12 results on '"McKeown, Neil"'
Search Results
2. Dibenzomethanopentacene‐Based Polymers of Intrinsic Microporosity for Use in Gas‐Separation Membranes.
- Author
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Chen, Jie, Longo, Mariagiulia, Fuoco, Alessio, Esposito, Elisa, Monteleone, Marcello, Comesaña Gándara, Bibiana, Carolus Jansen, Johannes, and McKeown, Neil B.
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MICROPOROSITY ,SEPARATION of gases ,GAS mixtures ,GAS separation membranes ,IDEAL gases ,POLYMERS - Abstract
Dibenzomethanopentacene (DBMP) is shown to be a useful structural component for making Polymers of Intrinsic Microporosity (PIMs) with promise for making efficient membranes for gas separations. DBMP‐based monomers for PIMs are readily prepared using a Diels–Alder reaction between 2,3‐dimethoxyanthracene and norbornadiene as the key synthetic step. Compared to date for the archetypal PIM‐1, the incorporation of DBMP simultaneously enhances both gas permeability and the ideal selectivity for one gas over another. Hence, both ideal and mixed gas permeability data for DBMP‐rich co‐polymers and an amidoxime modified PIM are close to the current Robeson upper bounds, which define the state‐of‐the‐art for the trade‐off between permeability and selectivity, for several important gas pairs. Furthermore, long‐term studies (over ≈3 years) reveal that the reduction in gas permeabilities on ageing is less for DBMP‐containing PIMs relative to that for other high performing PIMs, which is an attractive property for the fabrication of membranes for efficient gas separations. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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3. An Interfacial Layer Based on Polymers of Intrinsic Microporosity to Suppress Dendrite Growth on Li Metal Anodes.
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Qi, Liya, Shang, Luoran, Wu, Kai, Qu, Liangliang, Pei, Hao, Li, Wen, Zhang, Lexiang, Wu, Zhengwei, Zhou, Henghui, McKeown, Neil B., Zhang, Weixia, and Yang, Zhengjin
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MICROPOROSITY ,DENDRITIC crystals ,COPPER electrodes ,ANODES ,POLYMERS ,ELECTROCHEMICAL electrodes ,METALS - Abstract
The performance and safety of lithium (Li) metal batteries can be compromised owing to the formation of Li dendrites. Here, the use of a polymer of intrinsic microporosity (PIM) is reported as a feasible and robust interfacial layer that inhibits dendrite growth. The PIM demonstrates excellent film‐forming ability, electrochemical stability, strong adhesion to a copper metal electrode, and outstanding mechanical flexibility so that it relieves the stress of structural changes produced by reversible lithiation. Importantly, the porous structure of the PIM, which guides Li flux to obtain uniform deposition, and its strong mechanical strength combine to suppress dendrite growth. Hence, the electrochemical performance of the anode is significantly enhanced, promising excellent performance and extended cycle lifetime for Li metal batteries. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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4. Low Frequency Vibrations and Diffusion in Disordered Polymers Bearing an Intrinsic Microporosity as Revealed by Neutron Scattering.
