Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 327

20 Å that do not contain "zeolitic" micropores are exhibited by the calcined solids
(Vaudry et al., 1996).
Rengaraj et al. (2004) prepared a novel type of mesoporous alumina adsorbent,
aminated and protonated alumina. It was employed for the removal of copper from
aqueous solution at concentrations between 5 and 30 mg / l, in batch equilibrium
experiments. The removal of copper by the adsorbents increases with increasing
adsorbent dosages. The adsorption mechanism is assumed to be an ion exchange
between copper and the hydrogen ions present on the surface of the mesoporous alumina.
Results showed that the intraparticle diffusion of Cu(II) on the mesoporous catalyst was
the main rate-limiting step (Rengaraj et al., 2004).
Xu et al. (1999) investigated removal of Pb 2+ ions from aqueous solution using
the adsorption process onto Ti-MCM-41. A simplified surface complexation model was
used to calculate the conditional binding constants for surface complexation of Pb 2+ ions
onto Ti-MCM-41. Dynamic modeling of the adsorption showed that the first-order
reversible kinetic model held for the adsorption process. The overall rate constant k , the
adsorption rate constant k 1 , the desorption rate constant k 2 , and the equilibrium constant
K e for the adsorption process were calculated from the results of the thermodynamic
analysis, and standard free energy G°, standard enthalpy H°, and standard entropy
S° of the adsorption process. Equilibrium modeling of the adsorption showed that the
adsorption of Pb 2+ ions can be fitted with a Freundlich isotherm (Xu et al., 1999).
Recently, Rengaraj et al. (2007) prepared Mg-mesoporous alumina (Mg-MA)
(Figure 11.4) via a templating method and used it to adsorb nickel from aqueous
solution. The result suggested that the Mg-MA can be employed as adsorbents for the
Ni(II) removal because the G value of Mg(II), which is present in mesoporous alumina,
has a more negative value than that of Ni ion. The removal of Ni(II) from 10 ppm
solution by these Mg-MA is > 99% (Rengaraj et al., 2007). In summary, all these studies
clearly signifies the great promise of using alumina-based NPM for groundwater
treatment. However detailed research is necessary on large-scale applications.
11.2.1.4 Titanium Dioxide
Titanium dioxide (TiO 2 ) is one of the most important semiconductors with large
potential in photocatalysis, solar cells, photochromism, sensoring, and other
applications. After the first report on a titanium dioxide (TiO 2 ) application for the
photocatalytic purification of water containing cyanide (Frank and Bard, 1977), this
material has been extensively used in environmental applications. The synthesis of
visible light-activated TiO 2 nanoparticles has attracted considerable interest (Asahi et al.,
2001; Bae and Choi, 2003; Adesina, 2004; Obare and Meyer, 2004). It is the most
popular and often used photocatalyst material in the photocatalytic oxidation process due