Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 377

other adsorbents, chemical processes are also used for improving adsorp-
tion properties and selectivity. For example, Sun and Yang [179] prepared
modified peat-resin by mixing oxidizing peat with polyvinyl alcohol and
formaldehyde. These materials possess a macroreticular porous struc-
ture with high physical characteristics and interesting adsorption perfor-
mances. Their studies demonstrated that modified peat can be used for the
removal of a variety of basic dyes. For example, the maximum adsorption
capacities for Basic Violet 14 and Basic Green 4 were 400 and 350 mg g -1
treated peat, respectively. Vecino et al. [182] also proposed a peat-based
hybrid material for effective dye removal: peat was entrapped in calcium
alginate beads. The mechanism by which dyes are adsorbed onto peat has
been a matter of considerable debate. Different studies have reached dif-
ferent conclusions. Various pollutant-binding mechanisms are thought
to be involved in the biosorption process including physical adsorption,
ion-exchange, complexation, adsorption-complexation and chemisorp-
tion [172]. Variations in peat type and adsorbent preparation also make
the comparison of results difficult [183]. However, it is now recognized
that ion-exchange is the most prevalent mechanism.

10.9 Chitin and Chitosan

Abundant information on chitin and chitosan for environmental purposes
can be found in the literature [187-193]. Crini and Badot [190] reviewed
over 100 papers (1998-2008) on the application of chitin and chitosan as
non-conventional efficient biosorbents for the removal of dyes from aque-
ous solutions even in low concentration. They concluded that the adsorp-
tion of dyes using these biopolymers is one of the reported emerging and
efficient biosorption methods for dye removal. Chitin and its derivative,
chitosan, are abundant, renewable and biodegradable resources. These
biopolymers are commercially extracted from crustaceans (crab, krill,
crayfish) primarily because a large amount of the crustacean's exoskeleton
is available as a byproduct of food processing [191]. Utilization of indus-
trial solid wastes for the treatment of wastewater from another industry
could be helpful not only to the environment in solving the solid waste dis-
posal problem, but also the economy [194]. Chitin contains 2-acetamido-
2-deoxy-β-D-glucose through a β (1 4) linkage. This waste product is
second only to cellulose in terms of abundance in nature. Chitosan con-
tains 2-acetamido-2-deoxy-β-D-glucopyranose and 2-amino-2-deoxy-β-
D-glucopyranose residues. Chitosan has drawn particular attention as a
complexing agent due to its low cost compared to activated carbon and