Carbon nanotubes from organometallic precursors

Accurate equilibrium structure of 3-aminophthalimide from gas electron diffraction and coupled-cluster computations and diverse structural effects due to electron density transfer

For the first time, the molecular structure of 3-aminophthalimide has been determined by the gas electron diffraction (GED) method supported by a mass-spectrometric analysis of the gas phase and results of quantum-chemical computations up to coupled-cluster level of theory, CCSD(T). The semiexperimental equilibrium structure, rsee, has been derived from the GED data by taking into account harmonic and anharmonic vibrational corrections estimated from the quantum-chemical force field (up to cubic terms). High accuracy structures have been exploited for the observation of fine structural effects arising due the presence of the electron-donating amino group and the formation of a hydrogen bond. Natural bond orbital (NBO) analysis and quantum theory of atoms in molecules (QTAIM) have been applied to explain these effects.

The CuAAC: Principles, Homogeneous and Heterogeneous Catalysts, and Novel Developments and Applications

The copper-catalyzed azide/alkyne cycloaddition reaction (CuAAC) has emerged as the most useful "click" chemistry. Polymer science has profited enormously from CuAAC by its simplicity, ease, scope, applicability and efficiency. Basic principles of the CuAAC are reviewed with a focus on homogeneous and heterogeneous catalysts, ligands, anchimeric assistance, and basic chemical principles. Recent developments of ligand design and acceleration are discussed.

Dramatically enhancing the yield of carbon nanotubes by simply adding oxygen-containing molecules in solid-state synthesis

Commercially available oxygen-containing molecules are utilized to enhance the yield of carbon nanotubes in the solid-state pyrolysis of organometallic precursors.

Carbon nanotubes part I: preparation of a novel and versatile drug-delivery vehicle

INTRODUCTION

It is 23 years since carbon allotrope known as carbon nanotubes (CNT) was discovered by Iijima, who described them as "rolled graphite sheets inserted into each other". Since then, CNTs have been studied in nanoelectronic devices. However, CNTs also possess the versatility to act as drug- and gene-delivery vehicles.

AREAS COVERED

This review covers the synthesis, purification and functionalization of CNTs. Arc discharge, laser ablation and chemical vapor deposition are the principle synthesis methods. Non-covalent functionalization relies on attachment of biomolecules by coating the CNT with surfactants, synthetic polymers and biopolymers. Covalent functionalization often involves the initial introduction of carboxylic acids or amine groups, diazonium addition, 1,3-dipolar cycloaddition or reductive alkylation. The aim is to produce functional groups to attach the active cargo.

EXPERT OPINION

In this review, the feasibility of CNT being used as a drug-delivery vehicle is explored. The molecular composition of CNT is extremely hydrophobic and highly aggregation-prone. Therefore, most of the efforts towards drug delivery has centered on chemical functionalization, which is usually divided in two categories; non-covalent and covalent. The biomedical applications of CNT are growing apace, and new drug-delivery technologies play a major role in these efforts.

Application of a new phosphorus-free palladium heterogeneous nanocatalyst supported on modified MWCNT the highly selective and efficient cleavage of propargyl, allyl, and benzyl phenol ethers under mild conditions

A stable and efficient phosphorus-free, low Pd-loading heterogeneous nanocatalyst comprising palladium and a multi-walled carbon nanotube was prepared and characterized by various techniques such as SEM, TEM, AFM, FT-IR, and Raman spectrometry, N2 adsorption isotherm and thermogravimetric analysis. This catalyst was used for the deprotection of phenol ethers. The catalyst selectivity for deprotection of between propargyl, allyl, and benzyl, as a protecting group, was studied. Also, the presence of different functional groups was studied to establish the scope and limitations of this method. The catalytic activity of recycled catalyst was evaluated. The results indicated that the catalyst is heterogeneous, stable, and very active under the established conditions, and it could be reused up to five times without any significant leaching. In addition, according to ICP analysis, low leaves of leaching of palladium from the catalyst was observed, which indicates that anthraquinone has an excellent ability to coordinate with palladium.

Laser-induced pinpoint hydrogen evolution from benzene and water using metal free single-walled carbon nanotubes with high quantum yields

Metal-free photocatalytic hydrogen evolution occurred efficiently in benzene containing single-walled carbon nanotubes under laser irradiation at 532 nm with an extremely high turnover number of 2 000 000 and a high quantum yield of 130%. The rate of hydrogen evolution increased with increasing laser intensity to exhibit a fourth power dependence, suggesting that hydrogen was evolved via four-photon processes in which the coupling of two radical anions derived from benzene is the rate-determining step and the benzene radical anion is produced by electron transfer from benzene to the doubly excited state of single-walled carbon nanotubes, which requires two photons. Polymerisation of benzene was induced by the photogenerated C6H6˙-, accompanied by hydrogen evolution, resulting in a leverage effect to increase the quantum yield of hydrogen evolution to well over the 25% expected for the four-photon process. Laser-induced hydrogen evolution also occurred in water containing single-walled carbon nanotubes. In contrast to the case of benzene, water was not oxidized but hydrogen evolution from water was accompanied by the multi-oxidation of single-walled carbon nanotubes. The yield of hydrogen based on one mole of single-walled carbon nanotubes with 1.4 nm diameter and 1-5 mm length was determined to be 2 700 000%, when oxidations of single-walled carbon nanotubes occurred to produce the polyhydroxylated product.

