Plasma Activation of Carbon Nanotubes for Chemical Modification

Pyridine Functionalized Carbon Nanotubes: Unveiling the Role of External Pyridinic Nitrogen Sites for Oxygen Reduction Reaction

Pyridinic nitrogen has been recognized as the primary active site in nitrogen-doped carbon electrocatalysts for the oxygen reduction reaction (ORR), which is a critical process in many renewable energy devices. However, the preparation of nitrogen-doped carbon catalysts comprised of exclusively pyridinic nitrogen remains challenging, as well as understanding the precise ORR mechanisms on the catalyst. Herein, a novel process is developed using pyridyne reactive intermediates to functionalize carbon nanotubes (CNTs) exclusively with pyridine rings for ORR electrocatalysis. The relationship between the structure and ORR performance of the prepared materials is studied in combination with density functional theory calculations to probe the ORR mechanism on the catalyst. Pyridinic nitrogen can contribute to a more efficient 4-electron reaction pathway, while high level of pyridyne functionalization result in negative structural effects, such as poor electrical conductivity, reduced surface area, and small pore diameters, that suppressed the ORR performance. This study provides insights into pyridine-doped CNTs-functionalized for the first time via pyridyne intermediates-as applied in the ORR and is expected to serve as valuable inspiration in designing high-performance electrocatalysts for energy applications.

Enhanced Catalytic Hydrodeoxygenation of Activated Carbon-Supported Metal Catalysts via Rapid Plasma Surface Functionalization

We employ a nonthermal, He/O₂ atmospheric plasma as an efficient surface functionalization method of activated carbons. We show that plasma treatment rapidly increases the surface oxygen content from 4.1 to 23.4% on a polymer-based spherical activated carbon in 10 min. Plasma treatment is 3 orders of magnitude faster than acidic oxidation and introduces a diverse range of carbonyl (C═O) and carboxyl (O-C═O) functionalities that were not found with acidic oxidation. The increased oxygen functionalities reduce the particle size of a high 20 wt % loading Cu catalyst by >44% and suppress the formation of large agglomerates. Increased metal dispersion exposes additional active sites and improves the yield of hydrodeoxygenation of 5-hydroxymethyl furfural to 2,5-dimethyl furan, an essential compound for biofuel replacement, by 47%. Surface functionalization via plasma can advance catalysis synthesis while being rapid and sustainable.

Bio-Inspired Synthesis of Carbon-Based Nanomaterials and Their Potential Environmental Applications: A State-of-the-Art Review

Providing safe drinking water and clean water is becoming a more challenging task all around the world. Although some critical issues and limits remain unsolved, implementing ecologically sustainable nanomaterials (NMs) with unique features, e.g., highly efficient and selective, earth-abundance, renewability, low-cost manufacturing procedures, and stability, has become a priority. Carbon nanoparticles (NPs) offer tremendous promise in the sectors of energy and the environment. However, a series of far more ecologically friendly synthesis techniques based on natural, renewable, and less expensive waste resources must be explored. This will reduce greenhouse gas emissions and harmful material extraction and assist the development of green technologies. The progress achieved in the previous 10 years in the fabrication of novel carbon-based NMs utilizing waste materials as well as natural precursors is reviewed in this article. Research on carbon-based NPs and their production using naturally occurring precursors and waste materials focuses on this review research. Water treatment and purification using carbon NMs, notably for industrial and pharmaceutical wastes, has shown significant potential. Research in this area focuses on enhanced carbonaceous NMs, methods, and novel nano-sorbents for wastewater, drinking water, groundwater treatment, as well as ionic metal removal from aqueous environments. Discussed are the latest developments and challenges in environmentally friendly carbon and graphene quantum dot NMs.

