Membrane Separation Research Articles

Selective mono/divalent ion separation in bifunctional ionomeric capacitive deionization incorporated with counter-charge ionomer layer

In this study, a carbon-based bifunctional ionomeric capacitive deionization (BICDI) system was successfully developed by applying a counter-charge ionomer layer to the BICDI electrode without the need of a monovalent ion exchange membrane (M-IEM) for the selective separation of mono/divalent ions. The counter-charge ionomer layer facilitates the selective separation of mono/divalent ions through a combination of mechanisms involving electrostatic repulsion, steric hindrance, and hydrophobic interactions. Meanwhile, the BICDI electrode matrix serves as an ion transport channel, enabling seamless ion transport and improving the electrosorption capacity of the electrode. SEM and EDS analyses have confirmed the presence of a counter-charge ionomer layer encapsulating the BICDI electrode. Notably, BICDI-C cell with counter-charge ionomer layer exhibits higher Li+ ion adsorption capacity and selectivity (321.6 μmol/g, βMg2+Li+=6.6) compared to commercial monovalent cation exchange membrane CDI (MCDI-C) cell (206.4 μmol/g, βMg2+Li+=1.4). The selectivity of the BICDI-C cell for mono/divalent ions can be optimized by adjusting various testing parameters, including flow rate, voltage, etc. More importantly, this versatile method is not only applicable for the separation of monovalent cation, but can also enhance the monovalent anion adsorption capacity and selectivity of BICDI-A (43.6 μmol/g, βSO42-Cl-=7.3) cell by incorporating a counter-charge ionomer layer onto the BICDI cathode. This approach allows for the efficient separation of both cationic and anionic species, broadening the range of potential applications for BICDI technology.

Asymmetric PDMS/PVDF Pervaporation Membrane for Separation of Ethanol/Water System

AbstractPreparing asymmetric pervaporation membranes is a kind of promising method to enhance pervaporation membrane flux. Hydrophobic PVDF polymer can be used to prepare asymmetric pervaporation membranes, but its separation factor is relatively low. In this work, to improve the performance of PVDF membrane pervaporation, PDMS polymer was added to the PVDF membrane, and asymmetric PDMS/PVDF permeable membranes were prepared by the non‐solvent induced phase separation (NIPS) method. The effects of mass ratios of PDMS to PVDF on the membrane structures and the membrane properties were characterized by SEM, XRD, FTIR, TGA, water contact angle and mechanical strength. The results showed that the ratios of the PDMS: PVDF affect its phase‐separation behavior. As the addition of PDMS increased, the finger‐like pores on the membrane section gradually became longer, the upper surface changed from less porous to porous structure, and the lower surface structure changed from interconnected flocculent structure to porous, and the best structure of the blend membrane was achieved when the PDMS: PVDF mass ratio was 1 : 5. Therefore, the membrane had the best separation performance in separating 15 wt. % ethanol aqueous solution with a permeate total flux of 273.65 g/(m2 h) and a separation factor of 9.09 when the mass ratio of PDMS: PVDF was 1 : 5.

Engineering polyvinylidene fluoride membranes using charge tunable dendrimer polyamidoamine to enable microporous membranes for protein separation

