Recent Submissions

  • Tumor-Associated-Macrophage-Membrane-Coated Nanoparticles for Improved Photodynamic Immunotherapy

    Chen, Cailing; Song, Meiyu; Du, Yangyang; Yu, Ying; Li, Chunguang; Han, Yu; Yan, Fei; Shi, Zhan; Feng, Shouhua (Nano Letters, American Chemical Society (ACS), 2021-06-16) [Article]
    Cell-membrane-coated nanoparticles have emerged as a promising antitumor therapeutic strategy. However, the immunologic mechanism remains elusive, and there are still crucial issues to be addressed including tumor-homing capacity, immune incompatibility, and immunogenicity. Here, we reported a tumor-associated macrophage membrane (TAMM) derived from the primary tumor with unique antigen-homing affinity capacity and immune compatibility. TAMM could deplete the CSF1 secreted by tumor cells in the tumor microenvironment (TME), blocking the interaction between TAM and cancer cells. Especially, after coating TAMM to upconversion nanoparticle with conjugated photosensitizer (NPR@TAMM), NPR@TAMM-mediated photodynamic immunotherapy switched the activation of macrophages from an immunosuppressive M2-like phenotype to a more inflammatory M1-like state, induced immunogenic cell death, and consequently enhanced the antitumor immunity efficiency via activation of antigen-presenting cells to stimulate the production of tumor-specific effector T cells in metastatic tumors. This TAM-membrane-based photodynamic immunotherapy approach offers a new strategy for personalized tumor therapy.
  • Molecular sieving using metal–polymer coordination membranes in organic media

    Hardian, Rifan; Pogany, Peter; Lee, Young Moo; Szekely, Gyorgy (Journal of Materials Chemistry A, Royal Society of Chemistry (RSC), 2021-06-10) [Article]
    Improving the chemical resistance of membranes without sacrificing their molecular sieving performance is highly challenging. Herein, a novel scalable methodology was developed for fabricating solvent-resistant nanofiltration membranes based on metal–polymer coordination (MPC) through a facile yet highly effective method. The controlled deposition of copper(I) iodide enabled the fine-tuning of the molecular sieving performance of MPC membranes by altering both their chemistry and morphology. Spectroscopic and morphological analyses were conducted to elucidate the microscopic and macroscopic properties of the membranes. The formation of coordination bonds between the metal and polybenzimidazole chains protected the membranes from dissolving in harsh organic solvents. Additionally, computational modeling was performed to reveal the stabilization energy and fractional free volume (FFV). Our work opens more sustainable avenues for robust membrane fabrication without conventional crosslinking, which requires reactive chemicals.
  • Insights into the Enhancement of MOF/Polymer Adhesion in Mixed-Matrix Membranes via Polymer Functionalization

    Carja, Ionela-Daniela; Tavares, Sergio Rodrigues; Shekhah, Osama; Ozcan, Aydin; Semino, Rocio; Kale, Vinayak Swamirao; Eddaoudi, Mohamed; Maurin, Guillaume (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-06-09) [Article]
    MOF-based mixed-matrix membranes (MMMs) prepared using standard routes often exhibit poor adhesion between polymers and MOFs. Herein, we report an unprecedented systematic exploration on polymer functionalization as the key to achieving defect-free MMMs. As a case study, we explored computationally MMMs based on the combination of the prototypical UiO-66(Zr) MOF with polymer of intrinsic porosity-1 (PIM-1) functionalized with various groups including amidoxime, tetrazole, and N-((2-ethanolamino)ethyl)carboxamide. Distinctly, the amidoxime-derivative PIM-1/UiO-66(Zr) MMM was predicted to express the desired enhanced MOF/polymer interfacial interactions and thus subsequently prepared and evaluated experimentally. Prominently, high-resolution transmission electron microscopy confirmed optimal adhesion between the two components in contrast to the nanometer-sized voids/defects shown by the pristine PIM-1/UiO-66(Zr) MMM. Notably, single-gas permeation measurements further corroborated the need of optimal MOF/polymer adhesion in order to effectively enable the MOF to play a role in the gas transport of the resulting MMM.
  • Nanoporous polyethersulfone membranes prepared by mixed solvent phase separation method for protein separation

