Study On The Photocatalytic Properties Of Layered Perovskite Oxides And Their Composites

Photocatalysis is a technology that converts solar energy into chemical energy at room temperature.It is an ideal technology to control environmental pollution and produce clean energy.In recent years,Bismuth-based Aurivillius compounds with layer structures have attracted extensive attention in the field of photocatalysis,whose general formula is expressed as(Bi2O2)2+(An-1BnO3n+1)2-.Their structures can be described as alternating configuration consisting of pseudo-perovskite units and layers along c axis.As for bismuth-layered oxides were choosen as research objects,the reasons are as follows:1.This kind of material has good visible light response.2.As the ferroelectric materials,its ferroelectric spontaneous polarization field can promote the separation of photogenerated carriers.3.By adjusting their structure and properties,synergistic effect can be realized among vaious fields,such as electric field,magnetic field,light field and stress field.Ferroelectric oxide has become a promising photocatalytic material due to its spontaneous polarization,which can effectively inhibits the recombination of photogenerated electrons and holes.Based on the above discussion,we tried to design and prepare highly efficient photocatalyst by introducing ionic groups,controlling the morphology and structure of materials and forming composites.Meanwhile,the recyclability of photocatalyst was necessary in the view of application.The effect of the built-in electric field on the photocatalytic performance and its mechanism were studied.The work are divided into the following parts:Chapter 1:The principle of photocatalysis and the basic characteristics of ferroelectric materials were introduced,and the influence of ferroelectric polarization on photocatalysis is summarized.Besides,the structure and research status of layered perovskite oxides are introduced reviewed.Chapter 2:The chemical reagents required,the methods for sample preparation,and the instruments and eqipments for characterization of samples are introduced.Chapter 3:Six-layered perovskite Bi7Fe3-xNixTi3O21(BFNTO-x)powder were prepared by hydrothermal method.Here Ni doping content x was 0.1,0.4,0.6 and 1.The morphology and structure of the samples were characterized,and their magnetic and photocatalytic properties were measured.It was found that the introduction of Ni not only increased the UV-Vis absorption and BET of the sample,but also improved the photocatalytic performance.In addition,room-temperature weak ferromagnetism was realized after Ni doping.The remnant magnetization of the samples first increase and then decrease with the increase of Ni content.When the doping amount is 0.6,the remnant magnetization 2Mr reaches a maximum of 3.58 emu/g.The magnetism makes it convenient to recycle from the liquid pollutants by using a magnet.Chapter 4:First,Bi4Ti3O12(BiTO)powder with hierarchical nanoflower structure was prepared by hydrothermal method,and its technological conditions were explored.Then,Ag2O/Bi4Ti3O12(A/BiTO)composites with different mass ratios were prepared.The 20%A/BiTO sample showed best photocatalytic efficiency.In order to further explore the influence of ferroelectricity and piezoelectricity on photocatalytic process,we compared the degradation of 20%A/BiTO samples toward RhB for photocatalysis,sonophotocatalysis,and sonocatalysis,and it was found that the efficiency of sonophotocatalysis was the highest.And then,we used the self-made corona polarization device to polarize the sample,and found that the external electric field polarization has a positive effect on both piezoelectric degradation and photodegradation.The influence and mechanism of ferroelectricity and piezoelectricity on photocatalytic process were analyzed.Chapter 5:TiO2/Bi4Ti3O12(T/BiTO)composite material with carbon paper as substrate was prepared.The photocurrent density of the composite material was significantly enhanced,because the ferroelectric built-in electric field of Bi4Ti3O12 promoted the separation of electron-hole pairs.Moreover,the composite materials prepared on the substrate are easy to be recycled without causing secondary pollution,which is the purpose of this chapter.Summary:The research of layered perovskite oxides and their composites is summarized,and the future work was prospected.