Isocyanate-modified TiO2 visible-light-activated photocatalyst

Visible-activated TiO2 photocatalysts were prepared by surface modification to TiO2 with different isocyanates, including conjugated structured Tolylene-2,4-diisocyanate (TDI) and unconjugated structured m-Xylylene diisocyanate (m-XDI). These two isocyanates could be anchored on the TiO2 surface via π-conjugated chemical bonds of –NHCOOTi, which were formed through the reaction between –NCO groups of isocyanates and the hydroxyl groups of TiO2, and confirmed by FT-IR, XPS and UV–Vis spectra. As a result, donor–acceptor type π-conjugated systems came into being between isocyanate and TiO2. Because the TDI molecules were conjugated themselves, perfect π-conjugated systems were produced in TDI-modified TiO2 samples. Nevertheless, m-XDI-modified TiO2 samples showed poor π-conjugation due to the lack of conjugation of m-XDI. Therefore, TDI-modified TiO2 materials exhibited stronger visible absorption than m-XDI-modified TiO2 in the range from 400 to 600 nm. Methylene blue, as a photodegradation target, was used to evaluate the photocatalytic performance, TDI-modified TiO2 materials exhibited higher photocatalytic activity than m-XDI-modified TiO2 and unmodified TiO2. Moreover, the higher dosage of isocyanate would lead to the better photocatalytic activity.