Interfacially polymerized thin film composite membranes containing ethylene oxide groups for CO2 separation

Preparation of a CPVC composite loose nanofiltration membrane based on plant polyphenols for effective dye wastewater treatment

The textile industry's high-salinity wastewater presents a significant difficulty for fractioning salts and dyes. To fractionate the dyes and salts, a high-performance CPVC composite loose nanofiltration membrane (LNM) was fabricated by interfacial polymerization. The organic phase was obtained by crosslinking polyethylenimine (PEI) with tannic acid (TA) and gallic acid (GA) using TMC. The resultant composite LNM performance was enhanced by adjusting the coating parameters, which included TA and GA concentrations as well as coating time. The study examined the effects of the total content of TA/PEI and GA/PEI concentrations on the chemical structure, surface roughness, and microstructure of the selective layer of LNM using SEM, AFM, FTIR, and water contact angle measurements. It also investigated the filtration performance of the membrane's selective layer, including pure water flux, PEG800 rejection rate, and membrane fouling analysis. However, the resultant membrane treated simulated reactive black 5 (RB5) dye wastewater. When the total content of TA/PEI is 4 kg L-1, the permeability of pure water flux is high at 7.5 L per m2 per h per bar when the total content of GA/PEI is 14 kg L-1 and the pure water flux is high at 8.8 L per m2 per h per bar. The overall PEG800 rejection rates were 97-98.98%. The optimal TA : PEI ratios reached a good pure water permeability up to 6.4 L per (m2 per h per bar) with a high rejection rate of 99.69% for a ratio 1/3 to dye, and GA : PEI ratios reached a good water permeability at 5.5 and 6.5 L per (m2 per h per bar) with rejection rates of 99.21% and 98.88% for ratio 1/3 and 3.5/10.5 for simulated RB5 dye, and the NaCl retention rate gradually decreased from 4% to 3%. The resultant LNM demonstrated promising applications in dye and salt fractionation.

Supported Ionic Liquid Membrane with Highly-permeable Polyamide Armor by In Situ Interfacial Polymerization for Durable CO2 Separation

Supported ionic liquid membranes (SILMs), owing to their capacities in harnessing physicochemical properties of ionic liquid for exceptional CO2 solubility, have emerged as a promising platform for CO2 extraction. Despite great achievements, existing SILMs suffer from poor structural and performance stability under high-pressure or long-term operations, significantly limiting their applications. Herein, a one-step and in situ interfacial polymerization strategy is proposed to elaborate a thin, mechanically-robust, and highly-permeable polyamide armor on the SILMs to effectively protect ionic liquid within porous supports, allowing for intensifying the overall stability of SILMs without compromising CO2 separation performance. The armored SILMs have a profound increase of breakthrough pressure by 105% compared to conventional counterparts without armor, and display high and stable operating pressure exceeding that of most SILMs previously reported. It is further demonstrated that the armored SILMs exhibit ultrahigh ideal CO2/N2 selectivity of about 200 and excellent CO2 permeation of 78 barrers upon over 150 h operation, as opposed to the full failure of CO2 separation performance within 36 h using conventional SILMs. The design concept of armor provides a flexible and additional dimension in developing high-performance and durable SILMs, pushing the practical application of ionic liquids in separation processes.

Membrane Separation Technology in Direct Air Capture

Direct air capture (DAC) is an emerging negative CO2 emission technology that aims to introduce a feasible method for CO2 capture from the atmosphere. Unlike carbon capture from point sources, which deals with flue gas at high CO2 concentrations, carbon capture directly from the atmosphere has proved difficult due to the low CO2 concentration in ambient air. Current DAC technologies mainly consider sorbent-based systems; however, membrane technology can be considered a promising DAC approach since it provides several advantages, e.g., lower energy and operational costs, less environmental footprint, and more potential for small-scale ubiquitous installations. Several recent advancements in validating the feasibility of highly permeable gas separation membrane fabrication and system design show that membrane-based direct air capture (m-DAC) could be a complementary approach to sorbent-based DAC, e.g., as part of a hybrid system design that incorporates other DAC technologies (e.g., solvent or sorbent-based DAC). In this article, the ongoing research and DAC application attempts via membrane separation have been reviewed. The reported membrane materials that could potentially be used for m-DAC are summarized. In addition, the future direction of m-DAC development is discussed, which could provide perspective and encourage new researchers' further work in the field of m-DAC.

