Controlling TiO2 photocatalytic behaviour via perhydropolysilazane-derived SiO2 ultrathin shell

Abstract

This study addresses the inherent photocatalytic activity of pure titanium dioxide (TiO2), which limits its application as an industrial pigment. To mitigate this issue, a core-shell structure was employed, where TiO2 cores were encapsulated within SiO2 shells. Perhydropolysilazane (PHPS) was introduced as a superior SiO2 precursor over tetraethylorthosilicate (TEOS), resulting in thinner and more uniform SiO2 shells. Utilizing TiO2's photocatalytic properties, hydroxyl radicals facilitated the conversion of PHPS into SiO2via native Si-H bonds, eliminating the need for additional reducing agents. The formation of PHPS-derived TiO2@SiO2 core-shell nanoparticles demonstrated inherent self-limiting behaviour, ensuring uniform shell thickness regardless of PHPS concentration, simplifying the process for large-scale industrial applications compared to TEOS, which demands precise parameter control. Photocatalytic evaluations highlighted significant passivation of TiO2 photocatalytic activity by PHPS-derived TiO2@SiO2 core-shell particles and TiO2/SiO2 thin films. Specifically, TiO2@PHPS nanoparticles achieved 89-96% passivation compared to 30% with TiO2@TEOS, while TiO2/PHPS films degraded only 12% of Eosin B versus 80% with TiO2 films. Moreover, both PHPS-derived nanoparticles and films maintained TiO2's inherent high whiteness and high-refractive-index optical properties, underscoring their suitability for applications in white paint production, cosmetics, and high-refractive-index coatings.