Porous Graphene Oxide/Porous Organic Polymer Hybrid Nanosheets Functionalized Mixed Matrix Membrane for Efficient CO2 Capture

Unraveling the Atomistic Mechanisms Underlying Effective Reverse Osmosis Filtration by Graphene Oxide Membranes

The graphene oxide (GO) membrane displays promising potential in efficiently filtering ions from water. However, the precise mechanism behind its effectiveness remains elusive, particularly due to the lack of direct experimental evidence at the atomic scale. To shed light on this matter, state-of-the-art techniques are employed such as integrated differential phase contrast-scanning transmission electron microscopy and electron energy loss spectroscopy, combined with reverse osmosis (RO) filtration experiments using GO membranes. The atomic-scale observations after the RO experiments directly reveal the binding of various ions including Na+, K+, Ca2+, and Fe3+ to the defects, edges, and functional groups of GO. The remarkable ion-sieving capabilities of GO membranes are confirmed, which can be attributed to a synergistic interplay of size exclusion, electrostatic interactions, cation-π, and other non-covalent interactions. Moreover, GO membranes modified by external pressure and cation also demonstrated further enhanced filtration performance for filtration. This study significantly contributes by uncovering the atomic-scale mechanism responsible for ion sieving in GO membranes. These findings not only enhance the fundamental understanding but also hold substantial potential for the advancement of GO membranes in reverse osmosis (RO) filtration.

Surface-Roughened Graphene Oxide Microfibers Enhance Electrochemical Reversibility

Here, we provide an optimized method for fabricating surface-roughened graphene oxide disk microelectrodes (GFMEs) with enhanced defect density to generate a more suitable electrode surface for dopamine detection with fast-scan cyclic voltammetry (FSCV). FSCV detection, which is often influenced by adsorption-based surface interactions, is commonly impacted by the chemical and geometric structure of the electrode's surface, and graphene oxide is a tunable carbon-based nanomaterial capable of enhancing these two key characteristics. Synthesized GFMEs possess exquisite electronic and mechanical properties. We have optimized an applied inert argon (Ar) plasma treatment to increase defect density, with minimal changes in chemical functionality, for enhanced surface crevices to momentarily trap dopamine during detection. Optimal Ar plasma treatment (100 sccm, 60 s, 100 W) generates crevice depths of 33.4 ± 2.3 nm with high edge plane character enhancing dopamine interfacial interactions. Increases in GFME surface roughness improve electron transfer rates and limit diffusional rates out of the crevices to create nearly reversible dopamine electrochemical redox interactions. The utility of surface-roughened disk GFMEs provides comparable detection sensitivities to traditional cylindrical carbon fiber microelectrodes while improving temporal resolution ten-fold with amplified oxidation current due to dopamine cyclization. Overall, surface-roughened GFMEs enable improved adsorption interactions, momentary trapping, and current amplification, expanding the utility of GO microelectrodes for FSCV detection.

Enhancing the seawater desalination performance of multilayer reduced graphene oxide membranes by introducing in-plane nanopores: a molecular dynamics simulation study

In this study, using MD simulation, the effect of creating in-plane nanopores in a reduced graphene oxide (rGO) membrane and the formation of a reduced nanoporous graphene oxide (rNPGO) membrane is proposed to increase salt rejection and water flux. To this end, the desalination performance of r1NPGO, r2NPGO and r4NPGO membranes, which have 1, 2 and 4 pore(s), respectively, with a diameter of 0.9 nm and the r1NPGO-3 nm membrane, which has 1 pore with an approximate diameter of 3.0 nm, was investigated and compared from a molecular point of view. The simulation results show that in the rNPGO membranes, by increasing the number of pores from 1 to 4, water flux increases by ∼6 times compared to the rGO membrane. Meanwhile, upon increasing the pore size from 0.9 to 3.0 nm, water flux is enhanced by ∼16 times compared to the rGO membrane. The simulation results also demonstrate that the rGO membrane has two paths for water penetration, which are called the interlayer pathway and in-slit pathway. Moreover, pores in the rNPGO membranes provide another additional path for water transfer by shortening the lateral size of the membranes. This path is referred to as the in-pore pathway. By increasing the size of the pore in the r1NPGO-3 nm membrane, the contribution of the in-pore pathway increases and plays an important role. Furthermore, the simulation results show that in all rGO and rNPGO membranes, the interlayer space acts as a barrier for ions. Therefore, complete salt rejection is observed. Interestingly, by increasing the pore size in the r1NPGO-3 nm membrane, this membrane still maintains complete salt rejection. The observed phenomenon can be a result of very high water flux in this membrane. By increasing water flux, the presence of water molecules around Na+ and Cl- ions decreases. As a result, the formation of Na+Cl- ionic clusters is strengthened in such a way that these clusters do not have the ability to pass through large pores of 3.0 nm.

