¸ßЧ·Ö×ÓÀë×Ó´«µÝĤ(Ó¢ÎÄ°æ)

¸ßЧ·Ö×ÓÀë×Ó´«µÝĤ(Ó¢ÎÄ°æ) ½ÚÑ¡

Chapter 1 Introduction to Membrane Jingtao Wang and Wenjia Wu In the past decades£¬ membrane technology has been widely utilized in various separation processes£¬ because of their low-energy consumption£¬ low-cost£¬ reliability£¬ and scalability when compared with conventional separation processes like distillation£¬ extraction£¬ or crystallization [1£¬2]. In order to further increase the competitiveness£¬ intensive efforts have been made from improving the separation efficiency of existing membrane processes to exploring new applications. As the core part£¬ membrane materials with high permeability£¬ high selectivity£¬ and high stability are extremely desired since they can significantly accelerate the practical application of membrane technology [3£¬ 4]. To date£¬ plenty of membranes with different pore sizes have been developed£¬ such as polymer membrane£¬ ceramic membrane£¬ two-dimensional (2D) lamellar membrane£¬ molecule sieving membrane£¬ hybrid membrane£¬ and composite membrane [5-10]. These membranes have been widely used for different separation processes including£¬ microfiltration£¬ ultrafiltration£¬ nanofiltration£¬ reverse osmosis£¬ gas separation£¬ and proton/ion conduction£¬ etc. [11£¬ 12]. For each category of membrane£¬ the physical and chemical environments of transfer channels are of great importance in manipulating the comprehensive properties. The physical environments are dictated by the connectivity£¬ tortuosity£¬ and size of transfer channels£¬ while the chemical environments are dictated by the type£¬ amount£¬ and distribution of functional groups within transfer channels [13]. Generally£¬ ideal transfer channels should integrate the following attributes: (i) they should be short with appropriate transfer environment to endow membranes with high permeability£¬ (ii) the channel size distribution should be narrow to endow membranes with high selectivity£¬ and (iii) the chemical and mechanical stability should be high to endow membranes with long-term operation stability [14]. Currently£¬ polymers are the dominant membrane materials£¬ due to their easy processability and high scale-up capability. For conventional polymer membranes£¬ breaking the permeability-selec-tivity or permeability-stability trade-off remains a challenge. The great progress in polymer membranes over the past decades has brought about the booming of novel kinds of structured membranes including£¬ hybrid membrane£¬ composite membrane£¬ and phase-separated membrane£¬ which push the separation performances of polymer membranes to new records [15-18]. Hybrid membrane is an intricately structured membrane configuration£¬ owing to its merit of coupling the good flexibility and processability of polymers with the regular topological structure as well as the tunable functionality of fillers [19£¬ 20]. Impermeable fillers such as silica particles£¬ graphene oxide (GO) nanosheets£¬ and organic/inorganic nanorods can induce a distortion of chain alignment to improve the free volume property or induce the construction of long-range£¬ ordered transfer channels in membrane [21£¬22]. Permeable fillers such as metal-organic frameworks (MOFs)£¬ covalent organic frameworks (COFs)£¬ and zeolite can afford additional transfer pathways and mechanisms to membrane including£¬ molecule sieving£¬ and selective adsorption [23£¬ 24]. Composite membrane for molecule transfer is generally a heterogeneous membrane with dense separation layer and porous support layer£¬ where the separation layer and the support layer can be separately optimized to achieve simultaneously high separation performance and stability [25£¬26]. Particularly£¬ the fabrication of composite membrane with an ultrathin separation layer is deemed as a delicate strategy to achieve highly permeable membrane£¬ which is one of the most important pursuits for membrane technology [27£¬ 28]. At present£¬ researches related to composite membranes mainly focus on the precise manipulation of physical structure and chemical component of separation layer; however£¬ these remain challenging due to the pursuit of ultrathin thickness. For proton/ion separation£¬ electrospinning is increasingly recognized as a powerful mean for introducing unique phase-separated architectures into composite membranes [29]. Indeed£¬ it allows the elaboration of composite membranes with a rather facile mean to control of the long-range organization/distribution/percolation ofhydrophilic and hydrophobic domains of the ionomer by adjusting the type of electrospun material£¬ the volume fraction of nanofibers£¬ and the experimental conditions [30]. Moreover£¬ electrospinning can impart uniaxial alignment of polymer chains within nanofibers£¬ resulting in enhanced mechanical properties. Importantly£¬ it can promote the formation of interconnected transfer channels£¬ which facilitate the improvement in proton/ion conduction [31]. In recent years£¬ 2D nanosheets£¬ with a thickness of one to a few atoms£¬ have become the promising building blocks for ad