Photoredox of Cr(III)–Malate Complex and Its Impacting Factors

Yang, Feng; Li, Hui; Zhang, Jing; Lan, Yeqing

Photoredox of Cr(III)–Malate Complex and Its Impacting Factors

2014

Yang, Feng | Li, Hui | Zhang, Jing | Lan, Yeqing

The transformation of less toxic Cr(III) species to harmful Cr(VI) is worth concerning. Compared with free Cr(III), however, the photo-oxidation of Cr(III)–organic acid complexes is seldom reported. In this study, Cr(III)–malate complex was synthesized and purified, and its photo-oxidation was investigated to reveal the potential conversion pathway of Cr(III) to Cr(VI). The results indicated that Cr(III)–malate complex could be gradually photo-oxidized to Cr(VI) through a ligand–metal charge transfer path. Higher pH and stronger light intensity promoted the conversion process. A 50-μM Cr(III)–malate complex was almost completely oxidized to Cr(VI) within 420-min irradiation of 500 W medium-pressure mercury lamp at pH 12. The introduction of H₂O₂, considered as a direct source of hydroxyl radicals (·OH) in the presence of Cr(II), markedly enhanced the yield of Cr(VI), and a complete oxidation of Cr(III)–malate complex (50 μM ) was realized within 20 min. Under a weak acidic condition, the production of Cr(VI) was coupled with the reduction of Cr(VI) by malic acid and its free radical generated from Cr(III)–malate complex, leading a gradual decrease in Cr(VI) concentration with the reaction.

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