Recent Submissions

  • Fluorine-Boosted Kinetic and Selective Molecular Sieving of C6 Derivatives.

    Moosa, Basem; Alimi, Lukman Olawale; Lin, Weibin; Fakim, Aliyah; Bhatt, Prashant; Eddaoudi, Mohamed; Khashab, Niveen M. (Angewandte Chemie (International ed. in English), 2023-09-25) [Article]
    Porous molecular sorbents have excellent selectivity towards hydrocarbon separation with energy saving techniques. However, to realize commercialization, molecular sieving processes should be faster and more efficient compared to extended frameworks. In this work, we show that utilizing fluorine to improve the hydrophobic profile of leaning pillararenes affords a substantial kinetic selective adsorption of benzene over cyclohexane (20:1 for benzene). The crystal structure shows a porous macrocycle that acts as a perfect match for benzene in both the intrinsic and extrinsic cavities with strong interactions in the solid state. The fluorinated leaning pillararene surpasses all reported organic molecular sieves and is comparable to the extended metal organic frameworks that were previously employed for this separation such as UIO-66. Most importantly, this sieving system outperformed the well-known zeolitic imidazolate frameworks under low pressure, which opens the door to new generations of molecular sieves that can compete with extended frameworks for more sustainable hydrocarbon separation.
  • Improving Co2 and Ch4 Conversions on Exsolved Ni-Fe Alloy Perovskite Catalyst by Enlarging the Three-Phase Boundary with Minimal Rh Doping

    Yao, Xueli; Cheng, Qingpeng; Bai, Xueqin; Davaasuren, Bambar; Melinte, Georgian; Morlanes, Natalia Sanchez; Olmo, Jose Luis Cerrillo; Velisoju, Vijay K.; Mohamed, Hend Omar; Kolubah, Pewee Datoo; Zheng, Lirong; Han, Yu; Bakr, Osman; Gascon, Jorge; Castaño, Pedro (Elsevier BV, 2023-09-23) [Preprint]
    Exsolved Ni-Fe alloy perovskite catalysts exhibit remarkable coking resistance in C–H activation. However, the utilization of active sites is typically incomplete, resulting in relative low catalytic activity. Herein, we investigated the minimal doping with Rh to boost the catalytic activity in dry reforming of methane by promoting exsolution and the enlargement of the three-phase boundary between the alloy, support, and reactants. The Rh influences the formation of the Ni-Fe alloy, as revealed by in-situ X-ray diffraction, and promotes the individual and collective CH4 and CO2 conversions, as revealed by packed bed reactor runs, temperature-programmed surface reactions, and operando infrared spectroscopy. A minimal 0.21 wt.% Rh addition enlarges the three-phase boundary while improving the oxygen mobility and storage. The oxygen mobility is responsible for promoting CH4dissociation and dynamic removal of carbon-containing intermediates, such that the catalyst remains stable for over 100 h under both 1 and 14 bar.
  • Long-Lived Hot Carriers in Two-Dimensional Perovskites: The Role of Alternating Cations in Interlayer Space

    Wei, Qi; Ren, Hui; Liu, Jinjie; Liu, Qi; Wang, Chenhao; Lau, Ting Wai; Zhou, Luwei; Bian, Tieyuan; Zhou, Yifan; Wang, Pengzhi; Lei, Qiong; Mohammed, Omar F.; Li, Mingjie; Yin, Jun (ACS Energy Letters, American Chemical Society (ACS), 2023-09-22) [Article]
    Solar absorbers featuring prolonged hot-carrier (HC) cooling are highly desired for the development of HC solar cells. Two-dimensional (2D) hybrid perovskites are known for their exceptional stability and tunable optoelectronic properties. Nevertheless, their hot-carrier dynamics have been inadequately investigated. Here, we demonstrate ultraslow hot-carrier cooling with a lifetime >2 ns and long HC diffusion length in 2D (ACA)(MA)PbI4 (ACA = acetamidinium) with alternating cations in the interlayer space (ACI), surpassing those of 3D MAPbBr3 and 2D Ruddlesden–Popper (PEA)2PbI4. Our nonadiabatic molecular dynamics simulations with spin–orbit coupling show that the enhanced HC cooling in the ACI-phase 2D perovskite is due to multiple split-off bands and reduced electron–phonon coupling. Furthermore, the hot electrons can be efficiently extracted from (ACA)(MA)PbI4 and then transferred to the electron-transporting layer. These new insights highlight the benefit of manipulating interlayer cations in 2D perovskites as an advantageous approach to control long-lived hot carriers, thus potentially enhancing photovoltaic device performance.
  • Solid-solvent processing of ultrathin, highly loaded mixed-matrix membrane for gas separation

