### Recent Submissions

• #### Nanofibrous membranes comprising intrinsically microporous polyimides with embedded metal–organic frameworks for capturing volatile organic compounds

(Journal of Hazardous Materials, Elsevier, 2021-09-25) [Article]
Here, we report the fabrication of nanofibrous air-filtration membranes of intrinsically microporous polyimide with metal–organic frameworks (MOFs). The membranes successfully captured VOCs from air. Two polyimides with surface areas up to 500 m2 g −1 were synthesized, and the impact of the porosity on the sorption kinetics and capacity of the nanofibers was investigated. Two Zr-based MOFs, namely pristine UiO-66 (1071 m2 g −1 ) and defective UiO-66 (1582 m2 g −1 ), were embedded into the nanofibers to produce nanocomposite materials. The nanofibers could remove polar formaldehyde and non-polar toluene, xylene, and mesitylene from air. The highest sorption capacity with 214 mg g−1 was observed for xylene, followed by mesitylene (201 mg g−1 ), toluene (142 mg g−1 ), and formaldehyde (124 mg g−1 ). The incorporation of MOFs drastically improved the sorption performance of the fibers produced from low-surface-area polyimide. Time-dependent sorption tests revealed the rapid sequestration of air pollutants owing to the intrinsic porosity of the polyimides and the MOF fillers. The porosity allowed the rapid diffusion of pollutants into the inner fiber matrix. The molecular level interactions between VOCs and polymer/MOFs were clarified by molecular modeling studies. The practicality of material fabrication and the applicability of the material were assessed through the modification of industrial N95 dust masks. To the best of our knowledge, this is the first successful demonstration of the synergistic combination of intrinsically microporous polyimides and MOFs in the form of electrospun nanofibrous membranes and their application for VOC removal.
• #### A Novel Low-Strain Phosphate Cathode for High-Rate and Ultralong Cycle-Life Potassium-Ion Batteries.

(Angewandte Chemie (International ed. in English), Wiley, 2021-09-24) [Article]
Most potassium-ion battery (PIB) cathode materials have deficient structural stability because of the huge radius of potassium ion, leading to inferior cycling performance. In this work, we report the controllable synthesis of a novel low-strain phosphate material K 3 (VO)(HV 2 O 3 )(PO 4 ) 2 (HPO 4 ) (denoted KVP) nanorulers as an efficient cathode for PIBs. The as-synthesized KVP nanoruler cathode can exhibit an initial reversible capacity of 80.6 mAh g -1 under 20 mA g -1 , with a large average working potential of 4.11 V. It can also manifest an excellent rate property of 54.4 mAh g -1 under 5 A g -1 , with an exceedingly high capacity preservation of 92.1% over 2500 cycles. The outstanding potassium storage capability of KVP nanoruler cathode originates from low-strain K + uptake/removal mechanism, inherent semiconductor characteristic, and small K + migration energy barrier. The high energy density and prolonged cyclic stability of KVP nanorulers//polyaniline-intercalated layered titanate full battery verifies the superiority of KVP nanoruler cathode in PIBs. Our results show that this high-voltage low-strain phosphate material is a competitive cathode for PIBs and will draw more attention and investigations in the future.
• #### Recent Progress on Polymers of Intrinsic Microporosity and Thermally Modified Analogue Materials for Membrane-Based Fluid Separations

(Small Structures, Wiley, 2021-09-14) [Article]
Solution-processable amorphous glassy polymers of intrinsic microporosity (PIMs) are promising microporous organic materials for membrane-based gas and liquid separations due to their high surface area and internal free volume, thermal and chemical stability, and excellent separation performance. This review provides an overview of the most recent developments in the design and transport properties of novel ladder PIM materials, polyimides of intrinsic microporosity (PIM–PIs), functionalized PIMs and PIM–PIs, PIM-derived thermally rearranged (TR), and carbon molecular sieve (CMS) membrane materials as well as PIM-based thin film composite membranes for a wide range of energy-intensive gas and liquid separations. In less than two decades, PIMs have significantly lifted the performance upper bounds in H2/N2, H2/CH4, O2/N2, CO2/N2, and CO2/CH4 separations. However, PIMs are still limited by their insufficient gas-pair selectivity to be considered as promising materials for challenging industrial separations such as olefin/paraffin separations. An optimum pore size distribution is required to further improve the selectivity of a PIM for a given application. Specific attention is given to the potential use of PIM-based CMS membranes for energy-intensive CO2/CH4, N2/CH4, C2H4/C2H6, and C3H6/C3H8 separations, and thin film composite membranes containing PIM motifs for liquid separations.
• #### Zeolitic imidazolate frameworks based porous liquids for promising fluid selective gas sorbents

