TiO2 doping by hydroxyurea at the nucleation stage: towards a new photocatalyst in the visible spectral range

We report an original method of preparation of OCN-doped TiO 2 for photocatalysis in the visible spectral range. The preparation is achieved by a sol-gel route using titanium tetraisopropoxide precursor. Special attention was paid to fluid micromixing, which enables homogeneous reaction conditions in the reactor bulk and monodispersity of the produced clusters/nanoparticles. The dopant hydroxyurea (HyU, CH 4 N 2 O 2 ) is injected into the reactive fluid at the nucleation stage, which lasts tens of milliseconds. The doping results in a strong yellow coloration of the nanocolloids due to the absorption band in the spectral range 380-550 nm and accelerates the aggregation kinetics of both nuclei at the induction stage and sub-nuclei units (clusters) at the nucleation stage. FTIR, Raman and UV-visible absorption analyses show the formation of a stable HyU-TiO 2 complex. EXAFS spectra indicate no appreciable changes of the first-shell Ti atom environment. The doping agent takes available surface sites of TiO 2 clusters/nanoparticles attaining ∼10% molar loading. The reaction kinetics then accelerates due to a longer collisional lifetime between nanoparticles induced by the formation of a weak &z.dbd;O Ti bond. The OCN-group bonding to titanium atoms produces a weakening of the C&z.dbd;O double bond and a strengthening of the C-N and N-O bonds. OCN-doped TiO 2 is prepared by sol-gel route with turbulent fluid micromixing, which enables homogeneous reaction conditions and monodispersed nanoparticles.