    Chen, Guining; Chen, Cailing; Guo, Yanan; Chu, Zhenyu; Pan, Yang; Liu, Guozhen; Liu, Gongping; Han, Yu; Jin, Wanqin; Xu, Nanping (Science, American Association for the Advancement of Science (AAAS), 2023-09-21) [Article]
    Mixed-matrix membranes (MMMs) that combine processable polymer with more permeable and selective filler have potential for molecular separation, but it remains difficult to control their interfacial compatibility and achieve ultrathin selective layers during processing, particularly at high filler loading. We present a solid-solvent processing strategy to fabricate an ultrathin MMM (thickness less than 100 nanometers) with filler loading up to 80 volume %. We used polymer as a solid solvent to dissolve metal salts to form an ultrathin precursor layer, which immobilizes the metal salt and regulates its conversion to a metal-organic framework (MOF) and provides adhesion to the MOF in the matrix. The resultant membrane exhibits fast gas-sieving properties, with hydrogen permeance and/or hydrogen–carbon dioxide selectivity one to two orders of magnitude higher than that of state-of-the-art membranes.
  • Unit-cell-thick zeolitic imidazolate framework films for membrane application

    Liu, Qi; Miao, Yurun; Villalobos, Luis Francisco; Li, Shaoxian; Chi, Heng-Yu; Chen, Cailing; Vahdat, Mohammad Tohidi; Song, Shuqing; Babu, Deepu J; Hao, Jian; Han, Yu; Tsapatsis, Michael; Agrawal, Kumar Varoon (Nature materials, Springer Science and Business Media LLC, 2023-09-21) [Article]
    Zeolitic imidazolate frameworks (ZIFs) are a subset of metal–organic frameworks with more than 200 characterized crystalline and amorphous networks made of divalent transition metal centres (for example, Zn2+ and Co2+) linked by imidazolate linkers. ZIF thin films have been intensively pursued, motivated by the desire to prepare membranes for selective gas and liquid separations. To achieve membranes with high throughput, as in ångström-scale biological channels with nanometre-scale path lengths, ZIF films with the minimum possible thickness—down to just one unit cell—are highly desired. However, the state-of-the-art methods yield membranes where ZIF films have thickness exceeding 50 nm. Here we report a crystallization method from ultradilute precursor mixtures, which exploits registry with the underlying crystalline substrate, yielding (within minutes) crystalline ZIF films with thickness down to that of a single structural building unit (2 nm). The film crystallized on graphene has a rigid aperture made of a six-membered zinc imidazolate coordination ring, enabling high-permselective H2 separation performance. The method reported here will probably accelerate the development of two-dimensional metal–organic framework films for efficient membrane separation.
  • Amine Chemistry of Porous CO2 Adsorbents

