10 research outputs found

    Electrospun Microfibrous Membranes Based on PIM-1/POSS with High Oil Wettability for Separation of Oil–Water Mixtures and Cleanup of Oil Soluble Contaminants

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    A series of PIM-1/POSS microfibrous membranes were fabricated by electrospinning technology. The addition of POSS particles could greatly enhance the hydrophobicity, and a superhydrophobic–superoleophilic membrane was obtained as the POSS concentration increased to 40 wt %. The scanning electron microscopy images indicate that the incorporation of POSS particles results in formations of hierarchical structures on the surface of the PIM-1/POSS fibers. Both the intrinsic hydrophobic nature of POSS and the increase in the fiber surface roughness led to the superhydrophobicity and superoleophilicity. The 40 wt % PIM-1/POSS fibrous membrane could not only separate a wide range of immiscible oil–water mixtures with efficiencies higher than 99.95% but also separate water-in-oil emulsions with efficiencies higher than 99.97%. Furthermore, because of the ultrahigh intrinsic microporosity of the PIM-1 polymer, the PIM-1 fibrous membrane exhibited the ability to adsorb a large amount of contaminants such as oil red O and solvent blue 35 from oils. Therefore, these membranes are multifunctional and can be applied to treating immiscible water–oil mixtures, water-in-oil emulsions, and cleanup of oil soluble contaminants

    Effects of Spinning Temperature on the Morphology and Performance of Poly(ether sulfone) Gas Separation Hollow Fiber Membranes

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    In this study, we demonstrated that poly­(ether sulfone) (PES) hollow fiber membranes with almost defect-free surfaces could be prepared at low PES concentrations if the hollow fibers were spun at low temperatures by dry-jet wet spinning. A series of hollow fiber membranes were spun at different coagulation batch temperatures (<i>T</i><sub>c</sub>) and dope solution temperatures (<i>T</i><sub>d</sub>). Effects of <i>T</i><sub>c</sub> and <i>T</i><sub>d</sub> on the membranes’ morphologies and gas separation performances were investigated. Membrane morphologies characterized by using a scanning electron microscope (SEM) showed that the skin layer thicknesses increased with the decreases in <i>T</i><sub>c</sub> and <i>T</i><sub>d</sub>. Moreover, mean surface pore sizes of the membranes, which were evaluated by using the gas permeation method, significantly decreased as <i>T</i><sub>c</sub> or <i>T</i><sub>d</sub> decreased. PES hollow fiber membranes spun at the lowest temperatures (<i>T</i><sub>c</sub> = 7 °C, <i>T</i><sub>d</sub> = 3 °C) showed O<sub>2</sub> and CO<sub>2</sub> permeances of 18.9 and 53.5 GPU, respectively. And selectivities of O<sub>2</sub>/N<sub>2</sub>, CO<sub>2</sub>/N<sub>2</sub>, and CO<sub>2</sub>/CH<sub>4</sub> gas pairs were 1.15, 3.26, and 1.24, respectively. After silicone coating, the selectivities increased to 7.24, 47.7, and 39.4, respectively, but O<sub>2</sub> and CO<sub>2</sub> permeances decreased to 4.85 and 31.9 GPU, respectively. To our best knowledge, the gas separation performance was the test among all PES hollow fiber membranes

    Fabrication of Superhydrophobic–Superoleophilic Fabrics by an Etching and Dip-Coating Two-Step Method for Oil–Water Separation

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    A dual-scale roughness structure superhydrophobic–superoleophilic fabric was fabricated by first etching the microscale fibers with alkali and then dip-coating in a mixed solution of a polymer of intrinsic microporosity (PIM-1) and fluorinated alkylsilane (PTES). Scanning electron microscopy analysis showed that the etching process created nanoscale pits on the fiber surface and subsequently formed hierarchical structures on the fabric surface. Coating of PIM-1–PTES on the etched fibers significantly lowered the surface energy of the fibers, thus causing the fabric surface to possess superhydrophobicity with a water contact angle of 158° and superoleophilicity with an oil contact angle of 0°. The obtained superwettable fabric was mounted in a leak-proof manner on the open-end glass bottle, like an oil skimmer container. Such a new surface-tension-driven, gravity-assisted, one-step, oil–water separation device was used to separate the oil–water mixture with a separation efficiency as high as 99.96% after 30 recycles

