【作者】 何铁石；

【导师】 徐卫兵；

【作者基本信息】 合肥工业大学 ， 材料学， 2009， 博士

【摘要】 半导体光催化剂,如二氧化钛(TiO2)和硫化锌(ZnS),在降解环境中有机污染物方面表现出了强氧化性、污染物矿化完全、催化效率高等特点,在处理水体系中难降解有机污染物方面具有潜在的应用前景。同时,粉体光催化材料在水处理的应用中存在太阳光利用率低、容易团聚、难回收利用等问题阻碍其在环境治理中的直接应用。为此开发出兼具半导体粒子高催化效率和聚合物柔韧性的负载型有机-无机复合光催化材料对于半导体光催化剂的规模化应用具有重要理论意义和实践价值。本博士论文研究重点是利用高压静电纺丝技术制备具有纳微米尺寸多孔结构、高透光率和较好耐光催化降解能力的含羧基氟碳聚合物电纺纤维毡,并以其作为载体,在低温液相条件下,采用外部负载法制备半导体-氟碳聚合物电纺纤维复合材料。在紫外光/可见光照条件下,以水溶液中有机染料为目标降解物,研究复合材料光催化活性和稳定性。主要内容包括以下4个部分:(1)聚偏氟乙烯电纺纤维的制备及其表面改性研究:利用高压静电纺丝技术制备了纤维直径分布在100nm-200nm,具有开放未交联结构的聚偏氟乙烯(PVDF)电纺纤维毡。为提高半导体粒子在PVDF电纺纤维表面的结合强度和负载率,本文采用两种方法进行PVDF电纺纤维表面羧基化改性:第一,利用丙烯酸和丙烯酸三氟乙酯的共聚物与PVDF共混进行静电纺丝,含羧基的氟碳共聚物与PVDF相容性良好,制备了表面含有羧基官能团的氟碳聚合物(MAA-co-TFA/PVDF)电纺纤维毡,其在水热150℃以下处理8h电纺纤维的形貌变化不大;第二,采用常压介质阻挡放电-紫外辐射方法制备PVDF电纺纤维表面接枝丙烯酸的含羧基氟碳聚合物(PVDF-g-AA)电纺纤维毡。放电处理60s和120s条件下制备的PVDF-g-AA电纺纤维毡具有较好的丙烯酸接枝率和纤维形貌。(2) ZnS-氟碳聚合物电纺纤维复合材料的制备及其光催化性能研究:本文采用2种方法制备了ZnS-氟碳聚合物电纺纤维复合材料。第一,常温溶液法:用(MAA-co-TFA/PVDF)电纺纤维毡作为载体,利用电纺纤维表面羧基对锌离子的络合能力,在常温溶液中用均匀沉淀法在纤维表面制备分布均匀、直径约50nm的ZnS-氟碳聚合物电纺纤维复合光催化材料,在紫外光照下它对水中次甲基蓝光催化降解质量残留百分率220min时为0.03%,低于同等条件下的纳米ZnS粉体,重复5次光催化降解仍具有较好的稳定性。第二,水热沉淀法:以PVDF-g-AA电纺纤维毡为载体,利用电纺纤维表面羧基对锌离子的络合能力,在水热条件下制备与纤维表面有化学键作用、均匀分布、直径0.5-2μm的ZnS/PVDF-g-AA纤维复合光催化材料。同时,以紫外灯为光源,甲基橙为目标光催化降解物,研究了复合材料的光催化活性。结果表明,ZnS/PVDF-g-AA纤维复合材料的高催化比表面积和复合材料间存在的吸附-迁移-光降解作用使其具有较高的光催化效率,重复8次光催化降解后仍具有较好的催化活性。另外,采用MAA-co-TFA/PVDF电纺纤维毡为载体,利用电纺纤维表面羧基对锌离子的络合能力控制ZnS晶体在纤维表面成核和增长,经水热共沉淀方法,在氟碳聚合物纳米纤维表面负载与纤维化学键合、粒径100nm-300nm的ZnS-氟碳聚合物电纺纤维复合材料。在紫外光照射下,对水中次甲基蓝光催化降解研究表明:ZnS-氟碳聚合物电纺纤维复合材料具有比纳米ZnS粉体高的光催化效率。重复10次光催化降解水中次甲基蓝实验,光催化降解率保持不变。(3) TiO2-(MAA-co-TFA/PVDF)电纺纤维复合光催化材料的制备和表征:利用含羧基的氟碳聚合物(MAA-co-TFA/PVDF)电纺纤维作为载体,首先通过表面羧基化改性的电纺纤维对钛离子进行络合吸附,然后在水热条件下,使TiO2粒子在氟碳聚合物电纺纤维表面成核、增长,得到粒径20nm以内、分布均匀的TiO2-(MAA-co-TFA/PVDF)电纺纤维复合光催化材料。在紫外光照射条件,以水溶液中次甲基蓝为目标光催化降解物,研究TiO2-(MAA-co-TFA/PVDF)电纺纤维复合光催化材料的光催化效率和稳定性。结果表明,水热反应6h制备的复合材料具有较好的对次甲基蓝的光催化降解率,远高于相同条件下纳米TiO2粉体的光催化降解率,其重复10次后的光催化降解率保持不变。(4)复合半导体-氟碳聚合物电纺纤维复合材料的制备及其可见光催化性能研究:用表面含有羧基的(MAA-co-TFA/PVDF)电纺纤维毡作为载体,利用电纺纤维表面的羧基对水溶液中的金属离子络合吸附作用,水热条件下控制半导体粒子在纤维表面的成核、增长。通过控制反应体系中掺杂离子的数量,制备与纤维表面有化学键合作用、分布均匀的粒径10nm-1.5μm的TiO2-ZnS/氟碳聚合物电纺纤维复合材料。在可见光照条件下,以水中次甲基蓝为目标光催化降解物,研究复合材料的光催化活性和稳定性。结果表明,复合材料的高催化比表面积和复合材料间存在的吸附-迁移-光降解作用使其具有较高的光催化效率。水热反应体系中ZnSO4:TiOSO4=0.625%制备的复合材料对次甲基蓝的光催化降解率120min时为100%,远高于相同条件下的纳米粉体TiO2光催化降解率,其重复10次的光催化降解率保持不变。更多还原

【Abstract】 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.更多还原