Membrane Separation Research Articles

Is Pt dissolution a concern from the counter electrode in electrochemical oxygen evolution reaction?

The Pt metal and its oxides dissolution from the counter electrode (CE, in hydrogen evolution reaction (HER)) has been suspected to affect the non-noble metal catalysts toward oxygen evolution reaction (OER). However, little effort has been devoted to this concern, and this work aims to determine the effect. The influence of electrolytes (H2SO4 and NaOH) and Pt CE (acid-treated and pristine) on the Pt dissolution and membrane separations (Nafion and PiperION) on preventing Pt species migration were evaluated. The results indicate only 11.2 ppb Pt from the cathodic electrolyte with Nafion 211 and 5 M NaOH electrolyte is observed, and no Pt is found from all other samples with acid-treated Pt CE. Regarding pristine Pt CE, 0.4 and 4.4 ppb Pt are observed from 0.5 M H2SO4 and 5 M NaOH electrolytes, respectively. The findings in this work include: (1) Nafion membrane can effectively prevent the migration of Pt species from the cathode to the anode side; (2) a simple acid treatment of Pt could minimize the Pt dissolution into the acid electrolyte while showing an opposite role in the alkaline electrolyte; (3) the Pt dissolution from all experiments is minor, indicating Pt is a suitable CE for OER.

Trifunctionalized Ionic Covalent Organic Framework-Engineered Mixed-Matrix Membranes for Rapid and High-Performance Adsorptive Separation of Charged Aqua Pollutants

Trifunctionalized Ionic Covalent Organic Framework-Engineered Mixed-Matrix Membranes for Rapid and High-Performance Adsorptive Separation of Charged Aqua Pollutants

Dual defense against membrane fouling for efficient and sustainable oil/water separation on a novel super-hydrophilic/underwater superoleophobic and catalytic nanofibrous membrane

Membrane separation technology is widely recognized as an efficient method for treating organically polluted wastewater in virtue of high performance and straightforward operation. However, the practical application of membranes is inevitably confronted with contamination issues, presenting a major challenge in terms of fouling resistance. To address this issue, a defensive-offensive dual-defense strategy based on wettability and catalytic ability control is proposed. With this concept, a novel nanofibrous membrane with a unique structure was successfully prepared through polyacrylonitrile (PAN) electrospinning, pre-oxidation, CoFe Prussian blue analogue (PBA) and polypyrrole (PPy) modification, and calcination processes. For the passive defense mode, the as-prepared membrane has shown good underwater-superoleophobicity for various types of oils, good separation capability for corresponding oil–water emulsions with retention ratios of above 99 % and fluxes ranging from 231.5 to 1524.2 L·m−2·h−1·bar−1, as well as organic solvent (dimethylformamide, DMF) resistance. For the offensive defense mode, this membrane exhibits well catalytic degradation performance for refractory pollutants with the assistance of peroxymonosulfate (PMS), which is due to the membrane being decorated with catalytic nanoparticles that contain abundant encapsulated ultra-small Fe doped Co3O4 (∼2.28 nm), and that is much smaller than the size of the pristine PBA (∼33.8 nm). Notably, the surfactants present in oil-in-water emulsions are found to be the main cause of membrane fouling, where the cationic surfactants exhibit the most significant fouling effect, while the introduction of photo-Fenton-like catalysis can endow the membrane with excellent antifouling performance and extended service life, and nearly a fully recover of emulsion separation performance was achieved. Overall, this work paves pathways to the design of advanced membranes for sustainable wastewater treatment.

Pentahomoserine functionalized graphene oxide decorated polyamide thin film for enhanced separation of green tea polyphenols

The isolation of valuable compounds from the byproducts of food processing industries presents a significant contemporary challenge. Thin film nanocomposite (TFN) membranes have been identified as potential media for separating bioactive compounds. In this work, pentahomoserine functionalized graphene oxide (FGO) based TFN membranes were prepared for the effective separation of tea polyphenols epigallocatechin (EGC) and epigallocatechin gallate (EGCG). The nanocomposite selective polyamide (PA) layer was prepared through the dispersion of FGO in an aqueous monomer solution. The prepared membranes possess high average surface roughness with improved hydrophilicity and thermal stability. Additionally, FGO membranes contain more hydroxyl or carboxyl groups with cross-linked PA layer through interfacial polymerization (IP) process. Moreover, FGO membranes featured increased hydroxyl or carboxyl groups, facilitating cross-linking with the PA layer via intermolecular forces. The effects of amine functionality on the membrane characteristics such as surface morphology, roughness and hydrophilicity were also investigated. Remarkably, the membranes demonstrated rejection efficiency of 96.3% towards polyphenols. Furthermore, comprehensive assessments of reusability performance of the membrane highlighted their potential for industrial applications. This study provides valuable insights into the fabrication of highly efficient TFN membranes for biomolecule separation across diverse technological domains.

