Preparation Of Bi₂MoO₆/Bi_xO_yI_z Heterojunction Nanofibers And Their Photocatalytic Performance

In recent years,antibiotic wastewater has caused serious pollution to the environment and ecosystems.It has the characteristics of high concentration,high biological toxicity and low biodegradability.Therefore,the development of efficient antibiotic wastewater treatment technology has become a difficult and hot topic in the field of wastewater treatment research.Semiconductor photocatalytic degradation of antibiotic wastewater has broad application prospects due to its simple process,environmental friendliness and mild reaction conditions.However,developing efficient photocatalytic materials still faces some challenges.Bismuth molybdate（Bi₂MoO₆）in Bismuth-based Semiconductor Oxides,exhibits excellent performance in visible light photocatalytic reactions.This is mainly ascribed to the narrow band gap（Eg≈2.69 e V）of Bi₂MoO₆,which can capture visible light.In addition,it has a special layered structure,which may facilitate the transfer of charge within the layer.However,like other single-component semiconductors,the photocatalytic activity of Bi₂MoO₆ was greatly limited due to the easy recombination of photogenerated carriers.Nano-sized photocatalysts usually exhibit high activity due to their high specific surface area,but their high surface can lead to the easy agglomeration of nanometer powders,thus reducing the active sites of surface reaction.At the same time,it was difficult to separate and recover in the liquid phase reaction.To further enhance the photocatalytic activity of Bi₂MoO₆,Bi₂MoO₆/Bi_xO_yI_z composite nanofibers were designed and constructed in this work by combining Bi₂MoO₆ with Bi-based metal iodine oxides（Bi OI,Bi₅O₇I）.The photogenerated charge separation ability and photocatalytic activity were improved by constructing a built-in electric field in semiconductor heterostructures;The separation and recycling ability of the material are improved by using its three-dimensional macro mesh felt structure.The influence of the loading amount and energy band structure of Bi_xO_yI_z on the photocatalytic activity of heterojunction and the reaction mechanism of photocatalytic degradation were systematically studied in this paper.The specific research contents are as follows:1.The preparation of Bi₂MoO₆/Bi OI and its photocatalytic performance.Bi₂MoO₆/Bi OI heterojunction nanofibers with different loadings were successfully prepared by combining electrospinning technology and solvothermal method.Photoelectrochemical tests show that constructing heterojunction could effectively reduce the recombination of photogenerated carriers,thereby promoting more photogenerated charges to participate in photocatalytic reactions.Photocatalytic experiments showed that 81%of tetracycline hydrochloride solution（20 ppm）can be degraded over Bi₂MoO₆/Bi OI heterojunction nanofibers within 75 minutes,and the degradation rate was about 2.0 times and 1.9 times than that of pure Bi₂MoO₆ and pure Bi OI,respectively.In addition,the three-dimensional network structure of Bi₂MoO₆/Bi OI heterojunction nanofibers makes them have good natural sedimentation characteristics and recycling performance.2.Preparation of Bi₂MoO₆/Bi₅O₇I heterojunction nanofibers and their photocatalytic properties.Bi₂MoO₆/Bi₅O₇I heterojunction nanofibers with different Bi₅O₇I loading capacities were successfully constructed by calcining Bi₂MoO₆/Bi OI heterojunction nanofibers 470℃to induce phase transformation.The results show that the Bi₂MoO₆/Bi₅O₇I heterojunction could realize the effective separation of photo-generated carrier,under visible light irradiation,Bi₂MoO₆/Bi₅O₇I could degrade 81%tetracycline hydrochloride solution（20 ppm）in 30minutes,and its degradation rate was 3.6 times and 2.0 times than that of pure Bi₂MoO₆ and pure Bi₅O₇I,respectively.Meanwhile,the degradation rate of Bi₂MoO₆/Bi₅O₇I heterojunction nanofibers was 1.8 times than that of Bi₂MoO₆/Bi OI heterojunction nanofibers.The results of capture experiments and electron spin resonance showed that the energy-band structure of Bi₂MoO₆/Bi_xO_yI_z heterojunction could be effectively regulated by changing the content of I element and crystal structure,which could produce more active free radicals to participate in the oxidation reaction.In addition,the Bi₂MoO₆/Bi₅O₇I heterojunction nanofibers had good natural sedimentation characteristics and cycle stability,which was conducive to the application in real life.