| Energy shortages and environmental pollution have seriously hindered the sustainable development of modern society,and the development of new green,efficient energy and environmental technologies has become an important task for modern society.Piezocatalysis is an emerging technology that can induce surface charge in piezoelectric materials by collecting mechanical energy such as vibration,friction,natural wind and tide,which in turn enables catalytic reactions,which shows great potential for clean energy conversion and water treatment.However,the research of piezocatalysis is still in its infancy,and the low catalytic activity of existing materials prevents the technology from being put into practical applications,making the development of efficient piezocatalysts a major challenge in the field of piezocatalysis.In this thesis,barium titanate-based piezoelectric materials were used as the research object,and nanocrystals with different compositions and morphologies were prepared by hydrothermal method,and the influence of material modification methods such as morphology modulation,ion doping and constructing heterojunctions on the piezocatalytic performance and the enhancement mechanism are systematically investigated.The main research contents of this thesis are as follows:(1)BaTiO3 nanocrystals with particle,fiber and sheet morphologies were prepared by the template hydrothermal method,respectively,and the effect of microstructure on the piezocatalytic activity of BaTiO3 nanomaterials was systematically investigated.Compared with nanofibers and nanoparticles,BaTiO3 nanosheets exhibited significantly enhanced piezocatalytic activity despite the smaller specific surface area,with the degradation rate of rhodamine B and hydrogen generation rate up to 0.128 min1 and 92 μmol g-1 h-1,respectively.Based on the finite element simulation of the piezoelectric potential analysis for BaTiO3 nanoparticles,nanofibers and nanosheets under ultrasonic vibration,the enhanced catalytic activity can be attributed to its large piezoelectric potential,which also demonstrates that the piezoelectric potential associated with the microstructure is the main factor in determining the piezocatalytic performance.(2)The effects of heterovalent ion doping on the piezocatalytic performance of BaTiO3 nanosheets were investigated by using Li(+1)and La(+3)for the acceptor and donor doping of Ba(+2)ions at the A-site of BaTiO3,respectively.The heterovalent ion doping enhanced the photocatalytic performance by modulating the energy band,which not only promoted the light absorption but also accelerated the carrier separation and migration.Under the simultaneous action of ultrasonic vibration and UV illumination,the hydrogen generation rates of Ba0.99Li0.01TiO3 and Ba0.98La0.02TiO3 nanosheets were as high as 3704 μmol g-1 h-1 and 3178 μmol g-1 h-1,respectively,which were 4.6 and 3.9 times higher than those of pure BaTiO3.The piezo-photocatalytic performance of Li or La-doped BaTiO3 nanosheets far exceeds the sum of both piezocatalysis and photocatalysis the sum of both due to the promotion of light-induced electron-hole pair separation by the built-in electric field generated by piezoelectric potential.Moreover,the selective catalytic enhancement of specific pollutants can be achieved through different modulation effects of the energy band structure by either donor or acceptor doping.Compared with pure BaTiO3,Ba0.99Li0.01TiO3 with more negative conduction band position possesses higher piezo-photocatalytic activity for anionic dyes such as methyl blue and malachite green with the degradation rates of 0.067 min-1 and 1.379 min-1,respectively,while Ba0.98La0.02TiO3 with more positive valence band position exhibits better piezo-photocatalytic activity for cationic dyes such as rhodamine B and methyl orange,and the degradation rates reached 0.274 min-1 and 0.029 min-1,respectively.(3)The morphotropic phase boundary was constructed in the BaTiO3-based ferroelectric material by the co-doping of Ca and Sn,and obtained excellent piezoelectric properties near Curie temperature,which led to a significant enhancement of the piezocatalytic performance of Ba0.95Ca0.05Ti0.9Sn0.1O3.The results demonstrated that the phase transition temperature of Ba0.95Ca0.05Ti0.9Sn0.1O3 was 46℃,the piezocatalytic activity of the material reached a maximum near the phase transition temperature,and the degradation rate of rhodamine B could reach 0.249 min-1 under ultrasonic excitation at 40 kHz and 100 W.(4)The Z-scheme heterojunction Ba0.95Ca0.05Ti0.9Sn0.1O3/g-C3N4 were designed and fabricated to investigate the influence of heterojunction on the piezocatalytic performance and to explore the application of piezocatalysis in the field of nitrogen fixation.The Z-scheme heterojunction structure effectively reduces the combination of carriers,while simultaneously possessing the strong oxidation potential of Ba0.95Ca0.05Ti0.9Sn0.1O3 and the strong reduction potential of g-C3N4,thus significantly enhancing the piezocatalytic degradation performance.The piezocatalytic degradation rate of Ba0.95Ca0.05Ti0.9Sn0.1O3-10%g-C3N4 heterojunction for rhodamine B can reach 0.503 min-1,which is about twice as high as that of pure Ba0.95Ca0.05Ti0.9Sn0.1O3.Moreover,the piezocatalytic nitrogen fixation performance of the composite catalyst was significantly enhanced by utilizing the promotion effect of heterojunction on nitrogen adsorption and activation.Without any sacrificial agent,the N2 fixation product of the composite catalyst was mainly nitrate,and the average rate of nitrate production was up to 1.40 mg g-1 h-1,which was 3.9 and 5.3 times higher than that of pure Ba0.95Ca0.05Ti0.9Sn0.1O3 and g-C3N4,respectively.(5)The type-I heterojunction was constructed by combining a photocatalyst CuO with excellent photoresponse and a piezocatalyst BaTiO3 with excellent piezoelectric response.The excellent piezo-photocatalytic activity was achieved through the synergistic effect of heterojunction and piezoelectric effect.Compared with pure BaTiO3 nanowires and CuO nanoparticles,the BaTiO3/CuO heterojunctions exhibited significantly enhanced piezo-photocatalytic degradation efficiency.Under the synergistic effect of ultrasonic vibration and UV light,the catalytic degradation rate of methyl orange by BaTiO3/CuO heterojunctions after corona polarization was as high as 0.05 min-1,which was 6.1 and 7 times higher than that of photocatalysis and piezocatalysis,respectively. |
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