Morpholine has been chosen for the study of the TiO₂ photocatalytic degradation of saturated heterocyclic compounds in water because it is found in a number of industrial effluents. Its disappearance rate was observed to be much greater with, than without, TiO₂ in the UV spectral range. Furthermore, comparison with a variety of aromatic pollutants has shown the high photocatalytic degradability of morpholine, despite its low coverage of the TiO₂ surface. Combined GC–MS and HPLC–photodiode-array analyses of the degradation intermediates have shown the formation of hydroxy and oxo derivatives of morpholine and oxidised five-membered ring compounds have shown the formation of hydroxy and oxo derivatives of morpholine and oxidised five-membered ring compounds have been tentatively identified. Intermediates have also been produced by coupling reactions, at least for high initial morpholine concentrations. Two nitrogen-containing aliphatic intermediates (HONHCHCH—O—C₂H₅ and CH₃—NH—CHO) have been found. Finally, low amounts of ethanoate ions and higher amounts of methanoate ions were produced. All the organic intermediates that were formed in amounts sufficient to be monitored were eventually found to be destroyed. Organic nitrogen was initially transformed into ammonium ions.