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

Anatase/silica core/shell particles were prepared bythe hydrolysisand condensation of tetraethyl orthosilicate on anatase particleswith the sizes of 9, 22, and 111 nm, respectively. The thickness ofthe silica layer was designed from ca. 3 to 14 nm by repeating thecoating procedure on anatase with a particle size of 22 nm. By theheat treatment at 1000 & DEG;C, though the pristine anatase particlestransformed to rutile, anatase remained for the silica-coated particles.Anatase particles (111 nm) transformed to rutile upon heating at 1100 & DEG;C, while the transformation was not observed for the smallerparticles (9 and 22 nm). With the increase of the silica thicknessto 14 nm, anatase did not transform to rutile even after heating at1150 & DEG;C, while resulting in varied compositions of anatase andrutile after heating at 1200 & DEG;C. The crystal growth of anataseand rutile was also suppressed for the silica-coated particles comparedwith that seen for pristine anatase. Thus, the thermal transformationand crystal growth of titania were controlled by the coating withsilica, and the effects were shown to affect the coating. The anatase to rutile-phase transformationwas shifted toa higher temperature and the crystal growth of the obtained rutilewas suppressed effectively in the anatase/silica core/shell hybrid.Silica shell was dissolved from the heated products to obtain size-controlledanatase and rutile particles with desired catalytic and absorptionproperties.

Automated summary

Anatase/silica core/shell particles were prepared with varying sizes (9, 22, and 111 nm) by coating tetraethyl orthosilicate on anatase particles. The thickness of the silica layer was controlled by repeating the coating procedure. The presence of silica coating inhibited the transformation of anatase to rutile and suppressed crystal growth of titania. The heated products could be dissolved to obtain size-controlled anatase and rutile particles.