title: Effect of thiols enrichment on Cr(VI) photo-reduction by natural organic matter (NOM).
abstract: Photochemical redox transformation of Cr(VI)-NOM complexes substantially affects transport and speciation of less toxic Cr(III) in natural waters. However, the underlying mechanisms remain unclear. This study reported photochemical reactions of Cr(VI) with thiol-enriched NOM under acidic condition. More effective thiols enrichment in humic acid (HA) was observed than that in fulvic acid (FA), thereby resulting in a higher reduction capacity and faster rate of Cr(VI) photo-reduction. Chemical addition of sulfide to HA formed a large number of S-containing molecular formulae, which subsequently disappeared following reactions with Cr(VI) under solar irradiation. Cr(VI) photo-reduction in thiol-enriched HA consumed more S-containing formulae. Solar irradiation caused a rapid loss of the reduction capacities and thiol contents in HA and FA. All these findings can provide useful information for understanding the biogeochemical cycles of chromium and sulfur, and are also of environmental significance because they may partially account for photo-transformation of Cr(VI) when chromium enters into the aquatic environment as acidic industrial effluents.
authors.affiliation: Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China; Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA; School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore. Electronic address: hwluo@ntu.edu.sg.
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Luo
keywords: Chromium; Natural organic matter; Photo-reduction; Thiols enrichment