Nanoscale Carbon Materials for Contaminant Separation - Nanotechnologies for Water Environment Applications - page 272

nanoporous carbon refers to every porous carbon with a pore size in the nanoscale range
(0.5 - 100 nm); nanoporous carbon includes both microporous carbon (< 2 nm) and
mesoporous carbon (2 - 50 nm). Since microporous carbon is known as an activated
carbon that can be used as a conventional adsorbent, in this chapter we only focus on
mesoporous carbon.

In basic terms, mesoporous carbon can be understood as a carbonaceous material
containing a predominant percentage of mesopores rather than micropores. We propose
a more specific classification of mesoporous carbon based on two categories: (1) ordered
mesoporous carbon, which is composed of uniform mesopores in an ordered structure;
and (2) mesoporous activated carbon, which contains a predominant amount of
mesopores and lesser amounts of micropores ordered in a random arrangement.

10.1.3.1 Ordered Mesoporous Carbon

The only route developed so far to produce ordered mesoporous carbon (OMC)
is referred to as nanocasting. This route was first developed in 1999 by Ryoo and his co-
workers (Ryoo et al., 1999). Here, ordered mesoporous silica containing an
interconnected pore system (3-D pore system) such as MCM-48 (Ryoo et al., 1999) or
SBA-15 (Jun et al., 2000) are used as hard templates. The pores of the silica matrix are
filled with a carbon-containing material such as sucrose or furfuryl alcohol, which is
then pyrolyzed. Removal of the silica mold is conducted with HF or NaOH, thereby
allowing a reverse of the original mold to be obtained. The nanocasting pathway is
illustrated in Figure 10.3.

Silica
removal

Introduction of
precursor

Mesoporous silica
(SBA-15, MCM-48)

Ordered mesoporous
carbon

Figure 10.3 Schematic illustration of the nanocasting pathway for preparing mesoporous
carbon (Song et al., 2006).

These OMC materials have Brunauer-Emmett-Teller (BET) surface areas up to
1800 m 2 /g and pore volumes up to 1.3 cm 3 /g; however, pore sizes are generally less than
10 nm. The OMCs have a structure that is the replica of the template structure, since the
OMC pores are formed by the dissolution of the silica framework. The size of pores is
controlled by the silica wall thickness. Thus, tuning the OMC pore sizes is much more