemical Characterization of NanostructuredMnO2on Nitrogen-Incorporated Carbon Nanotubes

This paper investigated the layered manganese dioxide with hydrate (MnO2⋅xH2O) deposits onto nitrogen-containing carbon nanotube (CNxNTs) as a hierarchical electrode for an energy-storage device. The dense and entangled CNxNTs were directly grown by microwave plasma-enhanced chemical vapor deposition (MPECVD) on a carbon cloth (CC), and subsequently used as a current collector. By controlling the pH value of KMnO4precursor solution, and incorporating nitrogen into CNTs as a reducing agent, the MnO2thin layer was uniformly fabricated on the CNxNTs at room temperature by using a spontaneous reduction method. The role of incorporation nitrogen is not only capable of creating active sites on the CNT surface, but can also donate electrons to reduceMnO4-to MnO2spontaneously. From the measurements of cyclic voltammograms and galvanostatic charge/discharge, MnO2/CNxNTs/CC composite electrodes illustrated excellent specific capacitance of 589.1 Fg-1. The key factor for high performance could be attributed to the thin-layered MnO2nanostructure, which resulted in the full utilization of MnO2deposits. Hence, the hierarchically porous MnO2/CNxNTs/CC electrodes exhibited excellent capacitive behavior for electrochemical capacitor application.

In vitro detection of superoxide anions released from cancer cells based on potassium-doped carbon nanotubes-ionic liquid composite gels

A newly developed electrochemical biosensor for the determination of superoxide anions (O(2)˙(-)) released from cancer cells using potassium-doped multi-walled carbon nanotubes (KMWNTs)-1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF(6)) ionic liquid composite gels is demonstrated. The KMWNTs-[BMIM]PF(6) can electrocatalyze oxygen reduction to generate a strong current signal in neutral solution. Compared with KMWNTs without [BMIM]PF(6) or MWNTs-[BMIM]PF(6) composites, the KMWNTs-[BMIM]PF(6) can enhance the oxygen reduction peak current by 6.2-fold and 2.8-fold, which greatly increases the detection sensitivity of oxygen. Then, O(2)˙(-) biosensors are fabricated by mixing superoxide dismutase (SOD) in the KMWNTs-[BMIM]PF(6) gels via monitoring oxygen produced by an enzymic reaction between SOD/O(2)˙(-) without the help of electron mediators. The resulting biosensors show a linear range from 0.04 to 38 μM with a high sensitivity of 98.2 μA mM(-1), and a lower detection limit of 0.024 μM. The common interferents such as hydrogen peroxide (H(2)O(2)), ascorbic acid (AA), uric acid (UA), and metabolites of neurotransmitters, do not interfere with the detection of O(2)˙(-). The proposed biosensor is tested to determine O(2)˙(-) in vitro and from liver cancer and leukemia cells and shows good application potential in biological electrochemistry.

TOWARDS THE SINGLE-WALLED B- AND/OR N-DOPED CARBON NANOTUBES

Soon after the discovery of carbon nanotubes (CNTs) in the early 1990's, the B - and/or N -doped CNTs began to attract increasing interest owing to their modified structural, physical and chemical properties. In comparison with the multi-walled nanotubes and nanofibers, substitutional doping of the single-walled nanotubes (SWNTs) has proved to be much more difficult, and it is only in very recent years that some experimental studies concerning the B - and/or N -doped SWNTs are emerging. This paper intends to provide an up-to-date overview of current research on the doped SWNTs, with scopes covering both the binary system of CB x- and CN x-SWNTs and the ternary B x C y N z-SWNTs. A survey of the latest achievements in the syntheses of doped SWNTs through either the direct syntheses methods or the post-synthetic substitution reaction route is first presented; then the aspects concerning their structural features, elemental compositions, dopants bonding configuration and atomic distributions, as well as their physical and chemical properties are discussed.

Microwave-assisted synthesis of a core-shell MWCNT/GONR heterostructure for the electrochemical detection of ascorbic acid, dopamine, and uric acid

In this study, graphene oxide nanoribbons (GONRs) were synthesized from the facile unzipping of multiwalled carbon nanotubes (MWCNTs) with the help of microwave energy. A core-shell MWCNT/GONR-modified glassy carbon (MWCNT/GONR/GC) electrode was used to electrochemically detect ascorbic acid (AA), dopamine (DA), and uric acid (UA). In cyclic voltammograms, the MWCNT/GONR/GC electrode was found to outperform the MWCNT- and graphene-modified GC electrodes in terms of peak current. For the simultaneous sensing of three analytes, well-separated voltammetric peaks were obtained using a MWCNT/GONR/GC electrode in differential pulse voltammetry measurements. The corresponding peak separations were 229.9 mV (AA to DA), 126.7 mV (DA to UA), and 356.6 mV (AA to UA). This excellent electrochemical performance can be attributed to the unique electronic structure of MWCNTs/GONRs: a high density of unoccupied electronic states above the Fermi level and enriched oxygen-based functionality at the edge of the graphene-like structures, as revealed by X-ray absorption near-edge structure spectroscopy, obtained using scanning transmission X-ray microscopy.

