Coupled Exfoliation and Surface Functionalization of Titanate Monolayer for Bandgap Engineering

Exfoliation of layered compounds generates nanosheets, such as monolayers and few‐layers. In general, it is not easy to control surface chemistry of the exfoliated nanosheets. Here, a new approach for surface functionalization of titanate monolayer coupled with exfoliation is reported. The precursor layered composite is prepared by intercalation of long‐chain alkyl‐ammonium ion, such as stearylammonium ion (C₁₈NH₃⁺), in the interlayer space of layered titanate. The layered composite of titanate and C₁₈NH₃⁺ (C₁₈TiO₂) is dispersed in the toluene solution containing dihydroxynaphthalene (DHN) for the coupled exfoliation and surface modification. The surface molecule is partially exchanged from the original C₁₈NH₃⁺ to the guest DHN. The resultant hydrophobic titanate monolayer with surface modification by the C₁₈NH₃⁺ and DHN (DHN/C₁₈TiO₂) shows the visible‐light absorption based on the charge‐transfer excitation from the highest occupied molecular orbital of the adsorbed DHN to the conduction band of the titanate. The present synthetic approach can be applied to synthesis of a variety of surface‐functionalized monolayers and their bandgap engineering.