    Li, Peipei; Thankamony, Roshni; Li, Xiang; Li, Zhen; Liu, Xiaowei; Lai, Zhiping (Journal of Membrane Science, Elsevier BV, 2021-06-08) [Article]
    Nanoporous polyethersulfone (PES) membranes with high surface porosity and uniform pore size distribution were prepared by combining the phase separation in NMP/nonane mixed solvent system with the traditional nonsolvent induced phase inversion process. The effects of PES concentration, nonane concentration, evaporation time, casting solution temperature, and varied mixed solvent systems on the porous PES membrane surface morphology were thoroughly investigated and optimized. The optimized nanoporous PES membrane showed a high surface porosity with a uniform pore size of 20 nm, rendering an exceptional molecular weight cut-off of as low as 100 k Dalton. In addition, the membrane exhibited a significant molecular size exclusion with water permeance of 121 LMH bar−1, bovine serum albumin (BSA) protein rejection of 60.1%, and γ-globulin protein rejection of 99.5% at 0.5 bar, respectively, demonstrating the potential of the as-prepared nanoporous PES membrane for application in protein separation.
  • Engineering the Coordination Sphere of Isolated Active Sites to Explore the Intrinsic Activity in Single-Atom Catalysts

    Wu, Xin; Zhang, Huabin; Zuo, Shouwei; Dong, Juncai; Li, Yang; Zhang, Jian; Han, Yu (Nano-Micro Letters, Springer Science and Business Media LLC, 2021-06-07) [Article]
    AbstractReducing the dimensions of metallic nanoparticles to isolated, single atom has attracted considerable attention in heterogeneous catalysis, because it significantly improves atomic utilization and often leads to distinct catalytic performance. Through extensive research, it has been recognized that the local coordination environment of single atoms has an important influence on their electronic structures and catalytic behaviors. In this review, we summarize a series of representative systems of single-atom catalysts, discussing their preparation, characterization, and structure–property relationship, with an emphasis on the correlation between the coordination spheres of isolated reactive centers and their intrinsic catalytic activities. We also share our perspectives on the current challenges and future research promises in the development of single-atom catalysis. With this article, we aim to highlight the possibility of finely tuning the catalytic performances by engineering the coordination spheres of single-atom sites and provide new insights into the further development for this emerging research field.
  • Operando Elucidation on the Working State of Immobilized Fluorinated Iron Porphyrin for Selective Aqueous Electroreduction of CO2 to CO

    Lu, Xiaofei; Ait Ahsaine, Hassan; Dereli, Busra; Garcia Esparza, Angel T.; Reinhard, Marco; Shinagawa, Tatsuya; Li, Duanxing; Adil, Karim; Tchalala, Mohammed; Kroll, Thomas; Eddaoudi, Mohamed; Sokaras, Dimosthenis; Cavallo, Luigi; Takanabe, Kazuhiro (ACS Catalysis, American Chemical Society (ACS), 2021-05-19) [Article]
    Iron porphyrin-based molecular catalysts can electrocatalyze CO2 reduction to CO at nearly 100% selectivity in water. Nevertheless, the associated active sites and reaction mechanisms remain debatable, impeding the establishment of design guidelines for effective catalysts. This study reports coupling in operando experiments and theoretical calculations for immobilized 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin Fe(III) chloride (FeF20TPP) for electrocatalytic CO2 reduction in an aqueous phase. In operando UV–vis and X-ray absorption near-edge structure spectra indicated the persisting presence of Fe(II) species during the cathodic reaction, acting as catalytic sites that accommodate CO as Fe(II)–CO adducts. Consistently, the density functional calculations pointed out that the ligand-reduced state with oxidized Fe, namely, [Fe(II)F20(TPP•)]−, prevails in the catalytic cycle prior to the rate-controlling step. This work provides the conclusive representation related to the working states of Fe-based molecular catalysts under reaction conditions.
  • Directional Exciton Migration in Benzoimidazole-Based Metal–Organic Frameworks

