Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 341

Macedo et al. (2006) prepared mesoporous activated carbon from coconut coir
dust as a support for adsorption of some model dye molecules from aqueous solutions.
Methylene blue (MB) and remazol yellow (RY) were chosen to represent cationic and
anionic dyes. The adsorption kinetics was studied with the Lagergren first- and pseudo-
second-order kinetic models as well as the intra-particle diffusion model. The results for
both dyes suggested a multi-mechanism sorption process. The dye adsorption in the dye/
activated carbon (AC) systems followed pseudo-second-order kinetics with a significant
contribution of intra-particle diffusion. The AC samples with both acidic and basic sites
were able to act as anchoring sites for both basic and acidic dyes simultaneously.
Calorimetric studies revealed that dye/AC interaction forces were correlated with the pH
of the solution, which could be related to the charge distribution on the AC surface.
These AC samples also exhibited very short equilibrium times for the adsorption of both
dyes (Macedo et al., 2006).
Mohamed (2004) prepared cetyltrimethylammonium bromide (CTAB)-modified
mesoporous molecular sieve FSM-16 by a hydrothermal process (373 K, 3 days). It was
tested as an adsorbent for acid dye (acid yellow, AY, and acid blue, AB) removal and
compared with that of as-prepared FSM-16 and activated carbon (AC) derived from rice
husk (50 vol% H 3 PO 4 , 773 K, 2.5 h). The adsorption isotherms, sorption kinetics, and
pH effects upon acid dyes sorption on the adsorbents were thoroughly investigated. The
ultimate capacity of the adsorbents were found to be varied in the order FSM-16 >
modified FSM-16 > AC. The adsorption followed first-order rate kinetics. The
adsorption isotherm of acid dyes on FSM-16 is of type IV, according to the IUPAC
classification. It is drastically different from that of CTAB/FSM-16, which showed a
type I isotherm. The latter sample had better adsorption performance at a low
concentration of acid dyes than the former. As compared to microporous activated
carbon, the CTAB/FSM-16 sample achieved higher performance at low concentrations.
This was due to the successful narrowing of the pore opening of FSM-16 using CTAB
with maintenance of a considerable portion of the pore volume.
Lin and Teng (2002) have used waste tire char as the precursor to produce
activated carbons with steam activation. Carbons with different porosities have been
obtained by activating the char to different extents of burn-off. Unlike commercial grade
carbons that are generally microporous, the pores of the tire-char carbons are mainly
composed of mesopores that have a mean size of 50 nm. Both the surface area and pore
volume of the carbons increase with the extent of activation and pass through a
maximum at a burn-off of 43%, above which the porosity decreases with further
activation. Adsorption of methylene blue from aqueous solutions shows monolayer
coverage of the adsorbate on the carbon surface and a full access of the adsorbate to all
the pores, which renders a high discoloration capability per unit area of the carbons. The
adsorption capacity of the carbons for methylene blue increases with the adsorption
temperature. Langmuir analysis shows that this increase in capacity with temperature