    Nguyen, Thien Si; Dogan, Nesibe A; Lim, Haeseong; Yavuz, Cafer T. (Accounts of chemical research, American Chemical Society (ACS), 2023-09-20) [Article]
    As renewable energy and CO2 utilization technologies progress to make a more significant contribution to global emissions reduction, carbon capture remains a critical component of the mission. Current CO2 capture technologies involve operations at point sources such as fossil fuel-based power plants or source-agnostic like in direct air capture. Each strategy has its own advantages and limitations, but in common, they all employ sorption-based methods with the use of sorbents strongly adhering to CO2. Amine solutions are the most widely used absorbents for industrial operations due to the robust chemical bonds formed between amines and CO2 under both dry and humid conditions, rendering excellent selectivity. Such strong binding, however, causes problematic regeneration. In contrast, purely physisorptive porous materials with high surface areas allow for the confinement of CO2 inside narrow pores/channels and have a lower regeneration energy demand but with decreased selectivity and capacity. The most promising solution would then be the unification of both types of sorbents in one system, which could bring about a practical adsorption–desorption process. In other words, the development of porous solid materials with tunable amine content is necessary to leverage the high contact surface of porous sorbents with the added ability to manipulate amine incorporation toward lower CO2 binding strength. To answer the call to uncover the most feasible amine chemistry in carbon capture, our group has devoted intense effort to the study of amine-based CO2 adsorbents for the past decade. Oriented along practicality, we put forth a principle for the design of our materials to be produced in no more than three synthetic steps with economically viable starting materials. Porous organic polymers with amine functionalities of various substitutions, meaning primary, secondary, and tertiary amines, were synthesized and studied for CO2 adsorption. Direct synthesis proved to be feasibly applicable for secondary and tertiary amine-incorporated porous polymers whereas primary-amine-based sorbents would be conveniently obtained via postsynthetic modifications. Sorbents based on tertiary amines exhibit purely physical adsorption behavior if the nitrogen atoms are placed adjacent to aromatic cores due to the conjugation effect that reduces the electron density of the amine. However, when such conjugation is inhibited, chemisorptive activity is observed. Secondary amine adsorbents, in turn, express a higher binding strength than tertiary amine counterparts, but both types can merit a strengthened binding by the physical impregnation of small-molecule amines. Sorbents with primary-amine tethers can be obtained via postsynthetic transformation of precursor functionalities, and for them, chemical adsorption is mainly at work. We conclude that mixed-amine systems could exhibit unprecedented binding mechanisms, resulting in exceptionally specific interactions that would be useful for the development of highly selective sorbents for CO2.
  • Solution-processable poly(ether-ether-ketone) membranes for organic solvent nanofiltration: from dye separation to pharmaceutical purification

    Alqadhi, Nawader; Abdellah, Mohamed; Nematulloev, Sarvarkhodzha; Mohammed, Omar F.; Abdulhamid, Mahmoud A.; Szekely, Gyorgy (Separation and Purification Technology, Elsevier BV, 2023-09-15) [Article]
    Through polymer engineering, the membrane properties can be considerably changed and its performance can be improved. Organic solvent nanofiltration (OSN) membranes require polymers with good solution processability to facilitate membrane preparation. However, the resultant membranes should have excellent solvent resistance. Poly(ether-ether-ketone) (PEEK) is a potential polymer for OSN applications because of its high thermal stability and excellent solvent resistance. However, commercial PEEK has limited solution processability, and its fabrication requires a harsh acidic environment. Herein, two customized PEEKs were synthesized by incorporating methyl (–CH3) and sulfonyl (SO2) groups into the polymer backbone. The membranes were prepared by phase inversion using N-methyl-2-pyrrolidone (NMP) and TamiSolve as a green alternative. The effects of the polymer structure, green solvent, and crosslinking on the membrane morphology, chemical and mechanical stability, as well as separation performance have been examined. The molecular interaction between organic solvents and PEEKs were investigated through molecular dynamic simulations and density functional theory. The molecular weight cutoff (MWCO) values of the membranes were 540–768 g mol−1, with a high corresponding permeance of 8.2–20 L m−2 h−1 bar−1 in acetone. The long-term stability of membranes was successfully demonstrated over two weeks through a continuous crossflow filtration using acetone under a pressure of 30 bar. The membranes demonstrated excellent active pharmaceutical ingredient purification through the removal a 2-methoxyethoxymethyl chloride (125 g mol−1) carcinogenic impurity from roxithromycin (837 g mol−1).
  • Multifunctional difluoroboron β-diketonate-based luminescent receiver for a high-speed underwater wireless optical communication system

