DEPOSITION OF COMPACT HYDROUS ALUMINUM SULFATE THIN-FILMS ON TITANIA PARTICLES COATED WITH ORGANIC SELF-ASSEMBLED MONOLAYERS

An organic self-assembled monolayer (SAM) was deposited on submicron-s ized pigment-grade TiO2 particles to create a highly hydrophilic surfa ce comprised of sulfonate groups. Hydrous aluminum-containing thin fil ms were uniformly deposited on the powder from aqueous solutions at 60 -80 degrees C. The as-deposited films were in the form of boehmite (Al O(OH)) or hydrous Al sulfate, depending on the Al salts used in the st arting solution. AlCl3 solutions gave rise to porous films of needleli ke crystalline boehmite, whereas mixed Al-2(SO4)(3)/Al(NO3)(3) solutio ns led to compact, uniform, adherent, dense amorphous sulfate-containi ng films up to similar to 5 nm thick. The sulfate anion in solution is thought to promote nucleation and growth of a solid phase through its relatively strong electrostatic field. However, the sulfate anion is weakly bound, and the sulfate films can be partly leached of sulfur in neutral or weakly basic solutions at room temperature without sacrifi cing their compact nature.