UV-a photocatalytic degradation of the radionuclide complexants tributylphosphate and dibutylphosphate

In this study, we evaluate and compare the photocatalytic degradation and mineralization of two alkylphosphates, tributylphosphate (TBP) and dibutylphosphate (DBP), in the presence of TiO2 and under ultraviolet A radiation. Tri- and dibutylphosphate are used as extractants in nuclear decontamination processes and thus could be found in reprocessing plant waste water. We have investigated the degradation of TBP by gas chromatography-mass spectrometry, the fate of phosphate species by 31P NMR and by ion chromatography, the mineralization kinetics of TBP and DBP by total organic carbon measurements, and finally, the formation of carboxylic acid by high-performance liquid chromatography with ultraviolet detection. Our results show that DBP is an intermediate product of the degradation of TBP by photocatalysis under ultraviolet A radiation and that the same types of carboxylic acids are formed during the degradation of both compounds. We also show that the kinetics of the mineralization process is well described in both cases by the Langmuir-Hinshelwood model, with identical rate constants.