Several studies were reported for the photocatalytic reduction of Cr(VI), which is mobile and highly toxic, compared to Cr(III), which is immobile and less harmful. Various unmodified and modified semiconductors were synthesized and characterized as photocatalysts. TiO2 thin films immobilized on glass plates and prepared by sol–gel technique wereinvestigated (Kajitvichyanukula et al., 2005). Cr(VI) was successfully removed, the photoactivity of the prepared TiO2 thin films exhibited a comparable efficiency with TiO2 powder, Degussa P-25 (Fig. 16). TiO2 modified with sulfate (Mohapatra et al., 2005) and TiO2 loading on zirconium phosphate (ZrP) and titanium phosphate (Dasa et al., 2006) were prepared and tested. Samples prepared at lower pH exhibit more surface area and higher reactivity than those prepared at higher pH (Fig. 17(a and b). Polyoxometalates (POM) PW12O403− or SiW12O404− as photocatalyst and an organic substrate (salicylic acid or propan-2-ol) as electron donor were also investigated (Gkika et al., 2006). Increase of POM or salicylic acid (SA) concentration accelerated, till a saturation value, with both the reduction of metal and the oxidation of the organic compound. The method is suitable for a range of chromium concentration from 5 to 100 ppm achieving complete reduction of Cr(VI) to Cr(III).