【作者】 张昊；

【导师】 马晓华；

【作者基本信息】 华东理工大学 ， 化学工程与技术， 2020， 硕士

【摘要】 为了缓解全球淡水资源污染和紧缺的严重势态,膜分离技术的发展越来越受到重视。纳滤技术是一种起步较晚的新型压力驱动膜分离技术,具有渗透性高、操作压力低等特点,在许多场合能够代替传统的反渗透技术。常见的纳滤膜为复合结构,即由不同材质的多孔支撑层和致密分离层组成,其中分离层的设计、制备及优化对于复合膜的整体性能具有重要影响。为了追求纳滤膜性能的进一步提升,纳米材料在近年来逐渐被用于新型纳滤膜的设计与开发之中,并表现出一定的优势。MoS2纳米片是一种常见的二维材料,其表面平整、机械强度高、易于化学改性,且组装形成的层叠膜在水体中不存在明显溶胀,近年来在反渗透、纳滤、渗透汽化等液体分离领域都获得了相应的研究,充分发挥了自身的优势。本文基于MoS2纳米片设计并制备了新型的复合纳滤膜,解决了 MoS2纳米片在陶瓷中空纤维膜(CHF)上难以组装形成致密活性层、MoS2纳米片在制备超薄纳米复合(TFN)膜时与聚酰胺基质兼容性较差等问题,并对所制备的复合膜进行了一系列的表征,同时考察了它们的分离性能。具体内容如下:(1)液相剥离法制备MoS2纳米片:采用液相剥离法制备了 MoS2纳米片,为了获得高浓度且大尺寸的MoS2纳米片,实验探究了 MoS2初始浓度对于纳米片产率的影响,并采用差速离心法对获得的MoS2纳米片进行尺寸分级。结果表明:在一定范围内,MoS2纳米片的浓度随着初始浓度的增加而线性增加,当MoS2初始浓度过高,纳米片的浓度则会出现急剧下降,导致产率的下降,实验选定MoS2初始浓度的最优值为5 mg mL-1。进一步采用差速离心法对MoS2纳米片的尺寸进行分级,当离心转速逐级降低至500 rpm时,纳米片的平均尺寸获得了明显增加。最后,我们对于分级后的MoS2纳米片进行了包括表面形貌、结晶性、亲水性和荷电性在内的表征。(2)基于CHF构筑MoS2/聚乙烯亚胺(PEI)复合纳滤膜:以大孔径的CHF作为原始支撑层,首先采用浸涂-烧结法在其表面制备TiO2修饰层,再以此为基底采用抽滤辅助法将MoS2纳米片和PEI共同组装至其外表面,获得了 MoS2/PEI复合膜。结果表明:TiO2层有效地降低了 CHF的孔径和表面粗糙度,使得MoS2纳米片能够实现在其表面的堆叠,而不至于从膜层渗透出去。PEI的加入对于MoS2/PEI复合膜的结构及性能都至关重要,其不仅提高了 MoS2纳米片之间以及MoS2/PEI分离层与基底之间的界面粘结力,而且赋予复合膜一定的表面亲水性,同时使复合膜表面带上正电荷。MoS2/PEI复合膜具有优异的纳滤性能,在保持4.6 L m-2 h-1 bar-1纯水通量的同时,对于MgCl2的截留率高达95.5%,并且能够高效地移除水体中常见的重金属离子(如Cu2+、Zn2+、Mn2+、Ni2+)。(3)界面聚合法构筑单宁酸(TA)-Fe3+改性MoS2 TFN膜:采用界面聚合的方法,将TA-Fe3+络合物改性后的MoS2纳米片负载于聚酰胺活性层内,制备了 TFN纳滤膜。结果表明:当TA-MoS2纳米片的负载量为0.01 wt%时,TFN膜的表面粗糙度显著增加,其表面出现许多突起状的结构。另一方面,TA-MoS2纳米片引入了界面交联,与酰氯的水解以及酰氯与水相单体的反应形成竞争,降低了 TFN膜的表面亲水性,而且提高了活性层的交联度。与不含TA-MoS2纳米片的膜相比,TFN膜的水通量提高了约60%,选择性也略微得到加强。更多还原

