Photonic titanium dioxide film obtained from hard template with chiral nematic structure for environmental application

Abstract In the present work, mesoporous TiO 2 with a photonic structure was elaborated using cellulose nanocrystals (CNCs) as a biotemplate by two-step hard template methods. This strategy enables to replicate the chiral nematic (CN) structure of the photonic films (biotemplate) in TiO 2 films. A series of iridescent CNCs films with different weight ratios of silica/CNCs composite photonic films were prepared via evaporation induced self-assembly (EISA) method. The films showed iridescent color and tuneable Bragg reflection wavelengths by solely changing the ratio between the silica and the CNCs biotemplate. Polarized optical microscopy (POM) performed on hydride SiO 2 /CNCs films showed a birefringence and typical fingerprint of chiral nematic structure. This birefringence was also observed for TiO 2 films obtained using SiO 2 films as a hard template, which suggested the transfer of the chiral nematic structure in TiO 2 materials. Afterwards, their optical, morphological and electronic properties were studied by scanning electron microscope (SEM), POM, energy-dispersive X-ray spectroscope (EDX) and time resolved microwave conductivity (TRMC). The photocatalytic activities were evaluated by following the phenol degradation using high performance liquid chromatography (HPLC). The results showed that the structuration of the TiO 2 film using a chiral nematic SiO 2 film as hard template enhances the photocatalytic performance compared to non-structured mesoporous TiO 2 .