Oxidative photodegradation of herbicide fenuron in aqueous solution by natural iron oxide α-Fe2O3, influence of polycarboxylic acids.

The photodegradation of the herbicide fenuron (1,1-dimethyl-3-phenylurea) by using a natural iron oxide (NIO), α-Fe2O3, in aqueous solution at acidic pH has been undertaken. The NIO was characterized by the Raman spectroscopy method. The degradation pathways and the formation of degradation products were studied. A high-pressure mercury lamp and sunlight were employed as light source. Fenuron photodegradation using NIO with oxalic acid followed the pseudo-first-order kinetics, the optimal experimental conditions were [oxalic acid]0 = 10(-3) M and [NIO] = 0.1 g L(-1) at pH 3. A UVA/NIO/oxalic acid system led to a low fenuron half-life (60 min). The results were even better when solar light is used (30 min). The variables studied were the doses of iron oxide, of carboxylic acids, the solution pH and the effect of sunlight irradiation. The effects of four carboxylic acids, oxalic, citric, tartaric and malic acids, on the fenuron photodegradation with NIO have been investigated, oxalic acid was the most effective carboxylic acid used at pH 3. A similar trend was observed for the removal of total organic carbon (TOC), 75% of TOC was removed. The analytical study showed many aromatic intermediates, short-chain carboxylic acids and inorganic ion.