Photoredox chemistry of iron(III) chloride and iron(III) perchlorate in aqueous media. A comparative study

Abstract

Photoredox chemistry of iron(III) chloride and iron(III) perchlorate in aqueous media was investigated in the wavelength range 250-425 nm. The effects of incident intensity, iron(III) and iron(II) concentrations, wavelength of irradiation, chloride concentration, radical scavengers, pH, time of irradiation, and temperature on product quantum yields were investigated. The primary photoreaction is postulated to be Fe3+-OH--Fe2+ 4--OH in iron (III) chloride and iron(III) perchlorate solutions; secondary reactions of • affect the product quantum yields. From the variation of quantum yields with the wavelength of irradiation the OH--*• Fe(III) charge-transfer excited state is concluded to be the one responsible for photoreduction. Under identical conditions, the product quantum yield ( 2+) for the photoreduction of iron(III) chloride is less than that of iron(III) perchlorate.

Acid Rivers and Lakes at Caviahue-Copahue Volcano as Potential Terrestrial Analogues for Aqueous Paleo-Environments on Mars

“…7.2) creates a short-lived OH · radical which is destroyed by reaction with other redox-sensitive species (Collienne 1983;Kimball et al 1992;Voelker et al 1997), such as dissolved organic carbon (DOC). David and David (1976) showed that photo-reduction of Fe(III) occurs in the ultraviolet (UV) to near-UV region of 200 to 450 nm, with a local maximum near 300 nm, and is sensitive to changes in pH, temperature, light intensity, major solute chemistry, and Fe(II) concentration. Collienne (1983) found that maximum Fe(III) photo-reduction rates take place in the pH range 2 to 4 where Fe(OH) 2+ is the dominant dissolved ferric species.…”

“…Most researchers discuss Fe II photo-oxidation (Cairns-Smith 1978, and the later work of Braterman et al 1983;Borowska and Mauzerall 1986;Lundgreen et al 1989;Kim et al 2013). Short wave-length UV-C light (maximum at 267 nm; Kim et al 2013) in controlled laboratory experiments created Fe II photo-oxidation, as opposed to Fe III photo-reduction, which is induced by light over a wider range of wavelengths (200 to 450 nm, maximum at 300 nm, David and David 1976). In the absence of a protective ozone layer in the upper atmosphere, UV-C radiation could have easily penetrated Mars' thin atmosphere, as it presumably did the atmosphere of early Earth.…”

Photoreduction of Fe(III) in the Acidic Mine Pit Lake of San Telmo (Iberian Pyrite Belt): Field and Experimental Work

“…As early as the 1930s, the photochemical reduction of Fe(III) salts in the presence of organic substances in laboratory conditions occupied the attention of scientists (e.g., Mata Prasad and Mohile 1936;Neiger and Neuschul 1936;Gopola et al 1955;David and David 1976) and the reduction of Fe 3? to Fe 2?…”

“…. The photoreduction process can take place via homogeneous (aqueous) and/or heterogeneous (solid surface) mechanisms, which are commonly represented by the following simplified equations (David and David 1976;Waite and Morel 1984;Kimball et al 1992):…”

Decolorization Kinetics of Acid Azo Dye and Basic Thiazine Dye in Aqueous Solution by UV/H2O2 and UV/Fenton: Effects of Operational Parameters

“…In previous studies, it was found that UV illumination of Fe 2+ / H 2 O 2 or Fe 3+ /H 2 O 2 system significantly increased the Fenton degradation rate of many organic substances [21], [22]. The effect of UV light is attributed to the direct • OH radical formation and regeneration of Fe 2+ from photolysis of the complex [Fe(OH)] 2+ in solution as following mechanism [23], [24]:…”