Nanoporous PBI membranes by track etching for high temperature PEMs

Silk nanofibrils-MOF composite membranes for pollutant removal from water

Membrane separation technology is considered an effective strategy to remove pollutants in sewage. However, it remains a significant challenge to fabricate inexpensive membranes with high purification efficiency. Therefore, the present study proposes the integration of silk nanofibrils (SNFs) and polydopamine⊂metal-organic framework (PDA⊂MOF) nanoparticles to prepare self-supporting membranes, which can effectively intercept nanoparticle pollutants through the size exclusion effect and can strongly adsorb organic dyes and metal ions by SNF. In addition, PDA⊂MOF enables these membranes to adsorb small molecules and heavy metal ions during the filtration process, thereby effectively removing various pollutants from sewage. The integration of size-exclusion and adsorption capabilities enables the SNF/PDA⊂MOF membrane to remove nanoparticles, small-molecule dyes, heavy metal ions, and radioactive elements. This work provides a rational approach for the design and development of the next generation of water treatment membranes and is expected to be used in environmental, food-related, and biomedical fields.

Subnanometer Ion Channel Anion Exchange Membranes Having a Rigid Benzimidazole Structure for Selective Anion Separation

Ion-conductive polymers having a well-defined phase-separated structure show the potential application of separating mono- and bivalent ion separation. In this work, three side-chain-type poly(arylene ether sulfone)-based anion exchange membranes (AEMs) have been fabricated to investigate the effect of the stiffness of the polymer backbone within AEMs on the Cl^-/NO₃^- and Cl^-/SO₄^2- separation performance. Our investigations via small-angle X-ray scattering (SAXS), positron annihilation, and differential scanning calorimetry (DSC) demonstrate that the as-prepared AEM with a rigid benzimidazole structure in the backbone bears subnanometer ion channels resulting from the arrangement of the rigid polymer backbone. In particular, SAXS results demonstrate that the rigid benzimidazole-containing AEM in the wet state has an ion cluster size of 0.548 nm, which is smaller than that of an AEM with alkyl segments in the backbone (0.760 nm). Thus, in the electrodialysis (ED) process, the former exhibits a superior capacity of separating Cl^-/SO₄^2- ions relative to latter. Nevertheless, the benzimidazole-containing AEM shows an inability to separate the Cl^-/NO₃^- ions, which is possibly due to the similar ion size of the two. The higher rotational energy barrier (4.3 × 10^-3 Hartree) of benzimidazole units and the smaller polymer matrix free-volume (0.636%) in the AEM significantly contribute to the construction of smaller ion channels. As a result, it is believed that the rigid benzimidazole structure of this kind is a benefit to the construction of stable subnanometer ion channels in the AEM that can selectively separate ions with different sizes.

Design of an efficient, tunable and scalable freestanding flexible membrane for filter application

To address the global challenge of water pollution, membrane-based technologies are being used as a dignified separation technology. However, designing low-cost, reusable, freestanding and flexible membranes for wastewater treatment with tunable pore size, good mechanical strength, and high separation efficiency is still a major challenge. Herein, we report the development of a scalable, reusable, freestanding, flexible and functionalized multiwalled carbon nanotube (FMWCNT) membrane filter with tunable pore size for wastewater treatment, which has attractive attributes such as high separation efficiency (>99% for organic dyes and ∼80% for salts), permeance (∼225 L h^-1 m^-2 bar^-1), tensile strength (∼6 MPa), and reusability of both the membrane as well as contaminants separately. This FMWCNTs membrane filter has been developed by a simple vacuum-assisted filtration technique followed by the synthesis of MWCNTs using a cost-effective spray pyrolysis assisted chemical vapor deposition (CVD) technique and chemical functionalization. This study deals with understanding the rejection, retrieval, and reusability of both the membranes as well as waterborne contaminants separately. The developed membrane filter has potential utility in many applications such as wastewater treatment, food industry, and life sciences due to its robust mechanical and separation performance characteristics.

Separation of Caustic Nano-Emulsions and Macromolecular Conformations with Nanofibrous Membranes of Marine Chitin

Sustainable development of nanotechnology is challenged by nanoscale pollutants and oily water. Biobased nanoporous membranes, though serving as one of the most eco-friendly separation technologies, cannot be applied widely because of their broad pore distributions, poor solvent resistance, and structural instability. In order to avoid possible leakage of nanoscale objects in caustic and organic solvents, herein, we endeavored to exfoliate chitin nanofibrils with identical chemical and crystalline structures to pristine chitin in portunid carapace and further produce nanoporous and mesoporous membranes with super structural stability, endurance, permeation flux and rejection. The final membranes had minimal ionization, controllable thickness, and tunable and narrow distribution of pore size, being able to separate nano-emulsions, nanoparticles, and rigid macromolecules in caustic aqueous solutions and organic solvents. Thus, these scalable, low-cost, and sustainable membranes may promise applications as diverse as in separating and concentrating nanoparticles in nanotechnology, oil/water separation in wastewater treatment, and molecular sieving in biomedicine and material science.

