Recent Submissions

  • Deep learning meets quantitative structure–activity relationship (QSAR) for leveraging structure-based prediction of solute rejection in organic solvent nanofiltration

    Ignacz, Gergo; Szekely, Gyorgy (Journal of Membrane Science, Elsevier BV, 2022-01) [Article]
    Methods for determining solute rejection in organic solvent nanofiltration (OSN) are time-consuming and expensive and still rely on wet-lab measurements, resulting in the slow development of membrane processes. OSN, similar to other membrane technologies, requires precise and comprehensive predictive models that can function on various solutes, membranes, and solvents. We present two prediction methods based on the quantitative structure–activity relationship (QSAR) using traditional machine learning (ML) and deep learning (DL) models. The partial least-squares regression model combined with the variable importance in projection and genetic algorithm achieves a slightly lower root-mean-square error score (8.04) than the DL-based graph neural network (10.40). For the first time, we visualize the effect of different solute functional groups on rejection, providing a new platform for a more in-depth investigation into the membrane–solute interactions, potentially enabling the design of membranes with improved selectivity. Our ML model is freely accessible on the OSN database website (www.osndatabase.com) for everyone.
  • Sustainable nanofiltration membranes based on biosourced fully recyclable polyesters and green solvents

    Hardian, Rifan; Cywar, Robin M.; Chen, Eugene Y.-X.; Szekely, Gyorgy (Journal of Membrane Science Letters, Elsevier BV, 2022-01) [Article]
    Herein, we report a new class of biosourced nanofiltration membranes based on chemically recyclable aliphatic polyesters (P(4,5-T6GBL)) and the use of green solvents. Given their chemical recyclability and potential biodegradability, these polyester membranes were designed to have a sustainable lifecycle. The effect of membrane thickness and solvent/non-solvent diffusivity on membrane morphology and organic solvent nanofiltration were investigated. Long-term membrane stability was tested in a continuous crow-flow filtration rig over a week, which exhibited stable methanol permeance at 8.6 ± 0.1 L m−2 h−1 bar−1. The rejection profiles of the pharmaceuticals oleuropein (540 g mol−1) and roxithromycin (837 g mol−1) were also found to be stable at 87% and 100%, respectively.
  • Solvent-Resistant Thin-Film Composite Membranes from Biomass-Derived Building Blocks: Chitosan and 2,5-Furandicarboxaldehyde

    Park, Sang-Hee; Yang, Cong; Ayaril, Nasser; Szekely, Gyorgy (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2021-12-30) [Article]
    To address the increasing interest in environmental issues, green and sustainable material-based membranes have attracted significant research interest with the promise to replace fossil-based membranes and to reduce waste generation. In this work, more sustainable thin-film composite (TFC) membranes are designed and fabricated via interfacial polymerization of green building blocks, namely, shrimp farming waste chitosan in the aqueous phase and plant-based 2,5-furandicarboxaldehyde in the organic phase, on an upcycled polyethylene terephthalate porous support. The TFC membranes showed excellent acetone permeance up to 12 L m–2 h–1 bar–1 with a molecular weight cutoff value of approximately 317 g mol–1. The membrane separation performance was optimized by fine-tuning the building block concentrations, which provided a new upper-bound in the plot of acetone permeance versus styrene dimer rejection. In addition, for the first time, TamiSolve was employed as a green solvent to activate the selective layer of the chitosan-based TFC membrane, resulting in a significant enhancement in the permeance of diverse pure solvents including ethanol, methyl ethyl ketone, acetone, and acetonitrile with no remarkable defects and high solute rejections. Our proposed green TFC fabrication platform enables the replacement of toxic and fossil-based solvents and reagents in developing high-performance and solvent-resistant nanofiltration membranes.
  • Fructose to Sorbents: Synthesis of Metal–Organic Frameworks Directly from Biomass for Humid Shale Gas Separation