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Zorn, Reiner, Szymoniak, Paulina, Kolmangadi, Mohamed A., Malpass-Evans, Richard, McKeown, Neil B., Tyagi, Madhusudan, Böhning, Martin, and Schönhals, Andreas
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NEUTRON scattering ,FREQUENCIES of oscillating systems ,MICROPOROSITY ,INELASTIC neutron scattering ,POLYMERIC membranes ,POLYMERS - Abstract
The microscopic diffusion and the low frequency density of states (VDOS) of PIM-EA-TB(CH
3 ) are investigated by inelastic and quasi-elastic neutron scattering where also the demethylated counterpart of PIM-EA-TB(H2 ) is considered. These intrinsic microporous polymers are characterized by large BET surface area values of several hundred m2 /g and pore sizes between 0.5 and 2 nm. Detailed comparison is made to the archetype of polymers of intrinsic microporosity, PIM-1, and polynorbornenes also bearing a microporosity. Due to the wavelength of neutrons, the diffusion and vibrations can be addressed on microscopic length and time scales. From the inelastic neutron scattering experiments the low frequency density of states (VDOS) is estimated which shows excess contributions to the Debye-type VDOS known as Boson peak. It was found that the maximum frequency of the Boson peak decreases with increasing microporosity characterized by the BET surface area. However, besides the BET surface area, additional factors such as the backbone stiffness govern the maximum frequency of the Boson peak. Further the mean squared displacement related to microscopic motions was estimated from elastic fixed window scans. At temperatures above 175 K, the mean squared displacement PIM-EA-TB(CH3 ) is higher than that for the demethylated counterpart PIM-EA-TB(H2 ). The additional contribution found for PIM-EA-TB(CH3 ) is ascribed to the rotation of the methyl group in this polymer because the only difference between the two structures is that PIM-EA-TB(CH3 ) has methyl groups where PIM-EA-TB(H2 ) has none. A detailed comparison of the molecular dynamics is also made to that of PIM-1 and the microporous polynorbornene PTCNSi1. The manuscript focuses on the importance of vibrations and the localized molecular mobility characterized by the microscopic diffusion on the gas transport in polymeric separation membranes. In the frame of the random gate model localized fluctuations can open or close bottlenecks between pores to enable the diffusion of gas molecules. [ABSTRACT FROM AUTHOR]- Published
- 2021
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5. Intrinsically Microporous Polymer Nanosheets for High‐Performance Gas Separation Membranes.
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Tamaddondar, Marzieh, Foster, Andrew B., Luque‐Alled, Jose M., Msayib, Kadhum J., Carta, Mariolino, Sorribas, Sara, Gorgojo, Patricia, McKeown, Neil B., and Budd, Peter M.
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GAS separation membranes ,POLYMERS ,SURFACE area ,MICROPOROSITY ,PERMEABILITY ,MATRIX effect - Abstract
Microporous polymer nanosheets with thicknesses in the range 3–5 nm and with high apparent surface area (Brunauer–Emmett–Teller surface area 940 m2 g−1) are formed when the effectively bifunctional (tetrafluoro) monomer used in the preparation of the prototypical polymer of intrinsic microporosity PIM‐1 is replaced with an effectively tetrafunctional (octafluoro) monomer to give a tightly crosslinked network structure. When employed as a filler in mixed‐matrix membranes based on PIM‐1, a low loading of 0.5 wt% network‐PIM‐1 nanosheets gives rise to enhanced CO2 permeability and CO2/CH4 selectivity, compared to pure PIM‐1. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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6. Polymers of intrinsic microporosity for aqueous organic redox flow batteries
- Author
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Ye, Chunchun, Mckeown, Neil, and Ferrari, Maria-Chiara
- Subjects
Polymers of Intrinsic Microporosity ,Ion Conductive Membranes ,Aqueous Organic Redox Flow Batteries - Abstract
Redox flow batteries (RFBs) based on aqueous organic electrolytes are promising technologies for large-scale, safe and cost-effective electrical energy storage. The membrane separator is the key component in a RFB system to keep redox-active species separate in two half cells while allow free transport of charge-balancing ions. Delivering fast and selective ion transport is critical for battery performance yet remains a challenge for current RFB separators, owing to the difficulty in generating membranes with well-defined sub-nanometre channels to serve as efficient molecular sieves. In this thesis, a new family of ion-sieving membranes, based on Polymers of Intrinsic Microporosity (PIMs) with different backbones and integrating varied ion-conductive groups, are developed and function as efficient and stable separators in aqueous organic RFBs. PIMs are platform materials with distinct combination of properties including high microporosity, exceptional chain rigidity and good solution processibility. A range of dibenzodioxin-based PIMs with varied spirocyclic and bridged bicyclic structural units are synthesised and provide a versatile post-functionalisation to introduce ionisable amidoxime groups. These membranes demonstrate the feasibility of PIM-based membranes serving as ion-conductive and low-resistant separators in alkaline aqueous RFB systems. Further, negative-charged sulfonate groups are introduced into spirobifluorene-based PIMs which exhibit exceptional efficiency and stability for battery operation at near neutral aqueous electrolytes, outperforming identical RFB cells that use commercial benchmark Nafion® membranes. PIMs containing Tröger's base building blocks enable the introduction of quaternary ammonium groups together with simultaneous crosslinking network, or zwitterionic groups on amine sites. The combination of polymer rigidity, high microporosity and ion-conductive functionalities of PIMs facilitates the formation of well-confined and sub-nanometre pathway, allowing fast transport of charge-balancing ions whilst unprecedented blocking redox-active species through membranes, fulfilling the function as efficient RFB separators hence achieving impressive performance in RFBs. These proof-of-concept demos using functionalised PIM membranes as efficient molecular sieves can guide the development of new generation membrane separators for a range of clean energy technology applications.
