【作者】 李东升；

【导师】 肖武；

【作者基本信息】 大连理工大学 ， 化学工程（专业学位）， 2021， 硕士

【摘要】 混合基质膜（MMM）的气体分离性能直接受填料性质的影响,而经过十余年的研究已经证明基于MOFs的MMM比传统无机填料的MMM更具优势。此外,二维纳米材料由于其易修饰、高纵横比的特点,也逐渐被纳入MMM的研究范畴,而且它还可与MOFs联用实现双向增强,被认为是继MOFs材料后最有发展前景的填料之一。MOFs基MMM虽有诸多优势,但也同时存在如填料呼吸效应、一定界面缺陷以及多孔填料被聚合物链堵孔等问题,本论文以骨架结构极稳定的ZIF-90作为掺杂材料,通过后合成修饰（PSM）方法使用胺烷对ZIF-90进行了表面修饰,并且考虑到了改性会对ZIF-90的孔结构等产生一定的负面影响,因此还采用了空间分化的修饰策略,通过改变胺烷的种类和用量来探究改性条件对ZIF-90和其Pebax基MMM气体分离性能的影响。实验发现,胺烷的改性不仅不会改变ZIF-90的晶体结构,还能够在ZIF-90表面形成有机-有机高相容的界面,并作为保护孔结构的保护层。除此之外,该保护层虽然会降低填料本身的比表面积及孔体积,但是在合适的空间分化度下会与聚合物产生某种特殊的有益于气体分离的相互作用,可以明显提高MMM的分离性能。其中使用正丙胺（PLA）改性的PLA@ZIF-90/Pebax系列混合基质膜相较于纯ZIF-90/Pebax相比,CO₂/N₂选择性与CO₂渗透性都有着不同程度的提高,分离性能最佳的混合基质膜的CO₂/N₂选择性为70,CO₂渗透率达到了140 Barrer,与纯Pebax相比分别提高了45.8%和79.4%。另一方面,二维纳米材料有着大多数MOFs材料所不具备的高纵横比和更高空间利用率的特性,在气体分离领域有着巨大优势和潜力。因此为了得到更高性能的混合基质膜,本文选择具有筛分孔结构的g-C₃N₄二维纳米片为模板,利用其表面的-NH₂实现了ZIF-90的原位生长,并将其与ZIF-90相结合构造出一种0维/2维复合材料。实验在25℃酸刻蚀条件下剥离得到了完整的二维g-C₃N₄纳米片,并在后续的生长实验中发现虽然ZIF-90在g-C₃N₄纳米片上生长密集度较低,但ZIF-90的生长可以在很大程度上改善柔性纳米片的折叠、堆叠现象,使纳米片在膜基质中可以完全伸展开,相较于不生长ZIF-90的g-C₃N₄纳米片空间利用率更高。最后通过气体测试实验证明了g-C₃N₄纳米片具有极强的CO₂/N₂筛分作用,ZIF-90/g-C₃N₄（ZCN）系列混合基质膜的气体分离性能远高于g-C₃N₄（CNN）系列混合基质膜,在8.0 wt.%ZCN负载量下处取得了最佳的分离效果,CO₂/N₂选择性为84.4,CO₂渗透率为110.5 Barrer,相比纯Pebax膜分别提升了75.7%和41.6%,突破了2008年Robeson上限。更多还原

【Abstract】 The gas separation performance of mixed matrix membranes（MMMs）is directly affected by the properties and quality of the filler.After decades of research,it has been proved that MMM based on MOFs is more advantageous than MMM based on traditional inorganic fillers.In addition,two-dimensional nanomaterials are gradually included in the research category of MMM due to their characteristics of easy modification,high aspect ratio,even can be combined with MOFs to improve their performance,thus it has been considered to be one of the most promising fillers after MOFs.Though the MOFs-based MMM has so many advantages,it also has problems such as the breathing effect of the fillers,the interface defects between the polymer and the fillers,and the blocking of the porous filler by the polymer material.In this work,ZIF-90 with extremely stable framework structure was used as the doping material.Afterwards,ZIF-90 was modified by post-synthetic modification（PSM）technology with amines,and a spatially differentiated modification strategy was used to explore the effect of modifiers with different chain length structures and their dosages on ZIF-90 and gas separation performance of its Pebax-based MMM.It was found that the modification of amine alkanes not only affect the crystal structure of ZIF-90,but can also form an“organic-organic”highly compatible interface on the surface of ZIF-90 and act as a protective layer to protect the pore structure.In addition,although the protective layer will reduce the specific surface area and pore volume of the filler itself,it will produce a special interaction with the polymer that is beneficial to gas separation under the appropriate degree of spatial differentiation,which can significantly improve the separation performance of MMM.Compared with ZIF-90/Pebax,the CO₂/N₂ selectivity and CO₂permeability of the PLA@ZIF-90/Pebax series MMM modified with n-propylamine（PLA）have been improved to some degrees respectively,the mixed matrix membrane with the best separation performance has a CO₂/N₂ selectivity of 70 and a CO₂ permeability of 140 Barrer,which is 45.8%and 79.4%higher than that of pure Pebax membrane.On the other hand,two-dimensional nanomaterials have the characteristics of high aspect ratio and higher space utilization that most MOFs do not have,so they have huge advantages and potentials in the field of gas separation.In order to obtain a higher performance mixed matrix membrane,in this paper,the two-dimensional nanosheet g-C₃N₄ with sieving pore structure was selected as templates,and then uses the-NH₂ on its surface to achieve the in-situ growth of ZIF-90,a 0-dimensional/2-dimensional composite material was constructed by combining g-C₃N₄ and ZIF-90.In the experiment,a complete two-dimensional g-C₃N₄nanosheet was obtained by peeling off under the acid etching condition at 25°C.In the subsequent growth experiment,it was found that ZIF-90 has a low growth density on g-C₃N₄nanosheet,but the ZIF-90 can greatly overcome the folding and stacking phenomenon of flexible nanosheets,the composite material can be fully stretched,caused much higher space utilization rate compared with the g-C₃N₄ nanosheets without growing ZIF-90.Finally,the gas test experiment proved that the g-C₃N₄ nanosheets have a strong CO₂/N₂screening effect.The gas separation performance of the ZIF-90/g-C₃N₄ series MMMs is much higher than that of the g-C₃N₄ series mixed matrix membranes.The best separation effect was achieved under the loading of 8.0 wt.%composite material.The CO₂/N₂ selectivity was 84.4,and the CO₂permeability was 110.5 Barrer.Compared with the pure Pebax membrane,it was increased by75.7%and 41.6%,which break through the Robeson upper bound in 2008.更多还原