Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 153

highest textile effluent dye removal efficiency (~88 mg.g -1 ). Succinylated
and EDTA dianhydride-modified sugarcane bagasse were prepared by
Gusmão et al. [61,62] and were successfully applied for the adsorption of
methylene blue and gentian violet from wastewater. The functionalization
was conducted by adding succinic anhydride or EDTA dianhydride to the
bagasse and heating the slurry under reflux condition for a long period of
time. The introduction of carboxylate functional groups was believed to
account for the successful modification of the precursor. The surface area
of the EDTA-modified sample was found to be very low (1.4 m 2 g -1 ), but
had a larger average pore diameter (7.8 nm) compared to activated car-
bons. Since the pH of zero charge point, pH PZC , for the prepared materials
was 7.5, the adsorbent becomes negatively-charged when the pH of the dye
solution is higher than pH PZC . The maximum adsorption capacity of the
succinylated and EDTA-modified sugarcane bagasse was determined to be
478 and 202 mg.g -1 for methylene blue and 1273 and 328 mg.g -1 for gentian
violet, respectively, whilst adsorption capacity of unmodified bagasse was
48.5 and 85.6 mg.g -1 for methylene blue and gentian violet, respectively. In
another attempt, the tetraethylenepentamine-modified sugarcane bagasse
(TEPA-SB) was successfully used to remove eosin Y from the effluent [63].
Due to the existence of amine functional groups on the surface of the mod-
ified material, a high adsorption capacity of 349.3 mg.g -1 for this dye was
obtained. The adsorption capacities of sugarcane bagasse modified with
various methods have been compared in Table 5.5.
5.2.3 Peat
Peat, consisting of a complex array of organic matter (lignin, cellulose
and humic substances), is formed through incomplete decomposition of
dead plant matters under limited oxygen and excess humidity conditions.
The existence of a variety of functional groups on this organic material,
including carboxylic acid, phenolic hydroxide, ester, aldehyde and ketone,
in addition to its polarity and porosity renders it a potential adsorbent to
bind with different types of pollutants in wastewater [64].
Ho and McKay [65] have explored the adsorption of two dyes onto
peat. It was found that the adsorption capacity of the peat for Basic Blue 69
(195 mg.g -1 ) is much higher than the Acid Blue 25 (12.7 mg.g -1 ). This
behavior was attributed to the surface characteristics of peat and the ionic
charges of the dye molecules. They observed that increasing the agitation
speed significantly enhances the adsorption capacity of the adsorbent due
to the decrease in the boundary layer resistance to mass transfer from the
bulk of the solution to the adsorbent surface. As shown in Figure 5.8, the