Anatase TiO2 nanosheets with surface acid sites for Friedel–Crafts alkylation

• Synthesis of ultrathin TiO2 nanosheets was optimized to give a high reproducibility.
• The TiO2 nanosheets have an anatase crystal structure with dominant (010) facet.
• The TiO2 nanosheets show an extremely large surface area.
• The surface acidity of TiO2 nanosheets was analyzed by solid state NMR spectroscopy.
• The TiO2 nanosheets exhibit high catalytic performance in Friedel–Crafts alkylation.

The solvothermal synthesis route to mesoporous TiO2 using a vinylphenol polymer structure-directing agent (SDA) was optimized to provide a high yield of bilayer nanosheets. The resultant TiO2 material exhibited a high BET area of 420 m2 g−1 after the removal of SDA. Structural analysis of the nanosheets was carried out using powder X-ray diffraction, high resolution-transmission electron microscopy, Raman spectroscopy and solid-state NMR. The results indicated that the TiO2 material consisted mainly of the bilayer nanosheets with (010) facet-dominant anatase crystal structure. The thickness of the nanosheet was 0.75 nm, corresponding to two unit-cell parameters along the b-axis in the anatase crystal system. More than 10% of the surface Ti atoms were terminated with bridging O–H groups and coordinatively unsaturated Ti atoms, which acted as Brönsted and Lewis acid sites. Accordingly, the anatase nanosheets exhibited catalytic performance in the liquid-phase Friedel–Crafts alkylation of aromatic compounds.

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