    Gu, Yi-Ming; Qi, Hai-Feng; Qadir, Salman; Liu, Xiaowei; Sun, Tian-Jun; Zhao, Sheng-Sheng; Lai, Zhiping; Wang, Shu-Dong (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2021-12-13) [Article]
    The synthesis of metal–organic frameworks (MOFs) directly starting from biomass, making the most of renewable feedstocks and allowing for coupled or continuous processing, is intriguing. The interference of water (vapor) greatly hinders the wide utilization of MOFs in, e.g., recovering ethane from humid shale gas, which is a critical process for purifying natural gas in practical scenarios. Here, we propose a concept of direct ligand and MOF synthesis in a continuous routine, i.e., a linear synthesis of a bioderived ligand (furan-2,5-dicarboxylic acid), starting from a biomass source (fructose), followed by the in situ synthesis of a series of different MOFs. This strategy is also exempt from the tedious and energy-intensive processes of filtering, purifying, or drying intermediate products. The obtained renewable MOFs, particularly MIL-160(Al), reveal superior ethane capture abilities from shale gas mixtures under ambient conditions compared to most of the MOF materials reported to date. MIL-160(Al) also demonstrates a remarkable cycling nature and facile sorption regenerability to selectively capture ethane even under high-humidity conditions, as verified by static gas sorption measurement, experimental breakthrough tests, and in-depth theoretical studies, further conferring it with great potential for industrial applications.
  • Propane Dehydrogenation Catalyzed by Isolated Pt Atoms in ≡SiOZn–OH Nests in Dealuminated Zeolite Beta

    Qi, Liang; Babucci, Melike; Zhang, Yanfei; Lund, Alicia; Liu, Lingmei; Li, Jingwei; Chen, Yizhen; Hoffman, Adam S.; Bare, Simon R.; Han, Yu; Gates, Bruce C.; Bell, Alexis T. (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-12-09) [Article]
    Atomically dispersed noble metal catalysts have drawn wide attention as candidates to replace supported metal clusters and metal nanoparticles. Atomic dispersion can offer unique chemical properties as well as maximum utilization of the expensive metals. Addition of a second metal has been found to help reduce the size of Pt ensembles in bimetallic clusters; however, the stabilization of isolated Pt atoms in small nests of nonprecious metal atoms remains challenging. We now report a novel strategy for the design, synthesis, and characterization of a zeolite-supported propane dehydrogenation catalyst that incorporates predominantly isolated Pt atoms stably bonded within nests of Zn atoms located within the nanoscale pores of dealuminated zeolite Beta. The catalyst is stable in long-term operation and exhibits high activity and high selectivity to propene. Atomic resolution images, bolstered by X-ray absorption spectra, demonstrate predominantly atomic dispersion of the Pt in the nests and, with complementary infrared and nuclear magnetic resonance spectra, determine a structural model of the nested Pt.
  • Optimizing Host–Guest Selectivity for Ethylbenzene Capture Toward Superior Styrene Purification

    Ding, Yanjun; Dey, Avishek; Alimi, Lukman Olawale; Bhatt, Prashant; Du, Jing; Maaliki, Carine; Eddaoudi, Mohamed; Jacquemin, Johan; Khashab, Niveen M. (Chemistry of Materials, American Chemical Society (ACS), 2021-12-08) [Article]
    The separation of ethylbenzene (EB) and styrene (ST) mixtures to obtain pure ST has been an enduring challenge for the petrochemical industry. So far, adsorptive separation using porous materials has mainly focused on capturing ST rather than EB, where high temperatures are needed to reactivate the sieving materials and collect the product. Here, we tuned the host–guest interactions in thienothiophene-based trianglimine (ThT-TI) macrocycles to selectively adsorb the unreacted EB over ST, after a dehydrogenation reaction, to readily provide pure ST without the need for further thermal treatments. This is the first report on the selective adsorptive separation of EB over ST using macrocycles as molecular hosts. Both crystalline and amorphous ThT-TI can be used to separate EB with 96% uptake capacity. Single-crystal and powder X-ray diffraction patterns suggest that this selective adsorption arises from a guest-induced structural reordering and involvement of the sulfur atoms in host/guest C–H···π interactions. We believe that this work paves the way for a new generation of molecular sieves that are designed to afford high-purity products by in situ capturing of the unreacted starting materials.
  • Molecular engineering of intrinsically microporous polybenzimidazole for energy-efficient gas separation

