KINETICS AND PRODUCTS OF THE TIO2 PHOTOCATALYTIC DEGRADATION OF PYRIDINE IN WATER

Pyridine (Pyr), a noxious chemical whose ring is part of the chemical structure of many pesticides, is more rapidly eliminated in water by p hotocatalysis over TiO2 than benzamide, whose nucleus has also a relat ively low electron density and whose extent of adsorption is equivalen t. Hydroxylation of Pyr first occurs only at position 2. Beside acetat e and formate, whose formation from Pyr is derived from ion chromatogr aphy analysis, seven aliphatic intermediates with one to five C atoms are identified by GC-MS. They all contain one or several C=O groups, a nd wherever the N atom subsists, it is as an amide, i.e., with an unch anged oxidation number. For relatively high initial Pyr concentrations (16.5 mmol/L), dipyridyl and carbamoyl pyridine isomers are also dete cted as intermediates, at much lower concentrations, however, than tha t of 2-hydroxypyridine; this shows the existence of coupling reactions . Within an UV irradiation period about 2.5 times as long as that nece ssary to eliminate Pyr, organic nitrogen is almost entirely mineralize d, mainly into NH4+ ions that are very slowly oxidized to nitrate.