Nikolai M. Bazhin

New Insight into Photochemistry of Ferrioxalate

Optical spectroscopy and nanosecond flash photolysis (Nd:YAG laser, 355 nm, pulse duration 5 ns, mean energy 5 mJ/pulse) were used to study the photochemistry of Fe(III)(C2O4)3(3-) complex in aqueous solutions. The main photochemical process was found to be intramolecular electron transfer from the ligand to Fe(III) ion with formation of a primary radical complex [(C2O4)2Fe(II)(C2O4(*))](3-). The yield of radical species (i.e., CO2(*-) and C2O4(*-)) was found to be less than 6% of Fe(III)(C2O4)3(3-) disappeared after flash. [(C2O4)2Fe(II)(C2O4(*))](3-) dissociates reversibly into oxalate ion and a secondary radical complex, [(C2O4)Fe(II)(C2O4(*))](-). The latter reacts with the initial complex and dissociates to Fe(II)(C2O4) and oxalate radical. In this framework, the absorption spectra and rate constants of the reactions of all intermediates were determined.

Mechanism of Fe(OH)2+(aq) photolysis in aqueous solution (technical report)

Experiments on laser flash photolysis (308 nm) of Fe(OH)2+(aq) complex in aqueous solution with addition of nitrobenzene demonstrate the formation of hydroxyl radical in the primary photochemical process.

[Fe(Ox)3]3- complex as a photodegradation agent at neutral pH: Advances and limitations

In the present work advances and limitations in the application of Fe(III)-oxalate complexes (namely, [Fe(Ox)3]3-) to the photodegradation of a model persistent organic contaminant - 2,4-dichlorophenoxybutanoic acid (2,4-DB) in neutral aqueous solutions were systematically investigated for the first time. It has been shown that the efficiency of [Fe(Ox)3]3- system greatly depends on the initial concentrations of oxalate ion due to the fast consumption of the ligand during photodegradation process leading to the formation of photochemically less active Fe(III) species. Efficiency of Fe(Ox)33- system normalized to UVA absorption at the excitation wavelength is practically independent on [Fe(III)]. Thus, it is highly probable that concentrations of Fe(III) as low as < 10-5 M could be applied in water treatment procedures using reactors with very long optical path. The system also keeps high efficiency at low concentration of pollutant (<10-5 M) though this results in higher relative consumption rate of Fe(III) and oxalate ions.

Intermediates in Photochemistry of Fe(III) Complexes in Water

The photochemistry of Fe(OH)2+ complex and complexes formed by Fe(III) and pyruvic (Pyr), tartaric (Tart), sulfosalycilic (SSA) and oxalic (Ox) acids in aqueous solutions were studied by means of stationary and nanosecond laser flash photolysis. The application of different scavengers of transient radicals has shown that the hydroxyl radical is the primary photochemical species in photochemistry of the FeOH2+ complex. In the photochemistry of FePyr2+ and FeTart+ complexes a weak absorption was found in the red spectral region which was attributed to [FeII…R-COO•]2+ radical complexes. Laser flash photolysis of FePyr2+ and FeTart+ complexes in the presence of methyl viologen (effective scavenger of different free radicals) gave evidence of MV•2+ radical cation formation with concentration as small as ~2% of Fe(III) complex disappeared. The reaction mechanism including inner-sphere electron transfer with the formation of [FeII…R-COO•]2+ radical complex and its transformation to the reaction products is proposed. The main photochemical process for FeIII(C2O4)33— complex in aqueous solutions was found to be intramolecular electron transfer from the ligand to Fe(III) ion with the formation of a primary radical complex [(C2O4)2FeII(C2O4•)]3−. The yield of free radical species (i.e., CO2•− and C2O4•−) was found to be less then 6% of FeIII(C2O4)33— disappeared after a laser pulse.