    Surface Hydrophilicity and Structure of Hydrophilic Modified PVDF Membrane by Nonsolvent Induced Phase Separation and Their Effect on Oil/Water Separation Performance

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    The hydrophilic polyvinylidene fluoride (PVDF) material was prepared by ozone-induced grafting polymerization of acrylic acid on PVDF chains, and used for preparing oil/water separation ultrafiltration membranes by the nonsolvent induced phase separation method. The effect of membrane casting conditions was studied, and the results showed that <i>N</i>-methyl-2-pyrrolidone (NMP) present in the coagulation bath affected the membrane surface hydrophilicity as well as the membrane structure, and that casting solution concentration and air exposure time affected pore size but had little influence on surface hydrophilicity. The effect of material hydrophilicity and pore size was investigated, and the results indicated that improvement in hydrophilicity not only increased water flux itself, but also enabled high oil retention of membranes with larger pore sizes which had much higher water flux. The highest flux for the membranes with kerosene retention over 90% can reach over 300 L/m<sup>2</sup>h. The membranes showed good reusability under simple back flush

    Molecular Design of Tröger’s Base-Based Polymers Containing Spirobichroman Structure for Gas Separation

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    Gas separation performance of glassy polymers can be improved by enhancing the polymer backbone stiffness to decrease the chain packing and increase the free volume and gas permeabilities. In this work, two Tröger’s base (TB)-based polymers were prepared by polymerization from two spirobichroman-containing diamine monomers, MSBC and SBC. The obtained TB-based polymers show good solubility in polar aprotic solvents including DMF, DMAc, NMP, and DMSO, high molecular weight, and high thermal stability. Gas separation performance of TB-MSBC and TB-SBC are much better than those of the 6FDA-MSBC and 6FDA-SBC, especially for H<sub>2</sub>/N<sub>2</sub> and H<sub>2</sub>/CH<sub>4</sub> gas pairs. Furthermore, the CO<sub>2</sub> permeability of TB-MSBC is about 7.6 times higher than that of 6FDA-MSBC. The much-improved separation performance of TB-based polymers can be mainly attributed to the ineffective chain packing via the incorporation of the spriobichroman structure and a ladder-type bridged bicyclic TB unit

    Electrospun Self-Supporting Nanocomposite Films of Na<sub>9</sub>[EuW<sub>10</sub>O<sub>36</sub>]¡32H<sub>2</sub>O/PAN as pH-Modulated Luminescent Switch

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    The continuous, flexible, and self-supporting nanocomposite films of EuW<sub>10</sub>/PAN (EuW<sub>10</sub> = Na<sub>9</sub>[EuW<sub>10</sub>O<sub>36</sub>]¡32H<sub>2</sub>O; PAN = polyacrylonitrile) have been successfully fabricated through electrospinning technique, and the resulting films display strong red emission of Eu­(III) ion. When the films are exposed to acidic gases such as HCl, H<sub>2</sub>S and SO<sub>2</sub>, the red luminescence can be quenched. Upon further exposure to NH<sub>3</sub> gas, the nanocomposite films show the recovered red luminescence. As such, the EuW<sub>10</sub>/PAN nanocomposite films exhibit reversible, high-contrast, and pH-modulated luminescent photoswitching, which involves two distinct states that can be interconverted between the protonation and deprotonation states of EuW<sub>10</sub>. This work could be of benefit for the design and fabrication of novel electro-optical devices

    Donor–Acceptor Small Molecules for Organic Photovoltaics: Single-Atom Substitution (Se or S)

