A facile interfacial assembling strategy for synthesizing yellow TiO2 flakes with a narrowed bandgap

Abstract

As a promising photocatalyst, the large bandgap (3.2 eV) of anatase TiO₂ seriously limits its light absorption of the UV portion of the solar spectrum, making it less applicable in industrial fields. A popular approach for enhancing visible light activity by narrowing the bandgap is doping, however, the dopant-induced defect states in the TiO₂ lattice may act as recombination centers for the photogenerated charge carriers. Here we report a facile soft-chemical route to engineer the surface properties of TiO₂ crystals using ethanol as the sole organic solvent. The individual TiO₂ nanocrystals synthesized in the first step, possessing high affinity with ethanol molecules, tend to assemble together by interfacial Ti–Ti bonding during the following ethanol evaporation induced self-assembly process. Formation of Ti–Ti bonds at the interface simultaneously brings about the decrease of surface oxygen atoms in the TiO₂ structural unit, which dramatically alters the electronic structure and extends the light absorption to ∼550 nm. Such a dopant-/additive-free TiO₂ assembly exhibits considerable photocatalytic activity under visible light due to its narrower bandgap than individual nanocrystals. Further, an electron paramagnetic resonance measurement is used to confirm the capability of generating reactive ˙OH radicals on the surface of assembled TiO₂ under visible-light irradiation.