TY - JOUR A1 - Meyer-Plath, Asmus A1 - Orts Gil, Guillermo A1 - Petrov, Sergej A1 - Oleszak, Franz A1 - Maneck, Heinz-Eberhard A1 - Dörfel, Ilona A1 - Haase, Oskar A1 - Richter, Silke A1 - Mach, Reinhard T1 - Plasma-thermal purification and annealing of carbon nanotubes N2 - We have developed a very fast and entirely gas-phase based purification technique for carbon nanotubes (CNT) that allows removing metal and metal oxide impurities with high effectiveness. CNT agglomerates from chemical vapor deposition (CVD) synthesis which contained carbon encapsulated catalysts were injected into an atmospheric plasma torch. Very high heating rates allow for quasi-instantaneous vaporization of catalyst particles. This way, metal vapors are hyposized to break mechanically instable encapsulations and effuse from incomplete ones faster than thermally induced graphitization stabilizes such particle encapsulations. The ash content of multi-walled (MW) CNT samples was reduced to less than 15% of the initial value within a few milliseconds. Also the metal content of single-walled (SW) CNT agglomerates was significantly reduced. Repeated injection of CNT agglomerates into the plasma torch resulted in higher-purity products of improved structural integrity and increased oxidation resistance. PY - 2012 U6 - https://doi.org/10.1016/j.carbon.2012.04.049 SN - 0008-6223 SN - 1873-3891 VL - 50 IS - 10 SP - 3934 EP - 3942 PB - Pergamon Press CY - New York, NY AN - OPUS4-25986 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hanelt, Sven A1 - Friedrich, Jörg Florian A1 - Orts Gil, Guillermo A1 - Meyer-Plath, Asmus T1 - Study of Lewis acid catalyzed chemical bromination and bromoalkylation of multi-walled carbon nanotubes N2 - Chemical functionalization of carbon nanotubes (CNT) with nucleophiles requires introduction of electrophilic reactive sites on the CNTs. This can, for instance, be accomplished by the chemical bromination procedure with elemental bromine and a set of Lewis acids (BBr3, BF3 × Et2O, AlBr3, FeBr3, ZnBr2, TiBr4, SiBr4, SnBr4, VBr3) or a radical starter like dibenzoylperoxide (DBPO) in appropriate solvents at varied temperature. The present approach to electrophilic sites relies on the well-known electrophilic aromatic substitution or addition of bromine with aromatic structural units. In addition to the use of bromine, the introduction of haloalkyl groups was also investigated here using bis-electrophiles or haloalcohols and Brønsted acids. The advantages and drawbacks of the studied reaction conditions, the obtained degree of bromination as analyzed by X-ray photoelectron spectroscopy (XPS) and the amount of introduced bromine that can be substituted by a nucleophile are presented and discussed. KW - Carbon nanotubes KW - Bromierung KW - Lewis Säure KW - Bromalkylierung KW - CNT PY - 2012 U6 - https://doi.org/10.1016/j.carbon.2011.11.009 SN - 0008-6223 SN - 1873-3891 VL - 50 IS - 3 SP - 1373 EP - 1385 PB - Pergamon Press CY - New York, NY AN - OPUS4-25207 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hanelt, Sven A1 - Orts Gil, Guillermo A1 - Friedrich, Jörg Florian A1 - Meyer-Plath, Asmus T1 - Differentiation and quantification of surface acidities on MWCNTs by indirect potentiometric titration N2 - Wet-chemically oxidized carbon nanotubes (CNTs) generally exhibit both covalently-bound acidic functional groups on the surface and surface-adsorbed acidic substances, i.e. carbonaceous CNT fragments from the oxidation procedure. Direct potentiometric titration of oxidizable high surface area materials with dynamically desorbing acidic fragments is slow and inaccurate. Adsorbed acidic fragments are deprotonated by sodium hydroxide and form anions in solution which is not the case for covalently bound acidic groups on the CNTs, so the following filtration after NaOH treatment separates desorbable acidic substances from non-desorbable or covalently bound groups. For a known concentration of NaOH, titration of the eluate with hydrochloric acid (HCl) allows determination of the concentrations of both types of acidities. However, contrary to reports in the literature, the NaOH consumed by non-desorbed acidic groups has to be accounted for and impedes distinction of desorbed acidic groups via their pKa values. Results are presented of a study on the information content and the reliability of indirect potentiometric Boehm titration for different oxidized multi-walled CNTs. PY - 2011 U6 - https://doi.org/10.1016/j.carbon.2011.03.016 SN - 0008-6223 SN - 1873-3891 VL - 49 IS - 9 SP - 2978 EP - 2988 PB - Pergamon Press CY - New York, NY AN - OPUS4-23625 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -