Self-Standing Covalent Organic Framework Membranes for H2/CO2 Separation

Covalent organic frameworks (COFs) are proposed as promising candidates for engineering advanced molecular sieving membranes due to their precise pore sizes, modifiable pore environment, and superior stability. However, COFs are insoluble in common solvents and do not melt at high temperatures, which presents a great challenge for the fabrication of COF-based membranes (COFMs). Herein, for the first time, a new synthetic strategy is reported to prepare continuous and intact self-standing COFMs, including 2D N-COF membrane and 3D COF-300 membrane. Both COFMs show excellent selectivity of H₂/CO₂ mixed gas (13.8 for N-COF membrane and 11 for COF-300 membrane), and especially ultrahigh H₂ permeance (4319 GPU for N-COF membrane and 5160 GPU for COF-300 membrane), which is superior to those of COFMs reported so far. It should be noted that the overall separation performance of self-standing COFMs exceeds the Robeson upper bound. Furthermore, a theoretical study based on Grand Canonical Monte Carlo (GCMC) simulation is performed to explain the excellent separation of H₂/CO₂ through COFMs. Thus, this facile preparation method will provide a broad prospect for the development of self-standing COFMs with highly efficient H₂ purification.     

Tailoring the Separation Behavior of Hybrid Organosilica Membranes by Adjusting the Structure of the Organic Bridging Group

Hybrid organically linked silica is a highly promising class of materials for the application in energy‐efficient molecular separation membranes. Its high stability allows operation under aggressive working conditions. Herein is reported the tailoring of the separation performance of these hybrid silica membranes by adjusting the size, flexibility, shape, and electronic structure of the organic bridging group. A single generic procedure is applied to synthesize nanoporous membranes from bridged silsesquioxane precursors with different reactivities. Membranes with short alkylene (CH₂ and C₂H₄) bridging groups show high H₂/N₂ permeance ratios, related to differences in molecular size. The highest CO₂/H₂ permeance ratios, related to the affinity of adsorption in the material, are obtained for longer (C₈H₁₆) alkylene and aryl bridges. Materials with long flexible alkylene bridges have a hydrophobic surface and show strongly temperature‐dependent molecular transport as well as a high n‐butanol flux in a pervaporation process, which is indicative of organic polymerlike properties. The versatility of the bridging group offers an extensive toolbox to tune the nanostructure and the affinity of hybrid silica membranes and by doing so to optimize the performance towards specific separation challenges. This provides excellent prospects for industrial applications such as carbon capture and biofuel production.     

High-performance Poly(biphenyl piperidinium) Type Anion Exchange Membranes with Interconnected Ion Transfer Channels: Cooperativity of Dual Cations and Fluorinated Side Chains

The performance of alkaline fuel cells is severely limited by substandard anion exchange membranes (AEMs) due to the lower ionic conductivity compared to the proton exchange membranes. The ionic conductivity of AEMs can be effectively improved by regulating the microphase structure, but it still cannot meet the practical use requirements. Here, enhanced microphase-separated structures are constructed by the cooperativity of highly hydrophilic dual cations and highly hydrophobic fluorinated side chains. Meanwhile, the introduction of  O enhances the flexibility of side chains and facilitates the formation of ion transport channels. The dual piperidinium cation functionalized membrane (PB2Pip-5C8F) which is grafted with the ultra-hydrophobic fluorocarbon chain exhibits a high conductivity of 74.4 mS cm⁻¹ at 30 °C and 168.46 mS cm⁻¹ at 80 °C. Furthermore, the PB2Pip-5C8F membrane achieves the highest peak power density of 718 mW cm⁻² at 80 °C under a current density of 1197 mA cm⁻² without back pressure. A long-term life cell test of this AEM shows a low voltage decay rate of 1.68 mV h⁻¹ over 70 h of operation at 80 °C.     

Defect Engineering of MOF-Based Membrane for Gas Separation

Metal–organic frameworks (MOFs) are highly versatile materials that have been identified as promising candidates for membrane-based gas separation applications due to their uniformly narrow pore windows and virtually unlimited structural and chemical features. Defect engineering of MOFs has opened new opportunities for manipulating MOF structures, providing a simple yet efficient approach for enhancing membrane separation. However, the utilization of this strategy to tailor membrane microstructures and enhance separation performance is still in its infancy. Thus, this summary aims to provide a guideline for tailoring defective MOF-based membranes. Recent developments in defect engineering of MOF-based membranes will be discussed, including the synthesis strategies for defective MOFs, the effects of defects on the gas adsorption properties, gas transport mechanisms, and recently reported defective MOF-based membranes. Furthermore, the emerging challenges and future prospects will be outlined. Overall, defect engineering offers an exciting opportunity to improve the performance of MOF-based gas membranes. However, there is still a long way to go to fully understand the influence of defects on MOF properties and optimize the design of MOF-based membranes for specific gas separation applications. Nonetheless, continued research in this field holds great promise for the development of next-generation membrane-based gas separation technologies.     

