Translating the remarkable mechanical properties of individual carbon nanotubes to macroscopic assemblies presents a unique challenge in maximizing the potential of these remarkable entities for new materials. Infinitely long individual nanotubes would represent the ideal molecular building blocks; however, in the case of length-limited nanotubes, typically in the range of micro- and millimeters, an alternative strategy could be based on the improvement of the mechanical coherency between bundles assembling the macroscopic materials, like fibers or films. Here, we present a method to enhance the mechanical performance of fibers continuously spun from a CVD reactor, by a postproduction processing methodology utilizing a chemical agent aided by UV irradiation. The treatment results in an increase of 100% in specific strength and 300% in toughness of the fibers with strength values rocketing to as high as 3.5 GPa SG(-1). An attempt has been made to explore the nature of the chemical modifications introduced in the fiber and the consequential effects on its properties.

A facile strategy for the synthesis of nitrogendoped, porous carbon materials was developed, with the first use of carbohydrate ionic liquids and salts as versatile precursors. Transformation of carbohydrate (biomass) into ionic species serves as a strategy to obtain precursors combining properties of carbohydrates, like high carbon content with ionic liquid properties such as high thermal stability, negligible vapor pressure, and the possibility to incorporate nitrogen-rich moieties as cations or anions. With precise design of the precursors at the molecular level, carbon materials with high specific surface areas (up to 946 m 2 /g) and/or high N contents (up to 9.6 wt %) can be readily obtained. The resulting metal-free nitrogen-doped carbons exhibit a noticeable electrocatalytic activity toward the oxygen reduction reaction. The structure−property relationship between the organic precursors and derived carbon materials in terms of yield, N content, and morphology was investigated.

No abstract

SummaryThe catalytic chemical vapour deposition (c-CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs). A mixture of toluene (main carbon source), pyrazine (1,4-diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C), composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs). As revealed by electron microscopy studies (SEM, TEM), the individual N-CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 108 nanotubes per mm2 (100 times more than for MWCNTs grown in the absence of nitrogen precursor). In turn, the internal crystallographic order of the N-CNTs was found to be of a ‘bamboo’-like or ‘membrane’-like (multi-compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp2-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a ‘mixed base-and-tip’ (primarily of the base-type) type as compared to the purely ‘base’-type for undoped MWCNTs.

Stealth technology combines numerous means and techniques to be 'invisible' for opponents in a battle field. Since metals are the key construction materials of military vehicles, weapon and equipment, they can be targeted and detected by RAdio Detection And Ranging (RADAR) systems. Radar-Absorbent Materials (RAMs)as crucial components of passive countermeasures in the modern-day military tacticsare used for absorption of electromagnetic waves. In the same time, mainly due to high electric conductivity, RAMsaccompanied by designed geometry of the objects they are incorporated intocan yield programmable reflection, multiple internal reflection and scattering towards Electromagnetic *Manuscript Click here to view linked References Interference (EMI) shielding. Nowadays, the latest achievements of nanotechnology have transformed stealth technology into an even more powerful tool. And among many nanomaterials, carbon nanotubes (CNTs) have arisen as one of the most promising active component of RAMs and EMI shielding materials. The unique sp 2 -derived macromolecular architecture equips CNTs with an exceptional combination of electromagnetic, mechanical and chemical properties. This review intends to summarize and critically evaluate the hitherto efforts in the production and applications of CNT nanocomposites/hybrid materials as key constructional civil and military elements, preferably as coatings, layers, films, textiles or panels, towards attenuation of the radio wave radiation.

No abstract

A new method for the chemo-enzymatic Baeyer–Villiger oxidation of cyclic ketones to lactones in the presence of a new heterogeneous nanobiocatalyst consisting of Candida antarctica lipase B immobilized on multiwalled carbon nanotubes (MWCNTs) has been developed. To ensure safety and meet the contemporary environmental criteria nanobiocatalyst was used for the in situ generation of peracid, thereby avoiding the direct handling of dangerous peroxy substance. The reaction was carried out under mild conditions at 20–40 °C using 30% aq H2O2 as the primary oxidant, with octanoic acid as the precursor of peracid. The influence of the reaction parameters and various carbon materials as supports were studied. The activities of the new biocatalysts were compared with the benchmark Novozyme-435. Recycling studies demonstrated the possibility of utilizing the most active MWCNTs-lipase biocatalyst five times without any significant loss of activity. The main advantage of this study is the superior activity of the new nanobiocatalyst, what caused a significant reduction of reaction times compared to those previously reported in the literature.

No abstract