الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 176 |  |  |
| | | from | 176 | | |
Abstract
The word nanotechnology is relatively new and is also related to the production and application of structures, devices and systems by controlling the shape and size at the nanometer scale dimensions. Nanotechnology is related to the various structures of matter with dimensions in the order of billionth of a meter. Nanoparticles with 10-6 atoms or less are generally characterized by some properties that are different from those of the same atoms bonded together
to form bulk materials because size-dependent properties are often exhibited [1, 2]. Nanoparticles
are generally known to form a number of atoms or molecules bonded together with a radius of less than 100 nm. A nanometerscale is 10-9 m or 10 A so particles having this radius can be considered to be nanoparticles, and can be more chemically reactive and conduct electricity more effectively
than other materials.The common characteristic of nanoscience and nanotechnology is the size of
the target objects [3]
Nanosized Metal Oxides (NMOs) as NanosorbentsNanoparticles have two key properties that make them particularly attractive as sorbents. On a mass basis, they have much larger surface areas than bulk particles. In addition, nanoparticles
can be also functionalized with various chemical groups to increase their affinity towards some target compounds, ions or species. Nanosized metal oxides (NMOs) have a broad range of physicochemical properties such as separation and reactive media for water treatment. NMOs, including nanosized ferric oxides, manganese oxides, aluminum oxides, titanium oxides, magnesium oxides, cerium oxides and silicon dioxide, are classified as the promising ones for heavy metals removal from aqueous systems [4]. One of their most interesting properties is that a
high percentage of the atoms of the nanoparticles are distributed on the surface. The unsaturated surface atoms can bind with other atoms that possess strong chemical activity. Consequently, NMOs can adsorb selective metal ions and exhibit very high sorption capacity characteristics. Moreover, NMOs exhibit intrinsic surface reactivity and high surface areas and can strongly chemisorb several substances. In recent years, these materials have been proposed and applied in the removal and pre-concentration of trace metals due to their high surface area, high sorption
capacity and high chemical reactivity On the other hand, the preparation of these sorbents is very simple and low cost when compared with other commercially available solid-phase materials.
Additionally, the coating of complexing agent onto NMOs increases the number of binding sites
that are able to interact with metal ions and change the binding sites in order to enhance the uptake
of metal ions.
Recent studies suggested that a number of NMOs can exhibit very favorable sorption to
heavy metals in terms of high capacity and selectivity, which result in excellent removal of toxic
metals to meet increasingly strict regulations [6]. However, as the size of metal oxides changes
from micrometer to nanometer levels, the increased surface energy inevitably leads to their poor
stability. Consequently, NMOs are prone to agglomeration due to Van der Waals forces or other
interactions [7], and the high capacity and selectivity of NMOs would be greatly decreased or even
lost. Moreover, NMOs are unusable in fixed beds or any other flow through systems because of the excessive pressure drops (or the difficult separation from aqueous systems) and poor
mechanical strength. To improve the applicability of NMOs in real wastewater treatment, they
were then impregnated into porous supports of large size to obtain composite sorbents
[8]. The
widely used porous supports include activated carbon, natural materials, synthetic polymeric hosts,
etc.
Besides traditional NMOs, magnetic NMOs attract increasing attentions because they can be easily separated from water by the action of a magnetic field [9]. Also, magnetic NMOs-based composite sorbents allowed easy isolation from aqueous solutions for recycling or regeneration
[10]. Such facile separation is essential to improve the operation efficiency and reduce the cost
during water/wastewater treatment.