Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 378

its high contents of amino and hydroxy functional groups showing high
potentials of a wide range of molecules, including phenolic compounds,
dyes and metal ions. This biopolymer represents an attractive alternative as
non-conventional materials because of its physicochemical characteristics,
chemical stability, high reactivity, excellent chelation behavior and high
selectivity toward pollutants, including dye molecules. Indeed, numerous
studies demonstrated that chitosan-based biosorbents are efficient materi-
als and have an extremely high affinity for many classes of dyes (Table 10.8).
They are also versatile materials, allowing the adsorbent to be used under
different forms, from flake-types, to gels, bead-types, or fibers. Wong et al .
[199] found that the maximum adsorption capacities of chitosan for Acid
Orange 12, Acid Orange 10, Acid Red 73 and Acid Red 18 were 973.3,
922.9, 728.2, and 693.2 mg g -1 , respectively. Wu et al . [195] also reported
the usefulness of chitosan for the removal of reactive dyes. Chiou and Li
[196] found that 1 g of chitosan adsorbed 2498 mg of Reactive Blue 2.
In general, chitosan-based biosorbents have demonstrated outstanding
removal capabilities for direct dyes [190]. In comparison with commercial
activated carbons, the beads exhibited excellent performance for adsorp-
tion of anionic dyes: the adsorption values were 3-15 times higher at the
same pH [197]. Hence chitosan chelation is a procedure of choice for dye
removal from aqueous solution. However, performances depend on the
different sources of chitin, the degree of N-acetylation, molecular weight

Table 10.8 Reported adsorption capacities q max (mg g -1 ) for chitosan and
chitosan-based biosorbents (selected papers).

Biosorbent Dye q max Reference

Chitosan Acid Orange 12 973.3 [198]

Chitosan Acid Orange 12 973.3 [199]

Chitosan Acid Orange 10 922.9 [199]

Chitosan Acid Orange 10 922.9 [198]

Chitosan Acid Red 73 728.2 [199]

Chitosan Acid Red 73 728.2 [198]

Chitosan Acid Red 18 693.2 [199]

Chitosan Acid Red 18 693.2 [198]

Chitosan Acid Green 25 645.1 [199]

Chitosan Acid Green 25 645.1 [198]

Chitosan Remazol Black 13 91.47 [200]

Chitosan Congo Red 78.9 [201]