How 2D Nanoflakes Improve Transport in Mixed Matrix Membranes: Insights from a Simple Lattice Model and Dynamic Mean Field Theory

Mixed matrix membranes (MMMs), incorporating graphene and graphene oxide structural fragments, have emerged as promising materials for challenging gas separation processes. What remains unclear is the actual molecular mechanism responsible for the enhanced permeability and perm-selectivity of these materials. With the fully atomistic models still unable to handle the required time and length scales, here, we employ a simple qualitative model based on the lattice representation of the physical system and dynamic mean field theory. We demonstrate that the performance enhancement results from the flux-regularization impact of the 2D nanoflakes and that this effect sensitively depends on the orientation of the nanoflakes and the properties of the interface between the nanoflakes and the polymer.

Heteroepitaxial growth of ZIF-67 nanoparticles on the ZIF-L(Zn) nanosheets for fabrication of Pebax mixed matrix membranes with highly efficient CO2 separation

ZIF-67 nanoparticles were grown on ZIF-L(Zn) nanosheets by in-situ heteroepitaxial method, resulting in ZIF-67@ZIF-L(Zn) as a charming two-dimensional (2D) nanocomposite for incorporation into the Pebax-1657 and improving its CO2/N2 separation performance. The fabricated nanofillers and membranes were analyzed by characterization tests (FTIR, XRD, FESEM, and EDAX-mapping) and gas separation experiments (effect of filler loading, filler type, feed pressure, and long-term stability). It was observed that the nanosheets were well dispersed in the matrix, and they had formed a proper interaction by creating hydrogen bonds at the interface; in addition, due to their crystalline nature, they increased the crystallinity of the MMMs. The results of the gas permeability test showed that these nanofillers, with their composite structure, had a synergistic effect on the gas solubility and screening and caused a significant improvement in the separation performance of MMMs. So that the best performance achieved with a CO2 permeability of 72.9 Barrer and a CO2/N2 selectivity of 102.9 at 10 bar for the MMM containing 2 wt% of ZIF-L(Zn)@ZIF-67, also exceeding Robeson's upper bound. Moreover, Mindex as a criterion for evaluation of the gas separation performance of MMMs in simultaneous improvement of the permeability and selectivity was proposed in this work. The Mindex values in the range of 0.5-1.5 were calculated for the MMM containing 2 wt% of ZIF-L(Zn)@ZIF-67 nanosheet which indicating a good quality for the gas separation performance. Furthermore, at equal filler loading (2 wt%), this membrane outperformed all MMMs containing other nanofillers (ZIF-67, ZIF-8, ZIF-L(Co), or ZIF-L(Zn)).

Fundamental Understanding of Ultrathin, Highly Stable Self-Assembled Liquid Crystalline Graphene Oxide Membranes Leading to Precise Molecular Sieving through Non-equilibrium Molecular Dynamics

Self-assembled graphene oxide lyotropic liquid crystal (GO LLC) structures are mostly formed in aqueous medium; however, most GO derivatives are water insoluble, so processing GO LLCs in water poses a practical limitation. The use of polar aprotic solvent (like dimethyl sulfoxide) for the formation of GO LLC structures would be interesting, because it would allow incorporating additives, like photoinitiators or cross-linkers, or blending with polymers that are insoluble in water, which hence would expand its scope. The well-balanced electrostatic interaction between DMSO and GO can promote and stabilize the GO nanosheets' alignment even at lower concentrations. With this in mind, herein we report mechanically robust, chlorine-tolerant, self-assembled nanostructured GO membranes for precise molecular sieving. Small-angle X-ray scattering and polarized optical microscopy confirmed the alignment of the modified GO nanosheets in polar aprotic solvent, and the LLC structure was effectively preserved even after cross-linking under UV light. We found that the modified GO membranes exhibited considerably improved salt rejection for monovalent ions (99%) and water flux (120 LMH) as compared to the shear-aligned GO membrane, which is well supported by forward osmosis simulation studies. Additionally, our simulation studies indicated that water molecules traveled a longer path while permeating through the GO membrane compared to the GO LLC membrane. Consequently, salt ions permeate slowly across the GO LLC membrane, yielding higher salt rejection than the GO membrane. This begins to suggest strong electrostatic repulsion with the salt ions, causing higher salt rejection in the GO LLC membrane. We foresee that the ordered cross-linked GO sheets contributed to excellent mechanical stability under a high-pressure, cross-flow, chlorine environment. Overall, these membranes are easily scalable, exhibit good mechanical stability, and represent a breakthrough for the potential use of polymerized GO LLC membranes in practical water remediation applications.

