Sławomir Boncel

Enhancement of the mechanical properties of directly spun CNT fibers by chemical treatment.

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.

En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen-doped carbon nanotube arrays

Summary The 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.

Interactions of carbon nanotubes with aqueous/aquatic media containing organic/inorganic contaminants and selected organisms of aquatic ecosystems - A review

Due to their unique molecular architecture translating into numerous every-day applications, carbon nanotubes (CNTs) will be ultimately an increasingly significant environmental contaminant. This work reviews qualitative/quantitative analyses of interactions of various types of CNTs and their chemically modified analogues with aqueous/aquatic media containing organic and inorganic contaminants and selected organisms of aquatic ecosystems. A special emphasis was placed on physicochemical interactions between CNTs as adsorbents of heavy metal cations and aromatic compounds (dyes) with its environmental consequences. The studies revealed CNTs as more powerful adsorbents of aromatic compounds (an order of magnitude higher adsorption capacity) than metal cations. Depending on the presence of natural organic matter (NOM) and/or co-contaminants, CNTs may act as Trojan horse while passing through biological membranes (in the absence of NOM coordinating metal ions). Nanotubes, depending on flow conditions and their morphology/surface chemistry, may travel with natural waters or sediment with immobilized PAHs or metals and/or increase cyto- and ecotoxicity of PAHs/metal ions by their release via competitive complexation, or cause synergic ecotoxicity while adsorbing nutrients. Additionally, toxicity of CNTs against exemplary aquatic microorganisms was reviewed. It was found for Daphnia magna that longer exposures to CNTs led to higher ecotoxicity with a prolonged CNTs excretion. SWCNTs were more toxic than MWCNTs, while hydrophilization of CNTs via oxidation or anchoring thereto polar/positively charged polymer chains enhanced stability of nanotubes dispersion in aqueous media. On the other hand, bioavailability of functionalized CNTs was improved leading to more complex both mechanisms of uptake and cytotoxic effects.

Alkaline lipase from Pseudomonas fluorescens non-covalently immobilised on pristine versus oxidised multi-wall carbon nanotubes as efficient and recyclable catalytic systems in the synthesis of Solketal esters

In order to produce effective and recyclable catalysts for enantioselective transesterification in the industrial applications, alkaline lipase from Pseudomonas fluorescens was non-covalently immobilised (ca. 6 wt%) on pristine multi-wall carbon nanotubes (MWCNTs) and oxidised MWCNTs (O-MWCNTs) using an adsorption technique. Mesoporous silica modified with n-octyl groups was used as a reference support. Irreversible transesterifications of three vinyl esters (acyl donors) by racemic Solketal with a chromatographically (GC) traced kinetics were selected as model reactions. The undertaken comparative studies revealed that different morphology and chemical functionalisation of the supports led to various enzyme loadings, catalytic activities and enantioselectivities. MWCNT-lipase emerged as the exceptionally active (yield up to 98%, t=1h, 1320 Ug(-1), i.e. 9 times more active than native enzyme) whereas lipase immobilised on O-MWCNTs as the most enantioselective system, particularly for longer acyl chain esters (e.e. up to 72% after 30 min at yield of 20%, 340 Ug(-1)). Moreover, the activity of all nanotube-based catalysts after 10 cycles of transesterification remained practically unchanged. The differences in performance of MWCNTs and O-MWCNTs as solid supports were found to be based on geometry of pores, dominating hydrophobic interactions and absence/presence of the surface polar groups. Due to an excellent activity and reusability of the nanotube-lipase catalysts one can propose (O-)MWCNT as supports of a prospective industrial relevance.

Magnetic carbon nanostructures in medicine

Magnetic carbon nanostructures are hybrid materials containing magnetic and carbon (mainly sp2) nanoallotrope components conjugated in various configurations. Their potential applications in medicine including drug delivery systems, magnetic particle/fluid hyperthermia anti-cancer therapy and magnetic resonance imaging are reviewed.

Dynamics of capillary infiltration of liquids into a highly aligned multi-walled carbon nanotube film.

