Synthesis And Photocatalytic Properties Of Bi₂O₃ And Its Composites

Along with the rapid development of the world economy,environmentalproblems have become increasingly serious,violating the goal of sustainable human development.In order to purify and repair the environment,many researchers use a variety of methods,such as biological methods,physical and chemical methods,advanced oxidation technology.As a method in advanced oxidation technology,semiconductor photocatalysis has become a promising method for solving environmental pollution problems due to its mild reaction conditions and almost degradation of all pollutants.The core requirement of photocatalytic technology is to develop efficient photocatalysts.However,the most studied and recognized high-efficiency Ti O₂photocatalyst?3.2e V?can only be excited by ultraviolet light in sunlight because its band gap is wide,and ultraviolet light only accounts for less than 4%of sunlight,which results in low utilization of sunlight.In order to use sunlight more effectively,researchers have developed a large number of photocatalysts that respond to visible light.Among these visible light responsive photocatalysts,Bi₂O₃ is widely used in sensors,batteries,coating films,and glass due to its high refractive index and good photoluminescence properties.In addition,studies have shown that Bi₂O₃ has good photocatalytic degradation of wastewater under visible light.However,the simple Bi₂O₃ visible light responsive photocatalyst still has some disadvantages,such as the narrow utilization range of visible light and the short lifetime of photogenerated carriers,which leads to further improvement of its photocatalytic performance.In this thesis,two different morphologies of Bi₂O₃ photocatalysts were designed and synthesized based on Bi₂O₃ to solve the above shortcomings.At the same time,the effects of calcination temperature,p H value and initial concentration on the photocatalytic degradation of rhodamine B were also studied.The main findings of this paper were as follows:1.Rod-shaped Bi₂O₃ and globular Bi₂O₃ were prepared by hydrothermal method and solvothermal method,respectively.These two photocatalysts with different morphologies could effectively utilize the visible light portion of sunlight,and had a good effect on rhodamine B under visible light.Photocatalytic degradation performance of rod-shaped Bi₂O₃ and globular Bi₂O₃ degraded 30%and 40%of rhodamine B after 2h of visible light irradiation,respectively.SEM was used to analyze the morphology of rod-shaped Bi₂O₃ and globular Bi₂O₃ ,and it was found that globular Bi₂O₃ had more pores than rod-shaped Bi₂O₃ ,and more pores were conducive to improving the contact surface area with pollutants,so as to improve the photocatalytic activity.XRD and XPS test results showed that the prepared products are pure rod-like Bi₂O₃ and globular Bi₂O₃ ,without other impurities.In addition,specific surface area also had an impact on photocatalytic effect.BET results showed that the BET specific surface area of rod-shaped Bi₂O₃ was1.500m²·g^-1,and that of globular Bi₂O₃ was 2.148m²·g^-1,while the larger specific surface area could provide more active sites for the reaction,so the photocatalytic performance of globular Bi₂O₃ was higher than that of rod-shaped Bi₂O₃ .Ultraviolet-visible diffuse reflectance spectrum analysis showed that the prepared rod-shaped Bi₂O₃ and globular Bi₂O₃ responded in the visible light range,in which the absorption band edge of rod-shaped Bi₂O₃ was at 535nm,and the absorption band edge of globular Bi₂O₃ was at570nm.From the empirical formula,the band gap values of rod-shaped Bi₂O₃ and globular Bi₂O₃ can be calculated to be 2.3e V and 2.1e V,respectively.Compared with rod-shaped Bi₂O₃ ,globular Bi₂O₃ 's absorption band edge moved in the direction of long wave,which would increase the absorption of light and thus improved the photocatalytic activity.In order to further determine the influencing factors of their photocatalytic performance,their precursors were calcined at different calcination temperatures of 200?,250?,300?,350?and 400?,respectively.The experimental results showed that the photocatalytic performance of rod-shaped Bi₂O₃ and globular Bi₂O₃ were greatly affected by calcination temperature.Among them,when the calcination temperature was 400?,rod-shaped Bi₂O₃ and globular Bi₂O₃ had the best photocatalytic degradation effect,degrading 30%and 40%of rhodamine B,respectively.When the calcination temperature was 200?,250?,300?,and 350?,rod-shaped Bi₂O₃ and globular Bi₂O₃ hardly degrade rhodamine B solution.2.In order to further improve the photocatalytic performance of rod-shaped Bi₂O₃ ,the rod-shaped Bi₂O₃ /BiOI complex was prepared by in situ treatment method through reasonable experiments.SEM morphology showed that the prepared composite was grown on rod-shaped Bi₂O₃ by sheet-like BiOI.XRD results showed that with the increase of HI content during the recombination process,the content of BiOI in the Bi₂O₃ /BiOI heterojunction also gradually increased,and the intensity of the tetragonal characteristic peak of BiOI gradually increased,while the intensity of the characteristic peak of tetragonal Bi₂O₃ decreased simultaneously.When HI is excessive,rod-shaped Bi₂O₃ completely transformed into the pure tetragonal BiOI phase?JCPDS 73-2062?.The XPS test results showed that the characteristic peaks of Bi,O,and I were mainly contained in the rod-shaped Bi₂O₃ ,BiOI,and Bi₂O₃ /BiOI?1:5?heterojunctions.The UV-visible diffuse reflectance spectrum showed that when the sheet-like BiOI was composited on the surface of rod-shaped Bi₂O₃ ,the band gap value of rod-shaped Bi₂O₃ /BiOI composite was smaller than that of rod-shaped Bi₂O₃ ,which indicated that the rod-shaped Bi₂O₃ /BiOI composite had better photocatalytic activity than pure rod-shaped Bi₂O₃ .In the photocatalytic degradation experiment,the degradation performance of rhodamine B solution with pure rod-shaped Bi₂O₃ ,pure BiOI and rod-shaped Bi₂O₃ /BiOI composites with different composite ratios was studied with 100 m L and 10 mg/L rhodamine B as the target pollutant.It was shown that after 2h of visible light irradiation,the Bi₂O₃ /BiOI?1:5?complex had the best photodegradation effect on rhodamine B,and achieved 82%degradation of rhodamine B.In addition,the effect of the initial p H value and initial concentration of rhodamine B solution on the degradation of rhodamine B by Bi₂O₃ /BiOI?1:5?was further studied.The p H values of the solutions were 3,5,7,9 and 11,respectively.Photocatalytic degradation was found to be most favorable for the photocatalytic degradation of rhodamine B when p H was 5,and 88%of the rhodamine B solution was degraded after 2h.The effects of the initial concentration on the degradation of rhodamine B were studied when the initial concentration of rhodamine B solution was10mg/L,20mg/L,and 30mg/L.When the initial concentration was 10mg/L,the effect of photocatalytic degradation of rhodamine B was the best.3.Compared with simple rod-shaped Bi₂O₃,the photocatalytic performance of rod-shaped Bi₂O₃ /BiOI composites had been significantly improved.However,since the globular Bi₂O₃ was better than the rod-shaped Bi₂O₃ in photocatalytic effect,in order to further improved the photocatalytic effect of the Bi₂O₃ /BiOI composite,globular Bi₂O₃ /BiOI composite was synthesized by in-situ compounding method.SEM analysis showed that this composite is a globular structure assembled from porous globular Bi₂O₃ and sheet-like BiOI,which could provide more active sites for photocatalytic reactions.All characteristic peaks in XRD correspond to standard colorimetric cards,indicating that the prepared sample had high purity.XPS analysis of globular Bi₂O₃ ,BiOI,and globular Bi₂O₃ /BiOI composites showed that characteristic peaks contained mainly Bi,O and I elements.The movement indicated that the globular Bi₂O₃ and the sheet-like BiOI were successfully combined together,and there was an interaction between the two,which was conducive to the improvement of photocatalytic activity.The UV-visible diffuse reflection analysis showed that when BiOI ws added to the globular Bi₂O₃ ,the band gap energy of the No.1 composite was reduced.The decrease of the band gap energy was beneficial to broaden the light absorption range and generated more electron-hole pairs,thus conducive to improving photocatalytic performance.The photocatalytic experiment showed that after2h of visible light irradiation,the optimal composite ratio of 0.1g of globular Bi₂O₃ /BiOI composite achieved 88%degradation of 100m L,10mg/L rhodamine B solution,and the improvement in photocatalytic performance was attributed to formation of heterojunctions between complexes.