Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 178

that not only new pores are created on the activated carbon, but also a por-
tion of the micropores are merged to develop mesopores. The Boehm titra-
tion method was employed to quantify the chemical functional groups. It
was found that the increase in the impregnation ratio does not have any
impact on the basic functional groups (carbonyl, pyrone and chromene),
but significantly increases the amount of acidic functional groups (carbox-
ylic and phenolic groups), and hence the surface of the activated carbon
becomes more acidic (see Table 5.19). The adsorption efficiency of the high
surface area activated carbon was tested by using methylene blue as adsor-
bate. At pH value of 6.5, the adsorption capacity of the coconut shell-based
activated carbon (AC-3) was determined to be 916.3 mg.g -1 . The activation
of coconut husk by a similar dehydrating agent, potassium hydroxide, also
provided promising results [110]. Tan et al. carried out the same procedure
used in the activation of oil palm fiber, where the precursor was carbonized
at 700 C in an inert atmosphere, the resultant char was soaked in KOH and
then activated at 850 C under CO 2 atmosphere. Very high BET surface area
and pore volume of 1940 m 2 .g -1 and 1.14 cm 3 .g -1 , respectively, were reported
for the honeycomb-shaped activated material with an average pore diam-
eter of 2.4 nm. Figure 5.21 shows the SEM images of the precursor and the
derived activated carbon. The creation of many large pores can evidently be
seen in these figures. The methylene blue adsorption capacity of the coconut

Table 5.18 Textural characteristics of the activated carbons derived from
coconut shells [109].

Carbon BET SA

( m 2 g -1 )

Pore
vol.
( cc.g -1 )

Average
Pore
Diameter
(nm)

Micropore
vol. ( cc.g -1 )

Mesopore
vol. ( cc.g -1 )

v micro /
v t (%)

Yield
(%)

AC-1 783 0.378 1.63 0.356 0.022 94.2 28.9

AC-2 1842 0.927 1.80 0.775 0.152 83.6 23.4

AC-3 2825 1.498 2.27 1.143 0.355 76.3 18.8

Table 5.19 Results of the Boehm and pH drift methods for the AC-1, AC-2 and
AC-3 [109].

Carbon Carboxylic

( mmol.g -1 )

Lactonic
( mmol.g -1 )

Phenolic
( mmol.g -1 )

Acid
( mmol.g -1 )

Basic
( mmol.g -1 )

Total
( mmol.g -1 )

pH drift

AC-1 0.37 0 0.38 0.75 0.73 1.47 6.00

AC-2 0.62 0 0.88 1.5 0.75 2.25 5.09

AC-3 0.75 0 1.00 1.75 0.75 2.50 5.01