PHOTOCATALYTIC DEGRADATION OF MONONITROPHENOL, DINITROPHENOL AND TRINITROPHENOL IN AQUEOUS TIO2 SUSPENSION

Three mononitrophenol compounds (2-, 3- and 4-) 2,4-dinitrophenol and picric acid (2,4,6-trinitrophenol) were photocatalytically degraded in aqueous TiO2 suspension. Among three mononitrophenol compounds the de gradation rate of 4- and 2-nitrophenol were larger than that of 5-nitr ophenol. The degradation rate decreased with the number of nitro group substituents. This reactivity follows Hammett law with regard to the effect of nitro group on phenolic functionality. Several polyhydroxyla ted aromatic intermediates were identified for mono- and dinitrophenol which indicated that the degradation started by the substitution of h ydrogen and nitro groups by hydroxyl radical. Organic acid intermediat es were identified besides aromatic compounds, among which formic and acetic acids were formed in the largest quantity. It was suggested for the transformation of nitro group that the formation ratio of NO3- an d NH4+ reflected the degradation mechanism of starting nitrophenolic c ompound.