Ultrathin Water-Cast Polymer Membranes for Hydrogen Purification

Among various H₂ purification technologies, the use of membrane technology has been considered an ecofriendly approach for addressing the increasing hydrogen demand. Although many H₂-selective membrane materials have been reported, processing them into hollow fibers or thin-film composites (TFCs) via traditional methods either affects the performance of the materials or renders their further processing into applicable membrane forms infeasible. Herein, we propose a water-casting method for fabricating TFC membranes for hydrogen purification with high permselectivity. The film integrity and thickness were manipulated by controlling the spreadability of the casting solution, and the resultant water-cast TFC membrane that comprised an ∼30 nm selective layer demonstrated high H₂ permeance and H₂/CH₄ selectivity of approximately 190 GPU and 100, respectively, under optimized conditions. We performed a mixed-gas permeation test using a simulated off-gas of steam-methane reforming from natural gas in a single-stage system and obtained hydrogen gas of >99 mol % purity. This indicates not only the suitability of the water-cast membranes for satisfying the demand for pure hydrogen as a fuel and chemical reagent but also the great potential of the water-casting method for high-performance membranes in various industrial and environmental applications.

Synthesis and Applications of Graphene Oxide

Thanks to the unique properties of graphite oxides and graphene oxide (GO), this material has become one of the most promising materials that are widely studied. Graphene oxide is not only a precursor for the synthesis of thermally or chemically reduced graphene: researchers revealed a huge amount of unique optical, electronic, and chemical properties of graphene oxide for many different applications. In this review, we focus on the structure and characterization of GO, graphene derivatives prepared from GO and GO applications. We describe GO utilization in environmental applications, medical and biological applications, freestanding membranes, and various composite systems.

Light-responsive metal-organic framework sheets constructed smart membranes with tunable transport channels for efficient gas separation

Exploring a new type of smart membrane with tunable separation performance is a promising area of research. In this study, new light-responsive metal–organic framework [Co(azpy)] sheets were prepared by a facile microwave method for the first time, and were then incorporated into a polymer matrix to fabricate smart mixed matrix membranes (MMMs) applied for flue gas desulfurization and decarburization. The smart MMMs exhibited significantly elevated SO₂(CO₂)/N₂ selectivity by 184(166)% in comparison with an unfilled polymer membrane. The light-responsive characteristic of the smart MMMs was investigated, and the permeability and selectivity of the Co(azpy) sheets-loaded smart MMMs were able to respond to external light stimuli. In particular, the selectivity of the smart MMM at the Co(azpy) content of 20% for the SO₂/N₂ system could be switched between 341 and 211 in situ irradiated with Vis and UV light, while the SO₂ permeability switched between 58 Barrer and 36 Barrer, respectively. This switching influence was mainly ascribed to the increased SO₂ adsorption capacity in the visible light condition, as verified by adsorption test. The CO₂ permeability and CO₂/N₂ selectivity of MMMs in the humidified state could achieve 248 Barrer and 103.2, surpassing the Robeson's upper bound reported in 2019.

New light-responsive MOF sheets were synthesized to fabricate a smart membrane, which displays switchable gas separation performance stimulated with UV-Vis light.

Recent advances in dual-filler mixed matrix membranes

Mixed matrix membranes (MMMs) have been widely developed as an attractive solution to overcome the drawbacks found in most polymer membranes, such as permeability-selectivity trade-off and low physicochemical stability. Numerous fillers based on inorganic, organic, and hybrid materials with various structures including porous or nonporous, and two-dimensional or three-dimensional, have been used. Demanded to further improve the characteristics and performances of the MMMs, the use of dual-filler instead of a single filler has then been proposed, from which multiple effects could be obtained. This article aims to review the recent development of MMMs with dual filler and discuss their performances in diverse potential applications. Challenges in this emerging field and outlook for future research are finally provided.

