Gradient Channel Segmentation in Covalent Organic Framework Membranes with Highly Oriented Nanochannels.

Covalent organic frameworks (COFs) offer an exceptional platform for constructing membrane nanochannels with tunable pore sizes and tailored functionalities, making them promising candidates for separation, catalysis, and sensing applications. However, the synthesis of COF membranes with highly oriented nanochannels remains challenging, and there is a lack of systematic studies on the influence of postsynthetic modification reactions on functionality distribution along the nanochannels. Herein, we introduced a "prenucleation and slow growth" approach to synthesize a COF membrane featuring highly oriented mesoporous channels and a high Brunauer-Emmett-Teller surface area of 2230 m2 g-1. Functional moieties were anchored to the pore walls via "click" reactions and coordinated with Cu ions to serve as segmentation functions. This led to a remarkable H2/CO2 separation performance that surpassed the Robeson upper bound. Moreover, we found that the functionalities distributed along the nanochannels could be influenced by functionality flexibility and postsynthetic reaction rate. This strategy paved the way for the accurate design and construction of COF-based artificial solid-state nanochannels with high orientation and precisely controlled channel environments.

2D Covalent Organic Framework for Water Harvesting with Fast Kinetics and Low Regeneration Temperature.

Atmospheric water harvesting represents a promising technique to address water stress. Advanced adsorbents have been rationally designed to achieve high water uptake, yet their water sorption kinetics and regeneration temperature greatly limit water production efficiency. Herein, we demonstrated that 2D covalent organic frameworks (COFs), featuring hydrophobic skeleton, proper hydrophilic site density, and 1D open channels significantly lowered the water diffusion and desorption energy barrier. DHTA-Pa COF showed a high water uptake of 0.48 g/g at 30 % R.H. with a remarkable adsorption rate of 0.72 L/Kg/h (298 K) and a desorption rate of 2.58 L/Kg/h (333 K). Moreover, more than 90 % adsorbed water could be released within 20 min at 313 K. This kinetic performance surpassed the reported porous materials and boosted the efficiency for multiple water extraction cycles. It may shed light on the material design strategy to achieve high daily water production with low-energy input.

Bulk COFs and COF nanosheets for electrochemical energy storage and conversion.

Covalent organic frameworks (COFs) as an emerging class of crystalline porous materials have received much attention due to their tunable porosity, modifiable skeletons, and atomically precise structures. Besides, COFs can provide multiple high-rate charge carrier transport (electron, hole, and ion) pathways, including conjugated skeletons, overlapped π electron clouds among the stacked layers, and open channels with a variable chemical environment. Therefore, they have shown great potential in electrochemical energy storage (EES) and conversion (EEC). However, in bulk COFs, the defects always impede charge carrier conduction, and the difficulties in reaching deep-buried active sites by either electrons or ions lead to limited performance. To overcome these obstacles, numerous research studies have been carried out to obtain COF nanosheets (NSs). This review first describes the preparation strategies of COF NSs via bottom-up and top-down approaches. Then, the applications of bulk COFs and COF NSs in EES and EEC are summarized, such as in batteries, supercapacitors, and fuel cells. Finally, key challenges and future directions in these areas are discussed.

Electropolymerization of Molecular-Sieving Polythiophene Membranes for H2 Separation.

Membrane technologies that do not rely on heat for industrial gas separation would lower global energy cost. While polymeric, inorganic, and mixed-matrix separation membranes have been rapidly developed, the bottleneck is balancing the processability, selectivity, and permeability. Reported here is a softness adjustment of rigid networks (SARs) strategy to produce flexible, stand-alone, and molecular-sieving membranes by electropolymerization. Here, 14 membranes were rationally designed and synthesized and their gas separation ability and mechanical performance were studied. The separation performance of the membranes for H2 /CO2 , H2 /N2 , and H2 /CH4 can exceed the Robeson upper bound, among which, H2 /CO2 separation selectivity reaches 50 with 626 Barrer of H2 permeability. The long-term and chemical stability tests demonstrate their potential for industrial applications. This simple, scalable, and cost-effective strategy holds promise for the design other polymers for key energy-intensive separations.