Dispersion stability of TiO 2 nanoparticles covered with SiO x monolayers in water

Abstract

The repetition of a two-step route consisting of chemisorption of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) and its subsequent photooxidation has formed SiO x monolayers on the surfaces of TiO 2 particles layer by layer (SiO x ( n ⩽ 4 )/TiO 2, n = repeated number ). The trace of these processes using diffuse reflectance FT-IR and solid-state 29Si NMR spectroscopy reveals that TMCTS is chemisorbed on TiO 2 through Ti–O–Si bonds followed by growth of Si–O–Si networks via dehydration–condensation of the Si–OH groups generated by TiO 2 photocatalytic oxidation of the Si–H and Si–CH 3 groups. The point of zero charge of the TiO 2 particles decreases from 6.5 to 5.4 at n = 1 , reaching 4.9 at n ⩾ 2 . As a result of coverage with the SiO x monolayers, the dispersion stability of TiO 2 particles in neutral water is significantly improved without changing their optical properties. The dispersion stability further increases with accumulation of SiO x monolayers.