Preparation And Photocatalytic Properties Of Bismuth Oxyhalides

In recent years,because of its high efficiency,greenness and environmentally friendly characteristics,photocatalytic technology has been attracted considerable attention in the fields of environment purification and energy conversion.Among the numerous semiconductor photocatalysts,a large number of investigations have focused on bismuth oxyhalide（BiOX（X=Br,I））due to its unique layered structure and special electronic transition modes.However,the rapidly recombination of photogenerated electron-hole pairs limits the development of bismuth oxyhalide photocatalysts.In order to reduce the recombination rate of photogenerated electrons and hole pairs,and improve the photocatalytic activity,more and more scientists have invested in the modification of bismuth oxyhalides.At present,the synthesis of non-stoichiometric bismuth oxyhalide compounds has been certified to be the effective strategies to improve the photocatalytic performance of BiOX.But the enhancement mechanism of activity has not been explored clearly.In this dissertation,we enhanced the ability of photocatalytic degradation of organic contaminants by preparing non-stoichiometric photocatalysts,in addition,the research and discussion on the mechanism of photocatalytic reaction,the main contents of this paper are as follows:（1）The electronic structure and band structure of Bi4O5I2 compounds were studied by first-principles CASTEP software,and the Bi4O5I2 photocatalysts was successfully synthesized via the solvothermal method,in addition,the structure,morphology,composition and light absorption range of Bi₄O₅I₂ compounds were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,UV-Vis diffuse reflectance spectroscopy（DRS）and Photoluminescence（PL）.The photocatalytic activities of Bi₄O₅I₂ was evaluated by the degradation of methyl orange（MO）,rhodamine B（RhB）,methylene blue（MB）,norfloxacin（NOR）organic pollutants under the visible light.The results show that the photodegradation of RhB reached 99%within 84 min,it is noteworthy that for degradation of methyl orange,the photocatalytic activity of Bi4O5I2 is about 10 times of that of BiOI.In addition,the mechanism of photocatalytic degradation of Bi4O5I2 was investigated by radical trapping experiments.The results showed that the active radicals that play a major role in the degradation process are h⁺and·O₂^-.Then,due to the action of dipole moments facilitates the charge separation of photogenerated electron-hole pairs.As the same time,both photoelectrochemical experiments and PL experiments further confirmed that the photogenerated electron and hole pairs of the Bi₄O₅I₂ photocatalyst have a higher migration rate and a lower recombination rate,and effectively improve the photocatalytic activity.（2）Bi₄O₅Br₂ photocatalysts was successfully synthesized via a facile solvothermal method,it is particularly noteworthy that the effect of pH on the synthesis of Bi4O5Br2compounds has also been studied,and the crystal structure,electronic structure,elemental composition,morphology and light absorption range of those sample with different pH values were elaborated.From the XRD analysis,it is indicated that the pH value of the solution is a key factor affecting the synthesis of Bi₄O₅Br₂ compounds,it is beneficial to the synthesis of Bi₄O₅Br₂ compounds under alkaline conditions,and the compound was converted from BiOBr to Bi₄O₅Br₂ as the pH increased.From the DRS analysis,the light absorption edge shifts to the long wave direction and red shift occurs,which causes the catalyst to use more visible light to degrade the contaminants.The photocatalytic performance of Bi₄O₅Br₂ under visible light irradiation was evaluated by the degradation of MO organic pollutants.The results show that Bi₄O₅Br₂ has the highest degradation efficiency.