Synthesis And Photocatalytic Properties Of Bi₅O₇I Based Composite Semiconductor Materials

Environmental pollution has been threatening people's health,especially the harm of antibiotic pollution.Solving these problems by sunlight has attracted widespread attention of researchers from the world.Semiconductor materials play a key role in solving this problem.Photocatalytic technology is gradually shifting from laboratory to practical application,but there are still great challenges,which require us to find a stable and efficient photocatalytic system to expand the range of light response,improve quantum efficiency and inhibit the recombination of photogenerated electron hole pairs.Among many photocatalytic materials,BiOI has been widely studied because of its narrow band gap,but with a narrow band gap,the valence band and conduction band can not be in a suitable location.In this paper,Bi₅O₇I is formed by the post-treatment of BiOI,and further compounded with BiOCl and g-C₃N₄ semiconductor materials to form a series of photocatalytic materials,which can promote the effective separation of photogenerated electron-hole pairs and enhance the photocatalytic activity.The details are as follows:Firstly,BiOI and BiOCl were prepared by simple alcoholic method,and BiOI/BiOCl composites with different proportions were prepared by adjusting the molar ratio of I source to Cl source.Bi₅O₇I/BiOCl composite semiconductor materials were prepared by calcining BiOI/BiOCl composite materials.The samples were characterized by XRD,SEM,TEM and UV-Vis DRS.The photocatalytic activity of Bi₅O₇I prepared by calcination of BiOI was tested by degradation of RhB solution and tetracycline hydrochloride?TC?solution.The results showed that Bi₅O₇I produced by calcination of BiOI had higher photocatalytic activity.Effects of BiOCl to Bi₅O₇I/BiOCl composite for the crystal phase,morphology and light response were analyzed.Compared with the single Bi₅O₇I and BiOCl semiconductor photocatalyst,Bi₅O₇I/BiOCl composite prepared have a higher photocatalytic activity for organic solutions under visible light irradiation,of which 40%Bi₅O_7I/BiOCl has the highest photocatalytic activity.Rhodamine B is completely degraded within 120 min,and tetracycline hydrochloride is completely degraded within 180 min.Bi₅O₇I and BiOCl are p-type semiconductor and form p-p heterojunctions on the surface by compounding,and form built-in electric field.Because of the existence of electric field,the migration of photogenerated electron-hole pairs is limited,the carrier lifetime is longer and the quantum efficiency is improved.On the other hand,BiOI and urea?CON₂H₄?will be fully mixed and grinded.BiOI/g-C₃N₄ composite can be obtained by calcining the mixture at a certain temperature for a certain period of time.Bi₅O₇I/g-C₃N₄ composite can be obtained by calcining again.Compared with the single Bi₅O₇I and g-C₃N₄ semiconductor photocatalysts,the prepared Bi₅O₇I/g-C₃N₄ composite have higher photocatalytic degradation activity for organic solution than the single Bi₅O₇I and g-C₃N₄ semiconductor photocatalys under visible light irradiation.Among them,8%Bi₅O₇I/g-C₃N₄ has the highest photocatalytic activity.It can completely degrade Rhodamine B within 120 min and tetracycline hydrochloride within180 min.The results show the two semiconductors form p-n heterojunctions on the surface by compounding,and form built-in electric field,which promotes the separation of photogenerated electron hole pairs and improves the quantum efficiency.