- Published
- 2021
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7. Design and synthesis of novel polymers of intrinsic microporosity for gas separations
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Chen, Jie, McKeown, Neil, and Ferrari, Maria-Chiara
- Subjects
660 ,polymers of intrinsic microporosity ,separation membranes ,PIMs ,fluorinated PIMs ,pore density - Abstract
Polymers of Intrinsic Microporosity (PIMs) are a new class of microporous material combining excellent solution processability with great structural diversity. The microporosity of PIMs derives from the inefficient packing of rigid and contorted polymeric chains. PIM membranes show great potential in gas separations (e.g., CO2/CH4, CO2/N2, O2/N2, H2/N2). However, they suffer from a well-defined tradeoff relationship between gas permeability and selectivity. Novel PIMs were designed and synthesised to investigate structure-property relationships and to provide a guideline for designing a new membrane material, which can provide a good balance of gas permeability and selectivity. In the first part of this thesis, two fluorinated benzotriptycene polybenzodioxin polymers were prepared. These benzotriptycene-based PIMs exhibit ultra-high permeability with remarkable selectivity for carbon capture (CO2/N2) and natural gas purification (CO2/CH4), and defined the new upper bounds for these gas pairs together with four other benzotriptycene PIMs. In particular, the fluorinated polymers showed a better performance for CO2/CH4 and He/CH4 than alkyl substituted benzotriptycene based PIMs due to their higher solubility selectivity resulting from the low CH4 sorption in the fluorinated polymers. In the second part, a fluorinated and non-fluorinated benzomethanoanthracene PIMs (PIM OCF and PIM-OCP) were designed and synthesized in which fluorine atoms illustrated a minor effect on polymer microstructure confirmed by molecular simulation. The improved CO2/CH4 solubility selectivity exclusively derives from the inclusion of the fluorocarbon unit. The perfluoroalkyl chain substituent was also observed to reduce the CH4 sorption and improve the solubility selectivities of CO2/CH4, He/CH4 and H2/CH4, although the reduced size selectivity of perfluoroalkyl chain substituted polybenzodioxin polymer and low surface area of the perfluoroalkyl chain substituted Tröger’s base polymer limit their potential applications. In the last chapter, dibenzeno-6,13-methanopentacene (DBMP), a bridged bicyclic structure with a bulkier structure than that of triptycene, was utilized for PIM synthesis. The membrane of the homopolymer (PIM-DBMP) proved too fragile for membrane fabrication. Therefore, the potential of DBMP for gas separations was investigated using a series of copolymers composed of DBMP and 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI). The gas permeability of the copolymers demonstrated that the introduction of DBMP improves the gas permeability and selectivity simultaneously, overcoming the challenging tradeoff relationship. PIM-DBMP was further modified via amidoxime functionalisation, which was anticipated to improve the membrane’s mechanical properties. As expected, a robust membrane of amidoxime-PIM-DBMP was achieved which showed promising gas separation performance.
