Piezoelectric built-in electric field advancing TiO2 for highly efficient photocatalytic air purification.

Photocatalytic air purification is a promising technology; however, it suffers from a limited rate of photocatalytic mineralization (easily inactivated surfactant sites of hydroxyls) and poor kinetics of degradation. Herein, we report a ferroelectric strategy, employing a polyvinylidene fluoride (PVDF) layer embedded with TiO2, where the polarization field of stretched PVDF dramatically enhances and stabilizes active adsorption sites for the promotion of charge separation. The F (-) and H (+) atomic layers with distinct local structures in stretched PVDF increase the electron cloud density around Ti which simultaneously promotes the dissociation of water to form hydroxyl groups which are easier to activate for adsorption of formaldehyde molecules. Besides, the ferroelectric field of stretched PVDF effectively separates the photogenerated charge carriers and facilitates the carriers' transportation of TiO2/PVDF. The optimal stretched TiO2/PVDF exhibits excellent photocatalytic mineralization for formaldehyde with considerable stability. This work may evolve the polarization field as a new method to enhance adsorption and activation of hydroxyls and disclose the mechanism by which hydroxyl radicals mineralize gaseous formaldehyde for photocatalytic air purification.