Dendrimers are structurally precise molecules, whose peripheral layer provides ample sites for anchoring functional groups of different charges and charge densities. This characteristic renders them capability of providing numerous target functional groups on the surface of filtration membranes when modified by dendrimers. Consequently, there has been a growing interest in dendrimer-modified membranes. In this study, we investigated the engineering of polyvinylidene fluoride (PVDF) membranes using polyamidoamine (PAMAM) dendrimers anchoring different functional groups to tune the charges and charge density of membranes to enable microporous membranes for separation of charged macromolecules. PVDF membranes were functionalized by grafting PAMAM-G3.0 (generation 3) dendrimers with amine groups onto their surfaces and internal surfaces of membrane pores. Subsequently, the peripheral functional groups of dendrimers on the membranes were replaced by carboxyl groups, quaternary ammonium groups, or sulfonic acid groups for charges of different nature and densities. Surface chemical properties, electrical properties, and morphology were characterized using various techniques, including attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and surface zeta potential measurement. The filtration performance of both PVDF and modified membranes was evaluated using polyethylene oxide (PEO), polyacrylic acid (PAA), and whey protein filtration. Among the modified membranes, the G3PA membranes, with carboxyl functional groups, exhibited the most effective whey protein separation performance. The whey protein rejection and permeate flux of the G3PA membranes were 79 % and 30.3 LMH, respectively. As a comparison, the whey protein rejection and permeate flux of the pristine PVDF membranes were 58.9 % and 15.3 LMH, respectively.

Research Progress on Metal Ion Recovery Based on Membrane Technology and Adsorption Synergy.

The development of modern industry will generate more and more waste containing metal ions. It is necessary to take appropriate measures to recover these ions, whether from the perspective of environmental protection or improving economic benefits. So far, scientists have studied many methods for recovering metal ions. Among these methods, adsorption and membrane separation have received widespread attention due to their own characteristics. Combining adsorption and membrane separation methods can better leverage their respective advantages to improve the ability of recovering metal ions. This review, therefore, focuses on the synergistic recovery of metal ions by adsorption and membrane separation methods. This article first briefly explains the theoretical principles of membrane separation and adsorption synergy, and then focuses on several technologies that have received attention in different chapters. In these chapters, membrane technology is briefly introduced, followed by the situation and progress of synergistic application with adsorption technology. Then, the article compares and elaborates on the advantages and disadvantages of the above technologies, and finally summarizes and looks forward to these technologies being used to solve the difficulties and challenges in industrial application.

Characterization of Low-Molecular-Weight Dissolved Organic Matter Using Optional Dialysis and Orbitrap Mass Spectrometry.

Low-molecular-weight (LMW, <1000 Da) dissolved organic matter (DOM) plays a significant role in metal/organic pollutant complexation, as well as photochemical/microbiological processes in freshwater ecosystems. The micro size and high reactivity of LMW-DOM hinder its precise characterization. In this study, Suwannee River fulvic acid (SRFA), a commonly used reference material for aquatic DOM, was applied to examine the optical features and molecular composition of LMW-DOM by combining membrane separation, ultraviolet-visible absorption and Orbitrap mass spectrometry (MS) characterization. The 100-500 Da molecular weight cut-off (MWCO) membrane had a better performance in regard to separating the tested LMW-DOM relative to the 500-1000 Da MWCO membrane. The ultraviolet-visible absorbance decreased dramatically for the retentates, whereas it increased for the dialysates. Specifically, carbohydrates, lipids and peptides exhibited high selectivity to the 100-500 Da MWCO membrane in early dialysis. Lignins, tannins and condensed aromatic molecules displayed high permeability to the 500-1000 Da MWCO membrane in late dialysis. Overall, the retentates were dominated by aromatic rings and phenolic hydroxyls with high O/Cwa (weighted average of O/C) and low H/Cwa. Conversely, such dialysates had numerous aliphatic chains with high H/Cwa and low O/Cwa compared to SRFA. In particular, LMW-DOM below 200 Da was identified by Orbitrap MS. This work provides an operational program for identifying LMW-DOM based on the SRFA standard and MS analysis.

A Rapid, Efficient Method for Anodic Aluminum Oxide Membrane Room-Temperature Multi-Detachment from Commercial 1050 Aluminum Alloy.