Selective protein transport through ultra-thin suspended reduced graphene oxide nanopores

The nanoporous free-standing graphene membrane is of great interest in high performance separation technology. In particular, the separation of biological molecules with similar sizes is one of the key challenges in the purification of biomaterials. Here, we report a reliable, cost-effective, and facile method for the fabrication of a graphene-based nanosieve and its application in the separation of similar-size proteins. A suspended reduced graphene oxide (rGO) nanosieve with ultra-thin, large-area, well-ordered, and dense 15 nm-sized pores was fabricated using block copolymer (BCP) lithography. The fabricated 5 nm-ultrathin nanosieve with an area of 200 μm × 200 μm (an ultra-high aspect ratio of ∼40 000) endured pressure up to 1 atm, and effectively separated hemoglobin (Hb) from a mixture of hemoglobin and immunoglobulin G (IgG), the common proteins in human blood, in a highly selective and rapid manner. The use of the suspended rGO nanosieve is expected to provide a simple and manufacturable platform for practical biomolecule separation offering high selectivity and a large throughput.

Design and function of biomimetic multilayer water purification membranes

Multilayer architectures in water purification membranes enable increased water throughput, high filter efficiency, and high molecular loading capacity. However, the preparation of membranes with well-organized multilayer structures, starting from the nanoscale to maximize filtration efficiency, remains a challenge. We report a complete strategy to fully realize a novel biomaterial-based multilayer nanoporous membrane via the integration of computational simulation and experimental fabrication. Our comparative computational simulations, based on coarse-grained models of protein nanofibrils and mineral plates, reveal that the multilayer structure can only form with weak interactions between nanofibrils and mineral plates. We demonstrate experimentally that silk nanofibril (SNF) and hydroxyapatite (HAP) can be used to fabricate highly ordered multilayer membranes with nanoporous features by combining protein self-assembly and in situ biomineralization. The production is optimized to be a simple and highly repeatable process that does not require sophisticated equipment and is suitable for scaled production of low-cost water purification membranes. These membranes not only show ultrafast water penetration but also exhibit broad utility and high efficiency of removal and even reuse (in some cases) of contaminants, including heavy metal ions, dyes, proteins, and other nanoparticles in water. Our biomimetic design and synthesis of these functional SNF/HAP materials have established a paradigm that could lead to the large-scale, low-cost production of multilayer materials with broad spectrum and efficiency for water purification, with applications in wastewater treatment, biomedicine, food industry, and the life sciences.

Constructing Straight Polyionic Liquid Microchannels for Fast Anhydrous Proton Transport

Polymeric ionic liquids (PILs) have triggered great interest as all solid-state flexible electrolytes because of safety and superior thermal, chemical, and electrochemical stability. It is of great importance to fabricate highly conductive electrolyte membranes capable to operate above 120 °C under anhydrous conditions and in the absence of mineral acids, without sacrificing the mechanical behavior. Herein, the diminished dimensional and mechanical stability of poly[1-(3H-imidazolium)ethylene]bis(trifluoromethanesulfonyl)imide has been improved thanks to its infiltration on a polybenzimidale (PBI) support with specific pore architecture. Our innovative solution is based on the synergic combination of an emerging class of materials and sustainable large-scale manufacturing techniques (UV polymerization and replication by microtransfer-molding). Following this approach, the PIL plays the proton conduction role, and the PBI microsieve (SPBI) mainly provides the mechanical reinforcement. Among the resulting electrolyte membranes, conductivity values above 50 mS·cm^-1 at 200 °C and 10.0 MPa as tensile stress are shown by straight microchannels of poly[1-(3H-imidazolium)ethylene]bis(trifluoromethanesulfonyl)imide cross-linked with 1% of dyvinylbenzene embedded in a PBI microsieve with well-defined porosity (36%) and pore diameter (17 μm).

Highly dispersed palladium nanoparticles on poly(N1,N3-dimethylbenzimidazolium)iodide-functionalized multiwalled carbon nanotubes for ethanol oxidation in alkaline solution

Multi-walled carbon nanotubes (MWCNTs) have been considered as good catalyst supporting materials, and their dispersion and functionalization are important, challenging problems for high-performance composite catalysts.