Recent Advances in Polymer-Inorganic Mixed Matrix Membranes for CO2 Separation

Since the second industrial revolution, the use of fossil fuels has been powering the advance of human society. However, the surge in carbon dioxide (CO2) emissions has raised unsettling concerns about global warming and its consequences. Membrane separation technologies have emerged as one of the major carbon reduction approaches because they are less energy-intensive and more environmentally friendly compared to other separation techniques. Compared to pure polymeric membranes, mixed matrix membranes (MMMs) that encompass both a polymeric matrix and molecular sieving fillers have received tremendous attention, as they have the potential to combine the advantages of both polymers and molecular sieves, while cancelling out each other's drawbacks. In this review, we will discuss recent advances in the development of MMMs for CO2 separation. We will discuss general mechanisms of CO2 separation in an MMM, and then compare the performances of MMMs that are based on zeolite, MOF, metal oxide nanoparticles and nanocarbons, with an emphasis on the materials' preparation methods and their chemistries. As the field is advancing fast, we will particularly focus on examples from the last 5 years, in order to provide the most up-to-date overview in this area.

Efficient CO2 Separation of Multi-Permselective Mixed Matrix Membranes with a Unique Interfacial Structure Regulated by Mesoporous Nanosheets

A facile strategy to elevate gas separation performances of polymers is to introduce a versatile particle. In this study, the novel F-Ce nanosheets are synthesized, and then F-Ce is functionalized with 1-ethyl-3-methylimidazole thiocyanate (ionic liquids, ILs), obtaining multifunctional f-F-Ce nanosheets by the facile and environment-friendly methods. The multifunctional f-F-Ce nanosheets are incorporated into the Pebax (Pebax 1657) matrix to fabricate mixed matrix membranes (MMMs) for efficient CO₂ separation. The f-F-Ce nanosheets play versatile parts in elevating membrane gas separation performance. On the one hand, f-F-Ce tends to arrange horizontally and constructs a unique interfacial structure for cross-layer CO₂ transport in MMMs. On the other hand, the abundant mesopores from f-F-Ce construct high-speed CO₂ transport channels in MMMs and notably elevate the gas permeability. Moreover, the as-prepared MMMs separate CO₂ efficiently due to the comprehensive improvements of diffusivity selectivity, solubility selectivity, and reactivity selectivity. First, the high aspect ratio of f-F-Ce provides the tortuous pathways for gas transport and generates the rigid interface between the Pebax matrix and f-F-Ce nanosheets, increasing the diffusivity selectivity. Second, SCN^- groups from ILs show excellent affinity to CO₂, enhancing the solubility selectivity. Third, amine groups from ILs with abundant methylimidazole generate reversible reaction with CO₂ to elevate reactivity selectivity. Consequently, the f-F-Ce-doped MMMs display excellent CO₂ permeability and CO₂/CH₄ selectivity. In particular, the MMM incorporated with 8 wt % f-F-Ce displays a CO₂ permeability of 1823 Barrer and a CO₂/CH₄ selectivity of 35, overcoming the Robeson upper bound line (2008).

Metal Organic Framework - Based Mixed Matrix Membranes for Carbon Dioxide Separation: Recent Advances and Future Directions

Gas separation and purification using polymeric membranes is a promising technology that constitutes an energy-efficient and eco-friendly process for large scale integration. However, pristine polymeric membranes typically suffer from the trade-off between permeability and selectivity represented by the Robeson's upper bound. Mixed matrix membranes (MMMs) synthesized by the addition of porous nano-fillers into polymer matrices, can enable a simultaneous increase in selectivity and permeability. Among the various porous fillers, metal-organic frameworks (MOFs) are recognized in recent days as a promising filler material for the fabrication of MMMs. In this article, we review representative examples of MMMs prepared by dispersion of MOFs into polymer matrices or by deposition on the surface of polymeric membranes. Addition of MOFs into other continuous phases, such as ionic liquids, are also included. CO2 separation from hydrocarbons, H2, N2, and the like is emphasized. Hybrid fillers based on composites of MOFs with other nanomaterials, e.g., of MOF/GO, MOF/CNTs, and functionalized MOFs, are also presented and discussed. Synergetic effects and the result of interactions between filler/matrix and filler/filler are reviewed, and the impact of filler and matrix types and compositions, filler loading, surface area, porosity, pore sizes, and surface functionalities on tuning permeability are discoursed. Finally, selectivity, thermal, chemical, and mechanical stability of the resulting MMMs are analyzed. The review concludes with a perspective of up-scaling of such systems for CO2 separation, including an overview of the most promising MMM systems.