Single-step synthesis of carbon nanotubes/iron/iron oxide composite films through inert-ambient CVD using ferric acetylacetonate as a precursor

Fe–Fe₃O₄–CNT composite thin film was obtained by single step chemical vapor deposition process using Fe(acac)₃ as the sole precursor. By changing the deposition pressure, the form of carbon deposited could be changed from amorphous to CNTs.

The partially controllable growth trend of carbon nanoparticles in solid-state pyrolysis of organometallic precursor by introducing POSS units, and their magnetic properties

Organometallic compounds T (without POSS unit) and PT (containing three POSS units) are synthesized for solid-state pyrolysis. When increasing the pyrolysis temperature, the precursors with and without POSS unit show opposite growth trend.

Carbon nanotubes: an emerging drug carrier for targeting cancer cells

During recent years carbon nanotubes (CNTs) have been attracted by many researchers as a drug delivery carrier. CNTs are the third allotropic form of carbon-fullerenes which were rolled into cylindrical tubes. To be integrated into the biological systems, CNTs can be chemically modified or functionalised with therapeutically active molecules by forming stable covalent bonds or supramolecular assemblies based on noncovalent interactions. Owing to their high carrying capacity, biocompatibility, and specificity to cells, various cancer cells have been explored with CNTs for evaluation of pharmacokinetic parameters, cell viability, cytotoxicty, and drug delivery in tumor cells. This review attempts to highlight all aspects of CNTs which render them as an effective anticancer drug carrier and imaging agent. Also the potential application of CNT in targeting metastatic cancer cells by entrapping biomolecules and anticancer drugs has been covered in this review.

Improvement of crystallization of borazine-derived boron nitride using small amounts of Fe or Ni nanoparticles

Homogenously dispersed Fe and Ni nanoparticles (NPs) are introduced into boron nitride (BN) by pyrolysis of cured borazine containing soluble ferrocene or nickelocene. The crystallization of the borazine-derived BN is significantly improved by using no more than 1 wt% NPs. X-ray diffraction (XRD) suggests that the improved BN obtained at 1200 °C exhibits a higher degree of crystallization close to that obtained at 1600 °C without additives. Transmission electron microscopy (TEM) indicates the formation of Fe or Ni NP-core multilayer BN spheres embedded in amorphous BN, and a corresponding core-shell model is suggested. The Ni NPs exhibit a higher crystallization than Fe NPs, possibly due to the higher solubility of boron in Ni NPs at elevated temperatures. In addition, we discuss the mechanisms by which Fe and Ni NPs improve the crystallization of BN from borazine.

Xenobiotic particle exposure and microvascular endpoints: a call to arms

Xenobiotic particles can be considered in two genres: air pollution particulate matter and engineered nanoparticles. Particle exposures can occur in the greater environment, the workplace, and our homes. The majority of research in this field has, justifiably, focused on pulmonary reactions and outcomes. More recent investigations indicate that cardiovascular effects are capable of correlating with established mortality and morbidity epidemiological data following particle exposures. While the preliminary and general cardiovascular toxicology has been defined, the mechanisms behind these effects, specifically within the microcirculation, are largely unexplored. Therefore, the purpose of this review is several fold: first, a historical background on toxicological aspects of particle research is presented. Second, essential definitions, terminology, and techniques that may be unfamiliar to the microvascular scientist will be discussed. Third, the most current concepts and hypotheses driving cardiovascular research in this field will be reviewed. Lastly, potential future directions for the microvascular scientist will be suggested. Collectively speaking, microvascular research in the particle exposure field represents far more than a "niche." The immediate demand for basic, translational, and clinical studies is high and diverse. Microvascular scientists at all career stages are strongly encouraged to expand their research interests to include investigations associated with particle exposures.

Zwitterionic half-sandwich Rh and Ir complexes containing a diphosphine nido-carborane ligand: synthesis, structure transformation and application in H2 activation

Several novel zwitterionic half-sandwich complexes and pseudocloso metallacarboranes based on 1,2-(PPh(2))(2)-1,2-C(2)B(10)H(10) were successfully prepared, and further study proved that some of them can activate H(2) to form the metal hydride complexes Cp*M(H)(7,8-(PPh(2))(2)-7,8-C(2)B(9)H(10)) (M = Rh, Ir).

CHEMICAL ROUTES TO NANOCRYSTALS, NANOWIRES AND NANOTUBES

Soft chemical routes are employed effectively for the synthesis of nanocrystals of semiconductor materials. Several methods have been developed for the synthesis of multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) and specially noteworthy are the precursor route and nebulized spray pyrolysis for the synthesis of MWNTs and junction nanotubes. Nanotubes of inorganic layered materials are obtained by ingenious chemical methods. Nanowires of inorganic materials can be synthesized not only by high-temperature methods such as the carbon-assisted route but also by soft chemical routes.

