Fabrication and photoactivity of a tunable-void SiO2–TiO2 core–shell structure on modified SiO2 nanospheres by grafting an amphiphilic diblock copolymer using ARGET ATRP

Abstract

SiO₂-based composites have important applications in various technological fields. In this work, a tunable-void SiO₂–TiO₂ core–shell structure was successfully prepared for the first time using SiO₂–polymethyl methacrylate (PMMA)–polyoligo(ethylene glycol)methyl ether methacrylate (PO(EO)_nMA) (n = 2, 5, and 8). An amphiphilic copolymer was used as the template, and calcination was performed using tetrabutyl titanate (TBT) as the titanium source. SiO₂–PMMA-b-PO(EO)_nMA microspheres were first synthesized through activators regenerated by electron transfer-atom transfer radical polymerization. Methyl methacrylate and O(EO)_nMA were grafted with different EO unit numbers onto the surface of the halogen functional group of SiO₂. TBT was hydrolyzed along with the PO(EO)_nMA chain through hydrogen bonding, and then the SiO₂–TiO₂ core–shell structure was acquired through calcination to remove the polymer. Simultaneously, amorphous TiO₂ crystallized during calcination. A series of characterizations indicated that the amphiphilic block copolymer was grafted onto SiO₂ mesoparticle surfaces, the titania samples existed only in the anatase phase, and the prepared SiO₂–TiO₂ had hierarchically nanoporous structures. The gradient hydrophilicity of the PMMA-b-PO(EO)_nMA copolymer template facilitated the hydrolysis of TBT molecules along the PO(EO)_nMA to PMMA segments, thereby tuning the space between the core and the shell. In addition, the space was about 6 nm when the EO number was 2, and the space was about 10 nm when the EO numbers were 5 and 8. The photocatalytic activities of the SiO₂–TiO₂ materials were tested on the photodegradation of methyl orange.