Changes in cell parameters and improvement in photocatalytic activity of KNbO3 and NaNbO3 crystals via polarization

A representative ferroelectric tetragonal potassium niobate (TKN) and antiferroelectric orthorhombic sodium niobate (ONN) crystalline powder samples were polarized by using an external electric field. The changes in lattice distortion and crystal symmetry of these samples polarized were revealed. The photocatalytic activities of the samples before and after the polarization were evaluated by photocatalytic decomposition of water and photocatalytic reduction of Ag+. The results imply that the polarization of such kind of perovskite-type niobate samples using the external electric field is one of effective ways to improve the photocatalytic performance, whether ferroelectric TKN or antiferroelectric ONN. The exploration of mechanism suggests that the polarization can change the ferroelectricity of niobate powder crystals. Furthermore, the photocatalytic activity on different exposed facets of these niobate crystals was also evaluated by detecting Ag content on the surfaces of sample via photocatalytic reduction of Ag+. It is found that {001} facet is the highest active facet of TKN, and {101} facet of ONN crystals has the highest photocatalytic activity among the exposed facets. The photocatalytic activity on each exposed facet can be increased to a certain extent by polarization, and the influence of polarization on photocatalytic activity is greater than that of surface energy. (c) 2018 Elsevier Ltd. All rights reserved.