Study On Piezo-photocatalytic Performance Of Niobate Based Ferroelectric Materials

With the development of science and technology,more and more organic compounds are released into the water,such as dyes discharged by printing,textile,leather,food or other industries,resulting in serious environmental pollution and health problems.Photocatalytic degradation of wastewater is one of the important means to solve the problem of environmental pollution.Improving photocatalytic degradation efficiency is a key issue in current technology applications.Piezoelectric effect assisted photocatalysis techniques,namely,piezo-photocatalysis,can greatly improve the performance of individual photocatalysis.Ferroelectric materials have a variety of properties in terms of ferroelectricity,piezoelectricity,pyroelectricity,etc.,which provide a broad prospect for the simultaneous collection of multiple energy sources for catalytic applications.In particular,good photogenic charge separation can be achieved by internal electric field induced by polarization.In this paper,ferroelectric catalysts with high piezo-photocatalytic performance were designed and prepared by introducing oxygen vacancy or other metal ions doping to optimize the surface structure or grain size,and constructing a heterojunction.And the related mechanisms were systematically studied.The research contents and results are as follows:(1)In Chapter 2,the Ag Nb O3 was firstly prepared by the one-step hydrothermal method,and then,the oxygen vacancy was introduced in Ag Nb O3 by nitrogen(N2)annealing.Through a series of characterization,it is confirmed that the phase structure and morphology have no obvious change before and after annealing,and more oxygen vacancy is introduced after annealing.Oxygen vacancy can reduce the band gap of Ag Nb O3,thus improve the visible light absorption and promote the separation of electron-hole pairs under the electric field,and finally enhance the piezo-photocatalytic performance.Furthermore,the theoretical calculation shows that the oxygen vacancy is beneficial to improve the reducing capacity of Ag Nb O3,and thus improve the piezo-photocatalytic degradation performance of organic dye(Rhodamine B).In addition,the piezo-photocatalytic efficiency is significantly higher than the piezoelectric efficiency and photocatalytic efficiency.The deeply investigation of the effect of oxygen vacancy on the piezo-photocatalytic performance can provide a reasonable way to optimize the efficiency of piezo-photocatalysis in the future.(2)In Chapter 3,Bi OCl/NaNb O3 piezoelectric composites were synthesized by a twostep hydrothermal method.Both Bi OCl and NaNb O3 are typical piezoelectric materials with piezoelectric properties.Bi OCl/NaNb O3 composite piezoelectric materials show better piezophotocatalytic performance than Bi OCl and NaNb O3 under UV-vis light irradiation and ultrasonic stimulation,which ascribed to the heterojunction structure.In addition,the piezophotocatalytic degradation efficiency of Rhodamine B by Bi OCl/NaNb O3 is higher than that of piezocatalysis and photocatalysis,indicating that the synergistic effect of piezocatalysis and photocatalysis plays a significant role in the degradation process.This work provides a feasible way for the development of highly efficient heterojunction piezo-photocatalysts.(3)In Chapter 4,the Na1-2x Bax Nb O3(x = 0,0.005,0.010,0.015,0.020)powders were successfully synthesized by simple sol-gel method.With the increase of Ba content,the phase structure of NaNb O3 changes from orthorhombic to orthorhombic-cubic mixed phase,and the morphology changes from sphere to cubic.The coexistence of two phases results in a higher piezoelectric response.The results show that the piezo-photocatalytic degradation efficiency of Na0.97Ba0.015 Nb O3 is better than that of NaNb O3.In addition,the density functional theory(DFT)calculations show that the adsorption energy of the Ba-doped NaNb O3 is more conducive to the adsorption of Rhodamine B,and thus improving the piezophotocatalytic activity.The enhanced piezo-photocatalytic activity of Na0.97Ba0.015 Nb O3 is ascribed to the higher piezoelectric response caused by the coexistence of two phases and optimal oxygen vacancy content.We regulate the phase structure of NaNb O3 by doping,enhance the piezoelectric response,and improve the piezo-photocatalytic performance of NaNb O3,which may have certain reference significance in the optimization of catalyst performance.(4)In Chapter 5,the Ag1-3x Bix Nb O3(x = 0,0.01,0.02,0.03,0.04)was prepared by conventional solid phase reaction method.Bi-doped Ag Nb O3 has better piezo-photocatalytic performance when calcined in air than that of calcined in oxygen,which may be attributed to the more oxygen vacancies.In addition,the experimental results of the piezo-photocatalytic degradation of Rhodamine B show that the Bi-doped Ag Nb O3 exhibits the best piezophotocatalytic activity when calcined in air(Ag0.91Bi0.03 Nb O3-air),which is mainly attributed to the small grain size,good piezoelectric property and large remanent polarization of the material.This work mainly highlights the advantages of donor doping technology in piezophotocatalysis,which can reasonably regulate the grain size and optimize the piezoelectric properties of the material.