Postsynthesis microwave treatment to give high-purity multiwalled carbon nanotubes

Carbon-supported gas-cleaning catalysts enable syn gas methanation at atmospheric pressure

Though feasible for CO methanations in gas-cleaning applications ([CO] < 1%), carbon-nanotube-supported catalysts have never been implemented for the production of synthetic natural gas.

A simple gas-solid route to functionalize ordered carbon

The reaction of nitric oxide (NO) and carbonaceous materials generates nitrogen functionalities on and in graphitic carbons and oxidizes some of the carbon. Here, we have exploited these phenomena to provide a novel route to surface-functionalized multiwalled carbon nanotubes (MWCNTs). We investigated the impacts of NO on the physical and chemical properties of industrially synthesized multiwalled carbon nanotubes to find a facile treatment that increased the specific surface area (SBET) of the MWCNTs by ∼20%, with only a minimal effect on their degree of graphitization. The technique caused less material loss (∼12 wt %) than traditional gas-based activation techniques and grafted some nitrogen functional groups (1.1 at. %) on the MWCNTs. Moreover, we found that Ni nanoparticles deposited on NO-treated MWCNTs had a crystallite size of dNi = 13.1 nm, similar to those deposited on acid-treated MWCNTs (dNi = 14.2 nm), and clearly much smaller than those deposited under the same conditions on untreated MWCNTs (dNi = 18.3 nm).

Multiwalled carbon nanotubes in alfalfa and wheat: toxicology and uptake

Data on the bioavailability and toxicity of carbon nanotubes (CNTs) in the environment, and, in particular, on their interactions with vascular plants, are limited. We investigated the effects of industrial-grade multiwalled CNTs (75 wt% CNTs) and their impurities on alfalfa and wheat. Phytotoxicity assays were performed during both seed germination and seedling growth. The germinations of both species were tolerant of up to 2560 mg l(-1) CNTs, and root elongation was enhanced in alfalfa and wheat seedlings exposed to CNTs. Remarkably, catalyst impurities also enhanced root elongation in alfalfa seedlings as well as wheat germination. Thus the impurities, not solely the CNTs, impacted the plants. CNT internalization by plants was investigated using electron microscopy and two-dimensional Raman mapping. The latter showed that CNTs were adsorbed onto the root surfaces of alfalfa and wheat without significant uptake or translocation. Electron microscopy investigations of internalization were inconclusive owing to poor contrast, so Fe(3)O(4)-functionalized CNTs were prepared and studied using energy-filter mapping of Fe(3)O(4). CNTs bearing Fe(3)O(4) nanoparticles were detected in the epidermis of one wheat root tip only, suggesting that internalization was possible but unusual. Thus, alfalfa and wheat tolerated high concentrations of industrial-grade multiwalled CNTs, which adsorbed onto their roots but were rarely taken up.