For commercial processes, through-hole AAO membranes are fabricated from high-purity aluminum by chemical etching. However, this method has the disadvantages of using heavy-metal solutions, creating large amounts of material waste, and leading to an irregular pore structure. Through-hole porous alumina membrane fabrication has been widely investigated due to applications in filters, nanomaterial synthesis, and surface-enhanced Raman scattering. There are several means to obtain freestanding through-hole AAO membranes, but a fast, low-cost, and repetitive process to create complete, high-quality membranes has not yet been established. Here, we propose a rapid and efficient method for the multi-detachment of an AAO membrane at room temperature by integrating the one-time potentiostatic (OTP) method and two-step electrochemical polishing. Economical commercial AA1050 was used instead of traditional high-cost high-purity aluminum for AAO membrane fabrication at 25 °C. The OTP method, which is a single-step process, was applied to achieve a high-quality membrane with unimodal pore distribution and diameters between 35 and 40 nm, maintaining a high consistency over five repetitions. To repeatedly detach the AAO membrane, two-step electrochemical polishing was developed to minimize damage on the AA1050 substrate caused by membrane separation. The mechanism for creating AAO membranes using the OTP method can be divided into three major components, including the Joule heating effect, the dissolution of the barrier layer, and stress effects. The stress is attributed to two factors: bubble formation and the difference in the coefficient of thermal expansion between the AAO membrane and the Al substrate. This highly efficient AAO membrane detachment method will facilitate the rapid production and applications of AAO films.

Mechanistic insights into the separation behaviors of polyamide desalination membranes for emerging micropollutants removal

As emerging micropollutants (EMPs) become a global environmental concern, it is crucial to devise energy-efficient methods that can effectively remove EMPs from water. Polyamide thin-film composite (PA-TFC) membranes are state-of-the-art water separation membranes and their applications for EMPs separations have been increasingly conscripted in recent years. However, a comprehensive fundamental understanding of the underlying relationship between membrane microstructures and EMPs transport across the PA-TFC membranes remains enigmatic. To address this gap, we thoroughly investigated the separation behaviors of two PA-TFC membranes with distinct PA microstructures toward a wide spectrum of EMPs with various dimensions and chemistries. By reconciling experimental evidence and density-functional theory (DFT), we disclosed that the water permeance of the PA-TFC membrane is predominately governed by the effective filtration area associated with surface protuberances and the intrinsic wall thickness of the PA microlayers. Precise control of the solute–PA interactions is explicitly important for membrane selectivity toward EMPs, which deserves more attention in future membrane design besides synchronously regulating membrane pore size and size distribution. This work represents a conspicuous step forward in the fundamental understanding of the structure–performance relationship of PA-TFC membranes for EMPs separations, which would inspire the rational construction and structural regulation of high-performance membranes for new pollutants removal.

Chemical and engineering bases for green H2O2 production and related oxidation and ammoximation of olefins and analogues.

Plastics, fibers and rubber are three mainstream synthetic materials that are essential to our daily lives and contribute significantly to the quality of our lives. The production of the monomers of these synthetic polymers usually involves oxidation or ammoximation reactions of olefins and analogues. However, the utilization of C, O and N atoms in current industrial processes is <80%, which represents the most environmentally polluting processes for the production of basic chemicals. Through innovation and integration of catalytic materials, new reaction pathways, and reaction engineering, the Research Institute of Petroleum Processing, Sinopec Co., Ltd. (RIPP) and its collaborators have developed unique H2O2-centered oxidation/ammoximation technologies for olefins and analogues, which has resulted in a ¥500 billion emerging industry and driven trillions of ¥s' worth of downstream industries. The chemical and engineering bases of the production technologies mainly involve the integration of slurry-bed reactors and microsphere catalysts to enhance H2O2 production, H2O2 propylene/chloropropylene epoxidation for the production of propylene oxide/epichlorohydrin, and integration of H2O2 cyclohexanone ammoximation and membrane separation to innovate the caprolactam production process. This review briefly summarizes the whole process from the acquisition of scientific knowledge to the formation of an industrial production technology by RIPP. Moreover, the scientific frontiers of H2O2 production and related oxidation/ammoximation processes of olefins and analogues are reviewed, and new technological growth points are envisaged, with the aim of maintaining China's standing as a leader in the development of the science and technologies of H2O2 production and utilization.

