Environmental Engineering Reference
In-Depth Information
intraparticle diffusion played an important role in the adsorption mecha-
nism of dye. Cellulose is also an inexpensive and promising polysaccharide
for environmental purposes because of its abundance and renewability
[278]. This biopolymer is the main constituent of plants and the most
abundant biomass in the world. However, raw cellulose has low adsorption
capacity as well as poor physical stability. Chemical modifications such as
graft copolymerization, crosslinking or amination have been used to over-
come these drawbacks. An excellent detailed discussion of cellulose-based
materials for dye removal may be found in the comprehensive review by
Hubbe et  al. [279]. In particular, the authors discussed factors affecting
adsorption processes. Alginate is another one of the most extensively
investigated polysaccharides for removal of pollutants from aqueous solu-
tion, as it is inexpensive, nontoxic and efficient [280-282]. Alginate is a
naturally linear carbohydrate polymer extracted from brown seaweeds. It
has a capacity to remove toxic pollutants due to its high carboxyl group
content as showed by Aravindhan et al. [282], and more recently by Khari
et al. [283]. Innovative magnetic alginate beads for dye removal were also
proposed by Rocher et al. [280].
Cyclodextrins, calix[n]arenes and cucurbituril have also been studied as
non-conventional adsorbents for pollutant removal. Cyclodextrins (CDs)
are torus-shaped cyclic oligosaccharides containing six to twelve glucose
units. The most characteristic feature of CDs is the ability to form inclusion
compound with various aromatic and phenolic molecules, and polymers.
However, in spite of varied interesting characteristics and properties, a lim-
ited number of dye adsorption studies have been carried out on CD-based
derivatives [9,8,284]. Morin-Crini and Crini [285] recently summarized
the developments in the use of CD-based materials for environmental pur-
poses. This comprehensive review provided a summary of information on
color removal obtained using batch methods. In general, from a point of
view of their high adsorption capacity to adsorb dyes, the CD materials
are interesting, although they are nonporous and possess low surface area.
Indeed, adsorption processes mainly occur by inclusion complex forma-
tion. Calix[n]arenes are the third major class of supramolecular host sys-
tems along with cyclodextrins and crown ethers. Their ease of synthesis
and relative simplicity of chemical modification have produced increased
interest in the host-guest chemistry over the last few years, although their
cost can be a disadvantage for environmental purposes. Calix[n]arenes are
cyclic oligomers composed of phenol units very well known as ionophores
and for the fact that they provide a unique three-dimensional structure.
The complexation properties of these molecules are highly dependent
upon the nature, number of donor groups and the conformation of the
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