二维金属有机骨架纳米片膜的可控修饰及H2高效分离研究

H2 is one of the most important industrial chemicals and a representative clean energy which has been widely deployed in the ammonia production, fuel cell and oil refining applications. H2 separation is a key process for H2 production with high purity with CO2, N2, CO and CH4 as major impurities. In contrast of cryogenic distillation and pressure swing adsorption, membrane-based gas separation is a new concept with low energy consumption, environmentally friendly and continuous operation. Gas separation based on ultrathin molecular sieve nanosheets membranes, the so-called “next generation membranes”, can realize precise and fast discrimination of gas molecules with different sizes. However, the molecular sieve nanosheets usually display outstanding flexibility, resulting in an uneven gap width within the nanosheets membranes. The distinctive character of these membranes will allow a considerable number of gas molecules bigger than H2 to pass through along the nanosheets interlayer galleries, leading to a bottleneck of separation efficiency promotion. Based on the achievements on the development of novel two-dimensional MOF nanosheets membranes and the tailor-made modification of MOF nanocages of the applicant, in this project, a novel “nanosheets stitching” strategy is put forward to inhibit big gas molecules pass through the nanosheets membranes by stitching nanosheets together with functional organic amines. This project aims at exploring the correspondence between amine type, the structure of modified nanosheets membranes and the gas separation performance, and studying the mass transfer mechanism of gas molecules based on the joint experimental and theoretical results. In a word, this project will develop a technology roadmap of two-dimensional MOF nanosheets membranes modification, and promote the practical applications of MOF nanosheets in the gas separation field, meanwhile it will shed light on the controllable synthesis of other nanosheets membranes.

H2是一种重要化工原料和清洁能源，被广泛应用于合成氨、燃料电池及石油炼制等领域，其分离是制备高纯H2至关重要的一步，其中CO2、N2、CO、CH4是制氢过程涉及的主要杂质气体。相比深冷精馏及变压吸附传统方法，膜分离技术具有能耗低、环境友好、可连续操作等优点，是气体分离领域研究热点。利用分子筛纳米片构筑超薄气体分离膜可实现不同尺寸气体精确、快速筛分，被誉为“下一代膜材料”。然而分子筛纳米片具有极佳柔性，膜内层间狭缝通道间距不均，导致H2分离中杂质大分子气体易沿层间狭缝通道扩散过膜，严重制约膜分子筛分性能的提升。结合申请人在二维MOF纳米片气体分离膜领域以及三维MOF孔笼结构定向调变方面所获成果，本项目提出一种“纳米片缝纫”改性策略，利用双齿有机胺同MOF纳米片上金属活性位点配位，封锁层间狭缝通道以抑制尺寸差异极小的大分子气体渗透；研究有机胺种类、改性MOF纳米片膜结构同气体分离性能间对应关系，并将实验结果同理论模型相关联，探索气体分子传质机理。本项目的开展将催生二维MOF纳米片膜改性技术路线，推动MOF纳米片在实际气体分离体系中的应用，也为其它二维纳米片膜可控合成提供借鉴。

相较于传统高能耗分离技术，低能耗、低碳排放的膜分离技术在缓解能源短缺和温室效应等关系人类生存发展重大问题方面具有广阔应用前景。膜材料是膜分离技术的核心。利用分子筛纳米片构筑的超薄分离膜具有两类分子传质通道，可以实现不同尺寸、不同形状分子的精确且快速的筛分。目前分子筛纳米片膜经典结构模型为水平物理堆垛型膜，膜内层间狭缝通道间距不均，分离体系中杂质大分子会沿相邻片层间狭缝通道扩散过膜，进一步溶胀纳米片层，严重制约这类分子筛膜分离性能的提升及实际应用潜力。.本项目为满足重要化工分离体系的需求，以高效二维金属-有机框架膜的结构设计、可控制备及定向改性为研究对象，发展了一系列二维金属-有机框架新材料，形成了面向特定分离体系的二维膜材料制备与纳微结构调控新方法，增强了二维膜内片层间作用力，限域了层间狭缝通道空间尺寸，探究了膜微观结构与分离性能间构效关系，提出了分离机制及影响膜内分子吸附、扩散行为的关键要素，实现了二维金属-有机框架膜在气（H2/CO2）、液相分离（纳滤）领域的高选择性、高渗透通量分离应用。成功将相关研究成果拓展至共价有机框架材料体系，形成了二维共价有机框架纳米片膜在合成气分离中的首个应用示例，并开创了具有放大制备能力的新型柔性无裂缺MOF复合膜概念。所获H2/CO2、CO2/H2分离性能均远超现有多晶膜及混合基质膜材料，满足工业应用需求。通过本项目的顺利实施，强化了项目团队在金属-有机框架膜研究领域的影响力，提供了切实可行的调控与改性新思路，显著推动了二维膜尤其是二维金属-有机框架膜在实际工业气体分离中的应用。