Life-Cycle Designed Hybrid Nanofibrous Membranes For X-Ray Protection And Photocatalysis

With the increasing density of ionizing radiation sources represented by X-rays for medical diagnosis,the development of personal X-ray protective equipment for health care workers and recipients has gradually attracted the attention of researchers.Personal protective clothing such as conventional lead rubber aprons is high-weight and poorly flexible,besides,lead and some of its compounds as toxic substances have many inconveniences in their processing and use,therefore,the design and manufacture of lightweight,lead-free,and flexible X-ray protective materials has recently become a challenge in the field of materials science.Researchers have found that high atomic number(Z)materials are essential raw materials for lead-free high-performance X-ray shielding fillers,based on which they can create a series of alternatives to lead rubber,but with few breakthroughs in areas such as wearing comfort and flexibility,they also face defects such as easy agglomeration of filler particles and resulting in reduced performance.In addition,as non-renewable resources,the development and utilization of high atomic number materials with limited reserves require long-term planning.In this thesis,based on the quest for a high-performance X-ray protective material that is light flexible and nontoxic,foothold electrospinning technology,a series of high-Z material heterojunction/polymer hybrid nanofibrous membranes were designed and synthesized based on the concept of life-cycle design,and the coverage of medical X-rays was achieved by adjusting the material composition,structure,and so on.Taking the characteristics of nanofibrous membrane as a bridge and effectively bridging the two main functions of X-ray protection and photocatalysis,it guarantees that the material can be easily recovered after its end of life as an X-ray protective filler and used as a photocatalyst in the field of wastewater treatment.The details are as follows:1.We construct semiconductor WO₃ on the surface of polyacrylonitrile(PAN)nanofibers modified with seed crystals via an electrospinning and solvothermal reaction,and build the semiconductor compound of bismuth on the basis of WO₃/PAN hybrid nanofibers to form heterojunctions for light flexible X-ray protective materials and photocatalysts as follows:(1)With partial WO₃ as tungsten source,Bi₂WO₆/WO₃/PAN hybrid nanofibrous membrane was constructed by using a further solvothermal reaction,and the mass attenuation coefficient of this material toward X-ray with photon energy of 83 ke V was 2.97 cm² g^-1,which was simple superposition of two single inorganic component/PAN hybrid nanofibrous membranes and lead glass,in photocatalytic tests after the membranes were recycled,under simulated sunlight irradiation,the Bi₂WO₆/WO₃/PAN nanofibrous membrane could degrade rhodamine B(Rh B)in aqurous solution by 99.4%within 4 h,and with excellent cycling stability.(2)Bi OX(X=Cl,Br,I)/WO₃/PAN hybrid nanofibrous membranes were prepared by sequential ionic layer adsorption and reaction(SILAR)based on WO₃/PAN hybrid nanofibrous membranes with mass attenuation coefficients exceeding those of lead glass for X-rays at 83 ke V photon energy(3.55,3.29,and 3.49 cm² g^-1 for Cl^-,Br^-,and I^-containing samples,respectively),while BiOI/WO₃/PAN by adding cheap high-Z element iodine,more balanced shielding performance can be achieved in the selected X-ray energy range.The optical properties of Bi OX(X=Cl,Br,I)and the higher charge separation efficiency of the heterojunctions allow this class of nanofibrous membranes to reach more than 97%for the degradation of Rh B in aqueous solution under visible light within 120 min with good cycling stability.2.Based on the WO₃/PAN hybrid nanofibrous membrane prepared in the previous work,semiconductor compounds comprising two fifth cycle high-Z elements,Ag and I,were introduced on it by using SILAR method to form heterojunctions with WO₃ on the surface of the nanofibers,for light flexible X-ray protective materials and for H₂O₂assisted visible light photocatalytic degradation of carbamazepine(CBZ)after recycling,the specific results are as follows:(1)Ag I/WO₃/PAN hybrid nanofibrous membranes were prepared by SILAR method,and the mass attenuation coefficients of X-ray at 65 ke V and 83 ke V photon energies were 3.56 and 3.44 cm² g^-1,respectively,which are over lead glass.After recycling,this fibrous membrane exhibited excellent H₂O₂-assisted-photocatalytic activity under visible light and could remove CBZ by 97.1%within 120 min with good stability.