Preparation And Piezo/Photocatalytic Performance Of Na_0.5Bi_0.5TiO₃-based Nanocomposites

With the rapid development of industrialization,the emission of refractory organic pollutants has posed a potential threat to human health and ecological environment.Photocatalysis,as a green and efficient pollutant treatment technology,has been widely applied.However,the low utilization of light energy and high recombination rate of photogenerated carriers in tradition photocatalysts limit the development of photocatalytic technology.For solve this problem,utilizing the built-in electric field of piezoelectric materials as the driving force can effectively promote carrier separation,and the built-in electric field will drive the surface catalytic reaction in a piezocatalytic manner.Na_0.5Bi_0.5TiO₃（NBT）is a promising catalyst with both piezoelectric and semiconductor optoelectronic properties.In this thesis,NBT was taken as the research object,and the phase structure and morphology were analyzed.The piezo/photocatalytic performance of NBT were evaluated through the degradation of rhodamine B（Rh B）,methylene blue（MB）,methyl orange（MO）and tetracycline hydrochloride（TH）.The charge transport ability was characterized by photoelectrochemical tests.And the catalytic activity enhancement mechanism was discussed.Meanwhile,the Ag₂O/NBT composites with different molar ratios were designed and synthesized by constructing the heterojunction,and the piezo-photocatalytic mechanism of heterojunction was analyzed based on the piezo/photocatalytic experimental results and characterization results.The main results are as follows:（1）Three kinds of NBT nanoparticles were synthesized by hydrothermal method using rutile TiO₂,C₁₆H₃₆O₄Ti and anatase TiO₂ as titanium source,respectively.The NBT synthesized with anatase TiO₂ as the titanium source shows smallest particle size of 140 nm and largest specific surface area of 13.57 m²/g.After ultrasonic vibration for 120 min,the degradation rates of Rh B,MB and MO are 95%,89%and 72%,respectively.The main active species in the reaction system are·OH and·O₂^-,which enable Rh B to be degraded mainly through N-deethylation process and conjugated structure cleavage.（2）The NBT nanoparticles were synthesized by solid-state method,and the catalytic efficiency of the material was improved by adjusting the calcining temperature（650,700,750,800,850℃）.With the increase of temperature,the grain size of NBT gradually increases,and the average grain sizes are 70.85 nm,88.76 nm,123.171 nm,490.00 nm and 680.02 nm,respectively.At 700℃,NBT shows the narrowest band gap of 2.87 e V,and the degradation rate of Rh B reaches 100%under the synergistic effect of piezo-photocatalysis.The degradation rate only decreases by 5%after 3 cycles,while TH can be degraded 90%within 80 min,showing the highest piezo/photocatalytic performance.Combining photoelectrochemical and ferroelectric characterizations,the excellent catalytic performance is ascribed to the lowest fluorescence intensity,smallest charge transfer resistance and largest remnant polarization,which effectively promotes carrier separation.The built-in electric field and band bending promote the separation ability of photogenerated carriers during the piezo-photocatalytic and enhance the piezo-photocatalytic activity.（3）The Ag₂O/NBT composites were synthesized by precipitation method with a band gap of 1.19 e V and absorption edge of 750-1040 nm.The photocurrent intensity increases by 36 times and charge transfer resistance decreases,thus the carrier separation efficiency increases.The Ag₂O/NBT composites with a molar ratio of 10:1 exhibit the best piezo/photocatalytic performance.The degradation rate of Rh B reaches 99%within 30 min under the synergistic effect of piezo-photocatalysis,and the reaction rate is 0.140 min^-1,which is 7.4 times and 5.4 times that of Ag2O and NBT,respectively.And the degradation rate remains above 95%after 5 cycles.The formation of heterojunction not only broadens the light absorption range,but also promotes charge separation,thus enhancing the catalytic activity.