Piezo-photocatalytic Properties Of AgNbO₃ Based On Photocatalytic Materials Constructed By Polarization Engineering And Heterojunction Strategy

As an efficient,safe and environmentally friendly pollutant purification technology,photocatalytic technology has great application potential in wastewater treatment.AgNbO₃ is a niobate antiferroelectric material with perovskite structure,which is responsive to visible light（the band gap is 2.7～2.8 eV）,and as a silver-containing photocatalyst,it has a unique d¹⁰electronic structure,and also has good piezoelectricity.Therefore,AgNbO₃ is a promising piezoelectric photocatalytic material.To further improve the photocatalytic performance of AgNbO₃-based materials,this paper optimizes the photocatalytic degradation performance of AgNbO₃ from the aspects of morphology and size regulation,polarization engineering,and heterostructure construction,and explores the relationship between its morphology and photocatalytic performance.The effects of polarization on the piezoelectric-photocatalytic performance,the relationship between the structure and size of the heterojunction and the piezoelectric-photocatalytic performance,and the photocatalytic and piezoelectric-photocatalytic mechanism have been investigated.On this basis,a AgNbO₃-based photocatalyst with excellent piezoelectric-photocatalytic performance was obtained.The main results are as follows:（1）Morphology regulation and photocatalytic performance of AgNbO₃ nano materialsAgNbO₃ photocatalytic materials were prepared by hydrothermal method,and the effects of hydrothermal reaction temperature（160～200℃）and reaction time（22～30 h）on microstructure and photocatalytic degradation performance of AgNbO₃ were investigated.The results showed that adjusting the hydrothermal reaction time did not significantly change the morphology of AgNbO₃ powders（all samples were cubic,without significant change in size）,while adjusting the hydrothermal reaction temperature（160～200℃）also failed to significantly change the morphology of AgNbO₃ powders（both are cubic）.But the hydrothermal reaction temperature has a certain control effect on the size.The samples prepared at the reaction temperature of 200℃have obvious differences in size（the minimum particle size is about 0.32μm,and the maximum particle size reaches 1.44μm）.The average particle size of the samples synthesized at 180℃is relatively small（～0.91μm）.With the rise of the hydrothermal reaction temperature,the photodegradation efficiency of AgNbO₃ to RhB first increased and then decreased.When the hydrothermal reaction temperature was 180℃,AgNbO₃ showed the best photocatalytic degradation performance（120 min for RhB degradation）.The degradation efficiency was 96%and the rate constant k was 0.022 min^-1).The results of trapping experiments showed that h⁺was the main active species for the photocatalytic degradation of RhB by AgNbO₃.（2）Piezoelectric photocatalytic performance of AgNbO₃ photocatalyst based on polarization engineeringOn the basis of（1）research,the AgNbO₃ photocatalytic material was polarized by corona polarization.By comparing the degradation performance of RhB under different conditions（illumination,ultrasound-assisted illumination）before and after polarization,the effects of polarization on its piezoelectric-photocatalytic performance were explored,and its piezoelectric photocatalytic degradation mechanism was elucidated.The results show that under the condition of ultrasonic-assisted illumination,the AgNbO₃ synthesized at 180℃without polarization has the best degradation effect on RhB.After 120 min of ultrasonic-assisted illumination,the degradation efficiency of RhB by AgNbO₃ reaches 96.3%,and the reaction rate is k=0.02281 min^-1,higher than the unpolarized sample(k=0.02245 min^-1)under light conditions;under only light,the degradation effect of AgNbO₃ on RhB after polarization is improved,and the photocatalytic activity of AgNbO₃ synthesized at 170℃is the best,and its rate constant(k=0.02537 min^-1)is about 1.6 times that of unpolarized samples(k=0.01563 min^-1);under the condition of ultrasonic-assisted illumination,the AgNbO₃ sample synthesized at170℃by polarized exhibits the best photocatalytic activity,and its rate constant(k=0.02978min^-1)is about 1.9 times that of unpolarized sample(k=0.01635 min^-1)under the condition of ultrasound and light;The main active species for the piezoelectric photocatalytic degradation of RhB is still h⁺.（3）Construction of CuBi₂O₄/AgNbO₃ composite photocatalyst and its piezoelectric-photocatalytic performanceRod-like CuBi₂O₄ was prepared by hydrothermal method,and then x%CuBi₂O₄/（1-x）%AgNbO₃ composite photocatalyst were fabricated by impregnation-thermal method.The effects of CuBi₂O₄ content on the piezoelectric-photocatalytic performance of the composite photocatalyst were investigated.The results show that the introduction of narrow-bandgap CuBi₂O₄ effectively expands the light absorption range of the composite photocatalyst;the 10%CuBi₂O₄/AgNbO₃ composite photocatalyst exhibits the best photocatalytic activity under only illumination.The degradation efficiency reached 95.4%,and its rate constant k is 0.02877 min^-1（1.84 times that of AgNbO₃）;under the condition of ultrasonic-assisted illumination,after 60min of illumination,the apparent rate constant of the 10%CuBi₂O₄/AgNbO₃ composite photocatalyst(k=0.03624 min^-1)is the highest,which is about 2.2 times that of AgNbO₃;under only illumination,the degradation effect of the polarized 10%CuBi₂O₄/AgNbO₃ sample is the best.Its rate constant(k=0.03800 min^-1)is the highest,which is about 1.32 times that of the unpolarized composite photocatalyst,and is 1.5 times that of the polarized AgNbO₃.Under ultrasound-assisted illumination,the degradation effect of 10%CuBi₂O₄/AgNbO₃ is the best,the degradation of RhB reached 96.56%for 60 min of illumination,and its rate constant(k=0.05611 min^-1)is about 1.5 times that of unpolarized AgNbO₃ and is about 3.4 times that of unpolarized AgNbO₃ and 1.9 times the polarized AgNbO₃.The trapping experiment results show that·O₂^-is the main active material for the composite photocatalytic piezoelectric-photocatalytic degradation of RhB.Z-scheme CuBi₂O₄/AgNbO₃ composite photocatalyst was successfully constructed,which significantly improved the photocatalytic degradation performance.