Role of block copolymer template for tailoring crystal structure and band gap of titania in mesoporous silica and organosilica particles

This work presents the tailoring of distinct titania (titania oxide) (TiO₂) crystal structures inside the mesoporous silica and organosilica using several different block copolymer templates in acidic aqueous solution with different acidity. Different crystal structures of TiO₂ have been obtained as rutile and anatase phases, mainly depending on the chemical composition of block copolymer templates used in this study. A PEO-PLGA-PEO (EO₁₇(L₂₈G₇)EO₁₇, LGE54) triblock copolymer, as well as typical Pluronic P123 (EO₂₀PO₇₀EO₂₀) and F127 (EO₁₀₆PO₇₀EO₁₀₆) triblock copolymers was employed as structure-directing templates for the sol-gel reaction of silane precursors. As silica and organosilica precursors, tetraethyl orthosilicate (TEOS), 1,2-bis(triethoxysilyl)ethane (BTEE), and 1,4-bis(triethoxysilyl)benzene (BTEB) were utilized with a titanium butoxide precursor. The crystal structure of TiO₂ and its corresponding band gap were investigated using X-ray diffraction (XRD) and ultraviolet–visible spectroscopy (UV–vis) measurements, respectively. Anatase crystalline phase of TiO₂ was found in the mesoporous sample prepared with Pluronic copolymer (i.e. P123 and F127) templates. On the other hand, the rutile phase was developed only in mesoporous samples prepared with an LGE54 PEO-PLGA-PEO triblock copolymer template. It was found the TiO₂ crystal structure is varied mainly depending on the polymer template under various strong acidic conditions. It seems that a thermodynamically more stable rutile phase can be formed using a more hydrophobic LGE54 template which supplies stronger micelle core as a platform. Further, it is known that the incorporation of TiO₂ in mesoporous silica and organosilica samples induces the conduction activity, especially toward the blue light region. Thus, this work can be applied to produce effective blue region semiconductor material with different crystallite structures by tuning the precursors and copolymer templates.