Nitrogen plasma modification boosts up the hemocompatibility of new PVDF-carbon nanohorns composite materials with potential cardiological and circulatory system implants application

To design new material for blood-related applications one needs to consider various factors such as cytotoxicity, platelet adhesion, or anti-thrombogenic properties. The aim of this work is the design of new, highly effective materials possessing high blood compatibility. To do this, the new composites based on the poly(vinylidene fluoride) (PVDF) support covered with a single-walled carbon nanohorns (CNHs) layer were prepared. The PVDF-CNHs composites were subsequently used for the first time in the hemocompatibility studies. To raise the hemocompatibility a new, never applied before for CNHs, plasma-surface modifications in air, nitrogen and ammonia were implemented. This relatively cheap, facile and easy method allows generating the new hybrid materials with high effectiveness and significant differences in surface properties (water contact angle, surface ζ-potential, and surface functional groups composition). Changing those properties made it possible to select the most promising samples for blood-related applications. This was done in a fully controlled way by applying Taguchi's "orthogonal array" procedure. It is shown for the first time that nitrogen plasma treatment of new surfaces is the best tool for hemocompatibility rise and leads to very low blood platelet adhesion, no cytotoxicity, and excellent performance in thromboelastometry and hemolysis tests. We propose a possible mechanism explaining this behavior. The optimisation results are coherent with biological characterisation and are supported with Hansen Solubility Parameters. New surfaces can find potential applications in cardiological and circulatory system implants as well as other blood-related biomaterials.

Fabrication of Metal/Carbon Nanotube Composites by Electrochemical Deposition

Metal/carbon nanotube (CNT) composites are promising functional materials due to the various superior properties of CNTs in addition to the characteristics of metals, and consequently, many fabrication processes of these composites have been vigorously researched. In this paper, the fabrication process of metal/CNT composites by electrochemical deposition, including electrodeposition and electroless deposition, are comprehensively reviewed. A general introduction for fabrication of metal/CNT composites using the electrochemical deposition is carried out. The fabrication methods can be classified into three types: (1) composite plating by electrodeposition or electroless deposition, (2) metal coating on CNT by electroless deposition, and (3) electrodeposition using CNT templates, such as CNT sheets and CNT yarns. The performances of each type have been compared and explained especially from the view point of preparation methods. In the cases of (1) composite plating and (2) metal coating on CNTs, homogeneous dispersion of CNTs in electrochemical deposition baths is essential for the formation of metal/CNT composites with homogeneous distribution of CNTs, which leads to high performance composites. In the case of (3) electrodeposition using CNT templates, the electrodeposition of metals not only on the surfaces but also interior of the CNT templates is the key process to fabricate high performance metal/CNT composites.

α-Helical peptides on plasma-treated polymers promote ciliation of airway epithelial cells

Airway respiratory epithelium forms a physical barrier through intercellular tight junctions, which prevents debris from passing through to the internal environment while ciliated epithelial cells expel particulate-trapping mucus up the airway. Polymeric solutions to loss of airway structure and integrity have been unable to fully restore functional epithelium. We hypothesised that plasma treatment of polymers would permit adsorption of α-helical peptides and that this would promote functional differentiation of airway epithelial cells. Five candidate plasma compositions are compared; Air, N₂, H₂, H₂:N₂ and Air:N₂. X-ray photoelectron spectroscopy shows changes in at% N and C 1s peaks after plasma treatment while electron microscopy indicates successful adsorption of hydrogelating self-assembling fibres (hSAF) on all samples. Subsequently, adsorbed hSAFs support human nasal epithelial cell attachment and proliferation and induce differentiation at an air-liquid interface. Transepithelial measurements show that the cells form tight junctions and produce cilia beating at the normal expected frequency of 10-11 Hz after 28 days in culture. The synthetic peptide system described in this study offers potential superiority as an epithelial regeneration substrate over present "gold-standard" materials, such as collagen, as they are controllable and can be chemically functionalised to support a variety of in vivo environments. Using the hSAF peptides described here in combination with plasma-treated polymeric surfaces could offer a way of improving the functionality and integration of implantable polymers for aerodigestive tract reconstruction and regeneration.

