Research progress on photocatalytic activity of ferroelectric materials

Abstract

Photocatalytic technology is considered to be the most promising treatment technology of environmental pollution. In this technology, the electronhole pairs generated by the light-responsive materials under sunlight irradiation will produce the oxidation-reduction reactions with the outside world. At present, there are still a series of problems needed to be solved in the photocatalytic technology, among which the recombination of photogenerated electron-hole pairs is a very important limitation. In recent years, the ferroelectric materials have attracted much attention as a new type of photocatalyst because the spontaneous polarizations of ferroelectric materials are expected to solve the recombination problem of electronhole pairs in the catalytic reaction process. However, there are no systematic analyses of the specific mechanisms for ferroelectric materials. In this paper, we review the effects of ferroelectric polarization of ferroelectric materials on photocatalytic activity from three aspects. Firstly, the polarization can give rise to depolarization field and band bending, thereby affecting the separation rate of electron-hole pairs, and speeding up the transmission rate. Therefore, in the first part, the effects of depolarization field and energy band bending on catalytic activity are summarized. This can conduce to understanding the influence of polarization on catalytic activity more clearly from the intrinsic mechanism. Next, the built-in electric field induced by the polarization of ferroelectric material can increase the separation rate of photogenerated carriers and improve the catalytic activity. However, the static built-in electric field easily leads to free carrier saturation due to the electrostatic shielding, which reduces the carrier separation rate. Thus, in order to eliminate the electrostatic shielding, the effects of three external field including temperature, stress (strain) and electric field, which can regulate polarization, on the separation of electronhole pairs and photocatalytic activity are summarized in the second part. Finally, detailed discussion is presented on how to exert effective external fields, such as strain, temperature, and applied electric field, and how to study the force catalysis or temperature catalysis under the no-light condition according to the piezoelectricity effect and pyroelectric effect of ferroelectric material in the last part.