(Journal of Molecular Liquids, Elsevier BV, 2021-09-09) [Article]
A kind of zeolitic imidazolate frameworks based porous liquids (e.g., ZIF-8 PLs) with permanent porosity was successfully fabricated by using amine-functionalized ZIF-8 nanoparticles (i.e., ZIF8-A) as the porous fillers and monoglycidyl ether terminated poly(dimethylsiloxane) (i.e., PDMS) as the hindered solvent, respectively. Those ZIF-8 PLs were homogenous and stable at room temperature because of the liquid-particle interaction derived from the epoxy-amine reaction. In addition, those ZIF-8 PLs have larger gas adsorption abilities than their reference hindered solvent because the well-preserved permanent porosity in ZIF-8 PLs could act as void space for gas accommodation. More importantly, those ZIF-8 PLs also show much higher propane adsorption capacity than both of carbon dioxide and nitrogen gas adsorption capacities under the same condition, suggesting that they could function as a kind of promising candidates for fluid selective gas sorbents.
• #### Bridging the interfacial gap in mixed-matrix membranes by nature-inspired design: Precise molecular sieving with polymer-grafted metal–organic frameworks

(Journal of Materials Chemistry A, Royal Society of Chemistry, 2021-09-02) [Article]
Membrane technology is a dynamically developing field of separation science that is poised to result in new and efficient processes, energy and cost savings, and sustainability benefits. A key challenge in this field is the development of highly selective membranes, which can be addressed by the development of mixed-matrix membranes (MMMs) containing fillers such as metal–organic frameworks (MOFs). However, the lack of interfacial adhesion causes nanosized gaps between the filler and the polymer matrix. In this study, we aim to elucidate the intrinsic properties of MMMs and bridge the gap between their material constituents. A series of novel membranes comprising MOF nanoparticles with similar chemical and morphological properties but increasing pore size (UiO-66–68-NH2) were prepared. The nanoparticles’ surface was covalently grafted with poly(N-isopropylacrylamide) (PNIPAM) chains, which could then become entangled with the membranes’ polymer matrix. Morphological characterization and organic solvent nanofiltration tests revealed that membranes with PNIPAM-grafted fillers do not suffer from the formation of pinholes at the filler–matrix interface that are detrimental to the filtration performance. For the first time, the experimental results showed an excellent match with a predictive model of nanofiltration built around the premise of liquid transport through the highly ordered pores of the MOF filler.
• #### The Complex Crystal Structure and Abundant Local Defects of Zeolite EMM-17 Unraveled by Combined Electron Crystallography and Microscopy

(Angewandte Chemie International Edition, Wiley, 2021-09-02) [Article]
Structure determination of zeolites is of great significance for understanding their fascinating properties. In this study, we successfully solve one of polymorphic structures (polymorph A) of zeolite EMM-17, which can only crystallize in sub-micron-sized crystals while containing complex stacking disorders, from the three-dimensional (3D) electron diffraction (ED) data. This is the first time that the atomic structure of this polymorph has been ab initio solved, and the result reveals a unique 10(12) X 10(12) X 11-ring channel system. Moreover, we acquire the first atomic-resolution images of EMM-17 using integrated differential phase-contrast scanning transmission electron microscopy. The images allow us to directly observe polymorphs B and C and discover a large number of local structural defects. Based on structural features unraveled from the reciprocal-space 3D ED data and real-space images, we propose a series of energetically feasible local structures in EMM-17. In addition, we demonstrate that the unique porous structure of EMM-17 enables efficient kinetic separation of C6 alkane isomers.
• #### CO2/CH4 mixed-gas separation in PIM-1 at high pressures: Bridging atomistic simulations with process modeling

