【作者】 王小平；

【导师】 夏圣骥；

【作者基本信息】 同济大学 ， 市政工程， 2022， 博士

【摘要】 聚酰胺复合纳滤膜能够有效去除水体中的有机小分子和无机盐组分,在水处理领域巨大应用潜力,但目前仍存在渗透-分离平衡上限的限制以及膜材料制备技术不足、缺少膜改性系统性研究以及相关机制理论不完善的问题。本研究以纳米材料在基膜和聚酰胺分离层中均能有效提升纳滤膜性能的理论基础,围绕二硫化钼（Mo S₂）纳米材料进行不同形式改性纳滤膜,开发了可应用于膜法水处理的新型高性能薄膜纳米复合（TFC）聚酰胺纳滤膜,探究了Mo S₂在膜材料中的丰度、空间分布及赋存形态等对纳滤膜微观结构和性能的影响,阐释Mo S₂的不同改性机理,及其对不同目标污染物的截留机理,并反馈优化制膜工况,实现了纳滤膜的渗透性-选择分离性能协同增强。本研究对于开发具有靶向污染物去除功能的新一代水处理膜理论和方法建立具有一定的指导意义。首先基于一步水热法成功制备了聚乙烯醇改性的亲水层插纳米花-Mo S₂（HF-Mo S₂）,并将其共混掺杂引入聚偏二氟乙烯（PVDF）超滤基膜中,进而通过界面聚合反应制备得到纳米材料改性复合纳滤膜,通过对改性膜形貌结构和理化性质的系统分析探究纳米材料改性对纳滤膜的影响。改性膜具有更薄的聚酰胺皮层厚度（56 nm）和在p H值3-10范围内更高的电势电位值,这一结果表明高盐截留率得益于空间位阻效应和唐南电荷排斥效应协同作用。HF-Mo S₂添加量为0.75 wt.%所制备的改性膜（MT-0.75%）具有最佳性能,纯水通量为21.5 LMH/bar,Mg SO₄和Na₂SO₄的截留率分别为97.75%和98.6%。还考察了复合膜的耐有机溶剂和长期运行稳定性,结果表明以PVDF为支撑层的聚酰胺纳滤膜均具有良好的有机溶剂耐受性和7天长期运行稳定性,同时改性膜对东海海水也具有更好的淡化效果,有望应用于海水淡化前处理领域。其次,在界面聚合反应过程中引入HF-Mo S₂纳米材料以实现聚酰胺层改性。首先通过探针超声和高速离心结合的方式制备得到能保持9个月长期稳定的HF-Mo S₂分散液,然后使用抽滤HF-Mo S₂/哌嗪水相共沉积于基膜表面的方法制备了具有明显褶皱纳米通道的改性纳滤膜。改性膜表面沉积的150-200 nm左右的HF-Mo S₂使得膜表面出现以纳米材料为中心的帐篷结构或条纹性褶皱结构形貌,而褶皱形貌正面细长、背面粗条的形貌特征证明了在聚酰胺层内围绕纳米颗粒形成向内凹陷的纳米水通道,显著增加了膜表面粗糙度和过水面积,有利于提升纳滤膜渗透性。HF-Mo S₂负载量为10μg/cm²制备得到的纳米材料改性膜（M3膜）性能最佳,水通量为18.4 LMH/bar,相比于空白对照膜M0（9.1 LMH/bar）,通量提升2倍。同时对常见Na Cl、Ca Cl₂、Mg Cl₂、Mg SO₄、Na₂SO₄等五种无机盐单组分溶液的截留率分别为30.85%、39.6%、45.6%、98.2%和99.1%。此外,改性膜的混盐溶液的渗透率相比空白膜提高了近3倍,同时保持良好的分离效果,具有更优的水处理应用前景。为了进一步降低无机Mo S₂纳米颗粒和有机聚酰胺基质的异质结构不相容问题而对聚酰胺层完整性的不良影响,本论文基于Mo S₂纳米片可以与巯基乙酸的化学偶联作用的机理,在HF-Mo S₂表面成功接枝羧基官能团,进而使用抽滤共沉积羧基@Mo S₂/哌嗪后界面聚合法制备得到改性聚酰胺纳滤膜。对比分析HF-Mo S₂改性纳滤膜和羧基@Mo S₂改性纳滤膜的负载量变化,计算得到平均每个Mo S₂分子表面接枝约10.13个羧基官能团,有效增加了材料的亲水性。改性后的Mo S₂纳米颗粒和聚酰胺基质具有更好的相容性,制备得到的改性聚酰胺膜完整性更好,并具有更高的膜表面亲水性和过水面积。负载量为49.7μg/cm²制备得到的M4膜性能最佳,水通量为25.8 LMH/bar,相比于空白膜M0（9.6LMH/bar）,通量提升2.7倍,同时对Mg SO₄和Na₂SO₄的单组分溶液截留率分别为97.8%和98.5%。改性后的羧基@Mo S₂改性纳滤膜相比直接水相掺杂改性表现出更优的纳滤膜性能,表明纳米材料表面改性也可以有效增强材料本身特性,而接枝有机官能团可以进一步增加和有机聚酰胺基质的相容性,减轻异质结构引起的膜缺陷问题,可以为纳米材料接枝改性提供一定的理论支撑。相比于水相改性,有机相改性方法在纳滤膜改性的应用也被关注和研究。通过在Mo S₂材料接枝酰氯基团,构建外部具有丰富酰氯官能团的酰氯@Mo S₂,材料表观形貌无明显变化,真空XPS验证了酰氯化成功。并将其以共价掺杂有机相方式引入分离层中,改性膜的膜表面Zeta电位和亲水性增强。分析空白对照膜和改性膜的基本分离性能,结果表明引入酰氯@Mo S₂材料可以显著提升纳滤膜的纯水渗透通量,最高可达34.2 LMH/bar,并且对无机盐溶液的截留率也有所提升,结合截留分子量结果分析证明了酰氯@Mo S₂材料固有的对金属离子的高分离性能主导了更高无机盐分离性能。在保持分离能力和空白膜相当的前提下,改性膜的混盐溶液渗透通量可以达15.6 LMH/bar,是空白膜M0（4.4LMH/bar）的3.5倍,这可以显著降低能耗,具有更优良的深度水处理应用前景。本论文构建并分析了Mo S₂四种不同改性方式制备的改性纳滤膜性能,结果表明,HF-Mo S₂不同改性方式均能提升纳滤膜性能,以期为制备高性能聚酰胺纳滤膜提供科学参考和技术支撑。更多还原

【Abstract】 Thin-film composite（TFC）polyamide（PA）nanofiltration（NF）membranes is considered as promising technologies for the removal of organic pollutants and inorganic salts during advanced water treatment.Although some improvements in the performance of the NF were achieved,a further application in the pilot and even larger-scale research was hindered,considering the trade-off between water permeability and salt selectivity,insufficient material preparation,and imperfect related mechanism theory.Based on the nanomaterials can effectively improve the performance of NF membranes by introducing into the substrates and the polyamide layer,we fabricated a new high-performance thin film nanocomposite（TFC）polyamide NF membrane by modified with different molybdenum disulfide（Mo S₂）nanomaterials introducing methods.In addition,the influence of Mo S₂ on the micro-structure and properties of NF membranes was explored.We revealed the underlying membrane modification mechanisms and its interception mechanism for different target pollutants.The membrane fabricated conditions were optimized basdd on the performance feedbacks,which help to enhance the permeability and selectivity synergistically.This research has some implications for the development of a new generation of water treatment membrane theory and method with targeted pollutant removal function.Firstly,based on the one-step hydrothermal method,polyvinyl pyrrolidone（PVP）-modified hydrophilic hierarchical flower-like structured molybdenum disulfide nanosheets（HF-Mo S₂）was successfully prepared.Then,we fabricated a thin-film composite membranes with a nanocomposite substrate（TFCn）nanofiltration