Size-selective photocatalytic reactions by titanium(IV) oxide coated with a hollow silica shell in aqueous solutions

A novel core-shell composite photocatalyst, commercially available titanium(IV) oxide (TiO2) particles directly incorporated into a hollow amorphous silica shell, was fabricated by successive coating of TiO2 with a carbon layer and a silica layer followed by heat treatment to remove the carbon layer. The composite induced efficient photocatalytic reactions when relatively small substrates were used, such as methanol dehydration and decomposition of acetic acid, without any reduction in the intrinsic activity of original TiO2, but did not exhibit efficient photocatalytic activity for decomposition of large substrates, methylene blue and polyvinyl alcohol. The uniquesize-selective properties of the composites are due to their structural characteristics, i.e., the presence of a pore system and a void space in the silica shell and between the shell and medial TiO2 particles, respectively. The loading of alkylsilyl groups on the surface of the composite led to highly photostable. oatability: the floated sample also induced efficient photocatalytic reaction for decomposition of acetic acid while retaining floatation at the gas/water interface.