(Journal of Membrane Science, Elsevier BV, 2021-09) [Article]
Polymeric membranes with intrinsic microporosity have been at the center of attention for gas separation applications since the introduction of PIM-1. This study utilizes atomistic simulations to model and to understand the pure- and mixed-gas transport properties of PIM-1 for the CO2/CH4 gas pair. Monte Carlo and molecular dynamics methods were combined in the estimation of sorption and diffusion of CO2 and CH4 in PIM-1. Simulated sorption and permeability data compared very well with experimental reports. Mixed-gas adsorption simulations proved the existence of competitive adsorption, favoring CO2, hence resulting in an increase in solubility selectivities. However, in mixed-gas environment CH4 permeabilities increased significantly compared to pure gas conditions, overall decreasing perm-selectivities of the polymer. Plasticization of the polymer around 25 bar CO2 partial fugacity was apparent both in pure- and mixed-gas conditions. Simulations at different gas feed compositions proved the dependence of competitive sorption and CO2-induced swelling in partial feed gas fugacities. Simulation results were combined to obtain a macroscopic permeability model that relates the multicomponent permeability to the permeate pressure and composition. Accurate estimations of permeabilities by the model were achieved allowing future implementation of the model in process simulation tools.
• #### Fluorinated thin-film composite membranes for nonpolar organic solvent nanofiltration

(Separation and Purification Technology, Elsevier BV, 2021-09) [Article]
Polyamide (PA) is highly effective as a selective layer in case of nanofiltration (NF) membranes, mainly for filtering water and other polar solvents. The incorporation of fluorinated monomers in a polyamide network is a novel strategy for obtaining membranes with enhanced permeability in case of nonpolar solvents. In this study, PA thin-film composite membranes were prepared by interfacially reacting trimesoyl chloride (TMC) and 4,4ʹ-(hexafluoroisopropylidene)bis(benzoyl chloride) (HFBC) in an organic phase with 5-trifluoromethyl-1,3-phenylenediamine (TFMPD) in an aqueous phase in a single step. The resulting membrane obtained using HFBC exhibited a considerably increased nonpolar solvent flux and selectivity in the nanofiltration range. Thus, the hydrophobicity of the PA layer and its permeance are effectively enhanced because of the incorporation of the fluorinated monomer. Therefore, high-performance membranes can be obtained for nonpolar solvent separation in petroleum refineries and purification in the pharmaceutical industry.
• #### Functional Crypto-Adenylate Cyclases Operate in Complex Plant Proteins.

(Frontiers in plant science, Frontiers Media SA, 2021-08-30) [Article]
Adenylyl cyclases (ACs) and their catalytic product cAMP are regulatory components of many plant responses. Here, we show that an amino acid search motif based on annotated adenylate cyclases (ACs) identifies 12 unique $\textit{Arabidopsis thaliana}$ candidate ACs, four of which have a role in the biosynthesis of the stress hormone abscisic acid (ABA). One of these, the 9-cis-epoxycarotenoid dioxygenase (NCED3 and At3g14440), was identified by sequence and structural analysis as a putative AC and then tested experimentally with two different methods. Given that the $\textit{in vitro}$ activity is low (fmoles cAMP pmol$^{-1}$ protein min$^{-1}$), but highly reproducible, we term the enzyme a crypto-AC. Our results are consistent with a role for ACs with low activities in multi-domain moonlighting proteins that have at least one other distinct molecular function, such as catalysis or ion channel activation. We propose that crypto-ACs be examined from the perspective that considers their low activities as an innate feature of regulatory ACs embedded within multi-domain moonlighting proteins. It is therefore conceivable that crypto-ACs form integral components of complex plant proteins participating in intra-molecular regulatory mechanisms, and in this case, potentially linking cAMP to ABA synthesis.
• #### Functional Crypto-Adenylate Cyclases Operate in Complex Plant Proteins.

