Transparent, anatase-free TiO2 nanoparticle dispersions.

Preparation of optically transparent dispersions of TiO2 nanoparticles which are free of the anatase polymorph is a challenging process which has been difficult to control to date. Here, we report and discuss the reproducible formation of such dispersions by hydrolysis of TiCl4. Clouding times of the dispersions and the finally resulting crystal modification of TiO2 was found to depend on a number of synthesis parameters, such as the temperature profile during the reaction, the ratio between the starting substances and the rate of TiCl4 addition. A low pH value and moderate reaction temperatures were required to yield rutile particles, which were established to be formed by transformation of initially amorphous particles just prior to clouding occurred. The latter phenomenon was found to be caused by agglomeration, and not by growth of primary nanosized particles.