Mixed-Matrix Organo-Silica-Hydrotalcite Membrane for CO2 Separation Part 2: Permeation and Selectivity Study

This study introduces an innovative approach to designing membranes capable of separating CO2 from industrial gas streams at higher temperatures. The novel membrane design seeks to leverage a well-researched, high-temperature CO2 adsorbent, hydrotalcite, by transforming it into a membrane. This was achieved by combining it with an amorphous organo-silica-based matrix, extending the polymer-based mixed-matrix membrane concept to inorganic compounds. Following the membrane material preparation and investigation of the individual membrane in Part 1 of this study, we examine its permeation and selectivity here. The pure 200 nm thick hydrotalcite membrane exhibits Knudsen behavior due to large intercrystalline pores. In contrast, the organo-silica membrane demonstrates an ideal selectivity of 13.5 and permeance for CO2 of 1.3 × 10-7 mol m-2 s-1 Pa-1 at 25 °C, and at 150 °C, the selectivity is reduced to 4.3. Combining both components results in a hybrid microstructure, featuring selective surface diffusion in the microporous regions and unselective Knudsen diffusion in the mesoporous regions. Further attempts to bridge both components to form a purely microporous microstructure are outlined.

Prediction of CO2 solubility in Ionic liquids for CO2 capture using deep learning models

Ionic liquids (ILs) are highly effective for capturing carbon dioxide (CO2). The prediction of CO2 solubility in ILs is crucial for optimizing CO2 capture processes. This study investigates the use of deep learning models for CO2 solubility prediction in ILs with a comprehensive dataset of 10,116 CO2 solubility data in 164 kinds of ILs under different temperature and pressure conditions. Deep neural network models, including Artificial Neural Network (ANN) and Long Short-Term Memory (LSTM), were developed to predict CO2 solubility in ILs. The ANN and LSTM models demonstrated robust test accuracy in predicting CO2 solubility, with coefficient of determination (R2) values of 0.986 and 0.985, respectively. Both model's computational efficiency and cost were investigated, and the ANN model achieved reliable accuracy with a significantly lower computational time (approximately 30 times faster) than the LSTM model. A global sensitivity analysis (GSA) was performed to assess the influence of process parameters and associated functional groups on CO2 solubility. The sensitivity analysis results provided insights into the relative importance of input attributes on output variables (CO2 solubility) in ILs. The findings highlight the significant potential of deep learning models for streamlining the screening process of ILs for CO2 capture applications.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

Innovative eco-friendly hydroxyethylcellulose matrix-based composite for enhanced gas separation: Insights from performance and structural characterization

With increasing concern for the environment, the demand for carbon dioxide separation, a key contributor to global warming, has escalated. Therefore, this paper focuses on carbon dioxide separation by creating an hydroxyethyl cellulose (HEC)(C2H6O2)x*(C6H7O2(OH)3)n/silver tetra fluoroborate (AgBF4)/aluminum nitrate (Al(NO3)3) composite film, demonstrating excellent separation performance with a permeance of 1.0 GPU and a selectivity of 100. Silver ions enhance the solubility of carbon dioxide, aiding in its separation, and we determined the optimal aluminum composition to stabilize the silver ions. To analyze this, we examined the cross-sections using SEM, confirming a selective layer of 1.7 μm for carbon dioxide separation. Furthermore, TGA, FT-IR, and NMR analyses were conducted to investigate the interaction between the polymer and additives. This revealed that the increased polymer chain due to the interaction between Ag and HEC, along with stabilized Ag facilitated by the addition of Al, maximized the interaction with carbon dioxide via the empty s-orbital. Additionally, SEM-EDX, UV-vis, XRD, XPS analyses were employed to elucidate the movement of ions within the membrane. These results provide insights into the performance of membranes based on cellulose polymer and offer valuable insights for future applications in gas separation technologies.