A review on microfiltration membranes: fabrication, physical morphology, and fouling characterization techniques

Microfiltration is a commonly used pressure-driven membrane separation process for various applications. Depending on the manufacturing method, either tortuous or capillary pore structures are obtained. The structure plays an important role in controlling flux, selectivity, but most importantly, the fouling tendency of the membrane. This review attempts to cover past and current developments in physical morphology and fouling characterization methods, along with the manufacturing methods for microfiltration membranes. The limitations and advantages of direct microscopic techniques and gas-liquid displacement as an indirect method are discussed for physical characterization. Additionally, the current state of the art and technical challenges for various in-situ and ex-situ fouling characterization techniques are also discussed. Finally, some directions for future research are outlined.

Antimicrobial Peptides Increase Line Tension in Raft-Forming Lipid Membranes.

The formation of phase separated membrane domains is believed to be essential for the function of the cell. The precise composition and physical properties of lipid bilayer domains play crucial roles in regulating protein activity and governing cellular processes. Perturbation of the domain structure in human cells can be related to neurodegenerative diseases and cancer. Lipid rafts are also believed to be essential in bacteria, potentially serving as targets for antibiotics. An important question is how the membrane domain structure is affected by bioactive and therapeutic molecules, such as surface-active peptides, which target cellular membranes. Here we focus on antimicrobial peptides (AMPs), crucial components of the innate immune system, to gain insights into their interaction with model lipid membranes containing domains. Using small-angle neutron/X-ray scattering (SANS/SAXS), we show that the addition of several natural AMPs (indolicidin, LL-37, magainin II, and aurein 2.2) causes substantial growth and restructuring of the domains, which corresponds to increased line tension. Contrast variation SANS and SAXS results demonstrate that the peptide inserts evenly in both phases, and the increased line tension can be related to preferential and concentration dependent thinning of the unsaturated membrane phase. We speculate that the lateral restructuring caused by the AMPs may have important consequences in affecting physiological functions of real cells. This work thus shines important light onto the complex interactions and lateral (re)organization in lipid membranes, which is relevant for a molecular understanding of diseases and the action of antibiotics.

Bioethanol production from cassava fed-batch fermentation in pervaporation membrane bioreactor with permeate fractional condensation

A new type pervaporation membrane bioreactor was developed by coupling cassava-based fed-batch fermentation and pervaporation membrane separation technology for bioethanol production. Membrane separation slowed down broth accumulation rate and mitigated ethanol product inhibition. The fermentation time, average sugar consumption rate, ethanol production and ethanol productivity were 131h, 6.6 gL-1h-1, 149.4 gL-1 and 2.5 gL-1h-1, respectively. They were improved by 55.9 %, 73.2 %, 32.3 % and 49.7 %, respectively, compared to those of conventional fed-batch fermentation. The average membrane flux and separation factor were 711.3 gm-2h-1 and 6.5, respectively, with an ethanol concentration of 24.4 wt% in the permeate. Throughout fermentation, the total mass transfer coefficient remained constant at 9.6 × 10-6 ms-1, with the convection mass transfer coefficient decreasing as the broth viscosity increasing while the membrane mass transfer coefficient slightly increasing. A two-stage condensation downstream the membrane achieved fractional vapor recovery. The primary condensate with low ethanol concentration (1.6 wt%) can be used for cassava hydrolyzation, saving 14.0 % of water requirement. Recovering ethanol from the high-concentration (32.6 wt%) secondary condensate required lower energy (46 %) compared to direct recovery from the total permeate.

