FTIR study of the photocatalytic degradation of NH4+ determination wastes

Abstract

In this work we present the results of the application of photocatalytic techniques to organic pollutants in water. Such aqueous wastes are produced during the UV–Vis spectrophotometric determination of the NH4+ ion in water. Processes taking place during the photocatalytic degradation of such organics have been studied by using FTIR, HLPC and TOC measurements.

The obtained results suggest that in the presence of light, air and a catalyst (TiO2 or Fe2+) one of the existing organics, nitroprusside is decomposed to CN−, NO2− and NO3−. Free CN− ions react with other intermediates yielding nitrogen-containing compounds such as acetaloximes and acetamides. The photocatalytic degradation of this kind of N-containing compounds seems to be more complicated than the corresponding alcohols and carboxylic groups generated during the individual degradation of phenol, citrate or ethanol.

A remarkable affinity of those nitrogenated species in adsorbing onto the TiO2 surface has been observed. This may be the cause of the reduced catalyst activity observed in the process. It has been also determined that CN− ions tend to react with Fe3+ ions to give complexes like [CN–Fe]2+ and [R–CN–Fe]2+ inhibiting this way the photo-Fenton reaction. In fact, no organic carbon reduction was observed during the application of the photo-Fenton reaction or TiO2 photocatalysis.

Toxicity of the samples was determined before and after the application of the photo-Fenton reaction and TiO2 photocatalysis. Toxicity as determined by using the algal species Phaedactylum tricornutum after the photocatalytic treatment was higher. This suggests the possible above mentioned recombination of chemical species during the degradation of the samples.