One of the major interests in carbon aerogels is making electrical conductors with high surface areas. One example of why this is useful is for production of supercapacitors.
The effects of the molar ratios of melamine to resorcinol (M/R), pH, Co content and carbonization temperature on the microstructure of the aerogels were investigated.
Synthesis of Co-loaded carbon aerogels for oxygen …
Hybrid RF-iron oxide aerogel (left), crosslinked RF-iron oxide aerogel (second from left), iron aerogel (second from right) made by pyrolysis of RF-iron oxide aerogel, iron/iron carbide aerogel (right) made by pyrolysis of crosslinked RF-iron oxide aerogel (image courtesy of Prof. Nicholas Leventis).
PDF Downloads : Oriental Journal of Chemistry
In the early 2000’s, Dr. Ted Baumann at Lawrence Livermore National Laboratory developed a technique for growing nanoparticles of metals inside carbon aerogels through a very clever technique. In this technique, resorcinol is replaced with 2,4-dihydroxybenzoic acid (DHBA), which is basically resorcinol with a carboxylic acid group attached to it. The DHBA (a weak acid) is then neutralized with potassium carbonate (a strong base) in water to produce potassium 2,4-dihydroxybenzoate (a water-soluble salt). Formaldehyde is added and the solution is cured at 80°C in sealed molds for 1-3 days. The resulting cranberry-sauce-red gels are similar to RF gels used to prepare carbon aerogels, except for that they are laced with potassium ion exchange sites throughout their structure. Soaking these gels in a solution of a metal salt, such as iron(III) nitrate, results in exchange of potassium ions with incoming metal ions which then attach to the gel’s polymer backbone. Think of it like hanging ornaments on a Christmas tree, where the ornaments are metal ions and the Christmas tree is the gel’s framework. The metal-doped gels can then be supercritically dried to make metal-doped organic aerogels and, finally, pyrolyzed to produce carbon aerogels. However, unlike typical carbon aerogels, during pyrolysis the added metal ions attached to the aerogel’s backbone reduce to metal atoms and coagulate into nanosized particles. The resulting material can be thought of kind of like a blueberry muffin morphology in which metal-containing nanoparticles (blueberries) are dispersed throughout a nanoporous carbon matrix (muffin). The presence of these particles does a number of things, for example, improves the electrical conductivity of the aerogel (compared with an undoped carbon aerogel of the same density), and gives the aerogel some catalytic properties characteristic of the dopant metal.
Journal of Nanoscience and Nanotechnology
Since the chemistry for doping the gels is done in water, a number of metals can be used to prepare metal-doped carbon aerogels including iron, cobalt, nickel, and copper.