Exploring the environmental performance of electroless plated palladium alloy membranes for H2 separation: A cradle-to-gate life cycle study

Metal-based membranes have emerged as a promising solution, providing selective permeability and impressive durability. However, a comprehensive understanding of their environmental performance across their entire life cycle remains elusive. This research offers a comprehensive life cycle assessment (LCA) of electroless plated palladium alloy-based membranes for hydrogen separation. It evaluates the environmental impacts across various stages, from the synthesis of supports to the application of intermediate and selective layers. Key findings include the identification of alumina supports and graphite intermediate layers as having minimal environmental impacts, and the Pd–Cu membrane as the most sustainable choice among palladium alloy membranes. This research advances our understanding of the eco-friendly performance of palladium based H2 separation membranes, guiding the development of more sustainable hydrogen separation technologies.

Perfluoroalkyl Functionalized Superhydrophobic Covalent Organic Frameworks for Excellent Oil-Water Membrane Separation and Anhydrous Proton Conduction.

Rapid economic development has led to oil pollution and energy shortage. Membrane separation has attracted much attention due to its simplicity and efficiency in oil-water-separation. The development of membrane materials with enhanced separation properties is essential to improve the separation-efficiency. Proton exchange membrane fuel cells (PEMFCs) are expected to replace conventional engines due to their high-power-conversion rates and other favorable properties. Anhydrous-proton-conductingmaterials are vital components of PEMFCs. However, developing stable proton-conducting materials that exhibit high conductivity at varying temperatures remains challenging. Herein, two covalent organic frameworks (COFs) with long-side-chains are synthesized, and their corresponding COF@SSN membranes. Both membranes can effectively separate oil-water mixtures and water-in-oil emulsions. The TFPT-AF membrane achieves a maximum oil-flux of 6.05×105g h-1 m-2 with an oil-water separation efficiency of above 99%, which is almost unchanged after 20 consecutive uses. COF@H3PO4 doped with different ratios of H3PO4 is prepared, the results show that the perfluorocarbon-chain system has excellent anhydrous proton conductivity, achieving an ultra-high proton-conductivityof 3.98×10-1Scm-1 at 125°C. This study lays the foundation for tailor-made-functionalization of COF through pre-engineering and surface-modification, highlighting the great potential of COFs for oil-water separation and anhydrous-proton-conductivity.

Ultrafiltration membranes for dye wastewater treatment: Utilizing cellulose acetate and microcrystalline cellulose fillers from Ceiba Pentandra

Dye hurts the threat of human health problems and environmental pollution. Microcrystalline cellulose (MCC) based membrane is a good material to be used as an dye separation membrane for having the high hydrophilicity of the membrane. It has been successfully isolated from kapok (ceiba pentandra) with characteristic X-ray diffraction patterns and FTIR absorption peaks, which corresponded to the typical peaks of cellulose. The ultrafiltration membrane was made up of a cellulose acetate matrix created using the phase inversion method. Characterization results indicated that the inclusion of MCC derived from kapok led to a reduction in the contact angle from 65 to 52o, and an increase in membrane porosity from 82 to 85%. In the separation of dye, the composite membrane incorporating MCC filler demonstrated superior performance compared to the membrane lacking MCC, manifesting in an elevated water flux from 43 to 84 L/m².h and methylene blue (MB) rejection from 64 to 99%. The use of MCC as a filler in cellulose acetate membranes can enhance the characteristics and performance of the membrane in MB separation.

Global Trends in the Research and Development of Petrochemical Waste Gas from 1981 to 2022

