Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 339

Table 11.6 for other porous carbon's properties). Aqueous treatment reduced the surface
area of this material to 364 m 2 /g (Laszlo et al., 2003). It was reported that the granular
nanoporous carbon prepared from PAN contains O and N related surface functional
groups. The surface concentration of both oxygen and nitrogen atoms was found to be
5.3% by XPS. Surface groups containing these hetero atoms are responsible for the acid-
base character of this carbon in aqueous solutions. This material was used to remove
weak aromatic acids from aqueous solutions. The acid-base behavior influences the
adsorption performance of the granular carbon in aqueous solutions of weak aromatic
acids, such as phenol and 2,3,4-trichlorophenol. Both the adsorption capacity and the
overall interaction parameter, K (both derived from a fit to the Langmuir equation)
depend on the adsorbed species and on the pH. The former is a consequence of the
different water solubilities of the solute molecules, while the latter stems from the pH
sensitivity of both the surface functional groups and these weak acids. The pH PZC of the
carbon is 8.4.
Han et al. (2003) reported a new type of nanoporous carbon materials (SMC1),
which were produced using silica sol particles as templates. It shows higher and faster
adsorption of humic acids than two commercial activated carbons (F400 and Norit SA).
In some cases, it showed the adsorption capacity 16 times of conventional activated
carbons. The adsorption of humic acids on SMC1 proceeded very quickly, reaching the
equilibrium concentration within 15 min (Han et al., 2003). Mariwala et al. (1998)
studied the adsorption isotherms of 16 halocarbons obtained in the mid to high range of
pressures and at room temperature on a zeolite-like nanoporous carbon molecular sieve
Carbosieve G (CSG). All the isotherms display Type I structure in the range
investigated. The extent of adsorption was found to be varied with molecule size. The
capacity of CSG for these C 1 molecules ranges between 4.7 and 7.5 mmol/g. For the
larger two-carbon species, C 2 , the adsorption is lower, in the range from 3.1 to 4.7
mmol/g. (Mariwala et al., 1998). Su et al. (2005) studied the adsorption behaviors of
phenol in aqueous solution on zeolite-templated porous carbons. Materials prepared
based on two carbon precursors (sucrose and furfuryl alcohol) in the presence of a
zeolite Y template led to different pore structures and surface properties (Table 11.6). It
was observed that phenol adsorption in dilute solution on template-synthesized porous
carbons depends on both surface oxygen groups and pore structures. Thermal treatment
of porous carbons under nitrogen can markedly facilitate phenol adsorption because of
the substantial removal of the oxygen groups (Figure 11.11 and Table 11.6). For porous
carbons with a similar surface chemistry, the maximum phenol adsorption capacity
increases with an increase in the surface area and micropore volume of the porous
carbons. The enhancement of phenol adsorption capacity after thermal treatment under
nitrogen can be explained by (a) fewer water clusters formed on the carbon surface due
to the removal of oxygen groups on carbon surface, (b) the stronger dispersive
interactions between the benzene ring of phenol and the carbon basal planes because of
the reduction of carboxylic groups and an increase of polyaromatic characters on carbon