Ewa Borowiak-Palen

Synthesis, dispersion, and cytocompatibility of graphene oxide and reduced graphene oxide.

The synthesis, characterization, and toxicity of graphene oxide and reduced graphene oxide are reported. Prior to the cytocompatibility tests the stability of the suspensions in a wide range of concentrations (3.125-100 μg/mL) of three different dispersants is studied. Polyethylene glycol (PEG), polyethylene glycol-polypropylene glycol-polyethylene glycol (Pluronic P123), and sodium deoxycholate (DOC) are investigated as the dispersants. The toxicity depends on the type of dispersant and concentration of the nanomaterials in the suspensions. Detailed analysis suggests that graphene oxide functionalized with PEG in the concentration range between 3125 μg/mL and 25 μg/mL exhibits the best biocompatibility with mice fibroblast cells (line L929).

Efficient production of B-substituted single-wall carbon nanotubes

We present an efficient method to achieve high-purity boron doped single-walled carbon nanotubes (SWCNT) using an adapted substitution reaction. We observe that around 15 at.% of the carbon atoms are substituted by boron, with local concentrations of up to 20 at.% (higher than previous report). The as-prepared material was characterised by local scale method: transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) as well as by bulk sensitive methods like optical spectroscopy in the infrared energy range (IR), X-ray photoemission spectroscopy (XPS) and bulk sensitive high-resolution EELS.

Reduced diameter distribution of single-wall carbon nanotubes by selective oxidation

We report an easy way to narrow the diameter distribution of single-walled carbon nanotubes (SWNT) by oxidization treatments. Both a chemical treatment in 2 M HNO3 as well as oxidation in a reduced O2 atmosphere lead to a selective burning of the narrower SWNT in bulk samples and to a diameter distribution which is smaller by a factor of two. This is a first important step towards a selective production of SWNT with a defined diameter on a bulk scale.

Synthesis of carbon nanotubes with and without catalyst particles

The initial development of carbon nanotube synthesis revolved heavily around the use of 3d valence transition metals such as Fe, Ni, and Co. More recently, noble metals (e.g. Au) and poor metals (e.g. In, Pb) have been shown to also yield carbon nanotubes. In addition, various ceramics and semiconductors can serve as catalytic particles suitable for tube formation and in some cases hybrid metal/metal oxide systems are possible. All-carbon systems for carbon nanotube growth without any catalytic particles have also been demonstrated. These different growth systems are briefly examined in this article and serve to highlight the breadth of avenues available for carbon nanotube synthesis.

Bulk synthesis of carbon-filled silicon carbide nanotubes with a narrow diameter distribution

We report on a simple and low-cost route to produce SiC nanotubes without the need for the more usual oxide based reactions using a high temperature substitution reaction between multiwall carbon nanotubes as a frame and Si powder. Local scale studies using transmission and scanning electron microscopy are also presented. The SiC nanotubes are carbon filled and open ended. Both their mean diameter and diameter distribution are smaller than previously reported for SiC nanotubes. Bulk scale studies using Raman and infrared as a probe showed the sample to be comprised of multiple polytypes and that finite size effects are present.

The catalytic potential of high-κ dielectrics for graphene formation

The growth of single and multilayer graphene nanoflakes on MgO and ZrO2 at low temperatures is shown through transmission electron microscopy. The graphene nanoflakes are ubiquitously anchored at step edges on MgO (100) surfaces. Density functional theory investigations on MgO (100) indicate C2H2 decomposition and carbon adsorption at step-edges. Hence, both the experimental and theoretical data highlight the importance of step sites for graphene growth on MgO.

Low temperature growth of carbon nanotubes from methane catalytic decomposition over nickel supported on a zeolite

Multi-walled carbon nanotubes from 8 to 63 nm in diameter and from 60 to 413 nm in length, were synthesized over nickel supported on a zeolite by the chemical vapor deposition of methane in the relatively low temperature range 400-550 degrees C. The carbon deposited was analyzed by x-ray powder diffraction, Raman spectroscopy, and scanning and transmission electron microscopy. The effects of the reaction temperature on the carbon nanotube formation and relative purity were evaluated.

Magnetic Silica Nanotubes: Synthesis, Drug Release, and Feasibility for Magnetic Hyperthermia

A new kind of silica nanotube with incorporated γ-Fe(2)O(3) nanoparticles has been successfully prepared through sol-gel processes. Hematite particles supported on carbon nanotubes served as templates for the fabrication of the magnetic silica nanotubes. The obtained nanostructures consisting of magnetic Fe(2)O(3) nanoparticles protected by a silica shell were fully characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), N(2) sorption and desorption, and magnetization studies. The hollow inner space and the magnetic functionalization render the material promising for applications in biology and medicine. This is underlined by studies in alternating magnetic fields which show a significant heating effect, i.e., the feasibility for applications in hyperthermia therapies. In addition, the material exhibits enhanced drug-loading capacity which is demonstrated by loading with rhodamine B molecules as drugs and corresponding release experiments. The results show that magnetic silica nanotubes can be straightforwardly synthesized and have a great potential as a multifunctional drug carrier system.

Facilitating the CVD synthesis of seamless double-walled carbon nanotubes

In this contribution we present a simple laser assisted chemical vapour (LA-CVD) technique that rapidly determines if a given catalyst and feedstock combination are appropriate for the bulk synthesis of double-walled carbon nanotubes (DWCNT) in conventional thermal CVD (T-CVD). Systematic T-CVD studies across a range of temperatures with a Fe–Co catalyst mix for two carbon feedstocks (ethanol and methane) were conducted to validate the LA-CVD technique. The T-CVD findings confirm that the LA-CVD route is appropriate as a fast and easy means to determine the primary carbon nanotube product for a selected catalyst and feedstock in T-CVD. The LA-CVD route reduces the optimization parameters in T-CVD to only that of temperature. The studies led to the bulk production of seamless DWCNT with yields better than 55%.

Carbon‐Nanotube‐Based Stimuli‐Responsive Controlled‐Release System

A stimuli-responsive controlled-release delivery system based on carbon nanotubes is demonstrated. Through TEM, FTIR spectroscopic, and thermogravimetric analysis, functional groups have been successfully attached to the open ends of the tubes, thereby enabling functionalized silica spheres to preferentially attach to the ends. This, in essence, plugs the ends of the tube. Controlling release of encapsulated materials within the tubes is illustrated by fluorescein-filled carbon nanotubes. The discharge process can be triggered by exposure to 1,4-dithiothreitol (DTT) or at elevated temperature. Moreover, both triggering systems, DTT and temperature, provide rate of release control through increased DTT concentration or temperature choice, respectively. This delivery system paves the way for the development of a new generation of site-selective, controlled-release, drug-delivery systems, and interactive nanosensor devices.