Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 147

the intraparticle diffusion rate of the dye molecules into the activated car-
bon pores. It was also found that the addition of salt barely had any effect
on the adsorption capacity of the activated carbon when the solution con-
centration is relatively low. As the solution concentration increased, the
effect of salt addition became more pronounced (see Figure 5.4). At such
high concentrations, the addition of salt was believed to result in a partial
neutralization of the surface positive charge on the activated carbon by Cl -
ions and consequent compression of the electric double layer, enhancing
the adsorption capacity of the activated carbon. Also, they hypothesized

Table 5.1 Summary of porous structure of the rice husk-based activated carbons
prepared at various conditions [49,50].
Activation condition

BET SA
( m 2 g -1 )

Pore vol.
( cc.g -1 )

Micropore SA
( m 2 g -1 )

Av. Pore Size
(Å)

750 C, 30 min 1886 0.98 721 20.00

1987 1.32 785 23.47

750 C, 60 min

2721 1.88 1044 25.79

750 C, 90 min

650 C, 120 min 1392 0.70 955 20.20

700 C, 60 min 1759 0.79 1735 17.89

1930 0.97 1090 20.02

750 C, 60 min

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.0 0.2 0.4 0.6 0.8 1.0

KCI Concentration (M)

Figure 5.4 Adsorption of RB on rice husk-based activated carbon as a function of
KCl [50]. (Conditions: contact time 2 h; adsorbent dosage 0.8 g/L; [RB] 1.2 mmol/L;
temperature 25°C)