    Abdulhamid, Mahmoud A.; Hardian, Rifan; Bhatt, Prashant; Datta, Shuvo Jit; Ramirez, Adrian; Gascon, Jorge; Eddaoudi, Mohamed; Szekely, Gyorgy (Applied Materials Today, Elsevier BV, 2021-12-04) [Article]
    Polybenzimidazole (PBI) is a high-performance polymer that exhibits high thermal and chemical stability. However, it suffers from low porosity and low fractional free volume, which hinder its application as separation material. Herein, we demonstrate the molecular engineering of gas separation materials by manipulating a PBI backbone possessing kinked moieties. PBI was selected as it contains NH groups which increase the affinity towards CO$_2$, increase sorption capacity, and favors CO$_2$ over other gasses. We have designed and synthesized an intrinsically microporous polybenzimidazole (iPBI) featuring a spirobisindane structure. Introducing a kinked moiety in conjunction with crosslinking enhanced the polymer properties, markedly increasing the gas separation performance. In particular, the BET surface area of PBI increased 30-fold by replacing a flat benzene ring with a kinked structure. iPBI displayed a good CO$_2$ uptake of 1.4 mmol g$^{−1}$ at 1 bar and 3.6 mmol g$^{−1}$ at 10 bar. Gas sorption uptake and breakthrough experiments were conducted using mixtures of CO$_2$/CH$_4$ (50%/50%) and CO$_2$/N$_2$ (50%/50%), which revealed the high selectivity of CO$_2$ over both CH$_4$ and N$_2$. The obtained CO$_2$/N$_2$ selectivity is attractive for power plant flue gas application requiring CO$_2$ capturing materials. Energy and process simulations of biogas CO$_2$ removal demonstrated that up to 70% of the capture energy could be saved when iPBI was used rather than the current amine technology (methyl diethanolamine [MDEA]). Similarly, the combination of iPBI and MDEA in a hybrid system exhibited the highest CO$_2$ capture yield (99%), resulting in nearly 50% energy saving. The concept of enhancing the porosity of PBI using kinked moieties provides new scope for designing highly porous polybenzimidazoles for various separation processes.
  • Experimental and Theoretical Insights into Transition-Metal (Mo, Fe) Codoping in a Bifunctional Nickel Phosphide Microsphere Catalyst for Enhanced Overall Water Splitting

    Pawar, S. M.; Aqueel Ahmed, Abu Talha; Lee, Chi Ho; Babar, Pravin Tukaram; Kim, J. H.; Lee, Sang Uck; Kim, Hyungsang; Im, Hyunsik (ACS Applied Energy Materials, American Chemical Society (ACS), 2021-12-02) [Article]
    The facile synthesis of efficient non-precious-metal-based bifunctional catalysts for overall water splitting is highly desirable from both industrial and environmental perspectives. This study reports the electrodeposition and characterization of a transition-metal (Mo, Fe)-codoped nickel phosphide (Ni3P:FeMo) bifunctional catalyst for enhanced overall water splitting in an alkaline medium. The Ni3P:FeMo catalyst exhibited outstanding electrocatalytic performance for both the hydrogen evolution reaction and oxygen evolution reaction with low overpotentials of −103 and 290 mV, respectively, at a high current density of 100 mA/cm2 along with fast electrocatalytic kinetics. A full water-splitting electrolyzer consisting of a bifunctional Ni3P:FeMo catalyst required a low cell voltage of 1.48 V to attain a current density of 10 mA/cm2 with excellent stability for more than 50 h. Density functional theory calculations provided insights into the microscopic mechanism of the effective modulation of the p- and d-band centers of the P and Ni active sites by the Mo and Fe codoping of Ni3P, thereby enhancing the bifunctional catalytic activity of Ni3P.
  • Facile electrodeposited NiMoSe nanospheres for hydrogen evolution reaction

    Patil, Komal; Babar, Pravin Tukaram; Li, Xue; Jang, Jun Sung; Kim, Dongmyeong; Cheol Baek, Myeong; Bhoite, Pravin; Hyeok Kim, Jin (Materials Letters, Elsevier BV, 2021-12-02) [Article]
    The search for effective electrocatalysts for energy conversion is crucial for the advancement of green energy. Electrodeposition is a simple but effective method of preparing improved electrodes for use in the electrochemical sector. In the present work, we have synthesized amorphous NiMoSe nanospheres on Ni foam (NF) via a simple electrodeposition method. The synthesized NiMoSe demonstrates outstanding catalytic activity for the hydrogen evolution reaction (HER), with a small overpotential of 130 mV at a current density of 10 mA cm−2 in 1 M KOH electrolyte and a small Tafel slope of 59 mV dec−1. Furthermore, NiMoSe also shows long-term durability over 45 h.
  • Tailored Pore Size and Microporosity of Covalent Organic Framework (COF) Membranes for Improved Molecular Separation

