Photocatalytic stability of organic phosphonates and phosphates on TiO2 nanoparticles

The stability of organic phosphonates and phosphates anchored to TiO2 under photocatalytic conditions was studied by illumination of modified particles with UV light. Spectroscopic characterization of the particles after different illumination intervals revealed that the organic moieties were completely degraded, while the Ti–O–P bond was stable, leaving phosphate species on the particles’ surface after illumination. The presence of degradation intermediates after moderate illumination times, identified by 13C CPMAS NMR, indicated a sequential degradation of the organic species. Furthermore, the kinetics of the degradation reactions were studied by means of infrared spectroscopy under different conditions. Phosphate anchoring groups were found to result in faster degradation of organic moieties compared to phosphonate coupling groups. Degradation kinetics were moderately slowed down in the absence of water, indicating a co-existence of hydroxyl radical initiated degradation and direct hole oxidation.

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► The photocatalytic degradation of organophosphonates on TiO2 nanoparticles is studied.
► The organic moieties are degraded while phosphate stays on the particle surface.
► The remaining phosphate enhances the photocatalytic activity of the particles.