(2)The Ag IO₃/WO₃/PAN hybrid nanofibrous membranes were fabricated by SILAR method and exhibited mass attenuation coefficients of 7.12,4.25 and 4.43 cm² g^-1 for 48 ke V,65 ke V and 83 ke V photon energy X-rays,respectively,which were superior to those of lead glass and above Ag I/WO₃/PAN hybrid nanofibrous membranes and can be attributed to the high loading capacity of Ag IO₃.This nanofiber can be used as a photocatalyst in H₂O₂ assisted photocatalytic degradation system after recovery and can catalytically degrade CBZ by75.3%in 120 min with good stability.Atrributing to the contribution of K-layer electron absorption of Ag and I elements for X-ray protection and the higher charge separation efficiency of heterojunction,respectively.3.To further improve the protective ability of the prepared hybrid nanofibrous membranes against medical X-rays to achieve a complete coverage of this photon energy range,the works of the above two parts were combined to utilize SILAR reaction to grow Ag I on the surface of Bi₂WO₆/WO₃/PAN and BiOI/WO₃/PAN hybrid nanofibrous membranes,respectively,to construct ternary heterojunctions on the surface of PAN nanofibers,and the two kinds of ternary heterojunction nanofibers were used for flexible and lightweight X-ray protective materials and photocatalytic degradation of antibiotics after recycling,as follows:(1)Ag I/Bi₂WO₆/WO₃/PAN hybrid nanofibrous membranes were prepared,and the X-ray mass attenuation coefficients were 23.98,8.45,4.47,and 4.19 cm² g^-1 for photon energies of 30 ke V,48ke V,65 ke V,and 83 ke V,respectively,which exceeded those of lead glass.After rececyling,this hybrid nanofiber membrane could degrade tetracycline hydrochloride in aqueous solution by 90.3%within 120 min under visible light,and the fiber membrane exhibited good stability as a photocatalyst.(2)The prepared Ag I/BiOI/WO₃/PAN hybrid nanofibrous membrane showed mass attenuation coefficients of 23.96,9.68,5.07 and 4.58 cm² g^-1 in response to X-rays with photon energies of 30 ke V,48 ke V,65 ke V and 83 ke V were prepared,which are higher than those of lead glass,and after recycling,this hybrid nanofibrous membrane could degrade levofloxacin in aqueous solution within 120 min under visible light by 86.1%,and the fiber membrane showed good stability as a photocatalyst.The enhancement of the X-ray protection performance of the ternary hybrid relative to the precursor binary heterojunction nanofibers in both systems is mainly because of the contribution of the large amount of introduced K-layer electrons of Ag and I into the system to the X-ray absorption,while the improved photocatalytic performance can be attributed to the higher charge separation efficiency of the ternary heterojunction.In summary,this thesis followed the concept of life-cycle design and presented a series of inorganic heterojunction/polymer hybrid nanofibers based on high-Z semiconductor compounds using electrospinning technology,and their protective properties against medical X-rays were investigated.It was found that by introducing multiple high-Z materials into the system,taking advantage of their K-layer electrons with absorption ability to X-rays of different photon energy to enlarge the range of materials with efficient attenuation ability for X-rays,effective protection against medical X-rays can be achieved.The prepared hybrid nanofibrous membrane can serve as a lead-free,lightweight and flexible X-ray protective material for use in the field of ionizing radiation protection,meanwhile,the exposed heterojunctions brought by the hybrid nanofibrous membranes guarantee the recyclable utilization of heterojunction nanofibrous membranes as photocatalysts for environmental applications after scrapping as X-ray protective materials,providing a new strategy for the design,use,and recovery of precious high atomic number materials.