As a highly energy-intensive and carbon-emitting industry with significant emissions of volatile organic compounds (VOCs), the petroleum and chemical industry is a major contributor to the global greenhouse effect and ozone layer destruction. Improper treatment of petrochemical waste gas (PWG) seriously harms human health and the natural environment. This study uses CiteSpace and VOSviewer to conduct a scientometric analysis of 1384 scholarly works on PWG and carbon sequestration published between 1981 and 2022, revealing the basic characteristics, knowledge base, research topic evolution, and research hotspots of the field. The results show the following: (1) In the early stages of the petrochemical industry, it was processed tail gas, plant leakage waste gas, and combustion flue gas that were investigated in PWG research. (2) Later, green environmental protection technology was widely studied in the field of PWG treatment, such as biotechnology, catalytic oxidation technology, membrane separation technology, etc., in order to achieve efficient, low energy consumption and low emissions of waste gas treatment, and the number of publications related to this topic has increased rapidly. In addition, researchers studied the internet of things and technology integration, such as the introduction of artificial intelligence, big data analysis, and other technologies, to improve the accuracy and efficiency of exhaust gas monitoring, control, and management. (3) The department has focused on how to reduce emissions by optimizing petrochemical process lines or improving energy efficiency. Emission reduction and low-carbon transition in the petrochemical industry will become the main trend in the future. Switching from renewable carbon to feedstock carbon derived from captured carbon dioxide, biomass, or recycled chemicals has become an attractive strategy to help curb emissions from the chemical industry. The results of our analysis can provide funding agencies and research groups with information to better understand the global trends and directions that have emerged in this field from 1981 to 2022 and serve as a reference for future research.

PH controllably induced PPTA/PEMs composite nanofiltration membranes for long-term acid-resistant separation

In this study, we deposited polyelectrolyte multilayers (PEMs) on Poly (p-phenylene terephthamide) (PPTA) ultrafiltration (UF) substrates with strong polyelectrolytes (PEs): polystyrene sulfonic acid (PSS) and poly (diallyldimethylammonium chloride) (PDADMAC). The growth pattern of PEMs was shifted from linear to exponential by changing substrate potential, which was attributed to synergism and antagonism of dispersion of PEs on hydrophilic substrates and electrostatic interaction between PEs and substrates. Eventually, PEMs of layer-dominated and pore-dominated regimes were successfully obtained. We focused on the transition from the pore-dominated to the layer-dominated regime of PEMs. The PEMs nanofiltration (NF) membranes in this situation showed a better separation performance due to the together work of the interface and in-pore energy barriers. The retention rate of Na2SO4 and MgSO4 was 98 % and 91 %. The eosin Y retention rate was 99.9 % and only declined 2 % after 100 h. The hindered deposition of pore-dominated regimes led to denser and thinner layers, which achieved long-term acid resistance. It maintained a stable salt retention after 185 h cross-filtration of 0.1 M H2SO4 feed solution. The performance of PEMs NF membrane was improved from a new perspective, and excellent acid-resistant nanofiltration membranes were obtained, which are expected to be used to treat industrial acidic wastewater.

Rational design of melamine-crosslinked poly(ethylene glycol) membranes for sour gas purification

Natural gas accounts for about a quarter of the world's energy consumption; however, most of the current natural gas reservoirs are sour. Sour natural gas containing significant amounts of hydrogen sulfide (H2S) along with carbon dioxide (CO2) must be purified to meet the strict requirements for transportation and storage in the industry. Sour natural gas purification involves two steps: acid gas removal (AGR) and acid gas enrichment (AGE), which currently use highly energy-intensive technologies. Membrane separation represents the most attractive technology to lower the operating cost and carbon footprint of these large processes. Guided by density functional theory (DFT) calculations, we rationally designed a crosslinked poly(ethylene glycol) (PEG) membrane for AGR and AGE applications. Specifically, PEG-bisazide monomers were crosslinked with a novel trialkyne-functionalized H2S-philic melamine via azide-alkyne cycloaddition click chemistry. The developed membranes were characterized and tested for (H2S + CO2)/CH4 and H2S/CO2 separations under realistic industrial conditions, targeting the AGR and AGE applications, respectively. These novel membranes achieved high H2S permeability while maintaining attractive H2S/CO2 selectivity.

