Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 321

The removal of Cu(II) by a mesoporous silicate, FSM-16 (surface area: 1003
m 2 /g), was studied in batch reactors. It was found that ~ 99 % of Cu(II) was removed by
0.2 g/L FSM-16 at pH 6.59 (Jung et al., 2001). They also confirmed the experimental
data using surface complexation modeling. Likewise, a novel nanocomposite sorbent
material, copper ferrocyanide immobilized within a mesoporous ceramic matrix (surface
area : 900 m 2 /g), was synthesized using a simple and direct technique and used as a
sorbent for cesium (Cs) adsorption (Fryxell et al., 2005). Loading capacity of > 1.35
mmol Cs per g of the sorbent material was achieved. The exceptionally fast binding
kinetics and high loading capacity, resulting from the rigidly open pore structure and the
extremely high surface area of the sorbent materials, make them potentially very useful
for Cs removal from nuclear wastes and contaminated groundwater. In addition,
mesoporous silica, containing surface aminopropyl-, aminoethyl-, and
propionamidephosphonate groups (SAMMS) were shown to perform well for actinide
adsorption (Fryxell et al., 2005).
A new approach to making heavy metal ion adsorbents, based on the covalent
grafting of 3-mercaptopropylsilyl groups to the framework pore walls of mesoporous
silica molecular sieves, has been investigated with respect to hydroxyl group densities,
channel dimensions, and morphologies (Mercier and Pinnavaia, 1998). Two types of
silicas were examined, namely, MCM-41 with an initially anionic silicate framework
and HMS with an electrically neutral framework. Consequently, the functionalized HMS
derivative was able to bind quantitatively more Hg (II) ions from aqueous solution as
compared to MCM-41. The HMS' adsorption capacities for Hg(II) were interpreted in
terms of the size and accessibility of the framework pore structure. Kalyanaraman et al.
(2001) described the synthesis procedure for making functionalized mesoporous silica
macrostructures that can serve as self-supporting adsorbents for environmental
remediation and other separations applications. The material, whose mesopores were
functionalized with 3-mercaptopropyltrimethoxysilane ligands, can be made into
spheres, irregular particles, and truncated cones having diameters from 1 to 15 nm
through a one-step emulsion synthesis procedure. Other shapes such as pellets can be
formed by molding the precursor gel. Surface areas of these materials were found to be
between 864 and 1184 m 2 /g. These materials were extremely effective to remove
mercury and silver ions from aqueous solutions. The amount of mercury adsorbed
ranged from 0.24 to 1.26 mmol/g, depending on the degree of functionalization. Silver
was less strongly adsorbed than mercury, with a maximum loading of 0.89 mmol/g. The
adsorption capacity of the functionalized materials for nitrogen is comparable to that of
unfunctionalized materials (Kalyanaraman et al., 2001).
Bou-Maroun et al. (2006) have studied the solid-liquid extraction of Cu(II) and
europium(III) by a mesostructured silica doped with two 4-acyl-5-hyroxy-pyrazole: 1-
phenyl-3- methyl-4-stearoyl-5-pyrazolone (HPMSP) with one chelating head and 1,12-
bis(1-phenyl-3-methyl-5-hydroxy-4-pyrazolyl) (HL-10-LH) with two chelating heads.