Preparation And Photocatalytic Properties Of Composite Nanofiber Membranes Loaded With ZnO/CQDs Heterostructure

With the rapid development of society,environmental problems such as water pollution and air pollution are becoming more and more serious.At present,the methods to solve environmental pollution mainly include physical adsorption,chemical precipitation,microbial method and catalytic degradation.Among them,photocatalytic degradation technology has huge potential for development in the field of environmental treatment due to its advantages of high efficiency,environmental protection and sustainability.Nano-semiconductor photocatalysts have been widely concerned and studied because of their high efficiency,low energy consumption,non-toxicity and harmless in wastewater treatment.Carbon quantum dots(CQDs)are a new type of fluorescent carbon nanomaterials with unique optical properties,which can broaden the absorption range of photocatalysts to sunlight and excite semiconductors to form more photogenerated electron-hole pairs,thereby improving the photocatalytic efficiency.The composite nanofiber membranes(CNFMs)loaded with nanoparticle photocatalysts prepared by electrospinning combined with other methods not only have the advantages of high specific surface area,controllable morphology and structure,recyclability,environmental friendliness,etc.,but also make the ZnO composite photocatalyst uniformly distribute on the surface of the nanofibers to achieve an ideal photocatalytic effect,thereby greatly improving its application potential.Therefore,in this paper,a combination of electrospinning,low-temperature heat treatment and hydrothermal synthesis was used to successfully prepare the CNFMs loaded with ZnO nanoflowers(Z-CNFMs),CNFMs loaded with ZnO/CQDs heterostructure(ZC-CNFMs)and CNFMs loaded with CuO/ZnO/CQDs heterostructure(CZC-CNFMs),and they were applied in the photocatalytic degradation of organic dye methylene blue(MB).The specific research contents and conclusions are as follows:(1)Zn(Ac)2/PAN CNFMs were prepared by electrospinning,and then were subjected to heat treatment and hydrothermal synthesis to obtain Z-CNFMs.The effects of heat treatment temperature,heat treatment time and hydrothermal growth solution concentration on their morphology,structure and properties were investigated.Finally,the Z-CNFMs obtained under different process parameters were applied to the photodegradation of MB.The results demonstrated that when the heat treatment temperature was 140℃,the heat treatment time was 3 h,and the growth solution concentration was 0.1 M,the morphology,structure and photocatalytic performance of the obtained Z-CNFM were relatively good.(2)The water-soluble CQDs were synthesized by the electrochemical oxidation of graphite rod,and the ZC-CNFMs were prepared by the combined method of electrospinning,heat treatment and hydrothermal synthesis.The effects of the addition amount of CQDs solution on the morphology,structure and properties of ZC-CNFMs were discussed.Moreover,the ZC-CNFMs were applied to the photocatalytic degradation of MB,and the results displayed that the optimal addition amount of CQDs solution was 300 μL.In addition,the photocatalytic reaction mechanism of ZnO/CQDs heterostructure was further revealed by Mott-Schottky test and radical trapping experiments.(3)Cu(Ac)2/Zn(Ac)2/PAN CNFMs(Cu(Ac)2/Zn(Ac)2/PAN-CNFMs)were prepared by electrospinning,and then were heat treated and hydrothermal synthesized with CQDs.The CZC-CNFMs were prepared,characterized and tested.The effects of the addition of CQDs and the synergistic effect of ternary components on the morphology,structure and photocatalytic performance of CZC-CNFMs were analyzed,and their photocatalytic mechanism was further discussed.The results showed that compared with the CNFM loaded with CuO/ZnO heterostructure(CZ-CNFM),the CZC-CNFM had better photocatalytic degradation performance.The degradation rates of MB by the CZC-CNFM under mercury lamp for 3 h and natural sunlight for 4 h reached 99.04%and 99.56%,respectively.