Effect of ceria morphology on hydrogen production via methane steam reforming for membrane reformer

AbstractHydrogen is a potential energy carrier in comparison to conventional fuels due to its high energy content. Methane is an attractive source for ‘on‐site’ production of hydrogen by using membrane reformer due to its low cost. However, such reformers are not well studied and high temperature operation of steam methane reforming (SMR) makes the integration with membrane separation difficult. Further, the main product of SMR is CO and H2 in which CO has an inhibition effect on the membrane separation process. Therefore, it is vital to synthesize a low temperature and low CO selective catalyst for a suitable integration with membrane reformer. Nickel‐based catalyst is widely used for SMR due to its low cost and high catalytic activity. CeO2 is a favoured support as it mobilizes the lattice oxygen and reduces the coke formation and CO selectivity. Though several studies are reported on CeO2 based support, the effect of CeO2 surface morphology is not studied for SMR. In the current work, Ni/CeO2 of different shapes (nanocube and nanorod) are synthesized. The complete characterization of the support was performed. The effect of support shape, calcination temperature, and reduction temperature on SMR activity is found at different operating temperatures. For each condition conversion, CO, CO2 selectivity, and hydrogen yield are calculated. The results show the CeO2 morphology has a considerable effect on conversion, CO selectivity, and hydrogen yield. It is found that ceria nanocube calcined at 550°C provides better performance at high temperature.

Inter-crosslinked spirocyclic mixed matrix membranes exhibiting enhanced gas permeability, selectivity, and plasticization resistance

Poor interfacial compatibility is the most common issue inhibiting performance enhancement in mixed matrix membranes (MMM) for gas and liquid separations. To address this issue, we fabricated highly selective and permeable inter-crosslinked mixed matrix membranes (IcMMMs) based on carboxylic-acid functionalized polymer of intrinsic microporosity-1 (CPIM) containing up to 30 wt % triptycene-isatin polymer porous network (PPN) particles. Polymer-filler inter-crosslinking is accomplished via thermal decarboxylation at 200 °C, which is the lowest temperature this reaction has been found to occur in the literature. This low temperature circumvents potential issues with degradation of porous supports or gutter layer materials, and thus enables these materials to be integrated into traditional membrane processes. The resulting IcMMMs exhibit gel fractions above 90 %. Beyond IcMMMs, membranes based on neat CPIM, thermally crosslinked CPIM, as well as non-crosslinked CPIM-PPN mixed matrix membranes were fabricated to elucidate the individual and synergistic effects of filler inclusion and thermal treatment. In addition to showing upper bound permeability-selectivity performance, IcMMMs also exhibit an almost unprecedented stability against plasticization upon extended exposure to CO2 up to 50 atm or above. This study shows that crosslinking across the polymer-filler interface is the key feature to achieve simultaneous enhancement in permeability, selectivity, and stability. To elucidate the molecular mechanism of these enhancements in the IcMMMs with respect to the baseline materials, permeability was broken into its sorption and diffusion contributions and an energetic analysis of sorption was performed. The low cost of PPNs coupled with the mild crosslinking temperature make this approach highly scalable, resulting in materials exhibiting high rigidity and structural stability with the potential to excel in aggressive separations, such as organic solvent separations or high-CO2 content, high-pressure natural gas sweetening.

Silk fibroin-graphene oxide composite membranes for selective separation of ions and molecules from water

Nanofiltration membranes with controlled pores are useful in many fields, such as pharmaceuticals, desalination, petroleum, and food processing. Recently, graphene oxide has emerged as a promising candidate for the fabrication of highly efficient and pressure-resistant nanofiltration membranes with excellent water permeability and solute rejection. However, it remains difficult to achieve increased permeability while maintaining excellent separation ability. Herein, we report a novel silk fibroin-graphene oxide (FGO) composite membrane prepared by using fibroin as a cross-link reagent, which is extracted from natural Bombyx mori silkworm cocoons. Such a FGO membrane shows a pure water permeance of ∼280 L m−2 h−1 bar−1, which is five times greater than previously reported GO-based membranes. Further, such a membrane also exhibits excellent separation efficiency (> 99 %) for different feed molecules. Additionally, these membranes exhibit high chemical stability in water, acidic and basic solutions for several days compared to pristine GO membranes.