Influence of iron salts on the photooxidation of poly(N-vinylpyrrolidone) in aqueous solution

This article reports on the effect of UV–vis radiation (λ ≥ 300 nm) on the degradation of poly(N-vinylpyrrolidone) PVP photoinduced by Fe(III) in aqueous solution and in the presence of oxygen. The formation of oxidation products was followed by infrared analysis of deposits obtained after evaporation of water and by UV–vis analysis of the irradiated polymer solutions. Size exclusion chromatography (SEC) was used for monitoring the variations of molar weight and intrinsic viscosity with irradiation time. Total organic carbon (TOC) measurements were performed with the aim of checking the mineralisation of aqueous solutions.Depending on the concentration of Fe(III), the concentration of PVP and the pH of the solution, we were able to show that the photooxidation of PVP leads to a chain scission and to a cross-linking mechanism, contrary to photooxidation of PVP in the absence of Fe(III) which only involves a mechanism of chain scission. A mechanism of PVP photooxidation until its possible mineralisation is proposed, taking into account the concentration of Fe(III) in the solution.