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- 2020
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8. Novel microporous polymers for gas separation membranes
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Felemban, Sarah Abdulhalim, McKeown, Neil, and Shaver, Michael
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547 ,polymers of intrinsic microporosity ,PIMs ,novel PIMs ,gas separation membranes ,Tro¨ger's base ,hypercrosslinked polystyrene ,thiathrene-based rigid monomer - Abstract
Polymers of intrinsic microporosity (PIMs) owe their microporosity to their rigid and contorted structure which prevents efficient space packing. Their microporosity and processability make them attractive for many industrial applications, such as heterogeneous catalysis, gas separation membranes, hydrogen storage and adsorbents for organic compounds. Our goal in this project is to broaden the spectrum of PIM structures by preparing novel PIMs with potential for different industrial applications but focusing on gas separation membranes. Characterisation of the novel polymers was achieved to establish their chemical and physical properties including solubility, surface area, thermal stability and their molecular weight. In some cases, casting the resulting PIMs from solution enabled the formation of self-standing films which could then be analysed for their ability to separate different gas mixtures. Three different types of PIM were targeted during the PhD programme. Firstly, the preparation of Tröger's base (TB) containing hypercrosslinked polystyrene was attempted. The first step was the nitration of polystyrene by using different reaction conditions, with the aim to introduce the highest possible number of nitro groups, followed by the reduction of nitropolystyrene to the aminated polystyrene. Finally, hyper-crosslinking of the amino-polystyrene was attempted by formation of TB units between polymer chains. Secondly, new ladder and network PIMs derived from different catechols monomers with 2,3,7,8-tetrafluoro-5,5',10,10'- tetraoxidethianthrene were synthesised. This thiathrene-based rigid monomer increases the distances between two consecutive "sites of contortion" within the polymer chains and provides sulfonyl functional groups, which may influence the adsorption and gas separation properties of the resulting polymers. Thirdly, a series of novel microporous polyimides (PIMPIs) were prepared using different diamine monomers and thiathrene-based dianhydride monomers. All polymers were characterized by using NMR, IR spectrometers and their chemical and physical properties were measured using a variety of techniques. In addition, for some polymers successful film formation via casting from solution allowed the measurement of their gas permeability to assess their ability to separate gas mixture. All chemical procedures for the synthesis of monomers and polymers, properties of the resulting polymers and comparisons with existing polymers are described in this thesis.
- Published
- 2019
9. Incorporation of novel structural units into polymers of intrinsic microporosity
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Kirk, Richard Andrew, McKeown, Neil, and Shaver, Michael
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541 ,micropores ,Polymers of Intrinsic Microporosity ,PIMs ,gas separation properties ,high surface area ,1,4-diaminotriptycene ,polyimide formation ,2,6(7)-diaminotriptycene ,BzMA based polymer ,DiBzMP diamine - Published
- 2019
10. The fabrication of ultrathin films and their gas separation performance from polymers of intrinsic microporosity with two-dimensional (2D) and three-dimensional (3D) chain conformations.