Nitrogen-doped carbon dodecahedron embedded with cobalt nanoparticles for the direct electro-oxidation of glucose and efficient nonenzymatic glucose sensing

Developing high-performance sensors for glucose detection is extremely desirable for clinical diagnostics and life sciences. Particularly, it is greatly attractive to exploit composite materials with large surface area, doped heterojunction and non-precious metal as highly active electro-catalysts for nonenzymatic glucose sensing. Herein, we reported a N-doped carbon dodecahedron embedded with Co nanoparticles (Co@NCD) for the direct electro-oxidation of glucose and efficient nonenzymatic glucose detection. Co@NCD was synthesized by the pyrolysis of zeolitic imidazolate framework (ZIF). Field emission scanning electron microscope, high-resolution transmission electron microscope, powder X-ray diffraction, X-ray photoelectron spectroscopy and nitrogen adsorption-desorption experiments were performed to investigate Co@NCD. A well-defined dodecahedron morphology with uniform size and shape was observed. Besides, the original framework was carbonized after pyrolysis leading to a hollow and porous graphite dodecahedron containing N-doped carbon heterojunction. Moreover, Co nanoparticles were evenly distributed into the dodecahedron. With porous structure, N-doped carbon and embedded Co nanoparticles, Co@NCD displayed a notable electro-catalysis towards the direct oxidation of glucose (onset potential: 0.20 V). By using Co@NCD as electro-catalyst, an efficient nonenzymatic glucose sensor was obtained with a rapid amperometric response (within 1 s), low detection limit (0.11 μM) and broad detection range (0.2 μM-12.0 mM). In addition, remarkable selectivity, repeatability, reproducibility and long-term stability were also observed. Finally, Co@NCD prepared sensor was also successfully applied to the detection of glucose in human serum. Our results suggested that ZIF templated method could be an innovative solution for active composite catalysts in biomolecular electro-catalysis and Co@NCD prepared sensor could be a substantial preferable sensing platform for the nonenzymatic glucose detection.

The electrochemical corrosion of an air thermally-treated carbon fiber cloth electrocatalyst with outstanding oxygen evolution activity under alkaline conditions

An air thermally-treated carbon fiber cloth CFC-450 with a low CO content exhibits excellent OER activity. In addition, an electrochemical corrosion phenomenon was observed.

Carbon Nanomaterials for Targeted Cancer Therapy Drugs: A Critical Review

Cancer represents one of the main causes of human death in developed countries. Most current therapies, unfortunately, carry a number of side effects, such as toxicity and damage to healthy cells, as well as the risk of resistance and recurrence. Therefore, cancer research is trying to develop therapeutic procedures with minimal negative consequences. The use of nanomaterial-based systems appears to be one of them. In recent years, great progress has been made in the field using nanomaterials with high potential in biomedical applications. Carbon nanomaterials, thanks to their unique physicochemical properties, are gaining more and more popularity in cancer therapy. They are valued especially for their ability to deliver drugs or small therapeutic molecules to these cells. Through surface functionalization, they can specifically target tumor tissues, increasing the therapeutic potential and significantly reducing the adverse effects of therapy. Their potential future use could, therefore, be as vehicles for drug delivery. This review presents the latest findings of research studies using carbon nanomaterials in the treatment of various types of cancer. To carry out this study, different databases such as Web of Science, PubMed, MEDLINE and Google Scholar were employed. The findings of research studies chosen from more than 2000 viewed scientific publications from the last 15 years were compared.

