Tailored Design of Hierarchically Porous UiO-66 with a Controlled Pore Structure and Metal Sites

Hierarchically porous metal–organic frameworks (MOFs) not only inherit the merits of MOFs such as high porosity, but they also possess distinct properties such as a broader pore size range and thus more rapid mass transport. Simple, controllable synthesis of hollow or mesoporous structures with tailored pore features and more metal sites is desired and remains challenging. Herein, we demonstrate a facile strategy for fabricating hollow/mesoporous UiO-66 through a designed defect density and subsequent etching process. The strategy relies on the construction of an inhomogeneous nanoarchitecture in which the addition of water in UiO-66 synthesis can facilitate the formation of linker defects by promoting the explosive nucleation of UiO-66 and acetic acid deprotonation, and the more defective core will be selectively etched by sodium hydroxide. The morphology, size, pore structure, and metal sites can be exquisitely designed by rationally adjusting the water dosage and etching conditions. Markedly, UiO-66 with larger mesopores contributes to excellent glyphosate adsorption capacity, and the hollow UiO-66 catalyst with more active metal sites exhibits superior performance in the [3 + 3] cycloaddition reaction

Stable Dicationic Covalent Organic Frameworks Manifesting Notable Structure-Enhanced CO₂ Capture and Conversion

Covalent organic frameworks (COFs) are a class of promising porous crystalline materials for both capturing and converting CO2 into high-value-added products. However, long synthesis time and the need for cocatalyst restrict its potential for CO2 conversion. Herein, bipyridine-based TAPT-BP-COF with high crystallinity as a skeleton is rapidly synthesized within only 1 h by the aid of supercritical CO2 (scCO2) activation. Then, the production of dicationic TAPT-BP2+-COF is accomplished by a quaternization reaction. The CO2 capture capacity of TAPT-BP2+-COF improved by 55.6% due to its CO2-philic groups (imine and triazine groups), polar groups (−OH), charged skeleton, and suitable pore size, thus ensuring sufficient CO2 around the catalytic active sites. Additionally, the outstanding structure-enhanced CO2 conversion performance is observed due to the presence of the synergistic effect between –OH and Br– in the TAPT-BP2+-COF skeleton. The rate-determining step of cycloaddition is significantly accelerated without any solvents and cocatalysts compared to individual TAPT-BP-COF and [OH-BP]2+[Br]2– (BP2+ moiety). Specifically, TAPT-BP2+-COF efficiently generates cyclic carbonate by heterogeneously catalyzing CO2-epoxide cycloaddition with the yield of 99.3% and has excellent stability that can be reused ten times without significant activity reduction. This work provides a novel perspective for the targeted design and rapid synthesis of charged dicationic COF-based catalysts for high efficiency and durability in CO2 capture and conversion

In Situ-Doped Sulfonated Schiff-Base Networks in SPEEK Composite Membranes with Enhanced Proton Conductivity

Sulfonated polyether ether ketone (SPEEK) has been widely investigated in proton exchange membrane fuel cells (PEMFCs) due to its excellent thermal stability, chemical stability, and low cost compared with Nafion. However, excessive degree of sulfonation will easily lead to the decrease in thermal stabilities and mechanical properties of SPEEK membranes, which limits the enhancement of proton conductivity. In this work, a series of Schiff-base networks (SNWs) with different contents are in situ synthesized in the SPEEK membrane by a Schiff-base co-condensation reaction, and then, the composite membranes are soaked in sulfonic acid for further improvement of proton conductivity. The highest doping amount of the SNW filler in SPEEK can reach 20 wt %. High loading and low leaching rate of H2SO4 are easily achieved owing to the similar size between sulfuric acid molecules and micropores in SNW. Moreover, abundant amino and imine groups in SNW networks contribute to the anchoring of H2SO4 into the pores by acid–base interactions. The proton conductivity of the SPEEK/S-SNW-15 composite membrane can reach 115.53 mS cm–1 at 80 °C and 100% RH. Meanwhile, the composite membrane also exhibits satisfied stability and mechanical property

Novel Quaternary Ammonium-Functionalized Covalent Organic Frameworks/Poly(2,6-dimethyl-1,4-phenylene oxide) Hybrid Anion Exchange Membranes with Enhanced Ion Conductivity and Stability

Here we report a new hybrid anion exchange membrane with enhanced hydroxide conductivity and excellent chemical and dimensional stability by incorporating quaternary ammonium (QA)-functionalized covalent organic framework into brominated poly­(2,6-dimethyl-1,4-phenylene oxide) (BPPO). N,N,N′,N′ -Tetramethyl-1,6-hexanediamine (TMHDA) was impregnated into the pores of COF-LZU1 via a vacuum-assisted method, followed by reacting with allyl bromide. The generated QA groups were immobilized within the highly ordered pores of COF-LZU1 via in situ polymerization, forming long-range ordered multiple ion channels. The obtained QA@COF-LZU1 was then mixed with QAPPO to construct a hybrid anion exchange membrane for anion exchange membrane fuel cells (AEMFCs). The hydroxide conductivity of QA@COF-LZU1/PPO hybrid membrane increased up to 168.00 mS cm–1 at 80 °C, about 77% higher than that of pristine membrane. In addition, alkaline stability and thermal stability of the hybrid membranes were obviously enhanced. The excellent performance and the outstanding chemical stability render the COF hybrid membrane a good candidate for the application in AEMFCs