    Gutierrez Arzaluz, Luis; Jia, Jiangtao; Gu, Chun; Czaban-Jozwiak, Justyna; Yin, Jun; Shekhah, Osama; Bakr, Osman; Eddaoudi, Mohamed; Mohammed, Omar F. (The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2021-05-19) [Article]
    Highly luminescent metal-organic frameworks (MOFs) have recently received great attention due to their potential applications as sensors and light-emitting devices. In these MOFs, the highly ordered fluorescent organic linkers positioning prevents excited-state self-quenching and rotational motion, enhancing their light-harvesting properties. Here, the exciton migration between the organic linkers with the same chemical structure but different protonation degrees in Zr-based MOFs was explored and deciphered using ultrafast laser spectroscopy and density functional theory calculations. First, we clearly demonstrate how hydrogen-bonding interactions between free linkers and solvents affect the twisting changes, internal conversion processes, and luminescent behavior of a benzoimidazole-based linker. Second, we provide clear evidence of an ultrafast energy transfer between well-aligned adjacent linkers with different protonation states inside the MOF. These findings provide a new fundamental photophysical insight into the exciton migration dynamics between linkers with different protonation states coexisting at different locations in MOFs and serve as a benchmark for improving light-harvesting MOF architectures.
  • Selective Conversion of Carbon Dioxide to Formate with High Current Densities

    Yang, Xiulin; Liu, Defei; Zhong, Shenghong; Zhou, Xiaofeng; Huang, Kuo-Wei; Li, Lain-Jong; Lai, Zhiping (Journal of Molecular and Engineering Materials, World Scientific Pub Co Pte Lt, 2021-05-10) [Article]
    Selective conversion of CO2 to formate with high current densities is highly desirable but still challenging. Copper hollow fibers with interconnected pore structures were fabricated via a facile method and used as a stand-alone cathode for highly efficient electrochemical reduction of CO2 to formate. Our studies revealed that delivering the reactant CO2 gas to the inner space of the hollow fiber could build up a higher CO2 partial pressure in the pores and presumably reduce the concentration of H[Formula: see text] from the electrolyte to effectively suppress the major competing reaction, hydrogen evolution reaction (HER), from 46.9% faradaic efficiency (FE) to 15.0%. A high selectivity for CO2 reduction to formate with a maximum FE of 77.1% was achieved with a high current density of 34.7[Formula: see text]mA cm[Formula: see text], which is one of the highest FEs on Cu-based materials. Mechanistic studies suggest that the abundant active sites along with the unique crystal facets induced by the high pressure of CO2 at the pore surface in the “gas in” mode are attributed to the superior electroactivity and selectivity for the CO2 reduction to formate. The Cu hollow fiber electrodes exhibit an outstanding long-term stability at high current density, showing great potential for large-scale practical applications.
  • 2D Covalent-Organic Framework Electrodes for Supercapacitors and Rechargeable Metal-Ion Batteries

    Kandambeth, Sharath; Kale, Vinayak Swamirao; Shekhah, Osama; Alshareef, Husam N.; Eddaoudi, Mohamed (Advanced Energy Materials, Wiley, 2021-05-05) [Article]
    Covalent-organic frameworks (COFs) represent a new frontier of crystalline porous organic materials with framework structures in 2D or 3D domains, which make them promising for many applications. Herein, the fundamental structural design aspects of 2D-COFs are reviewed, which position them as suitable electrodes for electrochemical energy storage. The ordered π–π stacked arrangement of the organic building blocks in juxtaposed layers provides a pathway for efficient electronic charge transport; the 2D structure provides a pathway for enhanced ionic diffusion, which enhances ionic transport. Importantly, the tunable pore size enables 2D-COFs to accommodate mobile ions with different sizes and charges, positioning them as prospect materials for various types of batteries. Distinctively, the ability to functionalize their pore system with a periodic array of redox active species, enriching their potential redox chemistry, provides a pathway to control the redox and capacitive contributions to the charge storage mechanism. The strong covalently linked framework backbone of COFs is an additional merit for achieving long cycle life, and stability against the “leaching out” problem of active molecules in strong electrolytes as observed in other organic materials applied in energy storage devices.
  • Luminescent Copper(I) Halides for Optoelectronic Applications

