Removal of aqueous chromate [Cr(VI)] through photocatalysis by using TiO_2-coated silica granules

摘要

The aim of this study was to determine the optimal conditions for the treatment of chromate [Cr(VI)]- contaminated water by UV photocatalysis using synthesized TiO_2-coated silica granules (φ 1.7-4.0 mm) containing 12.4% of TiO_2 in a batch method. The effect of the volume of the solution on Cr(VI) removal was investigated in the photocatalysis process by using 10 g of TiO_2-coated silica granules in water samples with a constant initial Cr(VI) concentration of 5 mg L~(-1). In a 10-mL solution, Cr(VI) concentrations were observed to decrease below the detection limit (<0.05 mg L~(-1)) in 300 min. Furthermore, Cr(VI) concentrations gradually decreased with time in other solutions with larger volumes. The capacity of the UV photocatalysis process to remove Cr(VI) using 10 g of TiO_2-coated granules did not fluctuate with the solution volume for samples with a constant initial Cr(VI) concentration. The lower the initial pH of the solution, the greater was the amount of Cr(VI) removed from the solution. The addition of chloride ions to the solutions accelerated the removal of Cr(VI) by UV photocatalysis. Ten grams of TiO_2-coated silica granules were repeatedly used to the 300-min treatment of the Cr(VI) solution (10 mL, 6 mg L~(-1)) till seven cycles. After four cycles of UV photocatalysis, Cr(VI) was completely removed from all the solutions. After the fifth cycle, the Cr(VI) removal capacity of the UV photocatalysis process decreased with the repeated use of the catalyst.