Polyvinyl alcohol and aminated cellulose nanocrystal membranes with improved interfacial compatibility for environmental applications

Biogas up-gradation is a useful method to control CO₂ emission and enhance the green process. The demand for renewable sources is increasing due to the depletion of fossil fuels. Thin-film nanocomposites functionalized with tunable molecular-sieving nanomaterials have been employed to tailor membranes with enhanced permeability and selectivity. In this work, the cellulose nanocrystals as a filler in the polyvinyl alcohol matrix are prepared to achieve high-performance facilitated transport membranes for CO₂ capture. Considering the mechanical stability, interfacial compatibility and high moisture uptake of the filler, the main objective of this work was to develop a novel aminated CNC (Am-CNC)/polyvinyl alcohol nanocomposite membrane for biogas upgrading. The hydroxyl groups (O-H) on the reducing end of the cellulose nanocrystals were replaced by amino groups (N-H₂). It was discovered through Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) that adding Am-CNCs in PVA membranes shows an increment in the CO₂ removal and effectively upgrades the biogas. The effect of change in concentration of Am-CNC and feed pressure was investigated. The results showed that with increasing Am-CNC concentration up to 1.5 wt%, the thickness of the selective membrane layer increased from 0.95 to 1.9 μm with a decrease in the moisture uptake from 85.04 to 58.84%. However, the best CO₂ permeance and selectivity were achieved at 0.306 m³/m².bar.h (STP) and 33.55, respectively. Furthermore, there was a more than two-fold decrease in CO₂ permeance and a 27% decrease in the CO₂/CH₄ selectivity when the feed pressure increased from 5 to 15 bar. It was revealed that PVA/Am-CNC membrane is high performing for the biogas upgradation.

Polymeric composite membranes in carbon dioxide capture process: a review

Carbon dioxide (CO₂) emission to the atmosphere is the prime cause of certain environmental issues like global warming and climate change, in the present day scenario. Capturing CO₂ from various stationary industrial emission sources is one of the initial steps to control the aforementioned problems. For this concern, a variety of resources, such as liquid absorbents, solid adsorbents, and membranes, have been utilized for CO₂ capturing from various emission sources. Focused on membrane-based CO₂ capture, polymeric membranes with composite structure (polymeric composite membrane) offer a better performance in CO₂ capturing process than other membranes, due to the composite structure it offers higher gas flux and less material usage, thus facile to use high performed expensive material for membrane fabrication and achieved good efficacy in CO₂ capture. This compressive review delivers the utilization of different polymeric composite membranes in CO₂ capturing applications. Further, the types of polymeric materials used and the different physicochemical modifications of those membrane materials and their CO₂ capturing ability are briefly discussed in the text. In conclusion, the current status and possible perspective ways to improve the CO₂ capture process in industrial CO₂ gas separation applications are described in this review.

Network Structure Engineering of Organosilica Membranes for Enhanced CO2 Capture Performance

The membrane separation process for targeted CO2 capture application has attracted much attention due to the significant advantages of saving energy and reducing consumption. High-performance separation membranes are a key factor in the membrane separation system. In the present study, we conducted a detailed examination of the effect of calcination temperatures on the network structures of organosilica membranes. Bis(triethoxysilyl)acetylene (BTESA) was selected as a precursor for membrane fabrication via the sol-gel strategy. Calcination temperatures affected the silanol density and the membrane pore size, which was evidenced by the characterization of FT-IR, TG, N2 sorption, and molecular size dependent gas permeance. BTESA membrane fabricated at 500 °C showed a loose structure attributed to the decomposed acetylene bridges and featured an ultrahigh CO2 permeance around 15,531 GPU, but low CO2/N2 selectivity of 3.8. BTESA membrane calcined at 100 °C exhibited satisfactory CO2 permeance of 3434 GPU and the CO2/N2 selectivity of 22, displaying great potential for practical CO2 capture application.

Tailoring the CO2-selectivity of interfacial polymerized thin film nanocomposite membrane via the barrier effect of functionalized boron nitride

Membrane-based separation is an appealing solution to mitigate CO₂ emission sustainably due to its energy efficiency and environmental friendliness. Attributed to its excellent separation endowed by nanomaterial incorporation, nanocomposite membrane is rigorously developed. This study explored the feasibility of boron nitride (BN) embedment and changes to formation mechanism of ultrathin selective layer of thin film nanocomposite (TFN) are investigated. The effects of amine-functionalization on nanosheet-polymer interaction and CO₂ separation performance are also identified. Participation of nanosheets during interfacial polymerization reduced the crosslinking of selective layer, hence, improved TFN permeance while the formation of contorted diffusion paths by the nanosheets favors transport of small gases. Amine-functionalization enhanced the nanosheet-polymer interaction and elevated the membrane affinity towards CO₂ which led to enhanced CO₂ selectivity. The best TFN prepared in this study exhibited 37% and 20% increment in permeability and selectivity, respectively with respect to neat thin film composite (TFC). It is found that the CO₂ separation performance of BN incorporated TFN is on par with many non-porous nanosheet-incorporated TFNs reported in literatures. The transport and barrier effects of BN and functionalized BN are discussed in detail to provide further insights into the development of commercially attractive CO₂ selective TFN membranes.