    Wang, Yue; Wang, Jian-Xin; Alkhazragi, Omar; Gutierrez Arzaluz, Luis; Zhang, Huafan; Kang, Chun Hong; Ng, Tien Khee; Bakr, Osman; Mohammed, Omar F.; Ooi, Boon S. (Optics Express, Optica Publishing Group, 2023-09-14) [Article]
    The last decade has witnessed considerable progress in underwater wireless optical communication in complex environments, particularly in exploring the deep sea. However, it is difficult to maintain a precise point-to-point reception at all times due to severe turbulence in actual situations. To facilitate efficient data transmission, the color-conversion technique offers a paradigm shift in large-area and omnidirectional light detection, which can effectively alleviate the étendue limit by decoupling the field of view and optical gain. In this work, we investigated a series of difluoroboron β-diketonate fluorophores by measuring their photophysical properties and optical wireless communication performances. The emission colors were tuned from blue to green, and >0.5 Gb/s data transmission was achieved with individual color channel in free space by implementing an orthogonal frequency-division multiplexing (OFDM) modulation scheme. In the underwater experiment, the fluorophore with the highest transmission speed was fabricated into a 4×4 cm2 luminescent concentrator, with the concentrated emission from the edges coupled with an optical fiber array, for large-area photodetection and optical beam tracking. The net data rates of 130 Mb/s and 217 Mb/s were achieved based on nonreturn- to-zero on-off keying and OFDM modulation schemes, respectively. Further, the same device was used to demonstrate the linear light beam tracking function with high accuracy, which is beneficial for sustaining a reliable and stable connection in a dynamic, turbulent underwater environment.
  • Discovery of a three-proton insertion mechanism in α-molybdenum trioxide leading to enhanced charge storage capacity

    Lei, Yongjiu; zhao, Wenli; Yin, Jun; Ma, Yinchang; Zhao, Zhiming; Yin, Jian; Khan, Yusuf; Hedhili, Mohamed N.; Chen, Long; Wang, Qingxiao; Yuan, Youyou; Zhang, Xixiang; Bakr, Osman; Mohammed, Omar F.; Alshareef, Husam N. (Nature Communications, Springer Science and Business Media LLC, 2023-09-07) [Article]
    The α-molybdenum trioxide has attracted much attention for proton storage owing to its easily modified bilayer structure, fast proton insertion kinetics, and high theoretical specific capacity. However, the fundamental science of the proton insertion mechanism in α-molybdenum trioxide has not been fully understood. Herein, we uncover a three-proton intercalation mechanism in α-molybdenum trioxide using a specially designed phosphoric acid based liquid crystalline electrolyte. The semiconductor-to-metal transition behavior and the expansion of the lattice interlayers of α-molybdenum trioxide after trapping one mole of protons are verified experimentally and theoretically. Further investigation of the morphology of α-molybdenum trioxide indicates its fracture behavior upon the proton intercalation process, which creates diffusion channels for hydronium ions. Notably, the observation of an additional redox behavior at low potential endows α-molybdenum trioxide with an improved specific discharge capacity of 362 mAh g−1.
  • How reproducible is the synthesis of Zr–porphyrin metal–organic frameworks? An interlaboratory study