Influence of oxygen partial pressure on homoacetogenesis and promotion of acetic acid accumulation through low pH regulation under microaerobic conditions

Homoacetogenesis is an important pathway for bio-utilization of CO2; however, oxygen is a key environmental influencing factor. This study explored the impact of different initial oxygen partial pressures (OPPs) on homoacetogenesis, while implementing low pH regulation enhanced acetic acid (HAc) accumulation under microaerobic conditions. Results indicated that cumulative HAc production increased by 18.2% in 5% OPP group, whereas decreases of 31.3% and 56.0% were observed in 10% and 20% OPP groups, respectively, compared to the control group. However, hydrogenotrophic methanogens adapted to microaerobic environment and competed with homoacetogens for CO2, thus limiting homoacetogenesis. Controlling influent pH 5.0 per cycle increased cumulative HAc production by 18.3% and 18.2% in 5% and 10% OPP groups, respectively, compared with the control group. Consequently, regulating low pH effectively inhibited methanogenic activity under microaerobic conditions, thus increasing HAc production. This study was expected to expand the practical application of homoacetogenesis in bio-utilization of CO2.

Enhancing CO2 capture through innovating monolithic graphene oxide frameworks

The advancement and engineering of novel crystalline materials is facilitated through the utilization of innovative porous crystalline structures, established via KOH-treated monolithic graphene oxide frameworks. These materials exhibit remarkable and versatile characteristics for both functional exploration and applications within the realm of CO2 capture. In this comprehensive study, we have synthesized monolithic reduced graphene oxide-based adsorbents through a meticulous self-assembly process involving different mass ratios of GO/malic acid (MaA) (1:0.250, 1:0.500, and 1:1 by weight). Building upon this foundation, we further modified MGO 0.250 through KOH-treatment by chloroacetic acid method, leading to the creation of MGO 0.250_KOH, which was subjected to CO2 capture assessments. The comprehensive investigation encompassed an array of parameters including morphology, specific surface area, crystal defects, functional group identification, and CO2 capture efficiency. Employing a combination of FT-IR, XRD, Raman, BET, SEM, HR-TEM, and XPS techniques, the study revealed profound insights. Particularly notable was the observation that the MGO 0.250_KOH adsorbent exhibited an exceptional CO2 capture performance, leading to a significant enhancement of the CO2 capture capacity from 1.69 mmol g-1 to 2.35 mmol g-1 at standard conditions of 25 °C and 1 bar pressure. This performance enhancement was concomitant with an augmentation in surface area, elevating from 287.93 to 419.75 m2 g-1 (a nearly 1.5-fold increase compared to MGO 1.000 with a surface area of 287.93 m2 g-1). The monolithic adsorbent demonstrated a commendable production yield of 82.92%, along with an impressive regenerability of 98.80% at 100 °C. Additionally, adsorbent's proficiency in CO2 adsorption, rendering it a promising candidate for post-combustion CO2 capture applications. These findings collectively underscore the capacity adsorbents to significantly amplify CO2 capture capabilities. The viability of employing this strategy as an uncomplicated pre-treatment technique in various industrial sectors is a plausible prospect, given the study's outcomes.

Facile Fabrication and Characterization of Amine-Functional Silica Coated Magnetic Iron Oxide Nanoparticles for Aqueous Carbon Dioxide Adsorption

Surface active amine-functionalized silica coated magnetic iron oxide nanoparticles were prepared by a simple two-step process for adsorbing CO2 gas from aqueous medium. First, oleic acid (OA) coated iron oxide magnetic particles (denoted as Fe3O4-OA) were prepared by a simple coprecipitation method. Then, the surface of the Fe3O4-OA particles was coated with silica by using tetraethyl orthosilicate. Finally, aminated Fe3O4/SiO2-NH2 nanoparticles were concomitantly formed by the reactions of 3-aminopropyl triethoxysilane with silica-coated particles. The formation of materials was confirmed by Fourier transform infrared spectral analysis. Transmission electron microscopic analysis revealed both spherical and needle-shaped morphologies of magnetic Fe3O4/SiO2-NH2 particles with an average size of 15 and 68.6 nm, respectively. The saturation magnetization of Fe3O4/SiO2-NH2 nanoparticles was found to be 33.6 emu g-1, measured by a vibrating sample magnetometer at ambient conditions. The crystallinity and average crystallite size (7.0 nm) of the Fe3O4/SiO2-NH2 particles were revealed from X-ray diffraction data analyses. Thermogravimetric analysis exhibited good thermal stability of the nanoadsorbent up to an elevated temperature. Zeta potential measurements revealed pH-sensitive surface activity of Fe3O4/SiO2-NH2 nanoparticles in aqueous medium. The produced magnetic Fe3O4/SiO2-NH2 nanoparticles also exhibited efficient proton capturing activity (92%). The particles were used for magnetically recyclable adsorption of aqueous CO2 at different pH values and temperatures. Fe3O4/SiO2-NH2 nanoparticles demonstrated the highest aqueous CO2 adsorption efficiency (90%) at 40 °C, which is clearly two times higher than that of nonfunctionalized Fe3O4-OA particles.