    Shinde, Digambar; Cao, Li; Liu, Xiaowei; Wonanke, Dinga A.D.; Zhou, Zongyao; Hedhili, Mohamed N.; Addicoat, Matthew; Huang, Kuo-Wei; Lai, Zhiping (Journal of Membrane Science Letters, Elsevier BV, 2021-12) [Article]
    Three highly crystalline truxene-based β-ketoenamine COF membranes (TFP-HETTA, TFP-HBTTA and TFP-HHTTA) are fabricated via a de novo monomer design approach to understand the fundamental correlations between pore structure and molecular separation performance. By introducing bulky alkyl groups into the truxene framework, the pore size of TFP-HETTA, TFP-HBTTA, and TFP-HHTTA are systematically tuned from 1.08 to 0.72 nm. Accordingly, the TFP-HETTA showed good water permeance of 47 L m−2 h−1 bar−1 along with a prominent rejection rate of Reactive Blue (RB, 800 Da) but less than 10% rejection rate of inorganic salts. In contrast, the TFP-HHTTA membrane with pore size of 0.72 nm can reject small dye molecules (SO, 350 Da) and trivalent salts but with a moderate water permeance of 19 L m−2 h−1 bar−1. The pore-flow model rooted from the viscous flow could well fit the observed organic solvent nanofiltration results of all three COF membranes.
  • Nearly 100% energy transfer at the interface of metal-organic frameworks for X-ray imaging scintillators

    Wang, Jian-Xin; Gutierrez Arzaluz, Luis; Wang, Xiaojia; Almalki, Maram M.; Yin, Jun; Czaban-Jozwiak, Justyna; Shekhah, Osama; Zhang, Yuhai; Bakr, Osman; Eddaoudi, Mohamed; Mohammed, Omar F. (Matter, Elsevier BV, 2021-12) [Article]
    In this work, we describe a highly efficient and reabsorption-free X-ray-harvesting system using luminescent metal-organic framework (MOF)-fluorescence chromophore composite films. The ultrafast time-resolved experiments and density functional theory calculations demonstrate that a nearly 100% energy transfer from a luminescent MOF with a high atomic number to an organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Such an unprecedented efficiency of interfacial energy transfer and the direct harnessing of singlet and triplet excitons of the TADF chromophore led to remarkable enhancement of radioluminescence upon X-ray radiation. A low detection limit of 256 nGy/s of the fabricated X-ray imaging scintillator was achieved, about 60 times lower than the MOF and 7 times lower than the organic chromophore counterparts. More importantly, this detection limit is about 22 times lower than the standard dosage for a medical examination, making it an excellent candidate for X-ray radiography.
  • AIE-Based Fluorescent Triblock Copolymer Micelles for Simultaneous Drug Delivery and Intracellular Imaging

    Kulkarni, Bhagyashree; Qutub, Somayah S.; Ladelta, Viko; Khashab, Niveen M.; Hadjichristidis, Nikos (Biomacromolecules, American Chemical Society (ACS), 2021-12-01) [Article]
    Fluorescent drug delivery systems have received increasing attention in cancer therapy because they combine drug delivery and bioimaging into a single platform. For example, polymers with aggregation-induced emission (AIE) fluorophores, such as tetraphenylethylene (TPE), have emerged as an elegant choice for drug delivery/bioimaging applications. In this work, we report one-pot sequential organocatalytic ring-opening polymerization of ε-caprolactone (CL) and ethylene oxide (EO) using TPE-(OH)2 as a difunctional initiator, in the presence of a t-BuP2/TEB Lewis pair (catalyst), in THF at room temperature. Two well-defined triblock copolymers with inverse block sequences, TPE-(PCL-b-PEO)2 and TPE-(PEO-b-PCL)2, were synthesized by altering the sequential addition of CL and EO. The physicochemical properties, including hydrodynamic diameter, morphology, and AIE properties of the synthesized amphiphilic triblock copolymers were investigated in aqueous media. The block copolymer micelles were loaded with anticancer drugs doxorubicin and curcumin to serve as drug delivery vehicles. In vitro studies revealed the accelerated drug release at lower pH (5.5), which mimics the tumor microenvironment, different from the physiological pH (7.4). In vitro cytotoxicity studies demonstrated that the neat block copolymer micelles are biocompatible, while drug-loaded micelles exhibited a significant cytotoxic effect in cancer cells. Cellular uptake, examined by confocal laser scanning microscopy, showed that the block copolymer micelles were rapidly internalized by the cells with simultaneous emission of TPE fluorophore. These results suggest that these triblock copolymers can be utilized for intracellular bioimaging.
  • Ultrafast Aggregation-Induced Tunable Emission Enhancement in a Benzothiadiazole-Based Fluorescent Metal–Organic Framework Linker