Summary The physical compatibility of a highly aligned carbon nanotube (HACNT) film with liquids was established using a fast and convenient experimental protocol. Two parameters were found to be decisive for the infiltration process. For a given density of nanotube packing, the thermodynamics of the infiltration process (wettability) were described by the contact angle between the nanotube wall and a liquid meniscus (θ). Once the wettability criterion (θ < 90°) was met, the HACNT film (of free volume equal to 91%) was penetrated gradually by the liquid in a rate that can be linearly correlated to dynamic viscosity of the liquid (η). The experimental results follow the classical theory of capillarity for a steady process (Lucas–Washburn law), where the nanoscale capillary force, here supported by gravity, is compensated by viscous drag. This most general theory of capillarity can be applied in a prediction of both wettability of HACNT films and the dynamics of capillary rise in the intertube space in various technological applications.

An electrically controlled drug delivery system based on conducting poly(3,4-ethylenedioxypyrrole) matrix.

As numerous therapeutic agents are not well tolerated when administrated systemically, localized and controlled delivery can help to decrease their toxicity by applying an optimized drug concentration at extended exposure time. Among different types of drug delivery systems, conjugated polymers are considered as promising materials due to their biocompatibility, electrical conductivity and ability to undergo controllable redox reactions. In this work poly(3,4-ethylenedioxypyrrole), PEDOP, matrix is described for the first time as a reservoir of a model drug, ibuprofen (IBU). Drug immobilization process is performed in situ, during the electrochemical polymerization of 10 mM EDOP in the presence of 5-50 mM IBU. The loading efficiency of polymer matrix is dependent on IBU concentration and reaches 25.0±1.3 μg/cm2. The analysis of PEDOP-IBU chemical structure based on Raman spectroscopy, energy dispersive spectroscopy and surface morphology data provided by scanning electron microscopy shows that IBU is accumulated in the structure of matrix and evidently influences its morphology. IBU is then released in a controlled way under the influence of applied potential (-0.7 V vs. Ag/AgCl). It is demonstrated that the judicious choice of the synthesis conditions leads to a tailored loading efficiency of PEDOP matrix and to a tunable drug release.

Durability and surface chemistry of horizontally aligned CNT films as electrodes upon electrolysis of acidic aqueous solution

We devised a simple and effective method of electrochemical functionalization of horizontally aligned CNT films in diluted HCl and H2SO4 solutions upon their electrolysis under a constant current mode. We were able to cause notable generation of carbon–oxygen and carbon–chlorine functional groups on the CNT film anodes as proven by EDX, XPS, and Raman spectroscopy. As a consequence, we observed significant changes of the morphology of the material under electron microscopy, what translated into improved compatibility of CNTs with hydrophilic media. In turn, application of CNT films as cathodes was found as a powerful tool for a thorough cleaning of the nanotubes. Finally, we demonstrated that by the selection of appropriate conditions, CNT films can act as easy-to-make and flexible electrodes with a high stability and performance superior to graphite for generation of non-oxidizing gases such as hydrogen from solution. CNT film electrodes are two orders of magnitude lighter and require much lower overpotential for faradaic splitting of water.

Novel Acyclic Amide-Conjugated Nucleosides and Their Analogues

An effective one-step synthesis of new amide-conjugated nucleosides and their analogues, in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) as the condensing agent, is presented. Substrate subunits carrying carboxylic group were obtained by acidic hydrolysis of Michael-type adducts of various 5-substituted uracil derivatives to methyl acrylate. Amine substrate was synthesized by reduction of 1-(2′-cyanoethyl)thymine with sodium borohydride in the presence of nickel (II) chloride as catalyst. Other applied amine substrates were 5′-amino-5′-deoxythymidine and 5-aminouracil.

Michael-type addition of azoles of broad-scale acidity to methyl acrylate

Summary An optimisation of Michael-type addition of azole derivatives of broad-scale acidity – ranging from 5.20 to 15.00 pK a units – namely 4-nitropyrazole, 3,5-dimethyl-4-nitropyrazole, 4(5)-nitroimidazole, 4,5-diphenylimidazole, 4,5-dicyanoimidazole, 2-methyl-4(5)-nitroimidazole, 5(4)-bromo-2-methyl-4(5)-nitroimidazole and 3-nitro-1,2,4-triazole to methyl acrylate as an acceptor was carried out. The optimisation process involved the use of an appropriate basic catalyst (DBU, DIPEA, NaOH, NaH, TEDA), a donor/base/acceptor ratio and the reaction temperature. The reactions were performed in DMF as solvent. Target Michael adducts were obtained in medium to excellent yields. Importantly, for imidazole and 1,2,4-triazole derivatives, no corresponding regioisomers were obtained.