Biomimetic Hygroscopic Fibrous Membrane with Hierarchically Porous Structure for Rapid Atmospheric Water Harvesting

Sorption-based atmospheric water generation (SAWG) is a promising strategy to alleviate the drinkable water scarcity of arid regions. However, the high-water production efficiency remains challenging due to the sluggish sorption/desorption kinetics. Herein, a composite sorbent@biomimetic fibrous membrane (PPy-COF@Trilayer-LiCl) is reported by mimicking nature's Murray networks, which exhibits outstanding water uptake performance of 0.77–2.56 g g⁻¹ at a wide range of relative humidity of 30%–80% within 50 min and fast water release capacity of over 95% adsorbed water that can be released within 10 min under one sun irradiation. The superior sorption–desorption kinetics of PPy-COF@Trilayer-LiCl are enabled by the novel hierarchically porous structure, which is also the critical factor to lead a directional rapid water transport and vapor diffusion. Moreover, as a proof-of-concept demonstration, a wearable SAWG device is established, which can operate 10 sorption–desorption cycles per day in the outdoor condition and produce a high yield of clean water reaching up to 3.91 kg m⁻² day⁻¹. This study demonstrates a novel strategy for developing advanced solar-driven SAWG materials with efficient water sorption–desorption properties.     

Harmonic analysis of GaN-HEMTs at different temperatures and frequencies using Volterra power series

In this study, the detailed harmonic analysis of GaN high electron mobility transistor (HEMT) at different temperatures and frequencies is presented. Volterra power series and multi-dimensional Laplace transform are used as a method. The Volterra power series is also solved up to third degree, and the small signal transfer functions of kernels (H₁, H₂ and H₃) are obtained. The relationship between drain inductance (L_d), gate–source voltage (V_gs), impedance (Z_L) and the effect of frequency (F_r) to the output gain is identified. Besides, the nonlinear gains of H₁, H₂ and H₃ kernels of the GaN-HEMT are obtained. The inverse relationship between the output gains of H₁, H₂ and H₃ kernels are derived. An unsuitable situation has also been identified for sub-carrier inter-modulation systems. In addition, an asymmetric structure is also obtained between the output gain of H₂ and side-band frequencies. The effects of other parameters are carried out for the output gain.     

Positively K+‐Responsive Membranes with Functional Gates Driven by Host–Guest Molecular Recognition

A novel positively K⁺‐responsive membrane with functional gates driven by host‐guest molecular recognition is prepared by grafting poly(N‐isopropylacrylamide‐co‐acryloylamidobenzo‐15‐crown‐5) (poly(NIPAM‐co‐AAB₁₅C₅)) copolymer chains in the pores of porous nylon‐6 membranes with a two‐step method combining plasma‐induced pore‐filling grafting polymerization and chemical modification. Due to the cooperative interaction of host‐guest complexation and phase transition of the poly(NIPAM‐co‐AAB₁₅C₅), the grafted gates in the membrane pores could spontaneously switch from “closed” state to “open” state by recognizing K⁺ ions in the environment and vice versa; while other ions (e.g., Na⁺, Ca²⁺ or Mg²⁺) can not trigger such an ion‐responsive switching function. The positively K⁺‐responsive gating action of the membrane is rapid, reversible, and reproducible. The proposed K⁺‐responsive gating membrane provide a new mode of behavior for ion‐recognizable “smart” or “intelligent” membrane actuators, which is highly attractive for controlled release, chemical/biomedical separations, tissue engineering, sensors, etc.     

高斯光束通过非轴对称光学系统的变换

高斯光束通过非轴对称光学系统时就变成像散椭圆高斯光束。本文使用矩阵方法研究了有简单像散高斯光束的变换特性,推导出像空间中xoz和yoz面上束腰重合和相等的条件,以及一股地,像空间中光斑椭圆变成圆和等相面为球面的条件,并以数值计算例说明。     

Scalable Flexible Hybrid Membranes with Photonic Structures for Daytime Radiative Cooling

Passive radiative cooling technology can cool down an object by reflecting solar light and radiating heat simultaneously. However, photonic radiators generally require stringent and nanoscale‐precision fabrication, which greatly restricts mass production and renders them less attractive for large‐area applications. A simple, inexpensive, and scalable electrospinning method is demonstrated for fabricating a high‐performance flexible hybrid membrane radiator (FHMR) that consists of polyvinylidene fluoride/tetraethyl orthosilicate fibers with numerous nanopores inside and SiO₂ microspheres randomly distributed across its surface. Even without silver back‐coating, a 300 µm thick FHMR has an average infrared emissivity >0.96 and reflects ≈97% of solar irradiance. Moreover, it exhibits great flexibility and superior strength. The daytime cooling performance this device is experimentally demonstrated with an average radiative cooling power of 61 W m^?2 and a temperature decrease up to 6 °C under a peak solar intensity of 1000 W m^?2. This performance is comparable to those of state‐of‐the‐art devices.     

Recent Advances of Cell Membrane‐Coated Nanomaterials for Biomedical Applications

Surface modification of nanomaterials is essential for their biomedical applications owing to their passive immune clearance and damage to reticuloendothelial systems. Recently, a cell membrane‐coating technology has been proposed as an ideal approach to modify nanomaterials owing to its facile functionalized process and good biocompatibility for improving performances of synthetic nanomaterials. Here, recent advances of cell membrane‐coated nanomaterials are reviewed based on the main biological functions of the cell membrane in living cells. An overview of the cell membrane is introduced to understand its functions and potential applications. Then, the applications of cell membrane‐coated nanomaterials based on the functions of the cell membrane are summarized, including physical barrier with selective permeability and cellular communication via information transmission and reception processes. Finally, perspectives of biomedical applications and challenges about cell membrane‐coated nanomaterials are discussed.