The Piezo-Photocatalytic Performance And Mechanism Of Silver Niobate-Based Ferroelectric Materials

Due to the development of the printing industry and neglect of natural environment protection,the dye wastewater discharged from the printing and dyeing industry is causing great damage to the natural waters.To degrade organic dyes,advanced catalysis technologies using green energy have been developed,such as photocatalysis and piezocatalysis.Although these techniques show their potential in degrading organic dyes,the degradation efficiency of photocatalysis and piezocatalysis is still hindered because of the low charge separation efficiency and rapid recombination of photo-generated carriers.To overcome these problems,researchers proposed piezo-photocatalytic technology by combining photocatalytic technology with piezo-catalytic technology.Piezo-photocatalysis has attracted worldwide attention because it can realize the effective separation and migration of photocarriers by using green energy such as light energy and mechanical energy simultaneously.The core of piezo-photocatalytic technology is the semiconductor material with the piezoelectric effect,however,due to the current research in piezo-photocatalysis is still in its infancy,few ferroelectric materials such as BaTiO₃and KNbO₃have been studied.Although these materials show excellent performance in degrading organic pollutants,the large bandgap（>3.2 e V）limits their ability to use visible light.Therefore,it is necessary to develop a ferroelectric material with a small bandgap for the piezo-photocatalytic field.Silver niobate（AgNbO₃）is lead-free,non-toxic and possesses a moderate band gap（～2.8 e V）,which has the potential to be applied in piezo-photocatalysis.In this study,the ferroelectric properties of AgNbO₃are modified,and its piezo-photocatalytic performance in degrading organic dye rhodamine B（Rh B）was studied.Our work provides a new idea for designing high-performance piezo-photocatalytic materials.The main contents of this study are as follows:（1）The influence of poling process on the piezo-photocatalytic performance of AgNbO₃powder was discussed.It is found that the enhanced poling electric field and poling time could effectively improve the piezo-photocatalytic performance.When the polarization electric field reaches 20 k V/cm and the polarization time reaches 2 h,the piezo-photocatalytic performance of AgNbO₃reaches the maximum,91%Rh B decolorization is achieved within 60 mins,and the reaction constant is calculated to be 0.04 min^-1.After three cycles,the Rh B decolorization performance of poled AgNbO₃decrease only 7%.The analysis of steady-state fluorescence spectra and ferroelectric performance tests indicates that the built-in electric field of AgNbO₃is enhanced by poling process,which can effectively separate photoelectron-hole pairs and migrate them to the surface of the catalyst,therefore the polarized AgNbO₃shows higher Rh B degradation ability in piezo-photocatalysis.（2）AgNbO₃is prepared by hydrothermal method and utilized for piezo-photocatalytic Rh B degradation.Compared with AgNbO₃prepared by the traditional solid-state reaction method,AgNbO₃prepared by hydrothermal method show higher performance of piezo-photocatalytic degradation of Rh B,which accomplishes total decolorization of Rh B within 60 minutes.The reaction constant of AgNbO₃prepared by the hydrothermal reaction method is 0.074 min^-1,which is 2.8 times than that of AgNbO₃prepared by the traditional solid-state reaction method.In the meantime,AgNbO₃prepared by the hydrothermal reaction method also show excellent cycling stability and total decolorization of Rh B within 60 mins after 3 cycles tests.The excellent piezo-photocatalytic performance of AgNbO₃prepared by the hydrothermal method can be ascribed to its higher spontaneous polarization derived from the high crystallinity,exposed high-energy（001）facet,smaller particle size and bandgap value.（3）Based on the ferroelectricity engineering strategy,A series of K⁺doped AgNbO₃are prepared by introducing K⁺ions,which greatly improved the piezoelectric photocatalytic performance.The results show that K⁺doping can stabilize the ferroelectric phase of AgNbO₃and form the Ag/AgNbO₃Schottky heterojunction,achieving a rate constant of 0.131 min^-1in K_0.2Ag_0.8NbO₃（20%KANP）,which is 7.8 times and 4.7 times higher than that of AgNbO₃under illumination-only condition and ultrasonic illumination condition.In the meantime,20%KANP also exhibits good cycling stability and acid-alkali resistance.The results demonstrate that the synergistic effect of ferroelectric and Schottky junction is the key to the excellent piezo-photocatalytic activity.