Synthesis of highly hydrophobic rutile titania-silica nanocomposites by an improved hydrolysis co-precipitation method

Highly hydrophobic rutile titania-silica nanocomposites were synthesized by an improved hydrolysis co-precipitation method using low-cost sodium metasilicate and titanium oxysulfate (TiOSO 4 ) as precursors, followed sequentially by calcination at 800   °C and modification with trimethylchlorosilane (TMCS). It was found that the resulting TiO 2 -SiO 2 nanocomposites had a Ti/Si molar ratio of 5:1 and exhibited single-phase rutile with a specific surface area of 269   m 2   g −1 . The addition of acetylacetone (AcAc) during the hydrolysis co-precipitation process played a key role in the growth of well-ordered TiO 2 -SiO 2 crystallites since the hydrolysis rate of TiOSO 4 might be retarded due to the complexation of AcAc to the Ti atoms in TiOSO 4 . The TMCS-modified TiO 2 -SiO 2 nanocomposites exhibited a high root-mean-square (RMS) roughness of 22   nm and good hydrophobicity with a static contact angle of 143.7°, highlighting its potential application as a filler in exterior wall coatings.