Suppressing the Photocatalytic Activity of Titania by Precisely Controlled Silica Coating

Controlled Phase Transformation and Crystal Growth of Titanium Dioxide from Anatase/Silica Core/Shell Particles

Anatase/silica core/shell particles were prepared by the hydrolysis and condensation of tetraethyl orthosilicate on anatase particles with the sizes of 9, 22, and 111 nm, respectively. The thickness of the silica layer was designed from ca. 3 to 14 nm by repeating the coating procedure on anatase with a particle size of 22 nm. By the heat treatment at 1000 °C, though the pristine anatase particles transformed to rutile, anatase remained for the silica-coated particles. Anatase particles (111 nm) transformed to rutile upon heating at 1100 °C, while the transformation was not observed for the smaller particles (9 and 22 nm). With the increase of the silica thickness to 14 nm, anatase did not transform to rutile even after heating at 1150 °C, while resulting in varied compositions of anatase and rutile after heating at 1200 °C. The crystal growth of anatase and rutile was also suppressed for the silica-coated particles compared with that seen for pristine anatase. Thus, the thermal transformation and crystal growth of titania were controlled by the coating with silica, and the effects were shown to affect the coating.

A six-fold difference in structure results in a six-order difference in conductivity: silica shell nanoarchitectonics on carbon black particles

Carbon black (Ketchen Black with a particle size of several tens of nm) was coated with silica with a varied thickness of 2 and 12 nm. Carbon/silica core-shell particles were grafted with the γ-methacryloxypropylsilyl group to be homogeneously dispersed into a poly(methyl methacrylate) film. The electrical conductivity of the poly(methyl methacrylate) films containing carbon/silica particles was successfully controlled by the thickness of the silica layer; silica coating with 2 nm thickness gave a conducting film, while that with 12 nm thickness gave a less conducting film with a remarkable difference on the order of 10⁶ (in volume conductivity).