Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 164

398.2 mg.g -1 for methylene blue at pH value of 7 and adsorbent dose of
0.5 g.L -1 . Also, the high iodine number of the prepared activated carbon
(1008.86 mg.g -1 ) was due to the ability of zinc chloride to produce a high
amount of micropores. Theydan and Ahmed [85] conducted a similar acti-
vation process, where ferric chloride was used as the activating agent at an
impregnation ratio of 1.5 and carbonization temperature of 700 C. The
yield and other characteristics of the prepared activated carbon have been
summarized in Table 5.10. This table shows a very high yield compared to
literature which use phosphoric acid as activating agent. It has been related
to the tendency of the ferric chloride to produce more microporous struc-
ture, whereas phosphoric acid tends to produce more macropores. The
surface area of the resultant activated carbon and its adsorption capacity
for methylene blue at a pH value of 7 and adsorbent dose of 0.5 g.L -1 were
found to be 780.1 m 2 .g -1 and 259.2 mg.g -1 . This dye uptake capacity is
equivalent to 90% of that of the prepared activating carbon using zinc chlo-
ride as dehydrating agent. In order to determine the rate-limiting step, the
adsorption process was divided into 4 steps, namely transport of dye mol-
ecules from the bulk to the boundary layer surrounding the adsorbent;
surface diffusion, which is defined as the transport of the dye molecules to
the external surface of the adsorbent; transport of the dye molecules from
the surface to the intraparticle active sites, or so-called pore diffusion, and;
adsorption of the dye molecules by the adsorbent surface sites. The first
and last steps are so fast that the probability of their being limiting steps is
ruled out. Also, because the linear regression coefficient for the intraparti-
cle diffusion model was low and the plot of q t versus t 1/2 did not pass
through the origin, intraparticle diffusion was also dismissed. The feasibil-
ity of the application of microwave-assisted activation was studied by Foo

Table 5.10 Effect of temperature on textural characteristics of bamboo
chars [85].

Characteristic Value

Yield (%) 47.08

Bulk density ( g.ml -1 ) 0.271

Ash content (%) 6.62

Moisture content (%) 12.54

Iodine number ( mg.g -1 ) 761.40

Surface area ( m 2 . g -1 ) 780.06

Micropore volume ( cm 3 . g -1 ) 0.468

Mesopore volume ( cm 3 . g -1 ) 0.105