    Yin, Jun; Lei, Qiong; Han, Yu; Bakr, Osman; Mohammed, Omar F. (Physica Status Solidi - Rapid Research Letters, Wiley, 2021-05-02) [Article]
    Lead-free copper(I) halides have been demonstrated to exhibit high photoluminescence quantum yields with high air and light stability, making them one of the most promising semiconductors for next-generation light-emitting diode devices. The low-dimensional structures and soft lattices of Cu(I) halides induce the formation of self-trapped excitons (STEs) to achieve broadband emissions with high quantum yields. Herein, the recent studies on the electronic and optical properties of Cu(I) halides (i.e., Cs3Cu2X5, CsCu2X3, and A2CuX3, where A = K+ or Rb+, X = Cl−, Br−, or I−) are reviewed and particular emphasis is placed on the role of the dimensionality and the halide in governing the electronic and optical properties (e.g., emission color and photoluminescence efficiency) via STEs. Several optoelectronic applications of Cu(I) halides are also discussed. In the last section, perspectives and challenges for the future development of Cu(I) halides in both optoelectronic and photocatalytic applications are outlined.
  • A Roadmap to Sorption-Based Atmospheric Water Harvesting: From Molecular Sorption Mechanism to Sorbent Design and System Optimization

    Yang, Kaijie; Pan, Tingting; Lei, Qiong; Dong, Xinglong; Cheng, Qingpeng; Han, Yu (Environmental Science & Technology, American Chemical Society (ACS), 2021-04-29) [Article]
    Sorption-based atmospheric water harvesting (SAWH), which uses sorbents to capture water vapor from the air and low-grade energy to produce fresh liquid water, has been recognized as a promising strategy for decentralized water supply in arid areas. This review aims to summarize the latest progress in this field and provide perspectives for the further development of SAWH, focusing on the design of sorbent materials and the optimization of the entire system. We first introduce the water sorption mechanisms on different sorbent materials. Next, we discuss the properties and performances of various sorbents developed for SAWH by categorizing them into specific groups: nanoporous solids, hygroscopic polymers, salt-based composites, and liquid sorbents; for each type of sorbent materials, we have analyzed its advantages and limitations, as well as design strategies. In addition, we discuss the influences of the mass and heat transport of the SAWH system on its overall performance in actual operations, and introduce different types of water harvesters developed for SAWH. In the last section, we outline the challenges in this field from fundamental research and practical application aspects, and describe roadmaps for the future development of this technology.
  • Nano-Confinement Effects on Structural Development and Organic Solvent-Induced Swelling of Ultrathin Carbon Molecular Sieve Films

    Ogieglo, Wojciech; Song, Kepeng; Chen, Cailing; Lei, Qiong; Han, Yu; Pinnau, Ingo (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-04-28) [Article]
    Successful implementation of carbon molecular sieve (CMS) membranes in large scale chemical processes inevitably relies on fabrication of high performance integrally skinned asymmetric or thin-film composite membranes. In principle, to maximize separation efficiency the selective CMS layer should be as thin as possible which requires its lateral confinement to a supporting structure. In this work, we studied pyrolysis-induced structural development as well as ethanol vapor-induced swelling of ultrathin CMS films made from a highly aromatic polyimide of an intrinsic microporosity (PIM-PI) precursor. Utilization of a light polarization-sensitive technique, spectroscopic ellipsometry, allowed for the identification of an internal orientation within the turbostratic amorphous CMS structure driven by the laterally constraining support. Our results indicated a significant thickness dependence both in the extent of pyrolytic collapse and response to organic vapor penetrant. Thinner, substrate-confined films (∼30 nm) collapsed more extensively leading to a reduction of microporosity in comparison to their thicker (∼300 nm) as well as self-supported (∼70 μm) counterparts. The reduced microporosity in the thinner films induced changes in the balance between penetrant-induced dilation (swelling) and filling of micropores. In comparison to thicker films, the initial lower microporosity of the thinner films was accompanied by slightly enhanced organic vapor-induced swelling. The presented results are anticipated to generate the fundamental knowledge necessary to design optimized ultrathin CMS membranes. In particular, our results reinforce previous findings that excessive reduction of the selective layer thickness in amorphous microporous materials (such as PIMs or CMS) beyond several hundred nanometers may not be optimal for maximizing their fluid transport performance.
  • Highly Active Heterogeneous Catalyst for Ethylene Dimerization Prepared by Selectively Doping Ni on the Surface of a Zeolitic Imidazolate Framework