High-Performance Polyimide CO2 Separation Membrane Prepared by Zn(II) Coordination Cross-Linking

High-Performance Polyimide CO₂ Separation Membrane Prepared by Zn(II) Coordination Cross-Linking

Development of high hydrogen permselective membranes by using a vapor treatment method

Abstract In recent years, the depletion of energy resources and global warming have led to the promotion of new energy resources. Hydrogen is attracting attention as one of the energy sources for the carbon-neutral society by 2050. Membrane separation is a method for separating and purifying hydrogen. In this study, we focused on developing high hydrogen permselectivity of silica membranes. We investigated the conditions necessary for membrane production to obtain a thin, dense separation layer. The results exhibited that the hydrogen permeation selectivity was enhanced in the silica membrane through the utilization of a 2-step deposition technique, which involves the combination of alternative feed and counter-diffusion chemical vapor deposition (CVD). The H2 permeance achieved by the 2-step method is 1.4×10−6 [mol m−2 s−1 Pa−1], representing 1.4 times higher than that of counter-diffusion CVD. In addition, the permeance ratio, which represents hydrogen selectivity, was significantly enhanced with the 2-step method, with H2/C3H8 = 260, twice as high as with CVD. Elemental mapping analysis of the cross-sectional structure revealed a concentration gradient in the deposited silica within the intermediate layer. This indicates that the silica separation layer may become an asymmetric structure. The 2-step method is expected to yield a thinner dense layer, which could contribute to improved permeance of silica separation membranes by reducing permeation resistance.

Techno-Economic Analysis of Hydrogen Generation in Hydrocarbon Reservoirs

Summary To reduce carbon emissions and meet increasing energy demands, efforts are being made to seek clean energy such as hydrogen (or H2). Currently, the dominant method to generate hydrogen is steam methane reforming at a surface plant. It would be ideal to extend this method to subsurface hydrocarbon reservoirs; hydrogen is separated from the other generated gases via a downhole hydrogen-selective membrane separator. By doing so, hydrogen is extracted from the wellhead, and other gases are left in the reservoir. The purpose of this paper is to provide a techno-economic analysis of this idea. The energy of generated hydrogen is compared with the energy of the hydrocarbon feedstock. The hydrogen selectivity (concentration) in the generated synthesis gas (syngas) and the amount of hydrogen generated per unit mass of oil in the literature are reviewed and discussed. The constraints to the hydrogen generation conditions in subsurface reservoirs are discussed. The effectiveness of the downhole membrane is discussed. It is found that the energy from generated hydrogen is much less than the energy input even in a surface reactor where reactants are fully mixed for reactions. In a subsurface reservoir, injected reactants cannot fully mix with the in-situ oil and gas, and reactions may occur only near the flood-front zone of a high temperature. As injected gas (such as steam or oxygen) displaces the oil and gases ahead, the produced hydrocarbons are much higher than hydrogen. Separation of hydrogen from other gases downhole presents challenges in many aspects in reality, such as membrane permeability or separation rate, work life (mechanical and chemical stability), and so on. Therefore, unless a revolutionary technology breakthrough occurs, the generation and production of hydrogen in a subsurface hydrocarbon reservoir may not be feasible.

Universal solution to the membrane selectivity challenge: Separation merit and efficiency

Membrane technology holds immense potential across multiple industries, offering sustainable solutions for challenging separations by reducing energy demand and transitioning from thermal to electrical energy. The inherent diversity of membrane technology results in various transport scenarios and phenomena, rendering robust process evaluation and optimization challenging. Addressing this problem, we formulate the cascading selectivity principle (CSP), a universal concept applicable across all membrane separation types, including gas, liquid, and particle filtration. Introducing a distinction between primary and secondary permselectivity, the CSP provides a theoretical basis for novel efficiency indices. We also present the first highly versatile selectivity merit descriptors for true membrane cross-comparison. We demonstrate the advantages of the novel descriptors through a series of real-life nanofiltration, ion separation, gas separation, membrane reactor, and ultrafiltration examples. Facilitated by an online calculator tool, this work offers a standardized framework for academic and industrial professionals to implement pioneering membrane separation systems efficiently across the multiple disciplines of membrane technology.

