Biosorption of Organic Dyes: Research Opportunities and Challenges - Green Chemistry for Dyes Removal from Wastewater - page 304

elucidated. They concluded that at pH < 7, electrostatic interactions
occurred between the functional groups on the surface of the biomass
and the dye molecules. However, at pH > 7, one different mechanism for
each dye was observed: For the Reactive Blue 4 (RB4), they concluded
that a chemical reaction between the hydroxyl group of the biomass and
two chlorine groups occurred. For the Reactive Orange 16 (RO16), the
hydroxyl groups of the biomass reacted with the vinyl sulfone group of
RO 16 by nucleophilic addition. For the Reactive Yellow 2 (RY2), a nucleo-
philic substitution reaction occurred. Du et al. [54] studied the biosorption
of the metal-complex dye Acid Black 172 by live and heat-treated biomass
of Pseudomonas sp. They found that the heat-treated biomass was more
efficient than live biomass. The maximum amount of the dye adsorbed by
the heat-treated biomass could reach up to 2961.2 mg g -1 . They also con-
cluded that the amine groups played a major role in the biosorption of
Acid Black 172 and that the heating of the biomass significantly increased
the permeability of the cell wall so that the dye could enter into the cells
and be adsorbed into intracellular proteins. Arunarani et al. [51] evaluated
the potential of Pseudomonas putida for the removal of Basic Violet 3 and
Acid Blue 93 from aqueous solutions. They verified that this microbe is an
efficient way to treat textile effluents.
8.2.4 Chitosan
Chitosan, a de-N-acetylated analog of chitin, is a heteropolysaccharide
consisting of linear b-1,4-linked GlcN and GlcNAc units [58]. The chemical
structure of chitosan is presented in Figure 8.1. It has been found by many
researchers that the OH and NH 2 on the chitosan structure (Figure 8.1) are
the main functional groups responsible for dye binding [59-65].
The use of chitosan for SODs removal from aqueous solutions is based
mainly on three factors: First, due to the fact that the chitosan-based
Figure 8.1 Chemical structure of chitosan (Haworth projection, based on references [9]
and [58]).