Tuning the stability of TiO2 nanoparticles in various solvents by mixed silane alkoxides.

The surface of TiO(2) nanoparticles which were well dispersed into acidic aqueous solution was successfully modified by silane alkoxides without strong aggregate formations. By adding decyltrimethoxysilane (DTMS) as silane alkoxides into the TiO(2) aqueous solution which were carefully diluted with methanol, DTMS slowly attached onto the TiO(2) surface without rapid hydrolysis and condensation reaction among DTMS. Because of the hydrophobicity of DTMS, the dispersed TiO(2) nanoparticles slowly formed flocks as DTMS reacted on TiO(2). These flocks were able to be completely redispersed into nonpolar solvents even after they were collected by centrifugation and drying under vacuum as dry powder. Furthermore the surface of TiO(2) nanoparticles have been successfully tuned by combining silane alkoxides which contains hydrophobic and hydrophilic groups such as DTMS and 3-aminopropyltrimethoxysilane (APTMS), respectively, toward their complete redispersion into various solvents. While TiO(2) nanoparticles modified by DTMS were redispersible into toluene, those modified by mixed alkoxides of 50 mol % DTMS and 50 mol % APTMS were redispersible into a mixed solution of toluene and methanol. Further when they were modified by mixed alkoxides of 25 mol % DTMS and 75 mol % APTMS, they were redispersible into polar solvents such as methanol with a little addition of acids.