The synergistic effect of attapulgite in the highly enhanced photoreduction of Cr(VI) by oxalic acid in aqueous solution.

Attapulgite (ATP), a widely existed clay in nature, was firstly and successfully applied to enhance the photoreduction of highly toxic Cr(VI) by oxalic acid (Ox). In ATP + Ox + UV system, batch effects (Ox concentration, initial Cr(VI) concentration, ATP dosage, and reusability of ATP) were investigated. By studying the impact of the initial pH in the solution, the change of pH and Fe species concentration as well as Ox concentration during the reaction, the free radical scavenging test, and the role of ATP, the mechanism of Cr(VI) removal by ATP + Ox + UV system was revealed. The methyl orange (MO) removal of ATP + Ox + UV system was also inspected. The results indicated that ATP showed the obvious enhancement in efficient photoreduction of Cr(VI) by Ox in water. The Fe and Si components in ATP played an important role in Cr(VI) removal by ATP + Ox + UV system: most of Cr(VI) was reduced by Fe(II) and CO produced by the Fe(III)-Ox complex from the dissolved Fe component in ATP under UV irradiation. Some of Cr(VI) was reduced by e and CO from the oxidation of Ox by h generated by the photocatalyzed SiO in ATP. Furthermore, ATP + Ox + UV system also showed excellent MO removal performance, indicating the great potential in practical applications.