The efficient removal of high-toxic Cr(VI) by the simply modified sepiolite synergized with oxalic acid under UV.

The modified sepiolite (H-Sep-OH) with high catalytic activity was simply prepared and used for the enhancement of hexavalent chromium(Cr(VI)) removal from water by oxalic acid (Ox) photoreduction. The effects of H-Sep-OH dosage, Cr (VI) concentration, initial concentration of Ox and initial pH on the Cr (VI) removal in the Ox + H-Sep-OH + UV system were investigated in detail. The mechanism of Cr (VI) removal of the Ox + H-Sep-OH + UV system was discussed by the effect of initial pH, the change of pH and Cr species in the solution during the process, the free-radical scavenging test, and the IR, XRD, UV-Vis diffuse reflectance and Mott-Schottky analysis. The results showed that H-Sep-OH could significantly synergize with Ox reduction to remove Cr(VI) under UV, and the concentration of Ox in the aqueous solution and the dosage of H-Sep-OH determined the amount of reducing substances and the speed of Cr(VI) reduction. Amorphous SiO₂ in the H-Sep-OH played an important catalytic role in the photoreduction of Cr(VI). During the Cr(VI) removal process in the Ox + H-Sep-OH + UV system, the reductive removal of Cr(VI) from the water was achieved synergistically by the effectively separated electron(e^-) (generated from the SiO₂ in H-Sep-OH under UV irradiation), and the produced •CO₂ ^- (derived from photolysis of Ox and the conversion of Ox by water and hole(h⁺).).