Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 167

the surface area of the date pits. In the physical activation method, the pre-
cursor was carbonized at 800 C for 1 hour at a nitrogen flow followed by
the activation at 971 C for 56 min under CO 2 atmosphere. These condi-
tions were chosen based on the reported optimum conditions for maxi-
mizing the yield and BET surface area of date palm pits by Reddy et al.
[89]. The chemical activation method involves the impregnation of the raw
material in phosphoric acid and its subsequent activation at 400 C under
self-generated gas atmosphere. The activated carbons obtained via these
two methods exhibited considerably different behaviors where H 3 PO 4 -
activated and CO 2 -activated samples had surface areas of 725 and 666 m 2 g -1 ,
respectively. The microporosities of these adsorbents were another major
distinction. It was observed that CO 2 -activated carbon was mainly micro-
porous, whereas in the case of the sample activated by H 3 PO 4 , only 31% of
the total volume was related to the micropores. The existence of a distinct
hysteresis verified the presence of mesoporosity in the latter activated car-
bon. The preparation conditions and the textural characteristics of the
optimized and the S BET -maximized date pit-based activated carbons have
been compiled in Table 5.13. A surface functional group study of the raw
date pit was compared with the two activated carbons. It was shown that
some of the functional groups disappeared upon activation. It was also
observed that other than the hydroxyl group peak, the rest of the bands
vanished for CO 2 - activated carbon compared to the H 3 PO 4 - activated
carbon. The adsorption capacity of the two activated carbons were deter-
mined to be 110 and 345 mg methylene blue per gram of CO 2 - and H 3 PO 4 -
activated carbon, respectively. The higher adsorption capacity of the latter
to the former adsorbent was related to the higher average pore size of the
H 3 PO 4 - activated carbon and easier diffusion of the large dye molecules

Table 5.13 Physical properties of the activated carbons derived from date palm
pits with different activation procedures [88].

Activation T, C t, min BET SA

( m 2 g -1 )

Pore vol.
( cc.g -1 )

v micro / v t D p , nm Yield

(%)

Physical
(optimized)

971 56 666 0.41 0.92 1.56 14.8

Chemical
(optimized)

400 58 725 1.26 0.31 2.90 44.0

Physical
(maximized)

1063 68 980 0.61 0.93 1.57 9.5

Chemical
(maximized)

450 75 952 1.38 0.36 2.91 41.0