Hierarchically Structured Porous Piezoelectric Polymer Nanofibers for Energy Harvesting

Hierarchically porous piezoelectric polymer nanofibers are prepared through precise control over the thermodynamics and kinetics of liquid-liquid phase separation of nonsolvent (water) in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) solution. Hierarchy is achieved by fabricating fibers with pores only on the surface of the fiber, or pores only inside the fiber with a closed surface, or pores that are homogeneously distributed in both the volume and surface of the nanofiber. For the fabrication of hierarchically porous nanofibers, guidelines are formulated. A detailed experimental and simulation study of the influence of different porosities on the electrical output of piezoelectric nanogenerators is presented. It is shown that bulk porosity significantly increases the power output of the comprising nanogenerator, whereas surface porosity deteriorates electrical performance. Finite element method simulations attribute the better performance to increased volumetric strain in bulk porous nanofibers.

A Study of the Reinforcement Effect of MWCNTs onto Polyimide Flat Sheet Membranes

Polyimides rank among the most heat-resistant polymers and find application in a variety of fields, including transportation, electronics, and membrane technology. The aim of this work is to study the structural, thermal, mechanical, and gas permeation properties of polyimide based nanocomposite membranes in flat sheet configuration. For this purpose, numerous advanced techniques such as atomic force microscopy (AFM), SEM, TEM, TGA, FT-IR, tensile strength, elongation test, and gas permeability measurements were carried out. In particular, BTDA-TDI/MDI (Ρ84) co-polyimide was used as the matrix of the studied membranes, whereas multi-wall carbon nanotubes were employed as filler material at concentrations of up to 5 wt.% All studied films were prepared by the dry-cast process resulting in non-porous films of about 30-50 μm of thickness. An optimum filler concentration of 2 wt.% was estimated. At this concentration, both thermal and mechanical properties of the prepared membranes were improved, and the highest gas permeability values were also obtained. Finally, gas permeability experiments were carried out at 25, 50, and 100 °C with seven different pure gases. The results revealed that the uniform carbon nanotubes dispersion lead to enhanced gas permeation properties.

A Convenient and Versatile Strategy for the Functionalization of Silica Foams Using High Internal Phase Emulsion Templates as Microreactors

Functional porous materials show extensive applications in the environment, biology, aerospace, and so on. In this work, the generation of silica foams and functionalization of pore surface were simultaneously realized through an interfacial sol-gel reaction within high internal phase emulsion (HIPE) microreactors, where a hyperbranched polyethoxysiloxane (PEOS) was used as the sole stabilizer for the HIPEs. With various functional substances containing amino, epoxy, and carboxyl groups initially dissolved in the aqueous phase of HIPEs, these functional groups could be grafted onto the pore surface in the process of forming silica foams. Amino-functionalized silica foam showed fast adsorption of sunset yellow, and the adsorption capacity could reach as high as 1213.13 mg/g. Sodium polyacrylate-modified silica foam exhibited good adsorption capacity of cationic dyes and metal ions, e.g., 280.11 mg/g to methylene and 226.24 mg/g to Cu(II). Epoxy-functionalized silica foam particles were confirmed with a pronounced activity at the oil/water interface due to their Janus-like surface, which could be used as Pickering stabilizer. This HIPE-based synthesis strategy for silica foams shows promising future in adsorption, emulsion stabilization, and compatibilization.

Facile synthesis of tetraphenylethene-based conjugated microporous polymers as adsorbents for CO2 and organic vapor uptake

We present three novel conjugated microporous polymers (CMP@1–3), which were formed by an imidization reaction between tetra-(4-aminophenyl)ethylene and anhydrides.

