NITRILOTRIACETIC ACID TRANSFORMATION PHOTOINDUCED BY COMPLEXATION WITH IRON(III) IN AQUEOUS-SOLUTION

The phototransformation of iron(III) nitrilotriacetate, Fe(NTA), was studied at 20-degrees-C under monochromatic excitation at different pHs. The conjugation of excitation wavelength and pH gives rise to different photochemical behaviour. In acidic medium, it always results in a redox process giving rise to Fe(II), HCHO and CO2 but the stoichiometry of the photoproducts depends on the excitation wavelength. At long wavelength (365 nm), the Fe(II)/HCHO ratio of unity implies a redox reaction between Fe(II) and the carboxylic group whereas at short wavelength (254 nm) the Fe/HCHO ratio is equal to 2 and implies a redox process between Fe(III) and a water ligand. In neutral solution and at 365nm, a photosolvation is observed with NTA release; at 254nm a subsequent redox process between OH and the hydrous ferric oxide is involved. In terms of the fate of Fe(NTA) in the environment at pH 5-6 and under sunlight, all of the above photochemical reactions can occur.