Mixed Matrix Membranes for Carbon Capture and Sequestration: Challenges and Scope

Carbon dioxide (CO₂) is a major greenhouse gas responsible for the increase in global temperature, making carbon capture and sequestration (CCS) crucial for controlling global warming. Traditional CCS methods such as absorption, adsorption, and cryogenic distillation are energy-intensive and expensive. In recent years, researchers have focused on CCS using membranes, specifically solution-diffusion, glassy, and polymeric membranes, due to their favorable properties for CCS applications. However, existing polymeric membranes have limitations in terms of permeability and selectivity trade-off, despite efforts to modify their structure. Mixed matrix membranes (MMMs) offer advantages in terms of energy usage, cost, and operation for CCS, as they can overcome the limitations of polymeric membranes by incorporating inorganic fillers, such as graphene oxide, zeolite, silica, carbon nanotubes, and metal-organic frameworks. MMMs have shown superior gas separation performance compared to polymeric membranes. However, challenges with MMMs include interfacial defects between the polymeric and inorganic phases, as well as agglomeration with increasing filler content, which can decrease selectivity. Additionally, there is a need for renewable and naturally occurring polymeric materials for the industrial-scale production of MMMs for CCS applications, which poses fabrication and reproducibility challenges. Therefore, this research focuses on different methodologies for carbon capture and sequestration techniques, discusses their merits and demerits, and elaborates on the most efficient method. Factors to consider in developing MMMs for gas separation, such as matrix and filler properties, and their synergistic effect are also explained in this Review.

Graphene in Polymeric Nanocomposite Membranes—Current State and Progress

One important application of polymer/graphene nanocomposites is in membrane technology. In this context, promising polymer/graphene nanocomposites have been developed and applied in the production of high-performance membranes. This review basically highlights the designs, properties, and use of polymer/graphene nanocomposite membranes in the field of gas separation and purification. Various polymer matrices (polysulfone, poly(dimethylsiloxane), poly(methyl methacrylate), polyimide, etc.), have been reinforced with graphene to develop nanocomposite membranes. Various facile strategies, such as solution casting, phase separation, infiltration, self-assembly, etc., have been employed in the design of gas separation polymer/graphene nanocomposite membranes. The inclusion of graphene in polymeric membranes affects their morphology, physical properties, gas permeability, selectivity, and separation processes. Furthermore, the final membrane properties are affected by the nanofiller content, modification, dispersion, and processing conditions. Moreover, the development of polymer/graphene nanofibrous membranes has introduced novelty in the field of gas separation membranes. These high-performance membranes have the potential to overcome challenges arising from gas separation conditions. Hence, this overview provides up-to-date coverage of advances in polymer/graphene nanocomposite membranes, especially for gas separation applications. The separation processes of polymer/graphene nanocomposite membranes (in parting gases) are dependent upon variations in the structural design and processing techniques used. Current challenges and future opportunities related to polymer/graphene nanocomposite membranes are also discussed.

Polydimethylsiloxane/Magnesium Oxide Nanosheet Mixed Matrix Membrane for CO2 Separation Application

Carbon dioxide (CO₂) concentration is now 50% higher than in the preindustrial period and efforts to reduce CO₂ emission through carbon capture and utilization (CCU) are blooming. Membranes are one of the attractive alternatives for such application. In this study, a rubbery polymer polydimethylsiloxane (PDMS) membrane is incorporated with magnesium oxide (MgO) with a hierarchically two-dimensional (2D) nanosheet shape for CO₂ separation. The average thickness of the synthesized MgO nanosheet in this study is 35.3 ± 1.5 nm. Based on the pure gas separation performance, the optimal loading obtained is at 1 wt.% where there is no observable significant agglomeration. CO₂ permeability was reduced from 2382 Barrer to 1929 Barrer while CO₂/N₂ selectivity increased from only 11.4 to 12.7, and CO₂/CH₄ remained relatively constant when the MMM was operated at 2 bar and 25 °C. Sedimentation of the filler was observed when the loading was further increased to 5 wt.%, forming interfacial defects on the bottom side of the membrane and causing increased CO₂ gas permeability from 1929 Barrer to 2104 Barrer as compared to filler loading at 1 wt.%, whereas the CO₂/N₂ ideal selectivity increased from 12.1 to 15.0. Additionally, this study shows that there was no significant impact of pressure on separation performance. There was a linear decline of CO₂ permeability with increasing upstream pressure while there were no changes to the CO₂/N₂ and CO₂/CH₄ selectivity.

Status and future trends of hollow fiber biogas separation membrane fabrication and modification techniques

With the increasing global demand for energy, renewable and sustainable biogas has attracted considerable attention. However, the presence of various gases such as methane, carbon dioxide (CO₂), nitrogen, and hydrogen sulfide in biogas, and the potential emission of acid gases, which may adversely influence the environment, limits the efficient application of biogas in many fields. Consequently, researchers have focused on the upgrade and purification of biogas to eliminate impurities and obtain high-quality and high-purity biomethane with an increased combustion efficiency. In this context, the removal of CO₂ gas, which is the most abundant contaminant in biogas, is of significance. Compared to conventional biogas purification processes such as water scrubbing, chemical absorption, pressure swing adsorption, and cryogenic separation, advanced membrane separation technologies are simpler to implement, easier to scale, and incur lower costs. Notably, hollow fiber membranes enhance the gas separation efficiency and decrease costs because their large specific surface area provides a greater range of gas transport. Several reviews have described biogas upgrading technologies and gas separation membranes composed of different materials. In this review, five commonly used commercial biogas upgrading technologies, as well as biological microalgae-based techniques are compared, the advantages and limitations of polymeric and mixed matrix hollow fiber membranes are highlighted, and methods to fabricate and modify hollow fiber membranes are described. This will provide more ideas and methods for future low-cost, large-scale industrial biogas upgrading using membrane technology.