Millisecond lattice gasification for high-density CO2- and O2-sieving nanopores in single-layer graphene

Etching single-layer graphene to incorporate a high pore density with sub-angstrom precision in molecular differentiation is critical to realize the promising high-flux separation of similar-sized gas molecules, e.g., CO₂ from N₂ However, rapid etching kinetics needed to achieve the high pore density is challenging to control for such precision. Here, we report a millisecond carbon gasification chemistry incorporating high density (>10¹² cm^-2) of functional oxygen clusters that then evolve in CO₂-sieving vacancy defects under controlled and predictable gasification conditions. A statistical distribution of nanopore lattice isomers is observed, in good agreement with the theoretical solution to the isomer cataloging problem. The gasification technique is scalable, and a centimeter-scale membrane is demonstrated. Last, molecular cutoff could be adjusted by 0.1 Å by in situ expansion of the vacancy defects in an O₂ atmosphere. Large CO₂ and O₂ permeances (>10,000 and 1000 GPU, respectively) are demonstrated accompanying attractive CO₂/N₂ and O₂/N₂ selectivities.

CO2 capture using membrane contactors: a systematic literature review

With fossil fuel being the major source of energy, CO2 emission levels need to be reduced to a minimal amount namely from anthropogenic sources. Energy consumption is expected to rise by 48% in the next 30 years, and global warming is becoming an alarming issue which needs to be addressed on a thorough technical basis. Nonetheless, exploring CO2 capture using membrane contactor technology has shown great potential to be applied and utilised by industry to deal with post- and pre-combustion of CO2. A systematic review of the literature has been conducted to analyse and assess CO2 removal using membrane contactors for capturing techniques in industrial processes. The review began with a total of 2650 papers, which were obtained from three major databases, and then were excluded down to a final number of 525 papers following a defined set of criteria. The results showed that the use of hollow fibre membranes have demonstrated popularity, as well as the use of amine solvents for CO2 removal. This current systematic review in CO2 removal and capture is an important milestone in the synthesis of up to date research with the potential to serve as a benchmark databank for further research in similar areas of work. This study provides the first systematic enquiry in the evidence to research further sustainable methods to capture and separate CO2.

Applications of tannic acid in membrane technologies: A review

Today, membrane technologies play a big role in chemical industry, especially in separation engineering. Tannic acid, one of the most famous polyphenols, has attracted widespread interest in membrane society. In the past several years, researches on the applications of tannic acid in membrane technologies have grown rapidly. However, there has been lack of a comprehensive review for now. Here, we summarize the recent developments in this field for the first time. We comb the history of tannic acid and introduce the properties of tannic acid firstly, and then we turn our focus onto the applications of membrane surface modification, interlayers and selective layers construction and mixed matrix membrane development. In those previous works, tannic acid has been demonstrated to be capable of making a great contribution to the membrane science and technology. Especially in membrane surface/interface engineering (such as the construction of superhydrophilic and antifouling surfaces and polymer/nanoparticle interfaces with high compatibility) and development of thin film composite membranes with high permselectivity (such as developing thin film composite membranes with ultrahigh flux and high rejection), tannic acid can play a positive and great role. Despite this, there are still many critical challenges lying ahead. We believe that more exciting progress will be made in addressing these challenges in the future.

Rational Design of Halloysite Surface Chemistry for High Performance Nanotube-Thin Film Nanocomposite Gas Separation Membranes

The interfacial region has a critical role in determining the gas separation properties of nanofiller-containing membranes. However, the effects of surface chemistry of nanofillers on gas separation performance of thin film nanocomposite (TFN) membranes, prepared by the interfacial polymerization method, have been rarely studied in depth. In this work, pristine and three differently surface-modified halloysite nanotubes (HNTs), by non- (SHNT), moderately (ASHNT), or highly CO₂-philic (SFHNT) agents, are embedded in the polyamide top layer of thin film nanocomposite (TFN) membranes for CO₂/N₂ and CO₂/CH₄ separations. Trimethoxyoctyl silane, 3-(2-aminoethylaminopropyl)trimethoxysilane, and poly(styrenesulfonic acid) are used as modifying agents to quantitatively investigate the effects of interfacial interactions between the polyamide and HNTs on the gas permeation of TFNs. This allows us to provide an interfacial design strategy to fabricate high-performance gas separation membranes. Pure gas permeations conducted on the TFNs at the feed gas pressure of 10 bar showed that CO₂ permeance and CO₂/N₂ and CO₂/CH₄ selectivities were increased by 145%, 130%, and 108%, respectively, after addition of 0.05 w/v% of sulfonated HNTs. The experimental gas permeations through all TFNs/HNTs, except TFNs/SFHNTs, agree well with predictions of a recently developed model, which suggests the importance of considering the neglected role of CO₂ interactions with the HNT/polyamide interface in the model. These results unambiguously proved that designing the interfacial layer thickness in the nanotube-containing membranes is an effective approach to tuning the gas separation properties. The results show that the dispersion of HNTs in the polyamide top layer and the experimental CO₂/gas selectivity was increased with increasing interfacial thickness, a_int, upon surface modification. Moreover, it is quantitatively demonstrated that the thickness of the interfacial layer between the filler and polymer matrix is a function of gas pressure applied on the membrane.