Superior thermomechanical and wetting properties of ultrasonic dual mode mixing assisted epoxy-CNT nanocomposites

High-performance epoxy-carbon nanotube (CNT) nanocomposites were prepared by simultaneous use of ultrasonication and mechanical stirring. The dynamic and static mechanical properties and wetting properties of the nanocomposites were investigated. The dynamic mechanical analysis presented significant enhancement in storage modulus (approximately 124%) and glass transition temperature (approximately 25.6%) of epoxy-CNT nanocomposite at an optimized concentration of the CNT (0.25 wt%) possibly due to the formation of a strong interface between the epoxy and CNT. The tensile test results showed the significant improvement in tensile strength (approximately 47%) and Young’s modulus (approximately 40%) of the epoxy-CNT (0.25 wt%) nanocomposite without significantly affecting its stiffness. The homogeneous dispersion of CNTs in the epoxy matrix resulted in the significant enhancement in the dynamic and static mechanical properties of the nanocomposites. The hydrophilic character of the neat epoxy was tuned to a highly hydrophobic one by incorporation of CNTs in it. A direct relation between the average roughness of the tensile fracture surfaces and the contact angle of the nanocomposites was identified with respect to the concentration of the CNTs. These high-performance highly hydrophobic nanocomposites have the great potential to be used as the structural and functional materials in humid environments.

Handspinning Enabled Highly Concentrated Carbon Nanotubes with Controlled Orientation in Nanofibers

The novel method, handspinning (HS), was invented by mimicking commonly observed methods in our daily lives. The use of HS allows us to fabricate carbon nanotube-reinforced nanofibers (CNT-reinforced nanofibers) by addressing three significant challenges: (i) the difficulty of forming nanofibers at high concentrations of CNTs, (ii) aggregation of the CNTs, and (iii) control of the orientation of the CNTs. The handspun nanofibers showed better physical properties than fibers fabricated by conventional methods, such as electrospinning. Handspun nanofibers retain a larger amount of CNTs than electrospun nanofibers, and the CNTs are easily aligned uniaxially. We attributed these improvements provided by the HS process to simple mechanical stretching force, which allows for orienting the nanofillers along with the force direction without agglomeration, leading to increased contact area between the CNTs and the polymer matrix, thereby providing enhanced interactions. HS is a simple and straightforward method as it does not require an electric field, and, hence, any kinds of polymers and solvents can be applicable. Furthermore, it is feasible to retain a large amount of various nanofillers in the fibers to enhance their physical and chemical properties. Therefore, HS provides an effective pathway to create new types of reinforced nanofibers with outstanding properties.

Progress towards high-power Li/CFx batteries: electrode architectures using carbon nanotubes with CFx

This perspective describes the current status of lithium–carbon monofluoride batteries and highlights the opportunities for the development of high-power Li/CF_x batteries via utilization of carbon nanotubes.

Doped graphene: synthesis, properties and bioanalysis

We discuss early advances in the preparation of doped graphene and its unique properties as well as its applications in bioanalysis.

Controllable synthesis of doped graphene and its applications

Graphene is a wonder material with the ultimate smallest thickness that is readily accessible to various approaches for engineering its excellent properties. Graphene doping is an efficient way to tailor its electric properties and expand its applications. This topic covers wide research fields and has been developing rapidly. This article presents a broad and comprehensive overview of the developments in the preparation and applications of doped graphene including doping methods, doping levels, doping effect and types of heteroatoms. Very recent advances are also presented. In addition, existing problems in terms of achieving greater control over and further developments of doped graphene are also discussed.

Functionalization of vertically aligned carbon nanotubes

This review focuses and summarizes recent studies on the functionalization of carbon nanotubes oriented perpendicularly to their substrate, so-called vertically aligned carbon nanotubes (VA-CNTs). The intrinsic properties of individual nanotubes make the VA-CNTs ideal candidates for integration in a wide range of devices, and many potential applications have been envisaged. These applications can benefit from the unidirectional alignment of the nanotubes, the large surface area, the high carbon purity, the outstanding electrical conductivity, and the uniformly long length. However, practical uses of VA-CNTs are limited by their surface characteristics, which must be often modified in order to meet the specificity of each particular application. The proposed approaches are based on the chemical modifications of the surface by functionalization (grafting of functional chemical groups, decoration with metal particles or wrapping of polymers) to bring new properties or to improve the interactions between the VA-CNTs and their environment while maintaining the alignment of CNTs.

