Photocatalysis Of BaTiO₃-TiO₂ Composites And There Applications In The Treatment Of Petroleum Wastewater

With the rapid development of the petroleum industry,the discharge of petroleum wastewater gradually increases,which is seriously harmful to the ecological environment and human health.Traditional treatment methods,such as physical,biological,and chemical methods,have problems of low efficiency,high cost,and difficulty in recycling.Photocatalytic technologys can be used in applications of degradation of pollutants,production of hydrogen and reduction of carbon dioxide by utilizing semiconductor photocatalysts to convert solar energy into chemical energy.Photocatalyst is the key of photocatalytic technology.Under light irradiation,semiconductor photocatalysts absorb photon energy to produce photogenerated carriers,and they migrate to the surface to participate in redox reaction.TiO2 is the most widely used semiconductor photocatalyst with high catalytic activity,low cost,and no toxicity.However,the photogenerated electron-hole pairs in TiO₂ are easily to recombine,which reduces the photocatalytic performance.Modification of TiO2 by semiconductor compostion,metal deposition and ion doping can effectively promote the separation of photogenerated carriers and thus improve the photocatalytic activity.Ferroelectric materials have attracted much attention because of the built-in electric field due to their unique spontaneous polarization.Therefore,we choose BaTiO3 with good ferroelectricity and TiO2 with high photocatalytic ability to form a composite,in which ferroelectric polarization-induced built-in electric field is introduced to promote the separation of photogenerated carriers and improve the photocatalytic efficiency.Different types of BaTiO3-TiO2 nanocomposites were prepared,and their structures,properties and photocatalytic degradation performance were characterized.The mechanism of ferroelectric polarization-induced built-in electric field and pyroelectric effect on photogenerated carrier separation was analyzed.The thesis mainly includes the following aspects:?1?BaTiO3-TiO2 mechanical mixtures were prepared by an ultrasonic dispersion method.The effects of mass ratio and temperature on photocatalytic performance were investigated.The results show that the best photocatalytic effect can be reached at the mass ratio of BaTiO₃ to TiO₂ of 1:1.5and at the temperature of 90°C.?2?BaTiO3-TiO2 nanocomposites were synthesized via a sol-gel method.The effects of mass ratio on the photocatalytic performance were investigated.The crystalline structure and morphology of BaTiO3-TiO2 nanocomposites were characterized using X-ray diffractometer?XRD?and transmission electron microscopy?TEM?.The ferroelectricity of BaTiO3 within the nanocomposites were confirmed by piezoresponse force microscopy?PFM?.The results show that the photocatalytic effect reached the best when the mass ratio of BaTiO₃ to TiO₂ is 1:1.5.?3?Core-shell BaTiO₃@TiO₂ nanocomposites were synthesized via a hydrothermal process.The effects of processing parameters?content of TIP and NH₃·H₂O,stirring rate?,mass ratio and temperature field?temperature change?T and change rate?on the photocatalytic properties were studied.The crystalline structure and morphology of the nanocomposites were characterized using XRD and TEM.Ferroelectricity of BaTiO₃ in the nanocomposites were confirmed by PFM.The results show that the core-shell structure has a relatively complete coating when the mass ratio of BaTiO₃ to TiO₂ is 1.2:1 with 0.16 mL TIP and 0.1 mL NH₃·H₂O at the stirring speed of 200 rpm.TiO₂ with a large specific surface area can provide rich surface active sites for photocatalytic reaction.At the same time,the built-in electric field induced by spontaneous polarization of BaTiO₃ can promote the separation of photogenerated carriers and thus improve the photocatalytic efficiency.When the temperature change?T=12?,a more effective dynamic built-in electric field can be generated at the interface,which can work for continuously separation of the photogenerated carriers,and thus further improve the photocatalytic efficiency.?4?The core-shell BaTiO₃@TiO₂ nanocomposites with good photocatalytic activities were used for photocatalytic degradation of petroleum wastewater.The results show that increasing the content of catalyst,adjusting pH and prolonging the photocatalytic reaction time are beneficial to improve the degradation rate of petroleum wastewater.