    Boström, Hanna L. B.; Emmerling, Sebastian; Heck, Fabian; Koschnick, Charlotte; Jones, Andrew J.; Cliffe, Matthew J.; Al Natour, Rawan; Bonneau, Mickaele; Guillerm, Vincent; Shekhah, Osama; Eddaoudi, Mohamed; Lopez-Cabrelles, Javier; Furukawa, Shuhei; Romero-Angel, María; Martí-Gastaldo, Carlos; Yan, Minliang; Morris, Amanda J.; Romero-Muñiz, Ignacio; Xiong, Ying; Platero-Prats, Ana E.; Roth, Jocelyn; Queen, Wendy L.; Mertin, Kalle S.; Schier, Danielle E.; Champness, Neil R.; Yeung, Hamish H.-M.; Lotsch, Bettina V. (Advanced Materials, Wiley, 2023-09-05) [Article]
    Metal–organic frameworks (MOFs) are a rapidly growing class of materials that offer great promise in various applications. However, the synthesis remains challenging: for example, a range of crystal structures can often be accessed from the same building blocks, which complicates the phase selectivity. Likewise, the high sensitivity to slight changes in synthesis conditions may cause reproducibility issues. This is crucial, as it hampers the research and commercialisation of affected MOFs. Here, we present the first-ever interlaboratory study of the synthetic reproducibility of two Zr–porphyrin MOFs, PCN-222 and PCN-224, to investigate the scope of this problem. For PCN-222, only one sample out of ten was phase pure and of the correct symmetry, while for PCN-224, three were phase pure, although none of these show the spatial linker order characteristic of PCN-224. Instead, these samples resemble dPCN-224 (disordered PCN-224), which was recently reported by us. The variability in thermal behavior, defect content, and BET surface area of the synthesised samples are also studied. Our results have important ramifications for field of metal–organic frameworks and their crystallisation, by highlighting the synthetic challenges associated with a multi-variable synthesis space and flat energy landscapes characteristic of MOFs.
  • Graphdiyne membranes for ultrafast desalination

    Cao, Li; Lai, Zhiping (Nature Water, Springer Science and Business Media LLC, 2023-09-04) [Article]
    Ultra-fast water transport with high salt rejection is achieved by a submicron graphdiyne membrane supported on a porous copper hollow fibre.
  • Ptychographic X-ray computed tomography of porous membranes with nanoscale resolution

    Gorecki, Radoslaw; Polo, Carla Cristina; Kalile, Tiago Araujo; Miqueles, Eduardo X. S.; Tonin, Yuri R.; Upadhyaya, Lakshmeesha; Meneau, Florian; Nunes, Suzana Pereira (Communications Materials, Springer Science and Business Media LLC, 2023-09-02) [Article]
    New visualization methods can be utilized to resolve structures at resolutions that were previously unachievable. 3D images of porous materials with high resolution have been so far obtained using transmission electron tomography or focused ion beam coupled with scanning electron microscopy. For these methods, ultra-vacuum is required, and only a small volume of the sample is visualized. Here, we demonstrate the application of ptychographic X-ray computed tomography for the visualization of soft matter with a resolution of 26 nm over large fields of view. Thanks to the high-penetration depth of the X-ray beam, we visualize the 3D complex porous structure of polyetherimide hollow fibers in a non-destructive manner and obtain quantitative information about pore size distribution and pore network interconnectivity across the whole membrane wall. The non-destructive nature of this method, coupled with its ability to image samples without requiring modification or a high vacuum environment, makes it valuable in the fields of porous- and nano-material sciences enabling imaging under different environmental conditions.
  • Anisotropic flexibility and rigidification in a TPE-based Zr-MOFs with scu topology.