    Gutierrez Arzaluz, Luis; Nadinov, Issatay; Healing, George; Czaban-Jozwiak, Justyna; Jia, Jiangtao; Huang, Zhiyuan; Zhao, Yan; Shekhah, Osama; Schanze, Kirk; Eddaoudi, Mohamed; Mohammed, Omar F. (The Journal of Physical Chemistry B, American Chemical Society (ACS), 2021-11-30) [Article]
    Aggregation-induced emission enhancement (AIEE) is a process recently exploited in solid-state materials and organic luminophores, and it is explained by tight-molecular packaging. However, solution-phase AIEE and its formation mechanism have not been widely explored. This work investigated AIEE phenomena in two donor–acceptor–donor-type benzodiazole-based molecules (the organic building block in metal–organic frameworks) with an acetylene and phenyl π-conjugated backbone tapered with a carboxylic acid group at either end. This was done using time-resolved electronic and vibrational spectroscopy in conjunction with time-dependent density functional theory (TD-DFT) calculations. Fluorescence up-conversion spectroscopy and time-correlated single-photon counting conclusively showed an intramolecular charge transfer-driven aggregate emission enhancement. This is shown by a red spectral shift of the emission spectra as well as an increase in the fluorescence lifetime from 746 ps at 1.0 × 10–11 to 2.48 ns at 2.0 × 10–3 M. The TD-DFT calculations showed that a restricted intramolecular rotation mechanism is responsible for the enhanced emission. The femtosecond infrared (IR) transient absorption results directly revealed the structural dynamics of aggregate formation, as evident from the evolution of the C≡C vibrational marker mode of the acetylene unit upon photoexcitation. Moreover, the IR data clearly indicated that the aggregation process occurred over a time scale of 10 ps, which is consistent with the fluorescence up-conversion results. Interestingly, time-resolved results and DFT calculations clearly demonstrated that both acetylene bonds and the sulfur atom are the key requirements to achieve such a controllable aggregation-induced fluorescence enhancement. The finding of the work not only shows how slight changes in the chemical structure of fluorescent chromophores could make a tremendous change in their optical behavior but also prompts a surge of research into a profound understanding of the mechanistic origins of this phenomenon. This may lead to the discovery of new chemical strategies that aim to synthesize novel chromophores with excellent optical properties for light-harvesting applications.
  • Perovskite-Nanosheet Sensitizer for Highly Efficient Organic X-ray Imaging Scintillator

    Wang, Jian-Xin; Wang, Xiaojia; Yin, Jun; Gutierrez Arzaluz, Luis; He, Tengyue; Chen, Cailing; Han, Yu; Zhang, Yuhai; Bakr, Osman; Eddaoudi, Mohamed; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2021-11-27) [Article]
    The weak X-ray capture capability of organic scintillators always leads to poor imaging resolution and detection sensitivity. Here, we realize an efficient and reabsorption-free organic scintillator at the interface of perovskite nanosheets using a very efficient energy transfer strategy. Our steady-state and ultrafast time-resolved experiments supported by density functional theory calculations demonstrate that an efficient interfacial energy transfer from the perovskite nanosheet to the organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Interestingly, we found that the direct harnessing of both singlet and triplet excitons of the TADF chromophores also contributed greatly to its remarkably enhanced radioluminescence intensity and X-ray sensitivity. A high X-ray imaging resolution of 135 μm and a low detection limit of 38.7 nGy/s were achieved in the fabricated X-ray imaging scintillator.
  • Oriented Two-Dimensional Covalent Organic Framework Membranes with High Ion Flux and Smart Gating Nanofluidic Transport.

