Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 187

agent and heated up to 450 C in an air atmosphere. The increase in the
amount of activating agent had a drastic effect on the porous structure of
the activated carbon. With an increase in the amount of phosphoric acid,
the surface area of the activated carbon was increased steadily from 514
to 925 m 2 .g -1 , as given in Table 5.22. This also resulted in the mergence
of the micropores favoring the formation of more mesopores on the acti-
vated carbon. However, the yield of the carbon was affected insignificantly
when the impregnation ratio was changed. The Boehm titration of the acti-
vated carbon with the lowest impregnation ratio revealed that its surface
mainly consisted of phenolic and carboxylic groups, whereas the carbon
with the highest impregnation ratio showed a decrease in the amount of
the carboxylic groups and increase in the carbonyl groups (see Table 5.23).
These findings were in total agreement with the PZC study results which
confirmed the PZC of 3.7 and 7.4 for the CGAC30 and CGAC180, respec-
tively. The thermogravimetric analysis illustrated four steps in the mass
loss, mainly due to the dehydration of the physisorbed water and the car-
bonization of the samples. The FTIR analysis not only confirmed the exis-
tence of the functional groups detected by the titration method, but also
indicated the development of phosphorous groups on the surface of the

Table 5.22 Textural properties of activated carbons derived from coffee waste
obtained by N 2 adsorption/desorption studies [117].
Property Calculation

Method

CGAC30 * CGAC60 * CGAC120 * CGAC

180 *

BET surface area
( m 2 g -1 )

BET 514 618 745 925

Micropore surface
area ( m 2 g -1 )

t-Plot 311 243 158 60

External surface
area ( m 2 g -1 )

t-Plot 202 376 587 864

Mesopore surface
area ( m 2 g -1 )

BJH
Desorption

103 205 417 821

Total pore volume
( cm 3 .g -1 )

Single-Point
Adsorption

0.280 0.338 0.446 0.718

Micropore volume
( cm 3 .g -1 )

t-Plot 0.169 0.143 0.100 0.046

Mesopore volume
( cm 3 .g -1 )

BJH
Desorption

0.066 0.124 0.279 0.666

Yield (%) 37.7 37.3 35.2 32.0

*CGAC(n) represents the activated carbon with an impregnation ratio of “n” wt%.