PHOTOCATALYTIC TRANSFORMATION AND MINERALIZATION OF 2,4,6-TRINITROTOLUENE (TNT) IN TIO2 SLURRIES

An analysis of the photodegradation of TNT in a TiO2 slurry reactor is presented. The rates and extent of TNT transformation and mineralizat ion are compared for photocatalytic and direct photolytic reactions un der conditions of varying light energies and in the presence and absen ce of oxygen. Certain initial organic transformation products are iden tified for both photocatalytic and photolytic reactions. Nitrate, nitr ite, and ammonium ions are analyzed and the possibility of semiconduct or sensitization by colored compounds is considered. TNT was transform ed rapidly under each set of photochemical conditions but destruction was faster and more complete with TiO2 photocatalysis. Transformation by-products were destroyed readily under oxygenated photocatalytic con ditions and were observed to be more refractory under direct photolyti c conditions. Mass balances performed on carbon and nitrogen revealed that when the TiO2 photocatalyst was utilized in the presence of oxyge n and near u.v. radiation (lambda > 340 nm) approx. 90% of the TNT was mineralized and 35% of the total nitrogen was recovered as ammonium i on after 120 min. Among the large number of organic transformation pro ducts produced photocatalytically, trinitrobenzoic acid, trinitrobenze ne and trinitrophenol have been identified as oxidative intermediate s pecies and dinitroaniline as a reduction product. The photocatalytic t ransformation of TNT appears to involve both oxidative and reductive s teps and sensitization by colored compounds plays no detectable role i n degradation.