    Cao, Li; Liu, Xiaowei; Shinde, Digambar B; Chen, Cailing; Chen, I-Chun; Li, Zhen; Zhou, Zongyao; Yang, Zhongyu; Han, Yu; Lai, Zhiping (Angewandte Chemie, Wiley, 2021-11-24) [Article]
    Nanofluidic ion transport holds high promise in bio-sensing and energy conversion applications. However, smart nanofluidic devices with high ion flux and modulable ion transport capabilities remain to be realised. Herein, we demonstrate smart nanofluidic devices based on oriented two-dimensional covalent organic framework (2D COF) membranes with vertically aligned nanochannel arrays that achieved a 2-3 orders of magnitude higher ion flux compared with that of conventional single-channel nanofluidic devices. The surface-charge-governed ion conductance is dominant for electrolyte concentration up to 0.01 M. Moreover, owing to the customisable pH-responsivity of imine and phenol hydroxyl groups, the COF-DT membranes attained an actively modulable ion transport with a high pH-gating on/off ratio of ~100. The customisable structure and rich chemistry of COF materials will offer a promising platform for manufacturing nanofluidic devices with modifiable ion/molecular transport features.
  • Editorial: Frontiers in Chemistry-Rising Stars: Asia

    Guo, Lei; Mohanty, Jyotirmayee; Liu, Wukun; Yonar, Taner; Sun, Hongyan; Minami, Tsuyoshi; Soleymani, Jafar; Moosa, Basem; Zhou, Qianxiong (Frontiers in Chemistry, Frontiers Media SA, 2021-11-24) [Editorial]
  • Selective Separation of Lithium Chloride by Organogels Containing Strapped Calix[4]pyrroles

    Wang, Hu; Jones, Leighton O.; Hwang, Inhong; Allen, Marshall J.; Tao, Daliao; Lynch, Vincent M.; Freeman, Benny D.; Khashab, Niveen M.; Schatz, George C; Page, Zachariah A.; Sessler, Jonathan L. (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-11-23) [Article]
    Reported herein are two functionalized crown ether strapped calix[4]pyrroles, H1 and H2. As inferred from competitive salt binding experiments carried out in nitrobenzene-d5 and acetonitrile-d3, these hosts capture LiCl selectively over four other test salts, viz. NaCl, KCl, MgCl2, and CaCl2. Support for the selectivity came from density functional theory (DFT) calculations carried out in a solvent continuum. These theoretical analyses revealed a higher innate affinity for LiCl in the case of H1, but a greater selectivity relative to NaCl in the case of H2, recapitulating that observed experimentally. Receptors H1 and H2 were outfitted with methacrylate handles and subject to copolymerization with acrylate monomers and cross-linkers to yield gels, G1 and G2, respectively. These two gels were found to adsorb lithium chloride preferentially from an acetonitrile solution containing a mixture of LiCl, NaCl, KCl, MgCl2, and CaCl2 and then release the lithium chloride in methanol. The gels could then be recycled for reuse in the selective adsorption of LiCl. As such, the present study highlights the use of solvent polarity switching to drive separations with potential applications in lithium purification and recycling.
  • Carbon dioxide/methane mixed-gas adsorption, permeation and diffusion in a carbon molecular sieve film: Experimental observation and modeling

    Genduso, Giuseppe; Hazazi, Khalid; Ali, Zain; Ghanem, Bader; Alhazmi, Abdulrahman; Pinnau, Ingo (Journal of Membrane Science, Elsevier BV, 2021-11-20) [Article]
    The CO2–CH4 pure- and mixed-gas transport properties (at 35 °C) of a carbon molecular sieve (CMS) film obtained by pyrolysis of a 6FDA-mPDA polyimide precursor at 900 °C are reported. The competitive mixed-gas adsorption of CO2 and CH4 was predicted by the Ideal Adsorbed Solution Theory (IAST) model. The CO2/CH4 mixed-gas solubility selectivity of the CMS film was lower than that of relevant glassy polymer films of various nature and increased with pressure. Mixed-gas adsorption data were coupled with gas permeation tests on the same film sample batch used for barometric adsorption measurements to derive concentration-averaged effective diffusion coefficients. Because of its large fraction of ultramicroporous bottlenecks, the diffusion coefficients of the CMS were of the same order of magnitude as those of glassy polymer films of low free volume (e.g., 6FDA-mPDA and CTA). In the range of pressures explored, the pure-gas and multicomponent CO2 diffusion coefficients overlapped; most importantly, the methane diffusion coefficient was enhanced by the presence of CO2. This result suggests that carbon dioxide dilated the sieving domains of the CMS matrix under mixed-gas environment containing highly sorbing gases such as CO2. Consequently, the CMS film lost some of its size-sieving properties as indicated by a drop in mixed-gas CO2/CH4 permselectivity relative to the values obtained under pure-gas conditions.
  • Highly dispersed Pd nanoparticles confined in ZSM-5 zeolite crystals for selective hydrogenation of cinnamaldehyde