【Abstract】 In order to relieve the severe situation of water contamination and shortage,membrane separation technology has received increasing attention.As a typical pressure-driven membrane technique,nanofiltration(NF)can replace reverse osmosis in some applications due to its many merits such as high water permeability and low operation pressure.Common NF membranes are based on a composite design,wherein a relatively dense skin layer is formed on a porous support layer(microfiltration/ultrafiltration membrane).It is worth mentioning that the design,fabrication,and optimization of the skin layer is of vital importance.To further improve the performance of NF membranes,various nanomaterials have been used to develop novel composite membranes.MoS2 nanosheets,as a sort of two-dimensional nanomaterial,have been applied in many water filtration techniques including reverse osmosis,NF,pervaporation,etc.Compared with graphene oxide(GO),MoS2 nanosheets have many advantages such as smooth surface,high rigidity,and easy functionality.Moreover,the lamellar MoS2 membrane has smaller swelling degree than the pure GO membrane.In this work,we fabricated novel composite NF membranes containing MoS2 nanosheets,which provides some useful guidelines for the assembling of MoS2 nanosheets on the surface of ceramic hollow fiber(CHF)to form selective separation layer,and the seamless incorporation of MoS2 nanosheets into the polyamide layer by interfacial polymerization.The detailed content of this paper is as follows:(1)Preparation of MoS2 nanosheets through liquid phase exfoliation:MoS2 nanosheets were obtained by liquid phase exfoliation.In order to gain MoS2 nanosheets with high concentration and large lateral size,we optimized the initial concentration of bulk MoS2,followed by size selection through controlled centrifugation.According to experimental results,we find that the concentration of MoS2 nanosheets increases linearly with the increase of the initial MoS2 concentration to 5 mg mL-1.Further increasing the initial MoS2 concentration would cause a sharp decline of the concentration of MoS2 nanosheets,which corresponds to a decrease of the yield of MoS2 nanosheets.Therefore,5 mg mL-1 was selected as the optimal initial MoS2 concentration.After size selection by controlled centrifugation with final centrifugation rate of 500 rpm,it is found that the lateral size of MoS2 nanosheets has been obviously augmented.Finally,MoS2 nanosheets with relatively large lateral size are systematically characterized in terms of surface morphology,crystallinity,hydrophilicity,and surface charge.(2)Construction of MoS2/polyethyleneimine(PEI)composite NF membranes on the CHF:Firstly,Tio2 interlayer was prepared on the outer surface of the original CHF with large pores via dip-coating and sintering.Then,we employed the filtration-assisted method to assemble MoS2 nanosheets and PEI on the surface of the TiO2-CHF substrate and thus obtained the MoS2/PEI composite membrane.According to experimental results,it is clear that the Tio2 interlayer substantially decreases the pore size as well as the surface roughness.It is found that PEI plays an important role in both the morphology and physicochemical properties of the membrane.That is,PEI enhances the interfacial adhesion between adjoining MoS2 nanosheets,as well as the MoS2/PEI layer and the substrate.Moreover,PEI endows the composite membrane with positively charged and hydrophilic surface.The obtained MoS2/PEI composite membrane displays an outstanding NF performance with pure water permeability of 4.6 L m-2 h-1 bar-1 and MgCl2 rejection of 95.5%,which can be used for efficient removal of heavy metal ions commonly found in water bodies(e.g.,Cu2+、Zn2+、Mn2+、Ni2+).(3)Construction of thin-film nanocomposite(TFN)membranes containing tannic acid(TA)-Fe3+modified MoS2 nanosheets:MoS2 nanosheets were modified with TA-Fe3+coordination complexes and then embedded within the polyamide layer to construct TFN NF membranes.It is observed that the TFN membrane with 0.01 wt%addition of TA-MoS2 nanosheets demonstrates increased surface roughness with the appearance of scattered protuberances.On the other hand,TA-MoS2 nanosheets introduce interfacial crosslinking,which can compete with the hydrolysis of acid chloride groups as well as the reaction between amine groups and acid chloride.Thus,the TFN membrane exhibits reduced surface hydrophilicity and enhanced crosslinking degree.Compared with the control membrane without the addition of TA-MoS2 nanosheets,the TFN membrane displays approximately 60%improvement of water permeability accompanied by slightly enhanced rejection properties.更多还原