Oxalic Acid from Corn Stalk for Photocatalytic Reduction of Cr(VI)

Abstract

Cr(VI) is toxic species of chromium in the aquatic environment. The reduced species, Cr (III), has lower toxicity than Cr(VI). The change of Cr(VI) species to Cr(III) can be conducted by photocatalytic reduction using oxalic acid as an oxidant with the aid of Fe(III) as a catalyst. Oxalic acid can be isolated from the biomass waste of corn stalk. This research aimed to isolate oxalic acid from corn stalk biomass as an oxidator for Cr(VI) photocatalytic reduction. The oxalic acid was isolated from corn stalks powder using NaOH, precipitated with the addition of CaCl2, acidified with H2SO4, and then crystalized to form the oxalic acid crystals. The photocatalytic reduction was carried out in a closed reactor equipped with two of 30-watt UV lights. About 30 mg of oxalic acid was used to reduce 300 mg/L Cr(VI) with the presence of 4 ml Fe(III) 100 mg/L as a catalyst. The process was conducted for 120 minutes while stirring. The reduction efficiency was calculated from the differentiation of the initial Cr(VI) concentration to the final ones. Cr(VI) concentrations were measured as Cr(VI)-diphenylcarbazide complex compound at pH 2 that could be detected at 540 nm. The results showed that the isolated oxalic acid has hydroxyl and carbonyl groups at 3441 cm−1 and 1627 cm−1 respectively identical with the oxalic acid standard. The crystals have melting point at 103°C. It could be used effectively to reduced Cr(VI) up to 45.9 %.