- Author
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Benito, Javier, Vidal, Julio, Sánchez-Laínez, Javier, Zornoza, Beatriz, Téllez, Carlos, Martín, Santiago, Msayib, Kadhum J., Comesaña-Gándara, Bibiana, McKeown, Neil B., Coronas, Joaquín, and Gascón, Ignacio
- Subjects
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THIN films , *POLYMERS , *MICROPOROSITY , *FABRICATION (Manufacturing) , *ALLOYS - Abstract
Graphical abstract Abstract The expansion of the use of polymeric membranes in gas separation requires the development of membranes based on new polymers with improved properties and their assessment under real operating conditions. In particular, the fabrication of ultrathin films of high performance polymers that can be used as the selective layer in composite membranes will allow large reductions in the amount of the expensive polymer used and, hence, the cost of membrane fabrication. In this contribution, two polymers of intrinsic microporosity (PIMs) with very different chain configurations (two-dimensional, 2D, chains or conventional contorted three-dimensional, 3D, conformation) have been compared in their ability to form ultrathin films, showing the relevance of polymer design to obtain compact and defect-free films. Monolayers of the 2D polymer PIM-TMN-Trip can be efficiently deposited onto poly[1-(trimethylsilyl)-1-propyne] (PTMSP) to obtain composite membranes with a CO 2 /N 2 selectivity similar to that of the corresponding thick membranes of the same PIM using only a small fraction of the selective polymer (less than 0.1%). [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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11. Polymers of Intrinsic Microporosity derived from a carbocyclic analogue of Tröger's base.
- Author
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Carta, Mariolino, Bezzu, C. Grazia, Vile, James, Kariuki, Benson M., and McKeown, Neil B.
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POLYMERIZATION , *MICROPOROSITY , *CARBOCYCLIC compounds , *ABSORPTION , *BICYCLIC compounds - Abstract
Tröger's base (TB) is often used as a building block for the synthesis of Polymers of Intrinsic Microporosity (PIMs) due to its rigid bicyclic V-shaped structure. In this study the TB component in the structure of a PIM is replaced by 2,3:6,7-dibenzobicyclo[3.3.1]nonane, a purely carbocyclic analogue of TB. This modification results in only a slightly reduced amount of microporosity as determined using nitrogen adsorption. Further comparisons with previously reported PIMs indicate that this building unit (and therefore TB) is significantly less effective for the generation of intrinsic microporosity than spirobisindane, a commonly used structural unit for PIM synthesis. It appears that the V-shape of the 2,3:6,7-dibenzobicyclo[3.3.1]nonane and TB units allows closer contact between polymer chains thereby enhancing packing efficiency. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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12. Hierarchically structured carbon electrodes derived from intrinsically microporous Tröger's base polymers for high-performance supercapacitors.
- Author
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Jeon, Jun Woo, Shin, Joobee, Lee, Jinyoung, Baik, Ji-Hoon, Malpass-Evans, Richard, McKeown, Neil B., Kim, Tae-Ho, Lee, Jong-Chan, Kim, Sung-Kon, and Kim, Byoung Gak
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MICROPOROSITY , *CARBON electrodes , *SUPERCAPACITOR electrodes , *POLYMERS , *POROUS materials , *ELECTRIC conductivity , *PHASE separation - Abstract
• PIM-EA-TB based hierarchically structured carbon for supercapacitor electrodes. • Phase separation process introduces meso-¯o-pores into the microporous polymer. • The hierarchical structure is retained even after carbonization. • The resulting carbon shows a high surface area and a good electrical conductivity. • These characteristics give it a high specific capacitance at a specific power. Three-dimensional (3D) hierarchically porous carbons have been extensively investigated as their large surface area and facile ion transport can provide high-performance in energy applications. Here we report new hierarchically porous carbon materials based on a polymer of intrinsic microporosity (PIM composed of ethanoeanthracene (EA) by Tröger base (TB) components (PIM-EA-TB)), for use in high-performance supercapacitor electrodes. Hierarchically structured carbon was prepared from nonsolvent-induced phase separation (NIPS) and subsequent carbonization. The intrinsic micropores of PIM-EA-TB and meso- and macro-pores formed via the NIPS process imbue the resulting carbon material with a hierarchical porous architecture with an exceptionally high surface area of 1966 m2 g−1 and a high electrical conductivity of 83.6 S cm−1. This well-organized structure provides pathways for efficient charge transportation, giving it a high specific capacitance of 46 F g−1 at 1 A g−1 and an excellent specific energy of 17 W h kg−1 at a specific power of 1 kW kg−1. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
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