Self-Induced and Progressive Photo-Oxidation of Organophosphonic Acid Grafted Titanium Dioxide

While synthesis-properties-performance correlations are being studied for organophosphonic acid grafted TiO2, their stability and the impact of the exposure conditions on possible changes in the interfacial surface chemistry remain unexplored. Here, the impact of different ageing conditions on the evolution of the surface properties of propyl- and 3-aminopropylphosphonic acid grafted mesoporous TiO2 over a period of 2 years is reported, using solid-state P-31 and C-13 NMR, ToF-SIMS and EPR as main techniques. In humid conditions under ambient light exposure, PA grafted TiO2 surfaces initiate and facilitate photo-induced oxidative reactions, resulting in the formation of phosphate species and degradation of the grafted organic group with a loss of carbon content ranging from 40 to 60 wt %. By revealing its mechanism, solutions were provided to prevent degradation. This work provides valuable insights for the broad community in choosing optimal exposure/storage conditions that extend the lifetime and improve the materials ' performance, positively impacting sustainability.

Automated summary

This study reports on the impact of different ageing conditions on the surface properties of organophosphonic acid grafted mesoporous TiO2. It reveals that under humid conditions with ambient light exposure, the surfaces initiate photo-induced oxidative reactions, resulting in the formation of phosphate species and degradation of the grafted organic group. By understanding the mechanism, solutions to prevent degradation were provided. This work provides valuable insights for the community in choosing optimal exposure/storage conditions to improve material performance and prolong lifetime, positively impacting sustainability.