The highly enhanced Cr(VI) photoreduction removal by oxalic acid coordinated with iron-loaded waste Loofah

Abstract

In order to remove high toxic Cr(VI) from the water with low cost and high efficiency, iron-loaded Loofah (Loofah-Fe) was prepared from agriculture waste Loofah and was applied in the Cr(VI) photoreduction remvoal by oxalic acid (Ox). The Cr(VI) removal of Loofah-Fe/Ox/UV system were investigated by the effect of initial Cr(VI) concentration, Ox concentration and Loofah-Fe dosage. The Cr(VI) removal mechanism in Loofah-Fe/Ox/UV system were discussed through the study of initial pH, the change (pH, Ox concentration, Fe(II) and Fe(III) concentration) in solution during the reaction, and the free radicals scavenging test. The role of Loofah-Fe in Loofah-Fe/Ox/UV system was further deduced by the analysis of XPS, EIS and Mott-Schottky. The results showed that Loofah-Fe remarkably enhanced the Cr(VI) photoreduction by Ox, 1 mM of Cr(VI) in aqueous solution was completely removed in 30 min by Loofah-Fe/Ox/UV system at pH = 3.0. The loaded Fe(III) and the contained SiO2 on Loofah-Fe played an important synergized photocatalytic role for Cr(VI) removal in Loofah-Fe/Ox/UV system. Fe(II) and CO2·-, which was continuously generated by photoactive Fe(III)-(C2O4)3 formed between Ox and Fe(III) dissolved from Loofah-Fe, reduced a large amounts of Cr(VI) in solution. The separated electron (e−) and the produced CO2·-, generated from the oxidized Ox by the hole (h+) through photoactive SiO2 on Loofah-Fe, also reduced part of Cr(VI).