The effect of the initial concentration of Cr(VI) on the
photocatalytic determination of COD by the UV/TiO2 process
at pH 0.5 was studied. The results are shown in Fig. 3.
The absorbance of Cr(III) increases with increasing Cr(VI)
concentration up to 0.01 mol l−1, the increase seemed to
change more slowly for higher Cr(VI) concentration.
With different initial concentrations, Cr(VI) adsorptions
on TiO2 varied. This is due to the alteration of different
Cr(VI) forms and concentration ranges, such as [26,27]