Alkaline composite inorganic membrane for high temperature carbon dioxide separation

Abstract The development of carbon dioxide separation and capture technologies is necessary to achieve a carbon-neutral society. Focusing on Direct Air Capture (DAC), a technology for the direct capture of carbon dioxide from the atmosphere. Although Li4SiO4-based membranes have been reported as a separation membrane development using alkali ceramics, the carbon dioxide desorption temperature of Li4SiO4 is high, around 700°C. To use it for CO2 methanation and methanolation reactions, it’s necessary to develop separation membranes for m-DAC using materials that can desorb CO2 at around 300°C. This hasn’t yet been considered. Therefore, the aim of this study was to develop an effective alkaline adsorbent for CO2 recovery that absorbs and desorbs CO2 at around 300°C. Membranes with Na2CO3 supported on an α-Al2O3 substrate showed a permeability of 3.58 x 10−10 [mol m−2 s−1 Pa−1] for N2 and 3.93 x 10−10 [mol m−2 s−1 Pa−1] for CO2 after two coatings, which is selective for CO2. However, the membranes didn’t show CO2 adsorption and the substrate broke after three coatings, suggesting that the α-Al2O3 substrate was alkali-sensitive and that the thermal decomposition of Na2CO3 wasn’t advanced.

Hydrogen permselective membrane prepared by plasma treatment of porous ceramic substrates

Abstract Demand for hydrogen is increasing as we move toward a decarbonized society. Membrane separation methods have attracted attention as a way to reduce the cost of hydrogen production. In this study, we focused on boron nitride (BN) as a chemically stable porous substrate material. CVD treatment at 250°C has been investigated for porous BN, but selectivity did not develop. Therefore, we focused on atmospheric pressure plasma as a treatment method. The objective of this study is to develop a membrane with high hydrogen selective permeance by immersion in silicon alkoxide after plasma treatment. After plasma treatment for 100 s, the H2 permeance was 3.52×10−6 [mol m−2 s−1 Pa−1] and the H2/N2 permeance ratio was 18.25. Since molecular hydrogen can pass between the BN crystal faces, it is considered that silica reacted with the hydroxy groups formed on BN by plasma treatment and blocked the space between crystals. Therefore, it is suggested that the performance of the separation membrane changes depending on the number and distribution of hydroxyl groups by plasma treatment, and further stabilization is needed.

Optimizing the separation process for improved zirconia molding through liquid crystal display 3D printing

Mask stereolithography 3D printing for zirconia ceramics has attracted increasing attention in the industrial manufacturing due to their advantages of complex shapes, precisely controlled internal structures and fine surface effects. However, high refractive index and expensive equipment cost have always affected its development. Herein, we combine liquid crystal display (LCD) light curing 3D printing with zirconia molding, which is free from environmental and price limitations. In the conventional method of operation, the cured layer is bonded to the bottom and cannot be manufactured. We put forward a strategy for optimizing separation process and investigate the mechanism of the separation process in depth for high-quality zirconia ceramics LCD 3D printing. The results show that the controlled adjustment of the surface free energy can achieve a great reduction in the separation force, which enabled the successful printing of zirconia ceramics based on LCD. The effect of physical properties of the separation membrane on the separation process was studied and the solid content and 3D printing parameters of ceramic paste were optimized. When the solid content is 72.5 wt%, high quality zirconia ceramic parts with flexural strength of 255 MPa and relative density of 98.1 % can be obtained. This work provides new ideas for the convenient customization of zirconia ceramics in many fields.

Construction of CS-SDAEM long-chain polysaccharide derivative on TA@CNTs coated PVDF membrane with effective oil-water emulsion purification and low contamination rate

Currently, the most effective way to improve the anti-fouling performance of water treatment separation membrane is to enhance the hydrophilicity of the membrane surface, but it can still cause contamination, leading to the occurrence of flux reduction. The construction of a strong hydration layer to resist wastewater contamination is still a challenging task. In this study, a defect-free hydration layer barrier was achieved by grafting chitosan polysaccharide derivatives (CS-SDAEM) on the membrane, which achieved in effective fouling prevention and low flux decline rate. A layer of tannic acid-coated carbon nanotubes (TA@CNTs) has been uniformly deposited on the commercial PVDF membrane so that the surface was rich in -COOH groups, providing sufficient reaction sites. These reactive groups facilitate the grafting of amphiphilic polymers onto the membrane. This modification strategy achieved in enhancing the antifouling performance. The modified membrane achieved low contamination rate with DR of 16.9 % for wastewater filtration, and the flux recovery rate was above 95 % with PWF of 1100 (L·m−2·h−1). The membrane had excellent anti-fouling performance, which provided a new route for the future development of water treatment membrane.