A Versatile Solvent-Induced Polymerization Strategy To Synthesize Free-Standing Porous Polymer Nanosheets and Nanotubes for Fast Iodine Capture

Two-dimensional (2D) porous polymers have demonstrated great potential in gas capture and surface catalysis as well as energy storage and conversion. Current synthesis of 2D porous polymers strongly depends on the usage of templates or an additional exfoliation process. The resultant products have uncontrollable morphology and structure, low structure integrity, and relatively low yield. Herein, a facile and high-throughput solvent-induced polymerization strategy to prepare ultrathin free-standing 2D porous hyper-cross-linked polymer nanosheets with large surface area and high sulfur content by cross-linking steric hexakis(benzylthio)benzene and thiophene is reported. Using this approach, the morphologies (nanosheets and nanotubes) and specific surface areas (658-1150 m² g^-1) of porous hyper-cross-linked polymers can be simply tailored by adjusting the cross-linking degree between monomers. The as-synthesized porous hyper-cross-linked polymer nanotubes exhibit promising iodine capture performance, including a superior iodine uptake capacity (∼270 wt %) and a rapid equilibrium adsorption (within 60 min). This method will pave a new avenue for the synthesis of advanced 2D porous polymers for various applications.

Mixed Nanosheet Membranes Assembled from Chemically Grafted Graphene Oxide and Covalent Organic Frameworks for Ultra-high Water Flux

2D graphene oxide (GO) membranes attract great attention because of their ultrathin thickness and superior molecular sieving ability, but their low flux and instability in aqueous environments are still the major challenges for practical applications. In this study, we designed hybrid nanosheets from chemically grafted GO and covalent organic frameworks (COFs) as building blocks to fabricate mixed nanosheet membranes. The covalent triazine framework (CTF), a triazine-based COF, is exfoliated into nanosheets and then reacted with GO to form the GO-CTF hybrid nanosheets, which are then assembled into GO-CTF mixed nanosheet membranes. The GO-CTF membranes show a layered configuration of ca. 32 nm thickness. The incorporation of CTF nanosheets inappreciably changes the interlayer distance of GO-CTF membranes, ensuring high rejections to organic dyes (>90%); meanwhile, the CTF nanosheets afford extra through-plane channels that significantly shorten the water transport pathway. The GO-CTF membranes exhibit a water flux of 226.3 L m^-2 h^-1 bar^-1, more than 12-fold higher than pure GO membranes. Besides, the strong chemical bonds between GO and COF render the GO-CTF membranes notably enhanced stability. Grafting of porous nanosheets onto nonporous nanosheets to acquire hybrid nanosheets as building blocks opens a new avenue to the fabrication of 2D membranes with promising application potential.

Constructing Unique Cross-Sectional Structured Mixed Matrix Membranes by Incorporating Ultrathin Microporous Nanosheets for Efficient CO2 Separation

Ultrathin microporous nanosheets denoted as Zn-tetra-(4-carboxyphenyl)porphyrin (Zn-TCPP) were synthesized and incorporated into a Pebax MH 1657 (Pebax) polymer to fabricate mixed matrix membranes (MMMs) for efficient CO₂ separation. The Zn-TCPP nanosheets with a microporous structure provide high-speed channels for fast CO₂ transport and shorten the diffusion pathways, both contributing toward high CO₂ permeability. Furthermore, scanning electron microscopy results indicate that the ultrathin Zn-TCPP nanosheets with an ultrahigh aspect ratio (>200) tend to arrange horizontally in the Pebax matrix. The obtained unique cross-sectional structure of the MMMs functions as a selective barrier, allowing repeated discrimination of gases due to the tortuous interlayer of horizontal nanosheets, thus improving the selectivity of the MMMs. In addition, the horizontally arranged microporous nanosheets were found to strongly interact with the membrane matrix and endowed the MMMs with excellent interfacial compatibility, which improved the CO₂ permeability and eliminated unselective permeation pathways. Significantly, the optimized CO₂ separation performance of the MMMs surpassed the 2008 Robeson's limit.

Rational design of functionalized covalent organic frameworks and their performance towards CO2 capture

We describe the design and synthesis of two new functionalized covalent organic frameworks, named Cz-COF and Tz-COF, by using monomers containing carbazole and benzobisthiazole as building blocks. The resultant materials possess high crystallinity, permanent porosities as well as abundant heteroatom activated sites in the framework. As solid adsorbents, both COFs exhibit excellent CO₂ uptake (11.0 wt% for Cz-COF and 15.4 wt% for Tz-COF), high adsorption selectivity for CO₂ over N₂ and good recyclability.

Two new functionalized covalent organic frameworks containing carbazole and benzothiazole displayed excellent CO₂ uptake.