Preparation And Piezo-photocatalytic Performance Of Tetragonal BaTiO₃ Nano-powder

As we all know,increasingly severe energy crisis and environmental problems need to be solved urgently.Finding abundant,renewable,and recyclable green clean energy has become an urgent task in the current industrial development.Semiconductor photocatalysis is an environmentally friendly pollutant treatment technology that uses solar energy for energy conversion and effectively removes organic pollutants in waste water and waste gas.It is highly efficient,environmentally friendly and harmless.In recent years,piezoelectric materials have attracted much attention because of their spontaneously polarized internal electric field,which can promote the separation of photogenerated electron-hole pairs,and exhibit excellent capabilities and effects in environmental protection applications.In this thesis,we pay close attention on the high-efficiency and low-consumption synthesis method of piezoelectric material BaTiO₃.At the mean while,Pt/BaTiO₃ heterojunction and Ag₂O/BaTiO₃ heterojunction were prepared by metal doping and hybrid modification methods,which significantly improved the catalytic activity of the catalyst.The main research results are as follows:（1）Prepare tetragonal BaTiO₃ nano-powder by low-temperature hydrothermal method.At the same time,a single variable is controlled to explore the influence of multiple factors such as temperature,time,raw material type,barium-titanium ratio and heat treatment on the microscopic morphology and crystal phase composition of BaTiO₃.The optimal reaction conditions are comprehensively determined as follows:Ba（OH）₂·H₂O and（C₄H₉O）₄Ti are used as barium source and titanium source,respectively,the ratio of barium to titanium is fixed at Ba/Ti=1.5,and ammonia is used as the mineralizer and ethanol is the solvent.The final mixed sample was hydrothermally heated at 200°C for 24 h.This synthesis path has many advantages,such as low cost,mild temperature,high efficiency and low consumption,energy saving and environmental protection.The prepared BaTiO₃ nanoparticles not only have high crystallinity and purity,but also have a smooth and regular morphology,narrow and uniform particle size distribution（average particle size of about 96 nm）,good dispersion performance,and more importantly,a high c/a radio（c/a=1.0073）.It meets the production requirements of multilayer ceramic capacitors and is expected to be more widely used in the high-precision electronics industry.（2）Common metal element deposition methods are used to modify the surface of BaTiO₃nanocrystals,and Pt nanoparticles are uniformly loaded on the surface of BaTiO₃ by photochemical reduction to construct a Pt/BaTiO₃ heterojunction.Compared with pure BaTiO₃,the light absorption cross section of Pt/BaTiO₃ heterojunction catalyst is increased,and the degradation efficiency of organic dye MO can be significantly improved under the full spectrum.The research results show that the content of Pt,the piezoelectric internal electric field of BaTiO₃ and the local surface plasmon resonance（LSPR）effect of Pt are crucial to the photocatalytic activity of Pt/BaTiO₃.However,under the synergistic effect of full-spectrum irradiation and ultrasonic vibration,the Pt/BaTiO₃ heterojunction shows the best catalytic performance when the Pt loading is 0.25 wt%,which can degrade up to 92.49%of MO within50 min.The generation of piezoelectric internal electric field in BaTiO₃ nanocrystals by ultrasonic treatment is the key to promoting photo-generated carrier migration and inhibiting photo-generated carrier recombination,which ultimately leads to a greater improvement in the catalytic performance of the Pt/BaTiO₃ heterojunction catalyst.（3）Building Ag₂O/BaTiO₃ heterostructure through simple chemical deposition reaction.Compared with pure BaTiO₃,the Ag₂O/BaTiO₃ heterojunction can significantly improve the degradation efficiency of MO under the three different conditions of visible light,dark field ultrasound,and the synergy of visible light and ultrasound.Among them,the 1.5-Ag₂O/BaTiO₃sample exhibits the strongest photocatalytic activity.Under the synergistic effect of visible light and ultrasonic vibration,it can make the degradation rate of MO reach 80.17%within 30minutes.Ag₂O nanoparticles respond to visible light and can generate photo-generated electron-hole pairs under light.During ultrasonic oscillation,the internal electric field generated by the piezoelectric effect in the BaTiO₃ nanocrystals is driven by the ultrasonic and changes alternately.After constructing the heterojunction,Ag₂O nanoparticles are tightly adsorbed on the smooth surface of BaTiO₃,which enlarges the response area of the catalyst to visible light and increases the active sites for photo-generated carrier reactions.Under the synergistic effect of visible light irradiation and ultrasonic excitation,the piezoelectric internal electric field derived from BaTiO₃ in the Ag₂O/BaTiO₃ heterojunction can promote the separation of the photo-induced charges inside the Ag₂O nanoparticles,so that they can fully participate in the redox reaction.Thereby significantly improving the photocatalytic performance of the heterojunction catalyst.