3.5. Effect of chitosan loading in TCF on photocatalytic activity and
kinetics
Fig. 6a Presents the effect of chitosan loading in TCF on the
removal of Cr(VI) with 150 ppm initial concentration at pH 3. The
amount of TiO2 in all TCF materials was fixed at 0.2% w/w and the
amount of chitosan was varied as of 1.0, 1.5, 2.0, and 2.5% w/w.
Normally, the photocatalytic process had two stages. The Cr(VI) can
be adsorbed on the surface of TCF in the dark during 30 min
adsorption process in the first stage. The reduction of Cr(VI) can occur by the photoreaction of Cr(VI) on TCF surface during 180
irradiation process in the second stage. Overall percentages of
photocatalytic reduction of Cr(VI) is accounted for the total percentage
of Cr(VI) removal. The Cr(VI) removals during dark
adsorption, irradiation, and total removal percentage under variation
of the amount of chitosan were shown in this graph. It was
observed that the adsorption amount of Cr(VI) increased with
increasing amount of chitosan. However, the Cr(VI) removal percentage
during irradiation was slightly different in each condition
(49.88% in average). The enhancement of the photocatalytic efficiency
due to the effect of chitosan had been exploited by previous
work (Nawi et al., 2011). However, its influence was clearly
demonstrated in the TCF from this work. The maximum protonated
amino group (eNH3
þ) which was a functional of the chitosan was
obtained in a higher content of chitosan in TCF, and it enhanced in
adsorbing Cr(VI) onto TCF surface. The photocatalytic reaction was
confined mostly to adsorption capacity of media under illumination.
The enhancement of photocatalytic activity was mainly
attributed to the synergistic effect of the combined photocatalysis
and adsorption processes.