    Meng, Sha-Sha; Xu, Ming; Guan, Hanxi; Chen, Cailing; Cai, Peiyu; Dong, Bo; Tan, Wen-Shu; Gu, Yu-Hao; Tang, Wen-Qi; Xie, Lan-Gui; Yuan, Shuai; Han, Yu; Kong, Xueqian; Gu, Zhi-Yuan (Nature communications, Springer Science and Business Media LLC, 2023-09-02) [Article]
    Tetraphenylethylene (TPE)-based ligands are appealing for constructing metal-organic frameworks (MOFs) with new functions and responsiveness. Here, we report a non-interpenetrated TPE-based scu Zr-MOF with anisotropic flexibility, that is, Zr-TCPE (H4TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene), remaining two anisotropic pockets. The framework flexibility is further anisotropically rigidified by installing linkers individually at specific pockets. By individually installing dicarboxylic acid L1 or L2 at pocket A or B, the framework flexibility along the b-axis or c-axis is rigidified, and the intermolecular or intramolecular motions of organic ligands are restricted, respectively. Synergistically, with dual linker installation, the flexibility is completely rigidified with the restriction of ligand motion, resulting in MOFs with enhanced stability and improved separation ability. Furthermore, in situ observation of the flipping of the phenyl ring and its rigidification process is made by 2H solid-state NMR. The anisotropic rigidification of flexibility in scu Zr-MOFs guides the directional control of ligand motion for designing stimuli-responsive emitting or efficient separation materials.
  • Controlling the degree of acetylation in cellulose-based nanofiltration membranes for enhanced solvent resistance

    Abdellah, Mohamed; Oviedo-Osornio, C. Iluhí; Szekely, Gyorgy (Journal of Membrane Science, Elsevier BV, 2023-09-01) [Article]
    Increasing concerns associated with the environment and global warming have triggered the exploration of the preparation of greener membranes. The abundance of renewable cellulosic biomass offers an excellent source material for membrane fabrication. In particular, cellulose acetate (CA) has been widely used as a membrane material. In this study, we explore the effect of the degree of acetylation (DoA) on membrane performance in organic solvents for the first time. We prepared CA membranes using nonsolvent-induced phase separation with Cyrene as a green solvent. Deacetylation was directly performed on the CA membranes to obtain a final DoA in the range of 1.2%–39.3%. The solvent resistance of the membranes increased as the DoA decreased. The membranes exhibited constant permeance at a pressure of 30 bar, which suggested the absence of compaction. Increasing the DoA increased the permeance of the polar aprotic solvents, whereas the permeance of the polar protic solvents showed the opposite trend. The hydrophilicity of the membranes increased with a decrease in the DoA, whereas the glass transition temperature remained quasi-constant and excellent thermal stability was maintained. The separation performance was fine-tuned with a molecular weight cut-off that ranged from 325 to 950 g mol−1 as a function of the DoA. Our results offer new avenues for tailoring solvent-resistant membrane materials from renewable polymers and solvents for application in harsh organic media.
  • The epoxy resin system: function and role of curing agents

    Aziz, Tariq; Haq, Fazal; Farid, Arshad; Cheng, Li; Chuah, Lai Fatt; Bokhari, Awais; Mubashir, Muhammad; Tang, Doris Ying Ying; Show, Pau Loke (Carbon Letters, Springer Science and Business Media LLC, 2023-09-01) [Article]
    Curing agents are critical components of aqueous epoxy resin systems. Unfortunately, its uses and applications are restricted because of its low emulsifying yields. Epoxy resins are frequently used in electrical devices, castings, packaging, adhesive, corrosion resistance, and dip coating. In the presence of curing agents, epoxy resins become rigid and infusible. Eco-friendliness and mechanical functionality have emerged as vulcanization properties. Curing agents are used for surface modification, thermodynamic properties, functional approaches to therapeutic procedures, and recent advances in a variety of fields such as commercial and industrial levels. The curing agent has superior construction and mechanical properties when compared to the commercial one, which suggests that it has the potential for use as the architectural and industrial coatings. The thermal stability of cured products is good due to the presence of the imide group and the hydrogenated phenanthrene ring structure. Over the course of the projection period, it is anticipated that the global market for curing agents will continue to expand at a steady rate. The growth of the market is mainly driven by its expanding range in future applications such as adhesives, composites, construction, electrical, electronics, and wind energy. This review focused on the most recent advancements in curing techniques, emphasizing their thermal and mechanical properties. The review also presents a critical discussion of key aspects and bottleneck or research gap of the application of curing agents in the industrial areas.
  • Electrocatalytic degradation of levofloxacin wastewater by Ru-Ti-Ni/CNT electrodes