membranes（NFMs）by interfacial polymerization on polyvinylidene fluoride（PVDF）substrates modified with HF-Mo S₂.The physical and chemical properties of the control membrane and the modified nanofiltration membrane were characterized by morphological characterization means and spectral chemical analysis methods.The TFCn membranes exhibited a water flux up to 21.5 LMH/bar and rejection rates of 98.6%for Na₂SO₄.Steric hindrance and Donnan exclusion together contributed to high salt rejection rates,as evidenced by a less polyamide layer thickness such as 56 nm and a high surface negative charge at p H 3-10.Note that the nanocomposite substrate became more porous,more hydrophilic,and rougher than the non-nanocomposite one,due to an increase in the fraction of macroporous on the surface,which was known to affect the performance of the polyamide layer.The high content of HF-Mo S₂ incorporated in PVDF substrate led to enhanced hydrophilicity and,consequently,a cross-linking degree of defect-free polyamide,resulting in declines in thickness and increases in water permeability and salt rejection.Furthermore,TFCn NFMs exhibited an excellent organic solvent resistance and long-term stability,indicating that HF-Mo S₂incorporation had no adverse effect but even improved their structural stability.Compared to NFMs without Mo S₂ modification,NFMs with Mo S₂ modification showed a better performance for desalination of mixed salt solution and excellent anti-biofouling properties for lysozyme and bovine serum albumin.Taking together,the TFN NFMs provide high permeability and rejection rate without a decline in structural stability.Therefore,TFCn NFMs were promising candidates for practical water desalination treatment.Then,we introduced the nanomaterials during the interfacial polymerization reaction to achieve polyamide matrix modification.First,we prepared the HF-Mo S₂dispersion solution with long-term stability for nine months by combining probe-ultrasonic and high-speed centrifugation.And then,the thin-film nanocomposite（TFN）membranes with crumpled nanochannels were fabricated by vacuum filtration assisted co-deposition of the HF-Mo S₂/piperazine（PIP）aqueous monomers.The PIP monomer solution stored in the space between nanosheets enabled HF-Mo S₂ to participate in the interfacial polymerization reaction,which will enhance the adhesion of the nanomaterial and polyamide cortex.And the prepared TFN membranes can maintain structural stability during the membrane filtration process.TFN has a rougher surface than the smooth surface of the control membrane,possibly because of the appeared tent structure centered on the nanomaterial or a striped crumpled structure morphology after150-200 nm HF-Mo S₂ deposited on PES substrate membrane surface.The features of the crumpled morphology of slender front and thick strips on the back prove that inwardly concave nano-water channels are formed around the nanoparticles in the polyamide layer.This structure significantly increaseed the surface roughness and the effective membrane surface area and provide additional water transport channels,which is conducive to improving the permeability of the NFMs.The M3 membrane prepared with a load of 10μg/cm² has the best performance with the water flux of 18.4 LMH/bar,which is nearly 2 times higher than that of control membrane（M0,9.1 LMH/bar）.At the same time,the retention rates of Na Cl,Ca Cl₂,Mg Cl₂,Mg SO₄ and Na₂SO₄ were30.85%,39.6%,45.6%,98.2%and 99.1%,respectively.Compared with the control membrane,the mixed salt solution permeability of M3 membrane is increased by nearly3 times,while maintaining the desalination effect on the mixed salt solution.The enhanced permeability and separation properties,and long-term operational stability of the TFN membrane make it have certain application prospects,especially in the field of drinking water treatment.To further decreace adverse effect on the integrity of the polyamide layer due to the heterostructural incompatibility