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 tunablevoid 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.