Strategy for carrier control in carbon nanotube transistors

Carbon nanotubes exhibit remarkable mechanical and electronic properties and are, therefore, being regarded as a new functional material for next generation electronics. Nevertheless, several obstacles still exist for an application in industry. The control of carriers in carbon nanotubes is of critical importance prior to an industrial application in transistors. As carbon nanotubes exhibit p-type behavior under ambient conditions, it is difficult to convert them from a p- to an n-type transistor. Also, doping control is a critical issue for applying traditional CMOS technology. Here, we discuss various approaches for preparing operating carbon nanotube transistors: i) impurity doping that employs conventional and interstitial insertion of group III or V materials, ii) chemical doping that induces charge transfer between chemicals and CNTs, iii) carrier control that utilizes the work function difference between metal and CNTs, iv) electrostatic doping that controls the carrier type by using a gate bias, and v) ambipolarity that does not use chemical doping. Advantages and drawbacks of these approaches will be discussed extensively in the text.

Theory, synthesis, and oxygen reduction catalysis of Fe-porphyrin-like carbon nanotube

We report the synthesis of a Fe-porphyrin-like carbon nanotube from conventional plasma-enhanced chemical vapor deposition. Covalent but seamless incorporation of the 5-6-5-6 porphyrinic Fe-N(4) moiety into the graphene hexagonal side wall was elucidated by x-ray and ultraviolet photoemission spectroscopies and first-principles electronic structure calculations. The resulting biomimetic nanotube exhibits an excellent oxygen reduction catalytic activity with the extreme structural stability over 0.1×10(6) cycles, vastly superior to the commercial Pt-C catalyst.

Effect of N/B doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons

Carbon nanotubes, carbon nanocones, and graphene nanoribbons are carbon-based nanomaterials, and their electronic and field emission properties can be altered by either electron donors or electron acceptors. Among both donors and accepters, nitrogen and boron atoms are typical substitutional dopants for carbon materials. The contribution of this paper mainly provides a comprehensive overview of the theoretical topics. The effect of nitrogen/boron doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons is reviewed. It is also suggested that nitrogen is more an n-type donor. The discussion about the mechanism of field emission for N-doped carbon nanotubes and electronic structures of N-doped graphene nanoribbons is interesting and timely.

Spin gapless semiconductor-metal-half-metal properties in nitrogen-doped zigzag graphene nanoribbons

The geometries, formation energies, and electronic and magnetic properties of N-doping defects, including single atom substitution and pyridine- and pyrrole-like substructures in zigzag graphene nanoribbons (ZGNRs), were investigated by means of spin-unrestricted density functional theory computations. The edge carbon atoms are more easily substituted with N atoms, and three-nitrogen vacancy (3NV) defect and four-nitrogen divacancy (4ND) defect also prefer the ribbon edge. Single N atom substitution and pyridine- and pyrrole-like N-doping defects can all break the degeneracy of the spin polarization of pristine ZGNRs. One single N atom substitution makes the antiferromagnetic semiconducting ZGNRs into spin gapless semiconductors, while double edge substitution transforms N-doped graphenes into metals. Pyridine- and pyrrole-like N-doping defects make ZGNRs into half-metals or spin gapless semiconductors. These results suggest the potential applications of N-doped ZGNRs in nanoelectronics.

First principles calculations of the optical properties of CxNy single walled nanotubes

The optical properties of (8, 0) single walled carbon nanotubes alloyed with nitrogen (N) have been examined using relaxed carbon-carbon (C-C) bond length ab initio density functional theory (DFT) calculations in the long wavelength limit. The maximum value of the absorption coefficient is shown to depend strongly on the concentration of N in a non-linear way as well as on the direction of polarization. The reflectivity at normal incidence vanishes at some unique concentration of N. It is also observed that the peak of the loss function (in parallel polarization and unpolarized cases) shifts to a higher frequency indicating the enhanced metallic character. The observed variation of the plasma resonance frequencies with N concentration indicates the existence of a unique maximum for parallel polarization and a step function like behavior for the unpolarized situation with concentration.