Catalytic Effects Of BaTiO₃-based Ferroelectric Materials And Fundamental Research On Their Applications

The piezo-catalysis and pyro-catalysis exhibited by ferroelectric materials have attracted considerable attention as a novel catalytic processes,and great progress has been made in the research of pollutant degradation,hydrogen preparation,tumor therapy and other fields.However,it is difficult to find the physical field that can stimulate the ferro-catalytic effect in natural environment.In addition,the lack of research on the reaction process in ferro-catalytic effect leads to the inability for improvement of catalytic performance in essence.These lead to the ferro-catalytic effect being extremely limited in practical applications.Tooth whitening based on piezo-catalysis and pyro-catalysis was realized by the collaboration of ferro-catalysis and stomatology in this dissertation.A novel magnetoelectric effect of magneto-thermal-pyroelectric mediated by heat was discovered,and pyro-catalysis driven by magnetic field was achieved.The reaction process in ferro-catalytic effect was explored,and the formation process of radicals was elucidated.The details of the research and the main results are as follows.（1）Study on piezo-catalysis effect and its application for non-destructive tooth whitening.In response to the challenge that mechanical vibrations that excite the piezo-catalytic effect are difficult to obtain,the application of tooth whitening based on piezo-catalytic effect was investigated using the vibration of tooth brushing.Ba Ti O₃nanoparticles of tetragonal phase were synthesized using a hydrothermal method,and were able to achieve a degradation rate over 92.7%within 35 min when Indigo Carmine was used as the target pollutant.Moreover,a complete whitening of stained tooth was achieved within 10 h,and the change in chroma of tooth enamel was close to 60 without damage to both morphology and function of the tooth.This study has successfully achieved a safe,efficient and non-destructive tooth whitening method based on piezo-catalytic effect,which has extended the application scenario of piezo-catalysis.（2）Study on the pyro-catalysis effect and its application in stomatology.In response to the demanding requirements of pyro-catalysis on temperature variation,a study on pyro-catalysis in stomatology was carried out using the temperature change induced by oral activities.Ba Ti O₃ nanowires with excellent pyro-catalytic properties were synthesized using a hydrothermal method,and over 95%of the Indigo Carmine solution can be degraded after 3 thermal cycles with a temperature difference of+20℃.Furthermore,a tooth whitening brace was prepared by compounding Ba Ti O₃ nanowires with hydrogel,which can achive a remarkable tooth whitening effect after 2000 thermal cycles.In addition,the pyro-catalytic effect can also eliminate bacterias in oral cavity.After 20 thermal cycles（20℃-45℃）,more than 64%streptococcus mutans can be eliminated,which can effectively prevent dental caries.This study realized a basic application of pyro-catalysis in stomatology by using the temperature changes caused by oral activities,and a suitable scenario for the practical application of pyro-catalysis effect has been found.（3）Study of pyro-catalysis based on magnetic-thermal-pyroelectric multi-physical fields coupling effects.In response to the challenge that the physical excitation required for the pyro-catalytic effect is difficult to obtain,the pyro-catalytic effect based on the coupling of magnetic-thermal-pyroelectric multi-physical fields was investigated.The magnetothermal-pyroelectric core-shell structure was constructed by combining magnetothermal and pyroelectric materials in both microscopic and macroscopic scales,utilising the coupled magneto-thermal-electric physical field to realise the pyro-catalytic effect with magnetic field as the source and heat as the medium.In the microscopic scale,Ba_0.7Sr_0.3TiO₃@La_0.7Sr_0.3MnO₃was able to degrade15%RhB solution after 10 magnetothermal cycles（26℃-66℃）;in the macroscopic scale,the composite structure prepared by using BaTiO₃ nanowire hydrogel encapsulated with Fe₃O₄ further enhanced the catalytic performance,and after 6magnetothermal cycles,the degradation rates of 4-CP,BP and BPA by the composite structures were 83.6%,69.3%and 62.6%,respectively.In this study,an innovative attempt to combine the magneto-thermal effect with the pyroelectric effect broadens the approach to excitation physical field realisation for pyro-catalysis.（4）Study on the processes of radical generation during piezo-catalysis.In response to the controversy of physicochemical processes in ferro-catalysis.The piezo-catalytic effect was used as an example to investigate the physicochemical processes involved.The dominant role of·OH during piezo-catalysis was clarified by adding radical trapping agents to reaction system,and the presence of H₂O₂ was confirmed.When p H≤7,H₂O₂ was generated from the conversion of·O₂^-,and when p H>7,excess·OH will combine with each other to generate H2O2,thus the pathway of H2O2generation under different reaction conditions was elucidated.The conversion of·O₂^-to·OH with H₂O₂ as an intermediate product during piezo-catalysis was also found.When pH≤7,·OH mainly comes from the conversion of ·O2^-,while pH>7,·OH was generated by the direct reaction of free charge with OH^-,thus the formation process of OH under different reaction environments was elucidated.Finally,the H₂O₂ generated during piezo-catalysis was utilised through the construction of a Piezo-Fenton system to enhance the piezoelectric catalysis performance.This study investigated the physicochemical processes during piezo-catalysis and revealed the pathway of radical generation,which has instructive implications for the practical application of piezo-catalysis.In summary,this dissertation provides an exhaustive study on the application of the ferro-catalytic effect as well as its physicochemical processes.The piezo-catalytic effect and pyro-catalytic effect based tooth whitening has been achieved by using the vibrational and temperature changes during oral activity,the combination of ferro-catalysis with stomatology expanded its application.The application scenario of the pyro-catalytic effect was further expanded by means of magneto-thermal-electric multi-physical field coupling,enabling its application under magnetic field excitation and lifting the environmental limitation of the pyro-catalytic effect.In addition,this dissertation clarified the physicochemical processes of ferro-catalysis in different reaction environments and promoted the development of ferro-catalysis.It is hoped that the work associated with this dissertation will contribute to the study of ferro-catalytic effect.