    Chen, Cailing; Alalouni, Mohammed R.; Dong, Xinglong; Cao, Zhen; Cheng, Qingpeng; Zheng, Lirong; Meng, Lingkun; Guan, Chao; Liu, L. M.; Abou-Hamad, Edy; Wang, Jianjian; Shi, Zhan; Huang, Kuo-Wei; Cavallo, Luigi; Han, Yu (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-04-28) [Article]
    The production of 1-butene by ethylene dimerization is an important chemical industrial process currently implemented using homogeneous catalysts. Here, we describe a highly active heterogeneous catalyst (Ni-ZIF-8) for ethylene dimerization, which consists of isolating Ni-active sites selectively located on the crystal surface of a zeolitic imidazolate framework. Ni-ZIF-8 can be easily prepared by a simple one-pot synthesis method in which site-specific anchoring of Ni is achieved spontaneously because of the incompatibility between the d<sup>8</sup> electronic configuration of Ni<sup>2+</sup> and the three-dimensional framework of ZIF-8. The full exposure and square-planar coordination of the Ni sites accounts for the high catalytic activity of Ni-ZIF-8. It exhibits an average ethylene turnover frequency greater than 1 000 000 h<sup>-1</sup> (1-butene selectivity >85%) at 35 °C and 50 bar, far exceeding the activities of previously reported heterogeneous catalysts and many homogeneous catalysts under similar conditions. Moreover, compared to molecular Ni complexes used as homogeneous catalysts for ethylene dimerization, Ni-ZIF-8 has significantly higher stability and shows constant activity during 4 h of continuous reaction. Isotopic labeling experiments indicate that ethylene dimerization over Ni-ZIF-8 follows the Cossee-Arlman mechanism, and detailed characterizations combined with density functional theory calculations rationalize this observed high activity.
  • Carbon nitride derived nitrogen-doped carbon nanosheets for high-rate lithium-ion storage

    Zhang, Wenli; Yin, Jian; Chen, Cailing; Qiu, Xueqing (Chemical Engineering Science, Elsevier BV, 2021-04-27) [Article]
    Carbonaceous materials are practical anodes for lithium-ion batteries. Commercial graphite anode has a limited theoretical capacity of 372 mAh g−1. Amorphous carbon anode could break the capacity limitation of the graphite anode, while nitrogen doping plays a critical role in effectively enhancing the reversible capacities and rate capability of carbonaceous anodes. Herein, we propose a new strategy for synthesizing nitrogen-doped carbon materials from graphitic carbon nitride. Zinc-assisted thermal treatment of graphitic carbon nitride enables the carbonization of graphitic carbon nitride and successful preparation of highly nitrogen-doped carbon. The obtained nitrogen-doped carbon material is doped with a high-level nitrogen of 21.6 at. % which enables high reversible capacity and rate capability. This work puts forward a new synthesis protocol of nitrogen-doped carbon materials for promising anodes of lithium-ion batteries.
  • Efficient wide-spectrum photocatalytic overall water splitting over ultrathin molecular nickel phthalocyanine/BiVO4 Z-scheme heterojunctions without noble metals

    Feng, Jiannan; Bian, Ji; Bai, Linlu; Xi, Shibo; Wang, Ya; Chen, Cailing; Jing, Liqiang (Applied Catalysis B: Environmental, Elsevier BV, 2021-04-27) [Article]
    Photocatalytic overall water splitting (OWS) is a promising route for sustainable production of hydrogen fuels. A grand challenge is developing efficient photocatalysts with extended light absorption, high charge separation and abundant catalytic sites. Here, we designed molecular nickel phthalocyanines on phosphate-functionalized bismuth vanadate nanosheets (NiPc/PO-BVNS) as ultrathin heterojunctions, targeting OWS without noble-metal cocatalysts or sacrificial agents. Optimal NiPc/PO-BVNS affords H2/O2 evolution rates of 23.89/12.23 μmol g−1 h−1 with stoichiometric ratio under UV–vis irradiation, which reaches remarkable 50-fold enhancement over the benchmark g-C3N4/BVNS. The excellent photoactivities are ascribed to the novel Z-scheme charge separation between NiPc and PO-BVNS, where phosphates are proved to induce quasi-single-molecule-layer dispersion of NiPcs by H-bonding effect meanwhile create negative field to trap holes. Moreover, well-defined Ni2+–N4 center of NiPc could function as the catalytic sites for H2 evolution. This work diversifies the artificial photosynthesis systems with a facile strategy of constructing novel Z-scheme organic/inorganic heterojunctions.
  • Unlocking mixed oxides with unprecedented stoichiometries from heterometallic metal-organic frameworks for the catalytic hydrogenation of CO2

