Photochemical Cycling of Iron Mediated by Dicarboxylates: Special Effect of Malonate
- 9 December 2009
- journal article
- Published by American Chemical Society (ACS) in Environmental Science & Technology
- Vol. 44 (1), 263-268
- https://doi.org/10.1021/es901956x
Abstract
Photochemical redox cycling of iron coupled with oxidation of malonate (Mal) ligand has been investigated under conditions that are representative of atmospheric waters. Malonate exhibited significantly different characteristics from oxalate and other dicarboxylates (or monocarboxylates). Both strong chelating ability with Fe(III) and strong molar absorptivities, but much low efficiency of Fe(II) formation (ΦFe(II) = 0.0022 ± 0.0009, 300−366 nm) were observed for Fe(III)−Mal complexes (FMCs). Fe(III) speciation calculation indicated that Mal is capable of mediating the proportion between two photoactive species of Fe(III)−OH complexes and FMCs by changing the Mal concentration. Spin-trapping electron spin resonance (ESR) experiments proved the formation of both the ·CH2COOH and ·OH radicals at lower total Mal concentration ([Mal]T), but only ·CH2COOH at higher concentrations of malonate, providing strong evidence for competition between malonate and OH− and subsequent different photoreaction pathways. Once FMCs dominate the Fe(III) speciation, both photoproduction and photocatalyzed oxidation of Fe(II) will be greatly decelerated. There exists an induction period for both formation and decay of Fe(II) until FeIII(OH)2+ species become the prevailing Fe(III) forms over FMCs as Mal ligand is depleted. A quenching mechanism of Mal in the Fe(II) photoproduction is proposed. The present study is meaningful to advance our understanding of iron cycling in acidified carbon-rich atmospheric waters.Keywords
This publication has 33 references indexed in Scilit:
- Transition Metals in Atmospheric Liquid Phases: Sources, Reactivity, and Sensitive ParametersChemical Reviews, 2005
- Photochemical Oscillation of Fe(II)/Fe(III) Ratio Induced by Periodic Flux of Dissolved Organic MatterEnvironmental Science & Technology, 2005
- Homogeneous photocatalysis by transition metal complexes in the environmentJournal of Molecular Catalysis A: Chemical, 2004
- Photochemical decomposition of oxalic, glyoxalic and pyruvic acid catalysed by iron in atmospheric watersAtmospheric Environment, 1994
- Photochemistry of aqueous iron(III)-polycarboxylate complexes: roles in the chemistry of atmospheric and surface watersEnvironmental Science & Technology, 1993
- Formation of hydrogen peroxide and depletion of oxalic acid in atmospheric water by photolysis of iron(III)-oxalato complexesEnvironmental Science & Technology, 1992
- Link between iron and sulphur cycles suggested by detection of Fe(n) in remote marine aerosolsNature, 1992
- Evidence for redox cycling of iron in atmospheric water dropletsNature, 1990
- Photolysis of Fe (III)-hydroxy complexes as sources of OH radicals in clouds, fog and rainAtmospheric Environment. Part A. General Topics, 1990
- Iron Photoreduction and Oxidation in an Acidic Mountain StreamScience, 1988