Vertically Aligned Carbon Nanotube Arrays Co-doped with Phosphorus and Nitrogen as Efficient Metal-Free Electrocatalysts for Oxygen Reduction

Using a mixture of ferrocene, pyridine, and triphenylphosphine as precursors for injection-assisted chemical vapor deposition (CVD), we prepared the first vertically aligned multiwalled carbon nanotube array co-doped with phosphorus (P) and nitrogen (N) with a relatively high P-doping level (designated as PN-ACNT). We have also demonstrated the potential applications of the resultant PN-ACNTs as high-performance electrocatalysts for the oxygen reduction reaction (ORR). PN-ACNT arrays were shown to exhibit a high ORR electrocatalytic activity, superb long-term durability, and good tolerance to methanol and carbon monoxide, significantly outperforming their counterparts doped with P (P-ACNT) or N (N-ACNT) only and even comparable to the commercially available Pt-C catalyst (45 wt % Pt on Vulcan XC-72R; E-TEK) due to a demonstrated synergetic effect arising from the co-doping of CNTs with both P and N.

Carbon nanomaterials for advanced energy conversion and storage

It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size-/surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy-conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.

Wall-selective chemical alteration of silicon nanotube molecular carriers

Recently, there has been significant interest in the synthesis and potential applications of semiconductor nanotubes (NTs). In this context, many efforts have been invested in developing new routes to control and engineer their surface chemistry. We report herein on a simple route to differentially and selectively functionalize the inner and outer surfaces of silicon nanotubes (SiNTs) with organic molecular layers containing different functional groups and hydrophobicity/hydrophilicity chemical nature, via covalent binding, to give nanotubular structures with dual chemical properties. Significantly, our unique synthetic approach can be further extended to directly form hollow crystalline nanotubular structures with their inner/outer surfaces independently and selectively altered chemically. Additionally, SiNTs inner and/or outer walls can be selectively decorated with metal nanoparticles. Both inner and outer walls can be individually and separately modified with the same metal nanoparticles, with different metal NPs in the inside and outside walls or with a combination of metal NPs decoration and molecular layers, if so required. Furthermore, the dually modified nanotubes were then exploited as phase extraction nanocarriers to demonstrate their potential in future chemical and biological separation, extraction, and filtering applications.

Super-long aligned TiO2/carbon nanotube arrays

5 mm long aligned titanium oxide/carbon nanotube (TiO(2)/CNT) coaxial nanowire arrays have been prepared by electrochemically coating the constituent CNTs with a uniform layer of highly crystalline anatase TiO(2) nanoparticles. While the presence of the TiO(2) coating was confirmed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and x-ray diffraction, the resultant TiO(2)/CNT coaxial arrays were demonstrated to exhibit minimized recombination of photoinduced electron-hole pairs and fast electron transfer from the long TiO(2)/CNT arrays to external circuits. This, in conjunction with the aligned macrostructure, facilitates the fabrication of TiO(2)/CNT arrays for various device applications, ranging from photodetectors to photocatalytic systems. Thus, the millimeter long TiO(2)/CNT arrays represent a significant advance in the development of new macroscopic photoelectronic nanomaterials attractive for a variety of device applications beyond those demonstrated in this study.

Fabrication of stable antibody-modified field effect transistors using electrical activation of Schiff base cross-linkages for tumor marker detection

In this paper, we present a method of fabricating a rigid antibody-immobilized surface using electric activation of a glutaraldehyde (GA)-modified aminopropylsilyl surface for stable antibody-modified field effect transistors (FETs). Electric activation of the GA-modified gate surface of the FET reduces Schiff bases, which are easily hydrolyzed and collapsed, formed between GA and 3-aminopropyltriethoxysilane, resulting in preventing the immobilized antibodies from desorbing from the surface. The lack of Raman peaks that could be assigned to a Schiff base after the electrical activation of the GA-modified surface indicated that the electric activation had reduced the Schiff base. The use of the antibody-modified FETs has three advantages for the detection of antigens: increased sensitivity, distinct recognition ability, and improved reproducibility. A tumor marker, alpha-fetoprotein (AFP), was quantitatively detected up to a concentration of 10 ng/mL using the antibody-modified FET. The detection ability of the FET accomplished a cutoff value of hepatic cancer. The quantitative detection of AFP in a solution with contaminating proteins was also demonstrated. This electric activation method is applicable to other antibody-modified FETs.