    Castells-Gil, Javier; Ould-Chikh, Samy; Ramírez, Adrian; Ahmad, Rafia; Prieto, Gonzalo; Gómez, Alberto Rodríguez; Garzon Tovar, Luis Carlos; Telalovic, Selvedin; Liu, Lingmei; Genovese, Alessandro; Padial, Natalia M.; Aguilar-Tapia, Antonio; Bordet, Pierre; Cavallo, Luigi; Martí-Gastaldo, Carlos; Gascon, Jorge (Chem Catalysis, Elsevier BV, 2021-04-26) [Article]
    Their complex surface chemistry and high oxygen lattice mobilities place mixed-metal oxides among the most important families of materials. Modulation of stoichiometry in mixed-metal oxides has been shown to be a very powerful tool for tuning optical and catalytic properties. However, accessing different stoichiometries is not always synthetically possible. Here, we show that the thermal decomposition of the recently reported metal-organic framework MUV-101(Fe, Ti) results in the formation of carbon-supported titanomaghemite nanoparticles with an unprecedented Fe/Ti ratio close to 2, not achievable by soft-chemistry routes. The resulting titanomaghemite phase displays outstanding catalytic activity for the production of CO from CO2 via the reverse water-gas shift (RWGS) reaction with CO selectivity values of ca. 100% and no signs of deactivation after several days on stream. Theoretical calculations suggest that the reaction proceeds through the formation of COOH* species, favoring in this way CO over other byproducts.
  • A facile approach to synthesize SSZ-13 membranes with ultrahigh N2 permeances for efficient N2/CH4 separations

    Li, Yanmei; He, Shengnan; Shu, Chaojiu; Li, Xinping; Liu, Bo; Zhou, Rongfei; Lai, Zhiping (Journal of Membrane Science, Elsevier BV, 2021-04-26) [Article]
    Separation of inert nitrogen from natural gas by membranes is much more energy-saving than cryogenic distillation but very challenging because the size difference of both gas molecules is quite small. Herein, high-quality and N2-selective SSZ-13 membranes on α-alumina tubes were prepared using a novel synthesis approach called seeded-gel synthesis. Seeded-gel synthesis was more convenient and credible than the conventional secondary growth because a seeding step on the substrate was omitted for the former method. The effect of calcination atmosphere on the quality of membranes was also discussed. SSZ-13 membranes had the fewest defects when ozone calcination was used. The predicted values of single-component N2 and CH4 permeances by the Maxwell-Stefan equations agreed well with the experimental ones. The SSZ-13 membrane exhibited ultrahigh N2 permeance of 850 × 10−9 mol m−2 s−1 Pa−1 (equals 2500 GPU) and a high N2/CH4 selectivity of 13.5 at 298 K and 0.303 MPa feed pressure (absolute). Membrane preparation by seeded-gel method had good reproducibility. The effects of temperature, pressure drop and feed flow rate on membrane performances were investigated for N2/CH4 mixture separations. The membrane also displayed good separation performance in N2/CH4 system either at 2.6 MPa feed pressure or under humid conditions. The continuous SSZ-13 thin membranes prepared by the simple seeded-gel synthesis showed great potentials for energy-efficient N2 removal from unconventional gases.
  • Molecular Scalpel to Chemically Cleave Metal-Organic Frameworks for Induced Phase Transition.