(Frontiers in plant science, Frontiers Media SA, 2021-08-30) [Article]
Adenylyl cyclases (ACs) and their catalytic product cAMP are regulatory components of many plant responses. Here, we show that an amino acid search motif based on annotated adenylate cyclases (ACs) identifies 12 unique $\textit{Arabidopsis thaliana}$ candidate ACs, four of which have a role in the biosynthesis of the stress hormone abscisic acid (ABA). One of these, the 9-cis-epoxycarotenoid dioxygenase (NCED3 and At3g14440), was identified by sequence and structural analysis as a putative AC and then tested experimentally with two different methods. Given that the $\textit{in vitro}$ activity is low (fmoles cAMP pmol$^{-1}$ protein min$^{-1}$), but highly reproducible, we term the enzyme a crypto-AC. Our results are consistent with a role for ACs with low activities in multi-domain moonlighting proteins that have at least one other distinct molecular function, such as catalysis or ion channel activation. We propose that crypto-ACs be examined from the perspective that considers their low activities as an innate feature of regulatory ACs embedded within multi-domain moonlighting proteins. It is therefore conceivable that crypto-ACs form integral components of complex plant proteins participating in intra-molecular regulatory mechanisms, and in this case, potentially linking cAMP to ABA synthesis.
• #### Ionic Functionalization of Multivariate Covalent Organic Frameworks to Achieve Exceptionally High Iodine Capture Capacity.

(Angewandte Chemie (International ed. in English), Wiley, 2021-08-25) [Article]
Adsorption-based iodine (I 2 ) capture is of great potential for the treatment of radioactive nuclear waste. Here we employ a "multivariate" synthetic strategy to construct ionic covalent organic frameworks (iCOFs) with large surface area, high pore volume, and abundant binding sites for I 2 capture. The optimized material iCOF-AB-50 exhibits static I 2 uptake capacity of 10.21 g·g -1 at 75 °C, and dynamic uptake capacity of 2.79 g·g -1 at ~400 ppm of I 2 and 25 °C, far exceeding the performances of previously reported adsorbents under similar conditions. It also shows fast adsorption kinetics, good moisture tolerance, and full reusability. The promoting effect of ionic groups on I 2 adsorption has been elucidated by experimentally identifying the iodine species adsorbed at different sites and calculating their binding energies. This work demonstrates the essential role of balancing the textural properties and binding sites of the adsorbent in achieving high I 2 capture performance.
• #### Possible Misidentification of Heteroatom Species in Scanning Transmission Electron Microscopy Imaging of Zeolites

(The Journal of Physical Chemistry C, American Chemical Society (ACS), 2021-08-24) [Article]
Atomic-resolution scanning transmission electron microscopy (STEM) can be used to determine the location and state of heteroatom species in zeolites, which is essential for understanding their catalytic behavior. However, because of the complexity of zeolite structures and low heteroatom content, STEM images must be carefully interpreted to avoid misidentification. In this work, Fe-doped silicalite-1 was used as an example to illustrate this problem by combining STEM image simulation and experiments. Simulation results indicated that, unless the specimen has only one unit cell thickness, it is impossible to reliably identify Fe atoms in a zeolite framework using high-angle annular dark-field STEM (HAADF-STEM). Experimental HAADF-STEM images could not distinguish Fe-doped silicalite-1 and Fe-free silicalite-1 samples, thus confirming the infeasibility of using HAADF-STEM to determine the preferential occupancy of Fe between different crystallographic sites. It was also found that integrated differential phase contrast STEM (iDPC-STEM) could detect extraframework Fe species located in microporous channels only when the physically adsorbed volatile organic compounds were properly removed before imaging. The findings of this investigation provide important precautions and guidance for related research work.
• #### Modifying Ionic Membranes with Carbon Dots Enables Direct Production of High-Purity Hydrogen through Water Electrolysis

(ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-08-16) [Article]
Traditional electrolysis of water produces hydrogen with a purity of ∼98%. Using ion transport membranes to prevent the migration of oxygen (O2) from the anode to the cathode, the purity of H2 can be increased to ∼99.8%, but it still cannot fulfill the requirement for use in fuel cells (>99.97%). Here, we report that modifying a commercial ionic membrane (Nafion) with carbon dots (CDs) can further inhibit O2 permeation across the membrane, while effectively improving its ion transportability. The key to achieve these effects is the rational design and proper loading of the CDs, which narrows the pore size of the membrane from ∼4 nm to <2 nm and alters its surface functionality. Using the CDs-modified Nafion membrane in an H-type electrolysis cell, we demonstrate that H2 with a purity of up to 99.98%, which meets the standards of hydrogen fuel cells, can be directly produced without any additional purification process. Our study provides a new route for the low-cost electrolysis of water to produce high-purity hydrogen.
• #### Tuning the porosity of triangular supramolecular adsorbents for superior haloalkane isomer separations