    Wang, Shengzhe; Lv, Hongxia; Jin, Chengyu; Wang, Yu; Wei, Huangzhao; Sun, Chenglin; Yu, Lian; Ma, Lei; Li, Xiangnan; Liu, Xiaowei (Catalysis Communications, Elsevier BV, 2023-09-01) [Article]
    We synthesized a series of Ru-Ti-Ni/CNT electrodes to degrade levofloxacin in wastewater. The unique structure of Ni single-atom-kernelled Ru nanoparticles regulates the reaction process, producing a notable synergistic effect. The reaction kinetics constant of Ru-Ti-Ni/CNT with a Ru: Ti ratio of 10:0 outperforms Ni/CNT by 3.7 times and CNT alone by 16.4 times. Comprehensive characterizations revealed its morphology and structure nature. Ru nanoparticles can shield Ni, while Ni single-atom facilitates electron transfer in Ru nanoparticles, generating abundant reactive oxygen radicals (ROS) that degrade pollutants.
  • Applications of Transmission Electron Microscopy in Phase Engineering of Nanomaterials

    Li, Guanxing; Zhang, Hui; Han, Yu (Chemical Reviews, American Chemical Society (ACS), 2023-08-29) [Article]
    Phase engineering of nanomaterials (PEN) is an emerging field that aims to tailor the physicochemical properties of nanomaterials by precisely manipulating their crystal phases. To advance PEN effectively, it is vital to possess the capability of characterizing the structures and compositions of nanomaterials with precision. Transmission electron microscopy (TEM) is a versatile tool that combines reciprocal-space diffraction, real-space imaging, and spectroscopic techniques, allowing for comprehensive characterization with exceptional resolution in the domains of time, space, momentum, and, increasingly, even energy. In this Review, we first introduce the fundamental mechanisms behind various TEM-related techniques, along with their respective application scopes and limitations. Subsequently, we review notable applications of TEM in PEN research, including applications in fields such as metallic nanostructures, carbon allotropes, low-dimensional materials, and nanoporous materials. Specifically, we underscore its efficacy in phase identification, composition and chemical state analysis, in situ observations of phase evolution, as well as the challenges encountered when dealing with beam-sensitive materials. Furthermore, we discuss the potential generation of artifacts during TEM imaging, particularly in scanning modes, and propose methods to minimize their occurrence. Finally, we offer our insights into the present state and future trends of this field, discussing emerging technologies including four-dimensional scanning TEM, three-dimensional atomic-resolution imaging, and electron microscopy automation while highlighting the significance and feasibility of these advancements.
  • A promising sensing platform for explosive markers: Zeolite-like metal-organic framework based monolithic composite as a case study.

    Yusuf, Kareem; Shekhah, Osama; Alharbi, Seetah; Alothman, Asma A; Alghamdi, Ali S; Aljohani, Reem M; Alothman, Zeid; Eddaoudi, Mohamed (Journal of chromatography. A, Elsevier BV, 2023-08-26) [Article]
    Preconcentration for on-site detection or subsequent determination is a promising technique for selective sensing explosive markers at low concentrations. Here, we report divinylbenzene monolithic polymer in its blank form (neat-DVB) and as a composite incorporated with sodalite topology zeolite-like metal-organic frameworks (3-ZMOF@DVB), as a sensitive, selective, and cost-effective porous preconcentrator for aliphatic nitroalkanes in the vapor phase as explosive markers at infinite dilution. The developed materials were fabricated as 18 cm gas chromatography (GC) monolithic capillary columns to study their separation performance of nitroalkane mixture and the subsequent physicochemical study of adsorption using the inverse gas chromatography (IGC) technique. A strong preconcentration effect was indicated by a specific retention volume adsorption/desorption ratio equal to 3 for nitromethane on the neat-DVB monolith host-guest interaction, and a 14% higher ratio was observed using the 3-ZMOF@DVB monolithic composite despite the low percentage of 0.7 wt.% of sod-ZMOF added. Furthermore, Incorporating ZMOF resulted in a higher percentage of micropores, increasing the degree of freedom more than bringing stronger adsorption and entropic-driven interaction more than enthalpic. The specific free energy of adsorption (ΔGS) values increased for polar probes and nitroalkanes, denoting that adding ZMOFs earned the DVB monolithic matrix a more specific character. Afterward, Lewis acid-base properties were calculated, estimating the electron acceptor (KA) and electron donor (KB) constants. The neat-DVB was found to have a Lewis basic character with KB/KA = 7.71, and the 3-ZMOF@DVB had a less Lewis basic character with KB/KA = 3.82. An increased electron-accepting nature can be directly related to incorporating sod-ZMOF into the DVB monolithic matrix. This work considers the initial step in presenting a portable explosives detector or preconcentrating explosive markers trace prior to more sophisticated analysis. Additionally, the IGC technique allows for understanding the factors that led to the superior adsorption of nitroalkanes for the developed materials.
  • Industrial Separation Challenges: How Does Supramolecular Chemistry Help?

