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

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)(n)MA) (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)(n)MA microspheres were first synthesized through activators regenerated by electron transfer-atom transfer radical polymerization. Methyl methacrylate and O(EO)(n)MA 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)(n)MA 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)(n)MA copolymer template facilitated the hydrolysis of TBT molecules along the PO(EO)(n)MA 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.