Multiscale Design of Graphyne‐Based Materials for High‐Performance Separation Membranes

By varying the number of acetylenic linkages connecting aromatic rings, a new family of atomically thin graph‐n‐yne materials can be designed and synthesized. Generating immense scientific interest due to its structural diversity and excellent physical properties, graph‐n‐yne has opened new avenues toward numerous promising engineering applications, especially for separation membranes with precise pore sizes. Having these tunable pore sizes in combination with their excellent mechanical strength to withstand high pressures, free‐standing graph‐n‐yne is theoretically posited to be an outstanding membrane material for separating or purifying mixtures of either gases or liquids, rivaling or even dramatically exceeding the capabilities of current, state‐of‐art separation membranes. Computational modeling and simulations play an integral role in the bottom‐up design and characterization of these graph‐n‐yne materials. Thus, here, the state of the art in modeling α‐, β‐, γ‐, δ‐, and 6,6,12‐graphyne nanosheets for synthesizing graph‐2‐yne materials and 3D architectures thereof is discussed. Different synthesis methods are described and a broad overview of computational characterizations of graph‐n‐yne's electrical, chemical, and thermal properties is provided. Furthermore, a series of in‐depth computational studies that delve into the specifics of graph‐n‐yne's mechanical strength and porosity, which confer superior performance for separation and desalination membranes, are reviewed.     

自具微孔聚合物PIM-1基热致刚性膜材料的制备及气体分离性能

以邻苯二酚和丙酮为原料,合成出四羟基化合物5,5′,6,6′-四羟基-3,3,3′,3′-四甲基-1,1′-螺旋双茚满,再与四氟对苯二腈发生聚合反应得到自具微孔聚合物PIM-1。然后,分别在300℃、350℃和400℃对PIM-1膜材料进行热处理得到热致刚性膜材料。利用核磁共振仪(NMR)、凝胶渗透色谱仪(GPC)、红外光谱仪(FTIR)、热重分析仪(TGA)、示差扫描量热仪(DSC)、X射线衍射仪(XRD)和扫描电镜(SEM)对所合成的四羟基化合物、PIM-1聚合物及热致刚性膜材料的结构和性能进行表征,并对其气体分离性能进行了测试。研究表明,所合成PIM-1的玻璃化转变温度为340℃,热分解温度为503℃。适当的热处理可提高PIM-1基热致刚性膜材料的气体分离性能,PIM-1-300对H_2、O_2、N2、CO_2和CH_4的渗透通量分别达到2 865Barrer、1 071Barrer、298Barrer、7 070Barrer和495Barrer。但随热处理温度升高,热交联程度增加,膜材料的气体渗透性逐渐降低,但选择性有所提高。PIM-1-400的CO_2/CH_4分离系数为18.51。     

Twinned Growth of Metal‐Free,Triazine‐Based Photocatalyst Films as Mixed‐Dimensional (2D/3D) van der Waals Heterostructures

Design and synthesis of ordered, metal‐free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed‐dimensional (2D/3D) metal‐free van der Waals (vdW) heterostructures based on triazine (C₃N₃) linkers grow as large area, transparent yellow‐orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E _g,opt = 1.91 eV, E _g,elec = 1.84 eV) and are moderately porous (124 m² g^?1). The material consists of a crystalline 2D phase that is fully sp² hybridized and provides structural stability, and an amorphous, porous phase with mixed sp²–sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one‐pot reaction mixture: unprecedented for metal‐free frameworks and a direct consequence of on‐catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal‐free, light‐induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h^?1 g^?1 without Pt). The results highlight that twinned growth mechanisms are observed in the realm of “wet” chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties.     

Towards High‐Performance Bioinspired Composites

Biological composites have evolved elaborate hierarchical structures to achieve outstanding mechanical properties using weak but readily available building blocks. Combining the underlying design principles of such biological materials with the rich chemistry accessible in synthetic systems may enable the creation of artificial composites with unprecedented properties and functionalities. This bioinspired approach requires identification, understanding, and quantification of natural design principles and their replication in synthetic materials, taking into account the intrinsic properties of the stronger artificial building blocks and the boundary conditions of engineering applications. In this progress report, the scientific and technological questions that have to be addressed to achieve this goal are highlighted, and examples of recent research efforts to tackle them are presented. These include the local characterization of the heterogeneous architecture of biological materials, the investigation of structure–function relationships to help unveil natural design principles, and the development of synthetic processing routes that can potentially be used to implement some of these principles in synthetic materials. The importance of replicating the design principles of biological materials rather than their structure per se is highlighted, and possible directions for further progress in this fascinating, interdisciplinary field are discussed.     

Wafer‐Scale Fabrication of High‐Performance n‐Type Polymer Monolayer Transistors Using a Multi‐Level Self‐Assembly Strategy

Wafer‐scale fabrication of high‐performance uniform organic electronic materials is of great challenge and has rarely been realized before. Previous large‐scale fabrication methods always lead to different layer thickness and thereby poor film and device uniformity. Herein, the first demonstration of 4 in. wafer‐scale, uniform, and high‐performance n‐type polymer monolayer films is reported, enabled by controlling the multi‐level self‐assembly process of conjugated polymers in solution. Since the self‐assembly process happened in solution, the uniform 2D polymer monolayers can be facilely deposited on various substrates, and theoretically without size limitations. Polymer monolayer transistors exhibit high electron mobilities of up to 1.88 cm² V^?1 s^?1, which is among the highest in n‐type monolayer organic transistors. This method allows to easily fabricate n‐type conjugated polymers with wafer‐scale, high uniformity, low contact resistance, and excellent transistor performance (better than the traditional spin‐coating method). This work provides an effective strategy to prepare large‐scale and uniform 2D polymer monolayers, which could enable the application of conjugated polymers for wafer‐scale sophisticated electronics.