Polyamide nanofilms synthesized via controlled interfacial polymerization on a "jelly" surface

A thermal-sensitive "jelly" was used to control the diffusion of a diamine monomer for synthesizing polyamide free-standing nanofilms with an adjustable thickness of 5-35 nm. The reduced reaction rate of the interfacial polymerization at the hexane-"jelly" interface made the synthesized nanofilms show high water permeation flux and suitable salt rejection, and they also have highly negative surface charges and fairly smooth surfaces.

Development of high-performance mixed matrix reverse osmosis membranes by incorporating aminosilane-modified hydrotalcite

Thin film nanocomposite (TFN) reverse osmosis (RO) membranes were prepared by dispersing 3-aminopropyltriethoxysilane (APTES) modified hydrotalcite (HT), designated as A-HT, in aqueous solution and incorporating the nanoparticles in polyamide layers during the interfacial polymerization process. Results of Fourier transform infrared spectroscopy and zeta potential characterization showed the successful modification of nanoparticles by APTES. In addition, Fourier transform infrared spectroscopy suggested that amidation would take place between the aminosilane on APTES and trimesoyl chloride in organic solution, providing firm covalent interaction between the nanoparticles and polyamide matrix. Dynamic light scattering and transmission electron microscopy indicated that aminosilane modification improved dispersibility of the nanoparticles in aqueous solution and obtained membranes, which suppressed the aggregation. Both the covalent interaction and aggregation suppression were beneficial to compatibility between nanoparticles and the polyamide matrix. TFN RO membranes incorporated with A-HT demonstrated excellent performance. Compared with the pristine RO membrane, the water flux of A-HT-0.050 prepared with an optimum A-HT concentration of 0.050 wt% was enhanced by 18.6% without sacrificing the salt rejection. Moreover, the selectivity of A-HT-0.050 was superior to that of HT-0.050 prepared with HT of 0.050 wt%, which proved aminosilane modification of hydrotalcite was beneficial to high membrane performance especially to selectivity.

Thin film nanocomposite reverse osmosis membranes were prepared by dispersing 3-aminopropyltriethoxysilane modified hydrotalcite in aqueous solution and incorporating the nanoparticles in polyamide layer during interfacial polymerization process.

Incorporating a silicon unit into a polyether backbone—an effective approach to enhance polyether solubility in CO2

A series of poly(silyl ether)s were prepared by condensation polymerization and hydrosilation polymerization through incorporating a silicon unit into a polyether backbone.

High-performance multilayer composite membranes with mussel-inspired polydopamine as a versatile molecular bridge for CO2 separation

It is desirable to develop high-performance composite membranes for efficient CO2 separation in CO2 capture process. Introduction of a highly permeable polydimethylsiloxane (PDMS) intermediate layer between a selective layer and a porous support has been considered as a simple but efficient way to enhance gas permeance while maintaining high gas selectivity, because the introduced intermediate layer could benefit the formation of an ultrathin defect-free selective layer owing to the circumvention of pore penetration phenomenon. However, the selection of selective layer materials is unfavorably restricted because of the low surface energy of PDMS. Various highly hydrophilic membrane materials such as amino group-rich polyvinylamine (PVAm), a representative facilitated transport membrane material for CO2 separation, could not be facilely coated over the surface of the hydrophobic PDMS intermediate layer uniformly. Inspired by the hydrophilic nature and strong adhesive ability of polydopamine (PDA), PDA was therefore selected as a versatile molecular bridge between hydrophobic PDMS and hydrophilic PVAm. The PDA coating endows a highly compatible interface between both components with a large surface energy difference via multiple-site cooperative interactions. The resulting multilayer composite membrane with a thin facilitated transport PVAm selective layer exhibits a notably enhanced CO2 permeance (1887 GPU) combined with a slightly improved CO2/N2 selectivity (83), as well as superior structural stability. Similarly, the multilayer composite membrane with a hydrophilic CO2-philic Pebax 1657 selective layer was also developed for enhanced CO2 separation performance.