Stabilisation of hollow colloidal TiO2 particles by partial coating with evenly distributed lobes

Abstract

Photo-catalytically active crystalline TiO₂ has attracted special attention due to its relevance for renewable energy and is typically obtained by the calcination of amorphous TiO₂. However, stabilising hollow colloidal TiO₂ particles against aggregation during calcination without compromising their photocatalytic activity poses two conflicting demands: to be stable their surface needs to be coated, while efficient photocatalysis requires an exposed TiO₂ surface. Here, this incompatibility is resolved by partially coating TiO₂ shells with evenly distributed 3-trimethoxysilyl propyl methacrylate (TPM) lobes. These lobes act both as steric barriers and surface charge enhancers that efficiently stabilise the TiO₂ shells against aggregation during calcination. The morphology of the TPM lobes and their coverage, and the associated particle stability during the calcination-induced TiO₂ crystallization, can be controlled by the pH and the contact angle between TPM and TiO₂. The crystal structure and the grain size of the coated TiO₂ shells are controlled by varying the calcination temperature, which allows tuning their photocatalytic activity. Finally, the durable photocatalytic activity over many usage cycles of the coated TiO₂ compared to uncoated shells is demonstrated in a simple way by measuring the photo-degradation of a fluorescent dye. Our approach offers a general strategy for stabilising colloidal materials, without compromising access to their active surfaces.