Two‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, ...metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.
Modification of nanosheet membranes by crosslinking and functionalization has improved their stability, their separation functionality, and the scalability of membrane production while retaining the membranes’ excellent molecular transport properties. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.
Microporous polymers are a class of microporous materials with high free volume elements and large surface areas. Microporous polymers have received much attention for various applications in gas ...separation, gas storage, and for clean energy resources due to their easy processability for mass production, as well as microporosity for high performance. This review describes recent research trends of microporous polymers in various energy related applications, especially for gas separations and gas storages. The new classes of microporous polymers, so-called thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIMs), have been developed by enhancing polymer rigidity to improve microporosity with sufficient free volume sizes. Their rigidity improves separation performance and efficiency with extraordinary gas permeability. Moreover, their solubility in organic solvents allows them to have potential use in large-scale industrial applications.
Recent progress in fluoropolymers for membranes Cui, Zhaoliang; Drioli, Enrico; Lee, Young Moo
Progress in polymer science,
January 2014, 2014, 2014-01-00, Letnik:
39, Številka:
1
Journal Article
Recenzirano
Fluoropolymers usually have high mechanical strength and excellent chemical stability and thus have been employed for the last several decades as materials for membrane separation processes, ...typically in water purification and energy applications such as microfiltration (MF), ultrafiltration (UF), fuel cells, battery separators, etc. Recently, new membrane operations such as membrane distillation (MD), membrane crystallization (MCr), membrane emulsification (ME) and membrane contactors (MC) have become popular. A much stronger understanding of the basic properties of the materials utilized is required for adopting the appropriate membrane and for finding the relationship among material properties, membrane morphology and the transport phenomena in the membranes. This review presents the structures and properties of fluoropolymers for membranes, the preparation and modification methods of fluoropolymer membranes, and their applications. Recent progress in the development of novel fluoropolymers for membranes and their fabrication and modification methods are reported as well.
The sensing performances of gas sensors must be improved and diversified to enhance quality of life by ensuring health, safety, and convenience. Metal-organic frameworks (MOFs), which exhibit an ...extremely high surface area, abundant porosity, and unique surface chemistry, provide a promising framework for facilitating gas-sensor innovations. Enhanced understanding of conduction mechanisms of MOFs has facilitated their use as gas-sensing materials, and various types of MOFs have been developed by examining the compositional and morphological dependences and implementing catalyst incorporation and light activation. Owing to their inherent separation and absorption properties and catalytic activity, MOFs are applied as molecular sieves, absorptive filtering layers, and heterogeneous catalysts. In addition, oxide- or carbon-based sensing materials with complex structures or catalytic composites can be derived by the appropriate post-treatment of MOFs. This review discusses the effective techniques to design optimal MOFs, in terms of computational screening and synthesis methods. Moreover, the mechanisms through which the distinctive functionalities of MOFs as sensing materials, heterostructures, and derivatives can be incorporated in gas-sensor applications are presented.
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Aliphatic/alicyclic (Al)-containing polyimides (PIs), including fully-Al-PIs and partially-Al-PIs, are widely employed in electric, electronics, optical materials, and other advanced ...material fields. Examples include high speed multiplayer printed wiring boards, alignment films for liquid-crystal displays, fuel cells, batteries, gas separation membranes, pervaporation membranes, biomedical applications, and composites/hybrid materials. In the past decades, research has focused on the synthesis and molecular design of fully-Al-PIs and partially-Al-PIs. However, the effects of aliphatic/alicyclic segments on the performance of fully-Al-PIs and partially-Al-PIs and their potential applications are not clear. Therefore, an overall clarification of aliphatic/alicyclic-containing monomers, the effects of aliphatic/alicyclic segments on PI performance, as well as recent applications for advanced technology are important topics for further study. This review systematically summarizes the available aliphatic/alicyclic monomers and clarifies the influence of aliphatic/alicyclic-containing segments in chain backbones on the morphology and properties of the resulting PIs. Further, the use of PIs in applications for advanced materials is discussed, along with the outlook for the future of aliphatic/alicyclic-containing polyimides and their advanced applications.
