Preparation And Photocatalytic Properties Of Bi₄Ti₃O₁₂-based Composite Nanomaterials

Due to the rapid development of global industrialization,people’s social activities not only bring scientific and technological progress,but also cause serious pollution to the ecological environment.Photocatalysis,which uses renewable solar energy to degrade pollutants,is a promising green and effective environmental treatment technology.A urivillius first discovered a layered perovskite oxide with the general structural formula（Bi₂O₂）²⁺(A_n-1B_nO_3n+1^2-,and ferroelectric materials with such a structure have attracted much attention in the field of photocatalysis.In this paper,we selected the three-layered layered perovskite material Bi₄Ti₃O₁₂ as the research object.As a ferroelectric material,the built-in electric field of Bi₄Ti₃O₁₂ can promote the separation of photogenerated carriers,reduce the recombination rate,and improve the photocatalytic efficiency.However,Bi₄Ti₃O₁₂ has a relatively wide band gap and cannot fully utilize solar energy,which limits its application in the field of photocatalysis.In order to solve this problem,we regulate the morphology of Bi₄Ti₃O₁₂（BTO）and then composited with narrow-bandgap semiconductors or noble metal particles in this thesis.The photocatalytic performances of the samples toward degrading various pollutants were carried out.The main contents are as follows:Chapter 1:Firstly,we summarized the research background,principle and development of photocatalytic technology,then introduced the basic characteristics of ferroelectric materials and their photocatalytic properties.Secondly,the structure of layered perovskite compounds and their photocatalytic research status are briefly described.Finally,the selected topic and research content of this paper are summarized.Chapter 2:The preparation methods used in the experiments and the required chemical reagents,as well as instruments were introduced.In addition,the structural characterization methods and the testing methods of photoelectrical properties are also summarized.Chapter 3:Firstly,BTO nanopowders were prepared by the hydrothermal method.W e adjusted the concentration of mineralizer NaOH to optimize the photocatalytic property of BTO.The experimental results showed that the optimal preparation conditions of BTO samples with nano flower-like structures were as follow:the concentration of NaOH is 5M,and the heat treatment temperature is at 200℃ for 36 h.On this basis,CdS/Bi₄Ti₃O₁₂（CdS/BTO） composites with different mass ratios were prepared by chemical bath deposition method.The results showed that with the increase of CdS content,the photocatalytic performance improves,and the sample with a CdS content of 5%had the highest photocatalytic efficiency.We compared the degradation performance of 5wt%CdS/BTO samples under sole visible light,sole ultrasound,and both ultrasound and light to study the effect of the ferroelectric and piezoelectric properties on the photocatalytic process.It was found that the photodegradation efficiency of the synergistic piezoelectric effect was the highest.Chapter 4:Aunanoparticles were deposited on BTO nanosheets by chemical bath deposition method,forming Au Bi₄Ti₃O₁₂（Au/BTO）composites.The crystal structure and morphological characteristics of the samples were analyzed and observed,and the LSPR effect of Au nanoparticles on the photocatalytic performance was investigated by photocatalytic degradation of RhB and tetracycline.In this paper,the free radical trapping experiment also proved that the active groups involved in the reaction are superoxide radical（·O2-）,hole（h+）and hydroxyl radical（·OH）,and the ·O2-and h+active species plays a leading role.Summary and prospect:In this paper,the photocatalytic properties of Bi₄Ti₃O₁₂ composite nanomaterials have been investigated.And the future work was discussed and prospected.