Making carbon attractive

The in-situ formation of iron nanoparticles in carbon produces highly adsorbent materials that are easily manipulated with magnets

Credit: © 2006 Manfred Schwickardi

‘Activated’ carbon is a highly porous biocompatible material that has an extremely large surface area. It is widely used as an adsorbent for purification or decontamination purposes, ranging from simple drinking-water filtration to the medical treatment of orally ingested poisons. In the laboratory, chemical catalysts are often supported on these inert materials because it makes their recovery much easier.

Magnetic activated carbon is attractive because it can be separated from a fluid with a magnetic field. Whereas previous approaches have relied upon pre-prepared cobalt nanoparticles, Ferdi Schüth and co-workers¹ from the Max-Planck-Institut für Kohlenforschung in Germany have used a method that forms iron nanoparticles directly in a carbon matrix. A solution of iron nitrate is first adsorbed by the activated carbon, which is then heated to 700 °C. The iron nanoparticles made during this process are then coated with a layer of carbon formed by chemical vapour deposition. Most of the nanoparticles are less than 10 nm in diameter and superparamagnetic. When sedimented in a solution, the material can simply be attracted with a permanent magnet and when the external field is removed, the material is easily redispersed in solution.

Schüth and co-workers demonstrate that the magnetic activated carbon is quite stable in either acidic or alkaline conditions and very little iron leaches out. Moreover, the synthesis is easily scaled which makes this material an attractive candidate for applications in supported catalysis and separation technology.