Preparation And Photocatalysis Of Semiconductor-fluoropolymer Electrospun Fiber Nanocomposites

The semiconductor photocatalyst, such as Titanium dioxide and Zinc Sulfide, has strong oxidation, mineralized completely and high photocatalytic activity for the organic pollutants in the environment, and then the semiconductor has potential application for the waste water remediation. But the semiconductor powders has the disadvantages of low visible light utilization efficiency, easy losing etc., all that restrict the scale application in the field of environment remediation. Therefore the preparation of semiconductor supported photocatalyst composites with high photocatalytic activity and good flexibility has the significance both theory and application.In this doctoral paper, the main study is that the electrospun fluoropolymer mats with nano-micro size interconnected open pore structure, high light transmission and good photocatalytic resistance ability were performed using high pressure electrospinning process, then the semiconductor particles were immobilized on the surface of fluoropolymer electrospun fiber mats through solution precipitation. The photocatalytic activity and stability of composites were tested on photodecolorization of dye solution under UV or Visible light.(1) The preparation and surface modified of PVDF electrospun fiber mats: The PVDF electrospun fiber mats comprised random nonwoven mesh of fibers about 100nm in diameter and an interconnected open pore structure. In this paper, the electrospun fiber mats containing carboxyl on the surface were prepared in 2 methods. First,poly(MAA-co-TFA)/PVDF electrospun fiber mats were prepared using a typical electrospinning process, and the electrospun fiber mats have good heat stability treated under 150 0C for 12h. Other, the PVDF-g-AA electrospun fiber mats were prepared using atmosphere dielectric barrier discharge-UV irradiation methods. The suitable grafting degree and good morphology of PVDF electrospun fiber mats can be achieved under 60s and 120s discharge treated.(2) The preparation and photocatalytic activity study of ZnS-fluoropolymer electrospun fiber composites. In this paper, the ZnS-fluoropolymer electrospun fiber composites were prepared in 2 methods. One is the solution precipitation at room temperature, the MAA-co-TFA/PVDF electrospun mats as the carrier, zinc sulfide (ZnS) particles of diameter of about 50nm were uniformly immobilized on the surface of fluoropolymer electrospun fiber through solution precipitation at room temperature. The degradation of methylene blue in solution was performed by ZnS-fluoropolymer composites under UV irradiation. The results show residual mass fraction of methylene blue is 0.03% by ZnS-fluoropolymer composites at 220min, and is lower than that of ZnS nanoparticles under the same condition. The ZnS-fluoropolymer composites still have good photocatalytic activity and stability after 5 repeated tests. Other is hydrothermal precipitation methods, the PVDF-g-AA as the carrier, the zinc sulfide (ZnS) particles of diameter of 0.5-2μm, which have strong chemical interaction with the fibers, were uniformly immobilized on the surface of the fluropolymer electrospun fiber through hydrothermal methods. The degradation of methylene orange in solution with ZnS/PVDF-g-AA composites as the catalyst was performed with the aid of UV light. The results showed that ZnS/PVDF-g-AA composites were of good photocatalytic efficiency. It is attributed to the higher SBET of ZnS/PVDF-g-AA composites and the absorption-migration-photodegradation effect. The composites retained high photocatalytic activity even after 8 times repeating tests.Another, the MAA-co-TFA/PVDF electrospun mats as the carrier, Zinc ions were introduced onto the surface of nanofibers by coordinating with the carboxyl of MAA, and then sulfide ions were added to react with zinc ions to produce ZnS particles under hydrothermal condition. The ZnS particles with diameter of 100nm-300nm were uniform immobilized on the surface of electrospun fiber. The Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) results reveal that a chemical interaction exists between ZnS and fluoropolymer fibers. The photodecolorized of methylene blue in ZnS-(MAA-co-TFA/PVDF) nanocomposite system was considerably higher than that of ZnS powders system under UV irradiation. The results showed that ZnS-(MAA-co-TFA/PVDF) fibril composites were of good photocatalytic efficiency. It is attributed to the higher SBET of ZnS-(MAA-co-TFA/PVDF) fibril composites and the absorption-migration-photodegradation effect. The photocatalytic activity of ZnS-(MAA-co-TFA/PVDF) fibril composites changes indistinctively after 10 times of repeated use.(3) Preparation and photocatalysis study of TiO2-(MAA-co-TFA/PVDF) electrospun fiber nanocomposites. The MAA-co-TFA/PVDF electrospun mats as the carrier, the complex was formed between carboxyl on fluoropolymer electrospun fiber surface and titanium ion, and then the TiO2 nanoparticles of about 20nm in diameter were immobilized on the surface of fluoropolymer electrospun fibers through hydrothermal complex-precipitation. By controlling the reaction conditions, different sizes and numbers of TiO2 nanocrystals can be obtained. The Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) results reveal that an interaction exists between TiO2 and fluoropolymer fibers. The degradation of methylene blue solution is performed by TiO2-fluoropolymer fiber nanocomposites under UV irradiation. The results showed that TiO2-(MAA-co-TFA/PVDF) fibril composites were of good photocatalytic efficiency. It is attributed to the higher SBET of TiO2-(MAA-co-TFA/PVDF) fibril composites and the absorption-migration-photodegradation effect. The experimental results show that the TiO2-(MAA-co-TFA/PVDF) fibril composites have good photocatalytic stability after 10 times repeated photodecolorized testes. (4) Synthesis and characterization of TiO2/ZnS-fluoropolymer nanocomposites. The MAA-co-TFA/PVDF electrospun mats as the carrier, the complex was formed between carboxyl on fluoropolymer electrospun fiber surface and mental ion, and then the semiconductor nanoparticles were immobilized on the surface of fluoropolymer electrospun fibers through hydrothermal complex-precipitation. By controlling the reaction conditions, the TiO2-ZnS particles of 15nm-1.5μm in diameter were immobilized on the surface of electrospun fiber. The Fourier Transform Infrared Spectroscopy (FTIR) results reveal that a chemical interaction exists between TiO2-ZnS and fluoropolymer fibers. The photodecolorized of methylene blue solution is performed by TiO2-ZnS/fluoropolymer nanocomposites prepared with ZnSO4:TiOSO4=0.625% under visible irradiation. The results show that the TiO2-ZnS/fluoropolymer nanocomposites photocolorized efficiency for MB solution was 100% at 120 min, considerably higher than that of the nano TiO2 powder under the same condition. The experimental results show that the TiO2-ZnS/fluoropolymer nanocomposites have good recycling and stability after 10 times repeated photodecolorized tests.