TiO ₂ Films with Macroscopic Chiral Nematic‐Like Structure Stabilized by Copper Promoting Light‐Harvesting Capability for Hydrogen Generation

Abstract Cellulose nanocrystals (CNCs) have inspired the synthesis of various advanced nanomaterials, opening opportunities for different applications. However, a simple and robust approach for transferring the long‐range chiral nematic nanostructures into TiO ₂ photocatalyst is still fancy. Herein, a successful fabrication of freestanding TiO ₂ films maintaining their macroscopic chiral nematic structures after removing the CNCs biotemplate is reported. It is demonstrated that including copper acetate in the sol avoids the epitaxial growth of the lamellar‐like structure of TiO ₂ and stabilizes the chiral nematic structure instead. The experimental results and optical simulation demonstrate an enhancement at the blue and red edges of the Fabry‐Pérot reflectance peak located in the visible range. This enhancement arises from the light scattering effect induced by the formation of the chiral nematic structure. The nanostructured films showed 5.3 times higher performance in the photocatalytic hydrogen generation, compared to lamellar TiO ₂ , and benefited from the presence of copper species for charge carriers’ separation. This work is therefore anticipated to provide a simple approach for the design of chiral nematic photocatalysts and also offers insights into the electron transfer mechanisms on TiO ₂ /Cu _x O with variable oxidation states for photocatalytic hydrogen generation.