Civil Engineering Reference
In-Depth Information
The condensation of two sheets happens by coordination of an oxygen atom
with one silicon atom in the tetrahedral sheet and two aluminium atoms in
the octahedral sheet. Clays undergo exchange interactions of adsorbed ions
with the outside too.
Although clays are very useful for many applications, they have one main
disadvantage, they lack permanent porosity. To overcome this problem,
researchers have been looking for a way to prop and support the clay layers
with molecular pillars. Most of the clays can swell and thus increase the
space in between their layers to accommodate the adsorbed water and ionic
species. Ding
et al.
(1999) and Ooka
et al.
(2004) prepared different kinds
of TiO
2
pillared clays from different raw clays and the adsorption and
photocatalytic-decomposition performance were evaluated. It was found
that surface hydrophobicity of pillared clays (especially TiO
2
) largely varied
with the host clay. Since the TiO
2
particles in the pillared clays are too small
to form a crystal phase, they presented poor photocatalytic activity.
Nanocomposite of iron oxide and silicate was also synthesized for deg-
radation of azo-dye orange (II) (Feng
et al.
, 2003). A new class of nano-sized
large porous titanium silicate (ETAS-10) and aluminium-substituted
ETAS-10 with different Al
2
O
3
/TiO
2
ratios were successfully synthesized by
Choi
et al.
(2006) and applied to the removal of heavy metals, in particular
Pb (II) and Cd (II).
Micelles are self-assembled surfactant materials in a bulk solution. Sur-
factants or 'surface active agents' are usually organic compounds that are
amphipathic, meaning they contain both hydrophobic groups (tails) and
hydrophilic groups (heads). Therefore, they are typically soluble in both
organic solvents and water. Surfactant-enhanced remediation techniques
have shown signifi cant potential in their application for the removal of
polycyclic aromatic hydrocarbon (PAHs) pollutants. Molecular self-
assembly is gathering of molecules without guidance or management from
an outside source. There are two types of self assembly: intramolecular and
intermolecular. Attaching a monolayer of molecules to mesoporous ceramic
supports gives materials known as self-assembled monolayers on mesopo-
rous supports (SAMMS). The highly ordered nanostructure of SAMMS is
the result of three molecular self-assembly stages. SAMMS of silica-based
materials are highly effi cient sorbents for target species, such as heavy
metals, tetrahedral oxometalate anions and radionuclides (Mansoori
et al.
,
2008).
Magnetic nanoparticles are generally studied as adsorbents and nano-
catalysts for water treatment. One of the major applications of magnetic
particles is in the area of magnetic separation. In this case, it is possible to
separate a specifi c substance from a mixture of different other substances,
called 'magnetically assisted chemical separation' (MACS). Hu
et al.
(2005)
developed an innovative process combining nanoparticle adsorption and
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