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.