Biological measures to recover nitrogen compounds from liquid and solid streams

Several studies have explored nitrogen recovery from waste streams, focusing on technologies and approaches like electrochemical processes and membrane separation. However, these approaches need to become economically feasible and reliable. The feasibility of recovery processes is strongly influenced by the concentration of nitrogen, which is an important technical challenge in nitrogen recovery. Biological approaches, such as the cultivation of microalgae as well as constructed wetlands, are in focus for addressing nitrogen concentration steps. These approaches allow the conversion of nitrogen compounds into proteins for various applications. The aim of this study was not to review treatment processes to avoid negative environmental consequences but to highlight technologies that allow the concentration, recovery, and circulation of nitrogen compounds.

Correction to “A Rapid and Facile Preparation of PVDF–PG/KH550 Bioinspired Membrane for Efficient Separation of Oil-in-Water Emulsions”

Correction to “A Rapid and Facile Preparation of PVDF–PG/KH550 Bioinspired Membrane for Efficient Separation of Oil-in-Water Emulsions”

Preparation, characterization and applications of polyethersulfone/bentonite clay composite for protein removal

In the current work, asymmetric polyethersulfone/bentonite clay nanocomposite (PES/BNT) membranes with differing clay dosages were successfully prepared by the phase inversion method aimed at protein separation. Means of characterization tools were harnessed to validate the fabrication process. The morphology and structure of membranes were examined by scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FTIR) while additional surface properties such as pore size, porosity and hydrophilicity measurements were assessed. The permeability-selectivity trade-off of the membranes were assessed to probe the influence of additive content on the ultimate membrane functionality. The results indicated that best membrane performance was achieved with a BNT content of 0.225 g, resulting in enhanced dispersibility within the polymeric matrix. Besides, the inclusion of clay additive led to an increase in pore size ratio in the skin layer, further improving membrane permeability. The optimal membrane exhibited a permeate flux of 20.5 kg.m−2.h−1, while rejected 93 % of bovine serum albumin (BSA). Meanwhile, porosity, pore size and the contact angle measurements have recorded 71.8 %, 22.6 nm and 40.53°, respectively. These findings suggested that the PES/BNT membrane's permeation and separation characteristics, rendering them a viable option for a wide range of water and wastewater treatment applications.

Biomimetic interlayer brought unexpected enhancement in permeability and rejection of polyamide nanofiltration membrane

Construction of interlayer between porous substrate and polyamide (PA) layer has been proved to be an effective way in improving membrane separation performance by the regulation of membrane structure and chemical properties. In present study, biomimetic material—1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) lipid bilayer was selected to serve as the interlayer prepared by suction filtration due to its unique advantages such as smooth, continuous, uniform and hydrophilic surface. The results showed that DOPE interlayer effectively lowered the diffusion rate of piperazine (PIP) from membrane surface to organic phase and thus contributing to the thinner and smoother PA layer. The permeability of the interlayer-based PA membrane reached 35.9 L/m2·h·bar, which was 190 % higher than pure PA NF membranes. More important, the interlayer-based PA membrane exhibited excellent Na2SO4 rejection about 99.8 % accompanied by a good separation selectivity between univalent and bivalent ions. Besides, the interlayer-based PA membrane possessed good stability to the changes of operating pressure, concentration and pH of feed solution, and the long-term NF test. Meanwhile, it performed well in removing NTU, TOC, Mg2+ and SO42− in the treatment of surface water and showed its potential in the practical application. In all, the present work brought new interlayer material in fabricating high-performance NF membrane.

CMPs membranes prepared using electrostatic spinning as a template for efficient oil-water separation

The development of efficient oil-water separation membrane technology is of great important for elimination of the serious environmental pollution issues caused by the frequent oils-spill or organics leakages in modern industry. Herein, we report the creation of conjugated microporous polymer membranes (CMPs@PMMA/PVDF), which were synthesized by a Sonogashira-Hagihara cross-coupling reaction using 1,3,5-triethynylbenzene and 2,6-dibromophenol as monomers in the presence of a template membrane prepared using poly (vinylidene fluoride) and poly (methyl methacrylate) as mixed solution via electrostatic spinning method, for efficient oil-water separation. The as-synthesized CMPs membrane shows excellent hydrophobicity with a water contact angle (WCA) of 150.8º and high permeate flux ( 865.8 L m−2 h−1). The tensile strength of CMPs@PMMA/PVDF was measured to be 3.13 MPa with an elongation of 10.32%. The TGA curve of CMPs@PMMA/PVDF membranes shows high thermal stability with mass loss decreasing by only 15.89% when the temperature rises to 414.3 ºC. Driven by gravity alone, the resulting membrane shows outstanding oil-water selectivity for oil-water separation (with a separation efficiency of up to 99.9%), its separation efficiency almost remains unchanged after 10 cycles with cyclohexane as the oil phase, and the separation efficiency still maintains up to 98.9% even after 50 cycles. In addition, the 3D-CMPs membrane also performs well in the separation of oil-water mixtures, and the separation efficiencies of various water-in-oil mixtures are maintained above 98.6% after ten cycles, showing that the CMPs membrane materials may have great potential for a broad application in the field of separation of oil-water mixtures.