Nitrogen Doped Carbon Nanotubes from Organometallic Compounds: A Review

Nitrogen doped carbon nanotubes (N-CNTs) have become a topic of increased importance in the study of carbonaceous materials. This arises from the physical and chemical properties that are created when N is embedded in a CNT. These properties include modified chemical reactivity and modified conductivity and mechanical properties. A range of methodologies have been devised to synthesize N-CNTs. One of the procedures uses a floating catalyst in which an organometallic complex is decomposed in the gas phase in the presence of a nitrogen containing reactant to give N-CNTs. Most studies have been limited to ferrocene, ring substituted ferrocene and Fe(CO)₅. This review covers the synthesis (and properties) of N-CNTs and other shaped carbon nanomaterials (SCNMs) produced using organometallic complexes. It summarizes the effects that physical parameters such as temperature, pressure, gas flow rates, type and concentration of N source etc. have on the N-CNT type, size and yields as well as the nitrogen content incorporated into the tubes that are produced from organometallic complexes. Proposed growth models for N-CNT synthesis are also reported.

Ferromagnetic Nanomaterials Obtained by Thermal Decomposition of Ferrocene

Ferromagnetic micro and nano particles that are chemically resistant have been obtained by thermal decomposition of ferrocenes in a tightly closed chamber at high pressures. The investigation is focused on the influence of decomposition temperature, work atmosphere, temperature-change rate and process duration. According to the conditions, Fe3C, Fe3O4 and pure α-Fe particles have been created. Their composition and structure have been studied by Mössbauer spectroscopy, Scanning and Transmission Electron Microscopy, Electron Probe X-ray Micro Analysis and Energy Dispersive X-ray Spectrometry. In a tightly closed chamber, all components obtained during the decomposition process remain there. This difference to the widely-used Chemical Vapor Deposition method is very important. It inhibits the decomposition process and growth of ordered structures, preventing the end materials to be separated from each other. During the process, iron is liberated from the ferrocene molecule. Experiments have shown that it is highly chemically active to carbon and oxygen. For example, creation of carbide occured in conditions that are not allowed according to the iron-carbon phase diagram valid for bulk iron. Parallel to the reaction of iron with carbon (according to work atmosphere), the surplus of carbon atoms causes emerging of carbon nanoparticles.

A homochiral nanotubular crystalline framework of metallomacrocycles for enantioselective recognition and separation

A highly ordered homochiral nanotubular crystalline framework was assembled from a hexameric Zn6L6metallaycle that was built from metallosalen ZnL units (H2L = (R,R)-(-)-N,N'-Bis(3-tert-butyl-5-(4- pyridyl) salicylidene)-1,2-diaminocyclohexane) by the complementary coordination of the pyridyl groups to the metal centers. Chiral channels and hydrophobic functionality presented by this structure make it an excellent host to recognize and separate racemic alcohols with high enantioselectivity (up to 99.5%). The crystalline solid can be easily recycled and reused five times without loss of crystallinity and enantioselectivity.

One-step solid-state thermolysis of a metal-organic framework: a simple and facile route to large-scale of multiwalled carbon nanotubes

We report a simple and facile solid-state approach to large-scale synthesis of multiwalled carbon nanotubes (MCNTs), for the first time, by one-step direct thermolysis of a metal-organic framework [Ni(3)(btc)(2).12H(2)O] (btc = benzene-1,3,5-tricarboxylato) in a one-end closed conventional horizontal tube furnace under relatively low temperature without using any additional carrier gas or catalyst.

Solid-phase synthesis of graphitic carbon nanostructures from iron and cobalt gluconates and their utilization as electrocatalyst supports

We present a novel and facile synthesis methodology for obtaining graphitic carbon structures from Fe(II) and Co(II) gluconates. The formation of graphitic carbon can be carried out in only one step by means of heat treatment of these organic salts at a temperature of 900 degrees C or 1000 degrees C under inert atmosphere. This process consists of the following steps: (a) pyrolysis of the organic gluconate and its transformation to amorphous carbon, (b) conversion of Fe(2+) and Co(2+) ions to Fe(2)O(3) and CoO and their subsequent reduction to metallic nanoparticles by the carbon and (c) conversion of a fraction of formed amorphous carbon to graphitic structures by Fe and Co nanoparticles that act as catalysts in the graphitization process. The removal of the amorphous carbon and metallic nanoparticles by means of oxidative treatment (KMnO(4) in an acid solution) allows graphitic carbon nanostructures (GCNs) to be selectively recovered. The GCNs thus obtained (i.e. nanocapsules and nanopipes) have a high crystallinity as evidenced by TEM/SAED, XRD and Raman analysis. In addition, we used these GCNs as supports for platinum nanoparticles, which were well dispersed (mean Pt size approximately 2.5-3.2 nm). Most electrocatalysts prepared in this way have a high electrocatalytical surface area, up to 90 m(2) g(-1) Pt, and exhibit high catalytic activities toward methanol electrooxidation.