Abstract
Formaldehyde, a probable carcinogen, is a ubiquitous indoor pollutant, but its highly selective detection has been a long-standing challenge. Herein, a chemiresistive sensor that can detect ...ppb-level formaldehyde in an exclusive manner at room temperature is designed. The TiO
2
sensor exhibits under UV illumination highly selective detection of formaldehyde and ethanol with negligible cross-responses to other indoor pollutants. The coating of a mixed matrix membrane (MMM) composed of zeolitic imidazole framework (ZIF-7) nanoparticles and polymers on TiO
2
sensing films removed ethanol interference completely by molecular sieving, enabling an ultrahigh selectivity (response ratio > 50) and response (resistance ratio > 1,100) to 5 ppm formaldehyde at room temperature. Furthermore, a monolithic and flexible sensor is fabricated successfully using a TiO
2
film sandwiched between a flexible polyethylene terephthalate substrate and MMM overlayer. Our work provides a strategy to achieve exclusive selectivity and high response to formaldehyde, demonstrating the promising potential of flexible gas sensors for indoor air monitoring.
PVDF is widely employed in membrane processes. Its crystals have five different polymorphs, α, β, γ, δ, and ɛ forms. In the past decades, research has been focused on the properties and performances ...of PVDF membranes. However, the formation mechanisms of the various polymorphs and their different effects on membrane performance are still not clear. Therefore, overall clarification of, conclusions about, and outlook on the effects of PVDF polymorphism on membrane properties and performance are important topics for further research. This manuscript systematically summarizes the structures and properties of PVDF crystals with different polymorphs, discusses the mechanisms of formation and transformation methods, reviews the crystallization and applications of different PVDF polymorphs in membrane separation, and presents the outlook for applications in membrane operations.
Microporous polyvinylidene difluoride (PVDF) hollow fiber membranes were fabricated via a thermally-induced phase separation (TIPS) method using an environmental-friendly hydrophobic solvent, acetyl ...tributyl citrate (ATBC, tradename Citroflex® A4). To maximize membrane tensile strength, the TIPS method was fully utilized by spinning fibers with high polymer content. It was observed that the fiber quality was significantly affected by the dope and bore flow rates and compositions, and an appropriate spinning range was established. The prepared membranes were subsequently stretched to tune the porosity, mean pore size, permeability, tensile strength, and fiber strain. A design of experiment (DOE) analysis was conducted using a 3-factor quadratic model to optimize the stretching conditions and to understand the effects of the parameters and interactions thereof. The permeability of the stretched membranes improved by a factor of 35 (15.1–538Lm−2h−1bar−1), and the tensile strength increased from 7.2MPa to 8.4MPa at the expense of the fiber strain. The DOE analysis revealed that the stretching ratio positively affects the permeability and porosity but decreases the fiber strain. On the other hand, it was determined that the stretching temperature positively influences the permeability and fiber strength. The stretched membranes exceeded the PVDF performance upper bound prepared by the TIPS method. The membranes were primarily in the α-phase polymorph, and stretching the fibers up to 40% at 90°C did not induce any detectable β-phase crystals. The proposed preparation method offers a feasible and sustainable alternative to fabricate hollow fibers membranes with high tensile strength and high permeability.
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•Microporous PVDF membranes were prepared via TIPS using a green hydrophobic solvent.•A stretching step was applied using a Design of Experiment (DOE).•Stretched membranes showed strong tensile strength and permeability improvement.
Water oxidation is considered an important reaction to attain sustainable energy systems. Inspired by the biological Mn
4
CaO
5
cluster, considerable effort has been devoted to developing efficient ...manganese-based heterogeneous catalysts for the water oxidation reaction. This review first describes the structural characteristics of the Mn
4
CaO
5
cluster and synthetic manganese oxides. Important features related to the electrocatalytic activity of manganese-based heterogeneous catalysts as well as recent
in situ
spectroscopic results for intermediate characterization are then summarized. Current understanding of the reaction mechanism at the atomic level and the rate-determining step is highlighted. Finally, future perspectives for the development of highly active and stable manganese-based water-oxidizing catalysts are proposed.
A review on manganese oxide-based electrocatalysts for the water oxidation reaction.
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