Core-shell graphene oxide-polymer hollow fibers as water filters with enhanced performance and selectivity

Commercial hollow fiber filters for micro- and ultrafiltration are based on size exclusion and do not allow the removal of small molecules such as antibiotics. Here, we demonstrate that a graphene oxide (GO) layer can be firmly immobilized either inside or outside polyethersulfone-polyvinylpyrrolidone hollow fiber (Versatile PES®, hereafter PES) modules and that the resulting core-shell fibers inherits the microfiltration ability of the pristine PES fibers and the adsorption selectivity of GO. GO nanosheets were deposited on the fiber surface by filtration of a GO suspension through a PES cartridge (cut-off 0.1-0.2 μm), then fixed by thermal annealing at 80 °C, rendering the GO coating stably fixed and unsoluble. The filtration cut-off, retention selectivity and efficiency of the resulting inner and outer modified hollow fibers (HF-GO) were tested by performing filtration on water and bovine plasma spiked with bovine serum albumin (BSA, 66 kDa, ≈15 nm size), monodisperse polystyrene nanoparticles (52 nm and 303 nm sizes), with two quinolonic antibiotics (ciprofloxacin and ofloxacin) and rhodamine B (RhB). These tests showed that the microfiltration capability of PES was retained by HF-GO, and in addition the GO coating can capture the molecular contaminants while letting through BSA and smaller polystyrene nanoparticles. Combined XRD, molecular modelling and adsorption experiments show that the separation mechanism does not rely only on physical size exclusion, but involves intercalation of solute molecules between the GO layers.

Performance of Nanocomposite Membranes Containing 0D to 2D Nanofillers for CO₂ Separation: A Review

Membrane technology has the potential to be an eco-friendly and energy-saving solution for the separation of CO₂ from different gaseous streams due to the lower cost and the superior manufacturing features. However, the performances of membranes made of conventional polymers are limited by the trade-off between the permeability and selectivity. Improving the membrane performance through the addition of nanofillers within the polymer matrix offers a promising strategy to achieve superior separation performance. This review aims at providing a complete overview of the recent advances in nanocomposite membranes for enhanced CO₂ separation. Nanofillers of various dimensions and properties are categorized and effects of nature and morphology of the 0D to 2D nanofillers in the corresponding nanocomposite membranes of different polymeric matrixes are discussed with regard to the CO₂ permeation properties. Moreover, a comprehensive summary of the performance data of various nanocomposite membranes is presented. Finally, the advantages and challenges of various nanocomposite membranes are discussed and the future research and development opportunities are proposed.

Synthesis and gas permselectivity of CuBTC–GO–PVDF mixed matrix membranes

A CuBTC (copper(ii) benzene-1,3,5-tricarboxylate) metal organic framework (MOF) and graphene oxide (GO) nanosheets were introduced into a semi-crystalline PVDF to produce mixed matrix membranes (MMMs) to promote gas separation performance.

Nanoparticles Embedded in Amphiphilic Membranes for Carbon Dioxide Separation and Dehumidification

Polymers containing ethylene oxide (EO) groups have gained significant interest as the EO groups have favorable interactions with polar molecules such as H₂ O, quadrupolar molecules such as CO₂ , and metal ions. However, the main challenges of poly(ethylene oxide) (PEO) membranes are their weak mechanical properties and high crystallinity nature. The amphiphilic copolymer made from PEO terephthalate and poly(butylene terephthalate) (PEOT/PBT) comprises both hydrophilic and hydrophobic segments. The hydrophilic PEOT segment is thermosensitive, which facilities gas transports whereas the hydrophobic PBT segment is rigid, which provides mechanical robustness. This work demonstrates a new strategy to design amphiphilic mixed matrix membranes (MMMs) by incorporating zeolitic imidazolate framework, ZIF-71, into the PEOT/PBT copolymer. The resultant membrane shows an enhanced CO₂ permeability with an ideal CO₂ /N₂ selectivity surpassing the original PEOT/PBT and Robeson's Upper bound line. The nanoparticles-embedded amphiphilic membranes exhibit characteristics of high transparency and mechanical robustness. Mechanically strong composite hollow fiber membranes consisting of PEOT/PBT/ZIF-71 as the selective layer were also prepared. The resultant hollow fibers possess an excellent CO₂ permeance of 131 GPU (gas permeation units), CO₂ /N₂ selectivity of 52.6, H₂ O permeance of 9300 GPU and H₂ O/N₂ selectivity of 3700, showing great potential for industrial CO₂ capture and dehumidification.

High-Strength Stereolithographic 3D Printed Nanocomposites: Graphene Oxide Metastability

The weak thermomechanical properties of commercial 3D printing plastics have limited the technology's application mainly to rapid prototyping. In this report, we demonstrate a simple approach that takes advantage of the metastable, temperature-dependent structure of graphene oxide (GO) to enhance the mechanical properties of conventional 3D-printed resins produced by stereolithography (SLA). A commercially available SLA resin was reinforced with minimal amounts of GO nanofillers and thermally annealed at 50 and 100 °C for 12 h. Tensile tests revealed increasing strength and modulus at an annealing temperature of 100 °C, with the highest tensile strength increase recorded at 673.6% (for 1 wt % GO). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) also showed increasing thermal stability with increasing annealing temperature. The drastic enhancement in mechanical properties, which is seen to this degree in 3D-printed samples reported in literature, is attributed to the metastable structure of GO, polymer-nanofiller cross-linking via acid-catalyzed esterification, and removal of intercalated water, thus improving filler-matrix interaction as evidenced by spectroscopy and microscopy analyses.