| With economic development and social progress,a large number of toxic organic pollutants and heavy metal ions,which are harmful to ecology and human health,are discharged into nature during industrial production.Pollutant emissions have caused environmental pollution problems to intensify and become a huge challenge for human society.Photocatalytic materials and technologies can be regarded as a kind of promising material technologies because of converting solar energy,the most abundant clean energy on the earth,into chemical energy to achieve the degradation of pollutants under mild conditions.The widely used photocatalytic materials such as TiO2 yield photocatalytic activity only by the radiation of ultraviolet(UV)light,while the proportion of UV light in the solar spectrum is less than 5%.In order to improve the utilization of sunlight,visible-light response photocatalytic materials have become a research hotspot.In this paper,the study on a new type of visible-light driven semiconductor bismuth ferrite(Bi2Fe4O9)was carried out.Firstly,the preparation method of Bi2Fe4O9 particles with specific morphology was explored,and the effects of different facets on their photocatalytic reactivity were investigated.Then,to solve the problem that the photo-generated carriers are easily recombined and respionse to Visible light is not enough in Bi2Fe4O9 and further improve the visible-light photocatalytic activity of Bi2Fe4O9,Bi2Fe4O9 has been modified by two ways,including self-doping Bi2Fe4O9 with oxygen vacancy and noble metal silver loading.The main research work and conclusions are as follows:(1)Bi2Fe4O9 with different morphologies was synthesized by template-free hydrothermal method.The effects of NaOH concentration,hydrothermal temperature and hydrothermal time on the crystal phase,morphology evolution and photocatalytic activities of Bi2Fe4O9 were investigated.The results show that when the concentration of NaOH is more than 9.4 M,a pure orthorhombic Bi2Fe4O9 submicron particle can be synthesized.Increasing the concentration of NaOH and hydrothermal temperature can significantly change the main exposed facet and microscopic morphology of Bi2Fe4O9 submicron particles.By prolonging hydrothermal time and increasing concentration of NaOH,morphology of Bi2Fe4O9 changes from flake to cube,and the surface of the particles exposes more non-preferentially grown crystal facets and high-index crystal faces,which promote the photocatalytic activity of Bi2Fe4O9.Cubic bulk Bi2Fe4O9 which was synthesized at 15.6 M NaOH concentration exhibit higher visible light catalytic performance with smaller specific surface area.The degradation rate of MB(3 hours)was 23.5%in the samples exposed the most non-(001)facet.(2)The Bi2Fe4O9 nanosheets with oxygen vacancy defect were successfully prepared by vacuum annealing and the effects of annealing time on the structure and photocatalytic activities of Be2Fe4O9 were investigated.The results show that the heat treatment in vacuum can effectively control the oxygen vacancy amount in Bi2Fe4O9 and with prolonging heat treatment time in vacuum,the surface oxygen vacancy concentration first increases and then decreases.The oxygen vacancies on Bi2Fe4O9 enhance its absorption of visible light,thereby improving photocatalytic performance.The K-value of the sample containing the most oxygen vacancies is 0.264 h'',which is 1.35 times higher than that of the sample treated in air atmosphere and 3.94 times higher than that of the blank experiment.(3)Ag/Bi2Fe4O9 photocatalytic composite materials were prepared by photo-reduction method on the surface of Bi2Fe4O9 particles.The effects such as AgNO3 concentration,irradiating time and morphology of Bi2Fe4O9 particles on the structure and photocatalytic performance of Ag/Bi2Fe4O9 photocatalytic composite materials were investigated.The results show that the Ag nanoparticles can be loaded on both the sheet and rod-like Bi2Fe4O9.By loading Ag nanoparticles on Bi2Fe4O9,the migration of photo-generated electrons were promoted,thereby improving the photo-generated carrier separation efficiency,therefore improving the visible-light photocatalytic activities of Bi2Fe4O9.The degradation rate of MB by Ag/Bi2Fe4O9 nanosheets prepared at Ag+ concentration of 0.21 M was 8%higher than that of pure samples. |
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