Molecular selective photocatalytic decomposition of alkylanilines by crystalline TiO2 particles and their nanocomposites with mesoporous silica

Abstract

Molecular selective photocatalytic decomposition of alkylanilines in water was investigated by using crystalline TiO₂ particles (P-25) and their nanocomposites with mesoporous silica. In the nanocomposites, pre-formed TiO₂ particles were embedded into surfactant-templated mesoporous silica with tuned pore sizes (1.4–5.3 nm) as described in our previous reports (Chem. Commun. 2005, 2131–2133; J. Mater. Chem. 2011, 21, 12117–12125). Contrary to the generally accepted knowledge of TiO₂ photocatalysts, pristine TiO₂ particles showed molecule selective photocatalysis: decomposition of 4-n-heptylaniline (NHA) was much faster than that of 4-n-butylaniline (NBA) or p-toluidine (4-methylaniline, PT) in a mixed aqueous solution. After NHA had almost disappeared, decomposition of NBA accelerated. When the TiO₂ particles were surrounded by mesoporous silica, the molecular selectivity was strongly modified: the nanocomposites showed high molecular selectivity for NBA decomposition and the reaction of PT was considerably suppressed. The origin of molecular selectivity can basically be ascribed to preferential molecular adsorption, and the difference in selectivity between alkylanilines and alkylphenols is discussed in terms of the interaction of the molecules with the nanocomposite surfaces.