of inorganic molybdenum disulfide nanoparticles and organic polyamide matrices,we successfully grafted the carboxyl functional group on the surface of HF-Mo S₂ based on the carboxyl functional mechanism for chemically conjugated of Mo S₂ nanosheets with thioglycolic acid.And then prepared a covalent modified TFN NFMs by vacuum filtration assisted co-deposition of the carboxyl@Mo S₂/PIP aqueous monomers.Comparative analysis of the load contents of HF-Mo S₂ direct modified nanofiltration membrane and carboxyl@Mo S₂ covalent modified nanofiltration membrane,it was calculated that about 10.13 carboxyl functional groups are successfully grafted on the surface of per Mo S₂ molecule,which effectively increases the hydrophilicity of the material.Benefiting from the better compatibility between carboxyl@Mo S₂ and polyamide matrix,the carboxyl@Mo S₂TFN membrane exhibites a better integrity and has a higher membrane surface hydrophilicity and water filtration area.The M4 membrane prepared with a load of 49.7μg/cm² had the best performance,with a water flux of 25.8 LMH/bar,which was 2.7times higher than that of the control film M0（9.6 LMH/bar）.The rejection of M4 for Mg SO₄ and Na₂SO₄ were 97.8%and 98.5%,respectively.Under the condition of maintaining a high retention of organic pollutants,the retention rate of calcium and magnesium ions by TFN membrane is significantly reduced,so that it can effectively remove harmful organic pollutants in practical applications and retain calcium and magnesium ions beneficial to the human body.The modified carboxyl@Mo S₂ modified nanofiltration membrane shows better nanofiltration membrane performance than direct aqueous phase doping modification,indicating that the surface modification of nanomaterials can also effectively enhance the characteristics of the material itself,and the grafted organic functional group can further increase the compatibility with the organic polyamide matrix,alleviate the membrane defect problem caused by heterogeneous structure,and provide certain theoretical support for the grafting modification of nanomaterials.Compared with aqueous phase modification,the organic phase modification method could make the nanomaterials distributed on the surface of the polyamide layer instead being covered.This structure enabled the nanomaterials contacted with water molecules or target pollutants directly during filtration process,which is more conducive to the advantages of the nanomaterials themselves.By grafting the acyl chloride group in the Mo S₂ material,we constructed a two-dimensional nanosheet nanoflower with rich acyl chloride functional group on the outside（acyl chloride@Mo S₂）.Though no obvious change in morphology of acyl chloride@Mo S₂,the vacuum XPS characterization proved the success of acyl chloride.And it was introduced into the PA layer of TFN by covalent doped organic phase.The zeta potential and hydrophilicity of TFN membrane surface were enhanced.The basic separation performance of the control membrane and the TFN membrane was analyzed,and the results showed that the introduction of the acyl chloride@Mo S₂ material could significantly improve the pure water flux,up to 34.2 LMH/bar,and the rejection of the inorganic salt solution was also improved.Under the rentention rates close to the control membrane,the mixed salt solution permeation flux of the modified film can reach 15.6LMH/bar,which is 3.5 times higher than that of the control membrane（M0,4.4LMH/bar）,which can significantly reduce the energy consumption and have a better application potential for water treatment.This paper constructed and analyzed the performance of modified nanofiltration membranes prepared by four different HF-Mo S₂ modification methods,and the results show all modification membrane could effectively improve the filtration performance,which to provide scientific reference and technical support for improving the performance of the polyamide nanofiltration membrane.更多还原