    Zhou, Xianlong; Dong, Juncai; Zhu, Yihan; Liu, L. M.; Jiao, Yan; Li, Huan; Han, Yu; Davey, Kenneth; Xu, Qiang; Zheng, Yao; Qiao, Shi-Zhang (Journal of the American Chemical Society, 2021-04-23) [Article]
    A bottom-up chemical synthesis of metal−organic frameworks (MOFs) permits significant structural diversity because of various combinations of metal centers and different organic linkers. However, fabrication generally complies with the classic hard and soft acids and bases (HSAB) theory. This restricts direct synthesis of desired MOFs with converse Lewis type of metal ions and ligands. Here we present a top-down strategy to break this limitation via the structural cleavage of MOFs to trigger a phase transition using a novel “molecular scalpel”. A conventional CuBDC MOF (BDC = 1,4-benzenedicarboxylate) prepared from a hard acid (Cu2+) metal and a hard base ligand was chemically cleaved by L-ascorbic acid acting as chemical scalpel to fabricate a new Cu2BDC structure composed of a soft acid (Cu1+) and a hard base (BDC). Controlled phase transition was achieved by a series of redox steps to regulate the chemical state and coordination number of Cu ions, resulting in a significant change in chemical composition and catalytic activity. Mechanistic insights into structural cleavage and rearrangement are elaborated in detail. We show this novel strategy can be extended to general Cu-based MOFs and supramolecules for nanoscopic casting of unique architectures from existing ones.
  • Molecular Scalpel to Chemically Cleave Metal-Organic Frameworks for Induced Phase Transition.

    Zhou, Xianlong; Dong, Juncai; Zhu, Yihan; Liu, L. M.; Jiao, Yan; Li, Huan; Han, Yu; Davey, Kenneth; Xu, Qiang; Zheng, Yao; Qiao, Shi-Zhang (Journal of the American Chemical Society, 2021-04-23) [Article]
    A bottom-up chemical synthesis of metal−organic frameworks (MOFs) permits significant structural diversity because of various combinations of metal centers and different organic linkers. However, fabrication generally complies with the classic hard and soft acids and bases (HSAB) theory. This restricts direct synthesis of desired MOFs with converse Lewis type of metal ions and ligands. Here we present a top-down strategy to break this limitation via the structural cleavage of MOFs to trigger a phase transition using a novel “molecular scalpel”. A conventional CuBDC MOF (BDC = 1,4-benzenedicarboxylate) prepared from a hard acid (Cu2+) metal and a hard base ligand was chemically cleaved by L-ascorbic acid acting as chemical scalpel to fabricate a new Cu2BDC structure composed of a soft acid (Cu1+) and a hard base (BDC). Controlled phase transition was achieved by a series of redox steps to regulate the chemical state and coordination number of Cu ions, resulting in a significant change in chemical composition and catalytic activity. Mechanistic insights into structural cleavage and rearrangement are elaborated in detail. We show this novel strategy can be extended to general Cu-based MOFs and supramolecules for nanoscopic casting of unique architectures from existing ones.
  • A single-molecule van der Waals compass

    Shen, Boyuan; Chen, Xiao; Wang, Huiqiu; Xiong, Hao; Bosch, Eric G. T.; Lazić, Ivan; Cai, Dali; Qian, Weizhong; Jin, Shifeng; Liu, Xin; Han, Yu; Wei, Fei (Nature, Springer Science and Business Media LLC, 2021-04-21) [Article]
    Single-molecule imaging is challenging but highly beneficial for investigating intermolecular interactions at the molecular level<sup>1-6</sup>. Van der Waals interactions at the sub-nanometre scale strongly influence various molecular behaviours under confinement conditions<sup>7-11</sup>. Inspired by the traditional compass<sup>12</sup>, here we use a para-xylene molecule as a rotating pointer to detect the host-guest van der Waals interactions in the straight channel of the MFI-type zeolite framework. We use integrated differential phase contrast scanning transmission electron microscopy<sup>13-15</sup> to achieve real-space imaging of a single para-xylene molecule in each channel. A good correlation between the orientation of the single-molecule pointer and the atomic structure of the channel is established by combining the results of calculations and imaging studies. The orientations of para-xylene help us to identify changes in the van der Waals interactions, which are related to the channel geometry in both spatial and temporal dimensions. This work not only provides a visible and sensitive means to investigate host-guest van der Waals interactions in porous materials at the molecular level, but also encourages the further study of other single-molecule behaviours using electron microscopy techniques.

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