Plasma nanocoated carbon nanotubes for heat transfer nanofluids

Multi-wall carbon nanotubes (CNTs) were plasma-treated using glow discharges of argon, oxygen and methane/oxygen mixtures and then dispersed into a base fluid of water. It was found that proper plasma treatments of CNTs using nanoscale plasma coatings significantly improve the dispersion and stabilize the suspension of CNTs in the base fluid. With 0.01 vol% addition of plasma-treated CNTs, a 25% initial increase in thermal conductivity was achieved and a stabilized 20% increase was observed with the resulting nanofluids after 5 days' settling. It should particularly be pointed out that such a large increase in thermal conductivity was achieved when plasma-treated CNTs were stably dispersed in water without adding any dispersing agents or surfactants. Surface modification of the CNTs was confirmed by Raman spectroscopy and ultra-thin (approximately 2 nm) plasma nanocoatings were noted on the treated CNT surfaces by transmission electron microscopy (TEM).

Edge-Functionalization of Pyrene as a Miniature Graphene via Friedel-Crafts Acylation Reaction in Poly(Phosphoric Acid)

The feasibility of edge-functionalization of graphite was tested via the model reaction between pyrene and 4-(2,4,6-trimethylphenyloxy)benzamide (TMPBA) in poly(phosphoric acid) (PPA)/phosphorous pentoxide (P(2)O(5)) medium. The functionalization was confirmed by various characterization techniques. On the basis of the model study, the reaction condition could be extended to the edge-functionalization of graphite with TMPBA. Preliminary results showed that the resultant TMPBA-grafted graphite (graphite-g-TMPBA) was found to be readily dispersible in N-methyl-2-pyrrolidone (NMP) and can be used as a precursor for edge-functionalized graphene (EFG).

Nitrogen-doped graphene and its application in electrochemical biosensing

Chemical doping with foreign atoms is an effective method to intrinsically modify the properties of host materials. Among them, nitrogen doping plays a critical role in regulating the electronic properties of carbon materials. Recently, graphene, as a true two-dimensional carbon material, has shown fascinating applications in bioelectronics and biosensors. In this paper, we report a facile strategy to prepare N-doped graphene by using nitrogen plasma treatment of graphene synthesized via a chemical method. Meanwhile, a possible schematic diagram has been proposed to detail the structure of N-doped graphene. By controlling the exposure time, the N percentage in host graphene can be regulated, ranging from 0.11 to 1.35%. Moreover, the as-prepared N-doped graphene has displayed high electrocatalytic activity for reduction of hydrogen peroxide and fast direct electron transfer kinetics for glucose oxidase. The N-doped graphene has further been used for glucose biosensing with concentrations as low as 0.01 mM in the presence of interferences.

Nitrogen-doped graphene as efficient metal-free electrocatalyst for oxygen reduction in fuel cells

Nitrogen-doped graphene (N-graphene) was synthesized by chemical vapor deposition of methane in the presence of ammonia. The resultant N-graphene was demonstrated to act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction via a four-electron pathway in alkaline fuel cells. To the best of our knowledge, this is the first report on the use of graphene and its derivatives as metal-free catalysts for oxygen reduction. The important role of N-doping to oxygen reduction reaction (ORR) can be applied to various carbon materials for the development of other metal-free efficient ORR catalysts for fuel cell applications, even new catalytic materials for applications beyond fuel cells.