| Membrane separation technology has lots of advantages, such as high separation efficiency, simple operation, low cost, ect. And it has broad application prospects in the fields of environment, electronics, chemistry, energy and bio medicine, therefore, it has received more and more attention in recent years. Reducing the cost and expanding the application of the membrane are the main factors to promote the progress of membrane separation technology. At present, the researchers are committed to improving the membrane fouling resistance, oil water separation performance and chemical resistance. There are some polymers which can be used as membrane materials, such as Polypropylene, Polyether sulfone, Polytetra fluorothylene and Polyvinylidene flroride.Polyvinylidene fluoride (PVDF) has received great attention as a membrane material because of its outstanding properties such as high mechanical strength, thermal stability, chemical resistance, and high hydrophobicity, compared to other commercialized polymeric materials. However, there are two main problems in the use of PVDF membranes. On one hand, it can be easily contaminated in the water separation process due to its hydrophilicity, which is not beneficial to practical application. So it is not conducive to the actual separation process. On the other hand, PVDF membrane does not possess super hydrophobicity, thus, it can’t be used as oil-water separation membrane. Therefore, it is of great significance to increase the hydrophilicity of PVDF membranes in order to prolong its service life or to prepare the PVDF membranes with super hydrophobicity by special methods for oil-water separation.The purpose of this paper is to prepare PVDF porous membrane with good hydrophilicity to prolong its service life or with super hydrophobicity for oil-water separation. First of all, this paper studied the influence of different additives on the morphology and crystal structure of PVDF membranes, such as graphene oxide, carbon nanotubes. Secondly, this paper studied the influence of PVP and GO on the PVDF porous membrane structure, and GO’s effect on PVDF porous membrane hydrophilicity and adsorption properties. In the end, prepared the PVDF/CNTs nano-composite fiber membrane with super hydrophobicity by means of electrospinning method and studied the oil-water separation property of the PVDF/CNTs fiber membranes. The main research results are as follows:(1) Porous membranes of PVDF/GO and PVDF/CNTs composites were prepared by immersion precipitation method. Because the surface of GO contains a large number of polar groups (carboxyl, hydroxyl, carbonyl), the presence of these polar groups can enhance the interaction between the casting membrane solution and water, in other words, the exchange rate between the solvent and the non solvent is increased. Therefore, the surface average pore size of PVDF/GO composite membrane decreased and the number of surface pores increased with the increase of GO, the size on the cross section increased with the increase of GO content. CNTs is an excellent nucleating agent for PVDF, and CNTs can induce the crystallization phase separation of PVDF in the membrane forming process, thus, the number of the surface pores decreased with the increase of CNTs. Since the surface of GO does not contain polar oxygen containing functional groups, the exchange rate of solvent and non solvent will not be accelerated. Therefore, the shape and the average pore size of PVDF/CNTs thin film are not changed.(2) Contact angle test showed that the contact angle of PVDF/PVP/GO composites membranes decreased with the increase of GO. Among them, the pure PVDF membrane had the largest water contact angle of 80.9°,and the PVDF/PVP/GO2 membrane had the smallest water contact angle of 49.7°. The SEM results showed that the addition of PVP could induce the formation of large pores on the surface and cross sections of the membrane. The addition of GO can decrease the average pore size on the surface and increase the average pore size on the cross section of the membrane. So the porosity of PVDF/PVP/GO composites increases with the addition of PVP and GO, the PVDF/PVP/GO2 membrane had the largest porosity of 93.3%. Through the adsorption performance test, it was found that the adsorption capacity of PVDF/PVP/GO composite porous membrane was enhancedwith the increase of GO content, and the PVDF/PVP/GO2 porous membrane has the best adsorption capacity to methylene blue.(3) The influences of solution concentration, solvent type and humidity on the structure of PVDF nano fiber membrane were studied. The PVDF concentration increased from 15%(mass volume ratio) increased to 25%, the beaded structure gradually disappeared and uniform diameter of fibers formed. Under the condition of humidification, the exchange of the solvent with water in the air lead the formation of the poor phase and rich phase of the polymer, and the poor phase is gradually grown up forming the pores on the fiber surface. Therefore, a lot of pores formed on the fiber surface in the humidification condition.The contact angle test showed that the water contact angle of PVDF/CNTs nano composite fiber membrane increased with the increase of CNTs content, all the fiber membranes have good oil water separation performance. The PVDF/CNTs1 sample has the best oil water separation performance. |
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