【作者】 马强；

【导师】 王政；

【作者基本信息】 宁夏大学 ， 应用化学， 2018， 硕士

【摘要】 膜分离技术具有操作简单、分离条件温和、能耗低、分离选择性高等优点,在化学分离中具有独特的应用优势。类沸石咪唑骨架(ZIFs)作为一种的新型金属有机骨架(MOFs)材料,继承和发展了无机分子筛材料优异的多孔性和化学物理稳定性,在混合体系的分离中具有很大的应用优势。本工作主要针对三种不同性质的混合体系,结合ZIF-L和ZIF-8两种经典的类沸石咪唑骨架材料的特殊理化性质,设计了三种不同功能的膜分离材料,并对不同性质的混合体系进行分离性能测试,主要研究内容如下:1.室温下制备得到了片径尺寸为6.3×2.54μm,厚度约为120 nm的“柳叶”状二维片层ZIF-L晶粒。采用简单的真空抽滤法在孔径为220 nm的尼龙载体表面制备得到了具有一定机械强度和不同厚度的ZIF-L膜,其中ZIF-L晶粒之间散乱无序的堆积形式形成了不规则的孔隙结构,ZIF-L膜基于自身不规则的孔隙结构实现了色素溶液高渗透通量下的高选择性分离,相比于同等质量ZIF-L晶粒对于色素分子的吸附作用,膜分离可以在短时间内实现色素溶液的高效分离,并且保持了较高的分离循环稳定性。上述研究为发展一种高效快速的色素溶液分离方法提供了新思路。2.室温下制备出粒径均匀尺寸约为200 nm且形貌规则的ZIF-8晶粒,通过将ZIF-8与聚乙烯亚胺(PEI)混合,采用Dip-coating法在不锈钢网表面制备得到致密的ZIF-8晶种层。经过二次晶化反应制备得到连续致密的ZIF-8/不锈钢网复合膜,通过控制晶化时间实现了不锈钢网孔径的调控。ZIF-8/不锈钢网复合膜具有空气中疏水和水下疏油性,在一定孔径范围内,其水下疏油性保持不变。当不锈钢网孔径由16.9 μm减小至14 μm时,其水下油的接触角由148.3°急剧增加至159.5。,表现出水下超疏油性。ZIF-8/不锈钢网复合膜对于分层油水混合物的分离效率高达99.0%以上,最大渗透通量为50 Lm-2 s-1,对于乳化油的分离效率仍可达到92.0%,渗透通量高于380 Lm-2h-]。10次循环分离测试后,复合膜分离效率和渗透通量保持不变,体现出了良好的循环分离稳定性,这为发展MOFs膜用于油水分离领域奠定了理论和实验基础。3.在前期研究基础上,进一步采用溶剂蒸发诱导自组装法在氧化铝表面经过多次组装制备得到具有不同密度的ZIF-8晶种层,通过控制二次晶化时间得到具有不同厚度和取向度的ZIF-8膜。SEM和XRD表征测试结果证实,ZIF-8膜致密性和取向度随着晶种层厚度和二次晶化时间的增加而进一步提高。经三次组装、二次生长4 h后制备得到厚度约为12.53μm,CPO(200)=0.84的高度c-轴取向的ZIF-8膜,单组份气体渗透测试结果证实,高度c-轴取向的ZIF-8膜具有良好的致密性。不同取向度ZIF-8膜的H2/CO2混合组分分离性能测试结果显示,分离系数随着取向度的增加而缓慢升高,证实ZIF-8膜取向度的提高对于H2/CO2混合组分的分离效果有促进作用。该研究为发展高度取向MOFs膜并用于气体分离领域提供了实验依据。更多还原

【Abstract】 Membrane separation technology has unique advantages in chemical separation due to its advantages of simple operation,mild separation conditions,low energy consumption and high separation selectivity.Zeolitic imidazolate frameworks(ZIFs)as a new type of metal organic frameworks(MOFs),inheriting and developing the excellent porosity,chemical and physical stability of inorganic zeolite,which contributes ZIFs possess great application advantages in the separation of mixtures.This work designs membrane materials with different functions consist of ZIF-L or ZIF-8 for three kinds of mixtrues separation.The main research as follows.1.The two-dimensional ZIF-L crystallites with leaf-shaped morphology with a diameter of 6.3×2.54 μm and a thickness of about 120 nm were prepared at room temperature.ZIF-L films with certain mechanical strength and different thicknesses were prepared on a nylon with a pore size of 220 nm by a simple vacuum filtration method.The Irregular structure of ZIF-L films formed by disordered stacked of ZIF-L crystals,which allowed ZIF-L films to achieve dyes removal with high selectivity under ultra-high flux.Membrane-based separation process can achieve highly efficient dyes removal in a short time and maintain high separation cycle stability compared with the adsorption of dyes by the same mass of ZIF-L crystals.The research provides a new ideal for developing an efficient and rapid membrane-based separation method for dyes removal.2.The ZIF-8 crystals with regular morphology and average size of about 200 nm were prepared at room temperature.The ZIF-8 nanocrystals were easily coated onto stainless steel meshes and a dense seed layer was formed under the action of polyethyleneimine(PEI).The ZIF-8 film coated stainless steel meshes were prepared by secondary growth method,and the pore size of the stainless steel mesh can be modulated by simply varying the crystallisation time.ZIF-8 film coated stainless steel meshes possess hydrophobicity in air and oleophobicity underwater,and its oleophobicity remains constant within a certain pore size range.The underwater oil contact angle of ZIF-8 film coated stainless steel mesh sharply increased from 148.3° to 159.5° when the pore size decreased from 16.9 to 14 μm,which indicates that the ZIF-8 film coated meshes possess underwater superoleophobicity.Both immiscible and emulsified oil/water mixture can be efficiently separated with the separation efficiency respectively high up to 99.0%and 92.0%,and the flux up to 50 L m-2 s-1 and 380 L r-2 h-1 respectively.After 10 cycles,the separation efficiency and flux of ZIF-8 film coated meshes remains constant,which proves that the ZIF-8 film coated stainless steel meshes possess excellent stability and recyclability.This work lays a foundation for the development of MOF films for oil/water separation under practical working conditions.3.On the basis of previous studies,ZIF-8 seed layers with different densities have been prepared on the surface of alumina by evaporation-induced self-assembly(EISA)method,and then ZIF-8 membranes with diffirent thicknesses and orientations were fabricated by controlling the crystallization time.The SEM and XRD comfirm that the compactness and orientation improved with the increase of seed layer thickness and crystallization time.Highly c-oriented ZIF-8 membrane with a thickness of about 12.53 μm and CPO(200)=0.84 is obtained after tertiary assembly and crystallizing for 4 h,the single gas permeation test confirmes that ZIF-8 membrane is defect-free.The separation performance of ZIF-8 membrane for H2/CO2 is improved with the increase of orientation,and it comfirms that there is a positive effect on gas sepatation performance to improve the membrane’s orientation.更多还原