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    Two isostructural low-band-gap small molecules that contain a one-atom substitution, S for Se, were designed and synthesized. The molecule 7,7′-[4,8-bis­(2-ethylhexyloxy)­benzo­[1,2-<i>b</i>:4,5-<i>b′</i>]­dithiophene]­bis­[6-fluoro-4-(5′-hexyl-2,2′-bithiophen-5-yl)­benzo­[<i>c</i>]­[1,2,5]­thiadiazole] (<b>1</b>) and its selenium analogue 7,7′-[4,8-bis­(2-ethylhexyloxy)­benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene]­bis­[6-fluoro-4-(5′-hexyl-2,2′-bithiophen-5-yl)­benzo­[<i>c</i>]­[1,2,5]­selenodiazole] (<b>2</b>) are both based on the electron-rich central unit benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene. The aim of this work was to investigate the effect of one-atom substitution on the optoelectronic properties and photovoltaic performance of devices. Theoretical calculations revealed that this one-atom variation has a small but measurable effect on the energy of frontier molecular orbital (HOMO and LUMO), which, in turn, can affect the absorption profile of the molecules, both neat and when mixed in a bulk heterojunction (BHJ) with PC<sub>71</sub>BM. The Se-containing variant <b>2</b> led to higher efficiencies [highest power conversion efficiency (PCE) of 2.6%] in a standard organic photovoltaic architecture, when combined with PC<sub>71</sub>BM after a brief thermal annealing, than the S-containing molecule <b>1</b> (highest PCE of 1.0%). Studies of the resulting morphologies of BHJs based on <b>1</b> and <b>2</b> showed that one-atom substitution could engender important differences in the solubilities, which then influenced the crystal orientations of the small molecules within this thin layer. Brief thermal annealing resulted in rotation of the crystalline grains of both molecules to more energetically favorable configurations

    Graphene Oxide as an Effective Barrier on a Porous Nanofibrous Membrane for Water Treatment

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    A novel graphene oxide (GO)-based nanofiltration membrane on a highly porous polyacrylonitrile nanofibrous mat (GO@PAN) is prepared for water treatment applications. GO with large lateral size (more than 200 μm) is first synthesized through an improved Hummers method and then assembled on a highly porous nanofibrous mat by vacuum suction method. The prepared GO@PAN membrane is characterized by scanning electron microscopy, transmission electron microscopy, Raman spectrum, X-ray diffraction, and so forth. The results show that graphene oxide can form a barrier on the top of a PAN nanofibrous mat with controllable thickness. The obtained graphene oxide layer exhibits “ideal” pathways (hydrophobic nanochannel) for water molecules between the well-stacked GO nanosheets. Water flux under an extremely low external pressure (1.0 bar) significantly increased due to the unique structure of the GO layer and nanofibrous support. Furthermore, the GO@PAN membrane shows high rejection performance (nearly 100% rejection of Congo red and 56.7% for Na<sub>2</sub>SO<sub>4</sub>). A hydrophilic–hydrophobic “gate”-nanochannel model is presented for explaining the water diffusion mechanism through the GO layer. This method for fabrication of the GO membrane on a highly porous support may provide many new opportunities for high performance nanofiltration applications

    How To Optimize Materials and Devices <i>via</i> Design of Experiments and Machine Learning: Demonstration Using Organic Photovoltaics

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    Most discoveries in materials science have been made empirically, typically through one-variable-at-a-time (Edisonian) experimentation. The characteristics of materials-based systems are, however, neither simple nor uncorrelated. In a device such as an organic photovoltaic, for example, the level of complexity is high due to the sheer number of components and processing conditions, and thus, changing one variable can have multiple unforeseen effects due to their interconnectivity. Design of Experiments (DoE) is ideally suited for such multivariable analyses: by planning one’s experiments as per the principles of DoE, one can test and optimize several variables simultaneously, thus accelerating the process of discovery and optimization while saving time and precious laboratory resources. When combined with machine learning, the consideration of one’s data in this manner provides a different perspective for optimization and discovery, akin to climbing out of a narrow valley of serial (one-variable-at-a-time) experimentation, to a mountain ridge with a 360° view in all directions
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