Research And Application Of Polarized Electric Field Modulation Catalysis And Enhanced Photocatalytic Reaction

Environmental pollution and energy shortage are the two main global problems as the increasing population in the world.Researchers develoed various methods to control the environmental pollution and develop new energy sources,but the results did not meet our expectation.Semiconductor photocatalysis is an advanced oxidation technology.By harvesting the energy-suitable photons,high energy electrons and holes were excited,combined with the derived free radicals,leading to the mineralization of organic pollutants,reduction of heavy metal ions,generation of hydrogen gas or liquid fuel.This technology posesses the advantages of high activity,non-toxic,and relatively mild reaction conditions,which has a broad application prospect.However,the recombination of free electron-hole pairs and the low photocatalytic efficiency restrains the daily application of this technology.Up to now,a variety of strategies have been developed to improve the activity of photocatalytic reaction.For example,heterojunction construction,bias voitage applying can promote the spatial separation of electron-hole pairs in bulk.Designing of superstructure,constructing an impurity level,surface sensitization can enhance the light absorption of semiconductor.Boosting the surface chemical reaction can also promote the photocatalytic reaction rate.We propose a new strategy based on the displacement current contributed from polarization to enhance the photocatalytic performance.The polarization based on displacement current can be piezoelectric polarization induced by strain force,spontaneous polarization from ferroelectric material,coupling effect of piezoelectricity and ferroelectricity,and electrostatic field induced by triboelectric nanogenerators.In this thesis,the flllowing parts of work were mianly foused on.?1?.Fluid energy induced piezoelectric field was introduced to enhance the performance of TiO₂ photocatalytic degradation of organic pollutants,and to study the mechanism of piezo-catalysis.In view of the mechanism research of piezo-catalysis,we designed three types of piezoelectric PZT catalyst.By comparing the sample before and after Rh B degradation,we confirmed the occurrence of piezo-catalysis on PZT.The degradation performance of RhB by PZT with different concentrations of equilibrium carriers indicates that free charges directly contribute to the piezocatalytic reaction,while the piezoelectric charges only promote the separation of free charges?equilibrium carriers?.This part of work distinguished the contribution of different types of charges in piezo-catalytic reaction and indicated the mechanism of the piezo-reaction.As for the following part,we prepared PZT/TiO₂ composite with core-shell structure.By tuning the stirring volecity of the solution,piezoelectric field with different intensities generated.Under the driven of piezoelectric field,TiO₂ showed enhanced separation rate of electron-hole pairs and higher performance in photocatalytic degradation of organics.?2?.The coupling effect of ferroelectricity and piezoelectricity,is considering to enhance the photocatalytic activity due to the limitation of ferroelectricity for the separation of carriers.Single domain PbTiO₃ ferroelectric single crystals were prepared.Under the co-modulation of ferroelectric polarization and piezoelectric polarization,PbTiO₃ crystal showed enhanced photocatalytic degradation of cationic organic pollutants,and surface selective deposition of Pt and Pd nanoparticles can be realized.Furthermore,PbTiO₃ with selectively deposited co-catalyst Pt showed more enhanced photocatalytic activity of hydrogen evolution than the non-selecitively deposited PbTiO₃,and hydrogen evolution increased under the driven of an augmented piezoelectric filed.?3?.By combining triboelectric nanogenerator?TENG?and photocatalysis technique,we demonstrated a concept of a self-powered filtering method for removing pollutants from indoor atmosphere.Both enhanced electrostatic adsorption and photocatalytic effect achieved on the filter device with a TENG combining.When employed for the degradation of formaldehyde,degradation efficiency within the same time was doubled under the drive of TENG.This work is a combinational study of TENG technique and photocatalytic air-pollution degradation,which can broaden the applications of selfpowered nanosystems.The demonstrated concept can be widely used in the field of haze governance,indoor air cleaning,and photocatalytic pollution removal.