    Zhang, Gengwu; Lin, Weibin; Huang, Feihe; Sessler, Jonathan L.; Khashab, Niveen M. (Journal of the American Chemical Society, American Chemical Society (ACS), 2023-08-25) [Article]
    The chemical industry and the chemical processes underscoring it are under intense scrutiny as the demands for the transition to more sustainable and environmentally friendly practices are increasing. Traditional industrial separation systems, such as thermally driven distillation for hydrocarbon purification, are energy intensive. The development of more energy efficient separation technologies is thus emerging as a critical need, as is the creation of new materials that may permit a transition away from classic distillation-based separations. In this Perspective, we focus on porous organic cages and macrocycles that can adsorb guest molecules selectively through various host-guest interactions and permit molecular sieving behavior at the molecular level. Specifically, we summarize the recent advances where receptor-based adsorbent materials have been shown to be effective for industrially relevant hydrocarbon separations, highlighting the underlying host-guest interactions that impart selectivity and permit the observed separations. This approach to sustainable separations is currently in its infancy. Nevertheless, several receptor-based adsorbent materials with extrinsic/intrinsic voids or special functional groups have been reported in recent years that can selectively capture various targeted guest molecules. We believe that the understanding of the interactions that drive selectivity at a molecular level accruing from these initial systems will permit an ever-more-effective "bottom-up" design of tailored molecular sieves that, in due course, will allow adsorbent material-based approaches to separations to transition from the laboratory into an industrial setting.
  • Precise molecular sieving of ethylene from ethane using triptycene-derived submicroporous carbon membranes

    Hazazi, Khalid; Wang, Yingge; Ghanem, Bader; Hu, Xiaofan; Puspasari, Tiara; Chen, Cailing; Han, Yu; Pinnau, Ingo (Nature Materials, Springer Science and Business Media LLC, 2023-08-24) [Article]
    Replacement or debottlenecking of the extremely energy-intensive cryogenic distillation technology for the separation of ethylene from ethane has been a long-standing challenge. Membrane technology could be a desirable alternative with potentially lower energy consumption. However, the current key obstacle for industrial implementation of membrane technology is the low mixed-gas selectivity of polymeric, inorganic or hybrid membrane materials, arising from the similar sizes of ethylene (3.75 Å) and ethane (3.85 Å). Here we report precise molecular sieving and plasticization-resistant carbon membranes made by pyrolysing a shape-persistent three-dimensional triptycene-based ladder polymer of intrinsic microporosity with unparalleled mixed-gas performance for ethylene/ethane separation, with a selectivity of ~100 at 10 bar feed pressure, and with long-term continuous stability for 30 days demonstrated. These submicroporous carbon membranes offer opportunities for membrane technology in a wide range of notoriously difficult separation applications in the petrochemical and natural gas industry.

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