    Alfilfil, Lujain; Ran, Jiansu; Chen, Cailing; Dong, Xinglong; Wang, Jianjian; Han, Yu (Microporous and Mesoporous Materials, Elsevier BV, 2021-11-16) [Article]
    Selective hydrogenation of α,β-unsaturated aldehyde catalyzed by supported Pd nanoparticles (NPs) is challenging, especially under harsh reaction conditions. Here, we report a facile method to prepare a catalyst composed of highly dispersed Pd NPs (∼2.6 nm) confined in zeolite ZSM-5 crystals. When used in the hydrogenation of cinnamaldehyde, the prepared catalyst (Pd@SG-ZSM-5) exhibited excellent performance for the selective production of hydrocinnamaldehyde (HCAL) due to the confinement effect. Compared with the traditional supported Pd catalyst prepared by impregnation, Pd@SG-ZSM-5 showed a 2.5-fold enhancement in the HCAL selectivity (73% vs. 30%). Liquid adsorption combined with infrared spectroscopy characterization revealed that compared with the traditional catalyst, Pd@SG-ZSM-5 adsorbed much less reactant as well as product molecules and desorbed the generated HCAL quickly, thereby suppressing the formation of by-products and leading to high selectivity of HCAL.
  • Toward Liquid Phase Processable Metal Organic Frameworks: Dream or Reality?

    Poloneeva, Daria; Datta, Shuvo Jit; Garzon Tovar, Luis Carlos; Durini, Sara; Rueping, Magnus; Eddaoudi, Mohamed; Bavykina, Anastasiya; Gascon, Jorge (Accounts of Materials Research, American Chemical Society (ACS), 2021-11-11) [Article]
    Conventionally, the virtue of porosity is only given to porous solids. Metal Organic Frameworks (MOFs), carbon materials, or zeolites are some examples. However, processing these solids is not a straightforward task. Here, we discuss how to endow porous solids (MOFs) with liquid phase processability. More specifically, we show that surface modification of MOF crystals can lead to the formation of porous liquids (PLs) that can be further processed in the liquid phase. For instance, when placed in mesitylene, ZIF-67 predictably sediments. In contrast, with the adequate surface modification, stable dispersion of ZIF-67 can be achieved. Our proposed surface modification is facile and rapid. N-Heterocyclic carbenes are chosen as modifying agents as they are similar to imidazole linkers present on ZIFs. A simple stirring of a MOF and carbene mixture results in a modified solid. The morphology and textural properties of the modified MOF do not change from the ones of its parent. Since the porosity in solution remains unoccupied, the obtained stable colloids behave as porous liquids. Research into porous liquids is an emerging field that has already shown great promise in gases storage. Our breakthrough experiments show that these particular PLs have large potential for the separation of CO2/CH4 mixtures. The surface functionalized ZIF-67 could also be coprocessed with polymers to yield highly loaded Mixed-Matrix Membranes (MMMs) that cannot be achieved with a pristine MOF. Dispersions of functionalized ZIF-67 were blended with 6FDA-DAM and other homemade polymers in a shape of MMMs. While MMMs based on a pure MOF maintain good physical resistance at low loadings, increasing the concentration of MOF results in brittle composites. In contrast, MMMs made from functionalized ZIF retain good mechanical strength even at ca. 47.5 wt % loadings. Such high loading was possible to achieve due the better dispersion of the MOF particles during MMM fabrication and to the better affinity of the modified MOF with the polymer. The results obtained for this MMM are among the best MMMs ever reported for high challenging C3H6/C3H8 separation. The method is not limited to ZIF-67 but can be applied to a large body of MOFs that are constructed from imidazole-based linkers, as shown in this Account. The factors that determine whether a PL is formed include, but are not limited to, surface to volume ratio, framework particle size, and topology. On top of that, we propose potential strategies for the expansion of this method by carefully choosing surface modifiers that will suit other families of MOFs.

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