Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 177

700 C under inert atmosphere. The activation mechanism using NaOH is
reported to occur according to the following reaction:

6 NaOH + 2 C 2 Na + 2 Na 2 CO 3 + 3 H 2 (5.1)
The yield of the prepared activated carbons ranged from 19-30% depend-
ing on the impregnation ratio used. As the impregnation ratio increased,
more carbon bonds were cleaved, more intense dehydrating reactions
occurred and consequently the yield decreased. Also the increase in the
impregnation ratio had a dramatic effect on the surface area, pore volume
and average pore size of the prepared activated carbons. Figure 5.20 shows
the N 2 adsorption-desorption isotherm curves for the activated carbons
prepared at impregnation ratios of 1, 2 and 3, labeled as AC-1, AC-2 and
AC-3, respectively. A progressive increase in the nitrogen volume uptake
is observed by increasing the impregnation ratio. Also, the adsorption and
desorption curves show a complete reversibility for all the activated carbons,
which is indicative of the existence of micropores and high affinity of the
adsorbate and adsorbents. Table 5.18 summarizes the porous characteristics
of the activated carbons derived from coconut shell. The highest surface
area and pore volume of the activated carbon (2825 m 2 .g -1 and 1.5 cm 3 .g -1 ,
respectively) were obtained when the impregnation ratio was the highest. As
well as these two parameters, the fraction of mesopores also increased with
increasing the impregnation ratio. The increase in the amount of micro- and
mesopores with an increase in the amount of dehydrating agent indicates

1000

900
800

AC-3

700

600

500
400

AC-2

300

200

AC-1

100

0

0.2 0.4 0.6 0.8 1.0

Relative Pressure (P/P 0 )

Figure 5.20 N 2 adsorption (closed symbols) and desorption (open symbols) isotherms at
77 K for the AC-1, AC-2 and AC-3 [109].