Joint experimental-computational: Revealing the role of sodium poly(heptazineimide) in the selective separation of CO2 in PEBAX-based mixed matrix membranes

Mixed matrix membranes (MMMs) with the dual properties of porous materials and polymer matrix membranes have become one of the most optimal solutions to the gas separation problem. However, the adapted porous material and the explicit transport mechanism of gases within the mixed matrix membrane hinder its further commercialization. Thanks to their porous nature and tunable gas adsorption properties, heteroatom-doped porous materials, especially nitrogen-doped porous materials, are widely used to design and prepare advanced CO2 separation membranes. Herein, a layered two-dimensional nano-sheet with a nitrogen content of 44.7 % was successfully synthesized via thermal polymerization. And nano-sheets were homogeneously dispersed in a Pebax matrix to make a composite film. Since the CO2 affinity of the nitrogen functional site and the PEO flexible chain, realizing the synergistic improvement of CO2 permeability and selectivity. A comprehensive combined permeation experimental/simulation characterization reveals the CO2 transport pathway within the membrane, indicating the mechanism of action of nitrogen-doped porous packing on CO2 diffusion. Among these, the CO2 permeability of the mixed matrix film containing 5 wt% sodium poly(heptazine imide) (NaPHI) reached 153 Barrer at a feed gas pressure of 9 bar, nearly 149 % compared to the pure Pebax film. The selectivity of CO2/N2 was enhanced to 105, exhibiting a remarkable increase of 159 % and exceeding the 2019 Robeson limit. Importantly, the present work further reveals and demonstrates the gas separation mechanism of nitrogen-doped porous filler/polymer hybrid matrix membranes, which provides new ideas for the design and application of heteroatom-doped porous fillers in the field of gas separation.

Application of physicochemical techniques to the removal of ammonia nitrogen from water: a systematic review.

Ammonia nitrogen is a common pollutant in water and soil, known for its biological toxicity and complex removal process. Traditional biological methods for removing ammonia nitrogen are often inefficient, especially under varying temperature conditions. This study reviews physicochemical techniques for the treatment and recovery of ammonia nitrogen from water. Key methods analyzed include ion exchange, adsorption, membrane separation, struvite precipitation, and advanced oxidation processes (AOPs). Findings indicate that these methods not only remove ammonia nitrogen but also allow for nitrogen recovery. Ion exchange, adsorption, and membrane separation are effective in separating ammonia nitrogen, while AOPs generate reactive species for efficient degradation. Struvite precipitation offers dual benefits of removal and resource recovery. Despite their advantages, these methods face challenges such as secondary pollution and high energy consumption. This paper highlights the development principles, current challenges, and future prospects of physicochemical techniques, emphasizing the need for integrated approaches to enhance ammonia nitrogen removal efficiency.

Congo red stitched covalent organic framework membrane for dye separation

Covalent organic framework (COF) membranes have shown great potential in dyes’ separation. However, COFs are difficult to form large-area and highly crystalline membranes, therefore there normally exists crystal and stacking defects in COF membranes, impairing their rejection performance. Herein, we discovered the prepared COF-TATP membranes have exceptional high rejection to Congo red (CR) solution. Further study showed the presence of small proportion of CR in other dye solutions also could enhance the rejection to those dyes. 3:100 CR/Brilliant blue R250 (BB) solution could obtain 99.81% rejection to BB. Characterizations indicated CR molecules could well merged into the COF layer and strongly bonded with its N/O groups via plentiful hydrogen bonds. Inspired by the finding, we proposed a strategy of using CR to stitch the defects in COF layer. Specifically, CR was embedded into and then chemically crosslinked with COF-TATP layer by glutaraldehyde to prepare LCR-TATP-NH2CS/nylon membranes. The membranes showed obviously enhanced rejection to all dyes tested, typically BB rejection of 99.75%. It also could selectively separate BB/Methyl orange mixed solutions. This study reveals some insights into dyes’ behavior on COF membranes, and provides a simple and feasible strategy for stitching COF membranes’ defects to enhance their performance.