Preparation And Catalytic Application Of Bismuth-Based Oxide Composites

Photocatalytic degradation has emerged as an advanced oxidation technology in the past few decades and has attracted much attention as it degrades dyes by absorbing light energy.In addition to light,vibration energy is also a new clean energy source in nature,such as the vibration energy generated by the flow of water.Piezoelectric catalysis is a new type of catalysis,which is realized by the piezoelectric effect and can convert vibration energy into electrical energy.When the vibration will cause the bending deformation of the material,the positive and negative charges will appear on both sides of the material,and the positive and negative charges will react with oxygen and hydroxide in the solution to produce active substances,thus degrading the dye solution.In recent years,bismuth-based catalysts have mostly reported in catalyst synthesis,but less research on improving catalytic performance.Chalcogenide BiFeO₃ is considered as one of the important oxides with typical ferroelectric and antiferromagnetic properties.There are many research reports on bismuth ferrate thin films and ferroelectric ceramics,while bismuth ferrate has less applied in piezoelectric catalysis.The advantages of BiVO₄ materials consist of long hole diffusion distance（60 nm）,long carrier lifetime（40 ns）,suitable band gap（2.4-2.5 e V）,well-defined electronic structure,and good response in both UV and visible regions,etc,photocatalytic degradation in the UV region has been less studied.Therefore,BiFeO₃,a bismuth-based oxide,was selected to study its piezoelectric properties and BiVO₄ was selected to study its photocatalytic properties.The main studies in this work are losted as follows:1)The performance of BiFeO₃/C composites for piezoelectric catalyzing degradation of dyes under ultrasonic vibration was investigated.The bismuth ferrate composites were successfully prepared by hydrothermal method.The stracture and morphology of materials were characterized and by using XRD and SEM.Combining with EDS and XPS tests,the results showed that the carbon spheres were successfully compounded with BiFeO₃.The degradation performance of Rh B dye by BiFeO₃/C piezoelecdric catalytic ultrasonic excitation was investigated by varying the mass fraction of C spheres.The results showed that the addition of carbon spheres with a mass fraction of 2%effectively improved the performance of piezoelectric catalytic degradation of Rh B by BiFeO₃ with a degradation rate of 75%.The hydroxyl radicals and superoxide radicals generated during the piezoelectric catalytic process were proved to play an important role on degrading Rh B by active matter detection experiments,Recycling experiments demonstrated that the BiFeO₃/C composite has good recycling performance.2)The piezoelectric catalytic degradation performance of BiFeO₃/ZnO composites was investigated under ultrasonic vibration.BiFeO₃ and ZnO composites with different bismuth-to-zinc molar ratios were prepared by hydrothermal method,and the structure and morphology of the composites were characterized by XRD and SEM.The piezoelectric catalytic degradation performance of Rh B solution was investigated by varying the bismuth-to-zinc ratio,and the results showed that BiFeO₃/ZnO（Bi:Zn=1:0.2）showed the best degradation rate of 92.7%for Rh B solution,which improved 17.7%compared with the piezoelectric catalytic performance of BiFeO₃/C in the previous chapter.In addition,the catalyst was tested through recycling experiments,and after three cycles of experiments,it was found that the piezoelectric catalytic degradation performance of the catalyst did not change obviously,proving that the BiFeO₃/ZnO composite piezoelectric catalyst has good stability.3)The photocatalytic dye degradation performance of CQDs/BiVO₄ composites under UV illumination was investigated.The structure and morphology of the composites were characterized by XRD and SEM tests,and the successful composite of CQDs with BiVO₄ was further demonstrated by EDS and XPS analysis.By varying the amount of carbon quantum dots in aqueous solution,the degradation of the CQDs/BiVO₄ composites was investigated.The results showed that the 16CQDs/BiVO₄ composite had the best degradation performance of88.4%for MB solution.After three cycles of experiments,it was found that the degradation rate of the photocatalytic degradation of MB solution did not change significantly,which proved that the CQDs/BiVO₄ composite catalysts have good recyclability performance.