(CHEMICAL SCIENCE, Royal Society of Chemistry (RSC), 2021-08-16) [Article]
Distillation-free separations of haloalkane isomers represents a persistent challenge for the chemical industry. Several classic molecular sorbents show high selectivity in the context of such separations; however, most suffer from limited tunability or poor stability. Herein, we report the results of a comparative study involving three trianglamine and trianglimine macrocycles as supramolecular adsorbents for the selective separation of halobutane isomers. Methylene-bridged trianglamine, TA, was found to capture preferentially 1-chlorobutane (1-CBU) from a mixture of 1-CBU and 2-chlorobutane (2-CBU) with a purity of 98.1%. It also separates 1-bromobutane (1-BBU) from a mixture of 1-BBU and 2-bromobutane (2-BBU) with a purity of 96.4%. The observed selectivity is ascribed to the thermodynamic stability of the TA-based host–guest complexes. Based on single crystal X-ray diffraction analyses, a [3]pseudorotaxane structure (2TA⊃1-CBU) is formed between TA and 1-CBU that is characterized by an increased level of noncovalent interactions compared to the corresponding [2]pseudorotaxane structure seen for TA⊃2-CBU. We believe that molecular sorbents that rely on specific molecular recognition events, such as the triangular pores detailed here, will prove useful as next generation sorbents in energy-efficient separations.
• #### Tuning the porosity of triangular supramolecular adsorbents for superior haloalkane isomer separations

(CHEMICAL SCIENCE, Royal Society of Chemistry (RSC), 2021-08-16) [Article]
Distillation-free separations of haloalkane isomers represents a persistent challenge for the chemical industry. Several classic molecular sorbents show high selectivity in the context of such separations; however, most suffer from limited tunability or poor stability. Herein, we report the results of a comparative study involving three trianglamine and trianglimine macrocycles as supramolecular adsorbents for the selective separation of halobutane isomers. Methylene-bridged trianglamine, TA, was found to capture preferentially 1-chlorobutane (1-CBU) from a mixture of 1-CBU and 2-chlorobutane (2-CBU) with a purity of 98.1%. It also separates 1-bromobutane (1-BBU) from a mixture of 1-BBU and 2-bromobutane (2-BBU) with a purity of 96.4%. The observed selectivity is ascribed to the thermodynamic stability of the TA-based host–guest complexes. Based on single crystal X-ray diffraction analyses, a [3]pseudorotaxane structure (2TA⊃1-CBU) is formed between TA and 1-CBU that is characterized by an increased level of noncovalent interactions compared to the corresponding [2]pseudorotaxane structure seen for TA⊃2-CBU. We believe that molecular sorbents that rely on specific molecular recognition events, such as the triangular pores detailed here, will prove useful as next generation sorbents in energy-efficient separations.
• #### Waltzing around the stereochemistry of membrane crosslinkers for precise molecular sieving in organic solvents

(Journal of Membrane Science, Elsevier BV, 2021-08-14) [Article]
• #### Electrochemical synthesis of continuous metal–organic framework membranes for separation of hydrocarbons

(Nature Energy, Springer Science and Business Media LLC, 2021-08-09) [Article]
Membrane-based approaches can offer energy-efficient and cost-effective methods for various separation processes. Practical membranes must have high permselectivity at industrially relevant high pressures and under aggressive conditions, and be manufacturable in a scalable and robust fashion. We report a versatile electrochemical directed-assembly strategy to fabricate polycrystalline metal–organic framework membranes for separation of hydrocarbons. We fabricate a series of face-centred cubic metal–organic framework membranes based on 12-connected rare-earth or zirconium hexanuclear clusters with distinct ligands. In particular, the resultant fumarate-based membranes containing contracted triangular apertures as sole entrances to the pore system enable molecular-sieving separation of propylene/propane and butane/isobutane mixtures. Prominently, increasing the feed pressure to the industrially practical value of 7 atm promoted a desired enhancement in both the total flux and separation selectivity. Process design analysis demonstrates that, for propylene/propane separation, the deployment of such face-centred cubic Zr-fumarate-based metal–organic framework membranes in a hybrid membrane–distillation system offers the potential to decrease the energy input by nearly 90% relative to a conventional single distillation process.