Unveiling the potential of membrane in climate change mitigation and environmental resilience in ecosystem

Carbon capture technologies are becoming increasingly crucial in addressing global climate change issues by lowering CO2 emissions from industrial and power generation activities. Post-combustion carbon capture, which uses membranes instead of adsorbents, has emerged as one of promising and environmentally friendly approaches among these technologies. The operation of membrane technology is based on the premise of selectively separating CO2 from flue gas emissions. This provides a number of different benefits, including improved energy efficiency and decreased costs of operation. Because of its adaptability to changing conditions and its low impact on the surrounding ecosystem, it is an appealing choice for a diverse array of uses. However, there are still issues to be resolved, such as those pertaining to establishing a high selectivity, membrane degradation, and the costs of the necessary materials. In this article, we evaluate and explore the prospective applications and roles of membrane technologies to control climate change by post-combustion carbon capturing. The primary proposition suggests that the utilization of membrane-based carbon capture has the potential to make a substantial impact in mitigating CO2 emissions originating from industrial and power production activities. This is due to its heightened ability to selectively absorb carbon, better efficiency in energy consumption, and its flexibility to various applications. The forthcoming challenges and potential associated with the application of membranes in post-carbon capture are also discussed.

Experimental kinetics and thermodynamics investigation: Chemically activated carbon-enriched monolithic reduced graphene oxide for efficient CO2 capture

In this research, we have developed solid MGOs by self-assembled reduction process of GO at 90 °C with different weight ratios of oxalic acid (1:1, 1:0.500, and 1:0.250). The as-synthesized monoliths were carbonized (at 600 °C) and chemically activated with varying proportions of NaOH (1:1, 1:2, and 1:3). This materials offer the CO2 adsorption effect under dynamic conditions, fast mass transfer, easy handling, and outstanding stability throughout the adsorption-desorption cycle. FE-SEM, and HR-TEM analyses confirmed the porous nature and shape of the adsorbents, while XPS examination revealed the presence of distinct functional groups on the surface of the monolith. By increasing the mass ratios (MGO:NaOH) from 1:1 to 1:2, the surface areas increased by approximately 2.6 times, ranging from 520.8 to 753.9 m2 g⁻1 (surface area of the untreated MGO was 289.2 m2 g⁻1). Consequently, this resulted in a notable enhancement of 2.10 mmol g⁻1 in dynamic CO2 capture capacity. The assessment encompassed the evaluation of production yield, selectivity, regenerability, kinetics, equilibrium isotherm, and isosteric temperatures of adsorption (Qst). The decrease in CO2 capture effectiveness with rising adsorption temperature indicated an exothermic and physisorption process. The regenerability of 99.1 % at 100 °C and excellent cyclic stability with efficient CO2 adsorption make this monolithic adsorbent appropriate for post-combustion CO2 capture. The significant Qst lend support to the heterogeneity of the adsorbent's surface, and the pseudo-second-order kinetic model along with the Freundlich isotherm model emerged as the most fitting. Therefore, the current investigation shows that the carbon-enriched adsorbents enhance the CO2 adsorption capacity. It may be used as a low-cost pretreatment method on an industrial scale before carbon capture.

Improving the Separation of CO2/N2 Using Impregnation of a Deep Eutectic Solvent on a Porous MOF

As the partial pressure of CO2 in flue gas is 0.1-0.2 bar, CO2 capture at a low pressure needs more attention. Under low pressure conditions, the functional metal-organic framework (MOF) is powerful for CO2 capture. One of the effective methods to increase the absorption capacity of the MOF is impregnation with deep eutectic solvents. In this research, NH2-MIL101(Cr) is impregnated with a deep eutectic solvent of choline chloride:urea (DES ChCl:urea) to enhance the adsorption capacity. The CO2 and N2 adsorption capacity of NH2-MIL101(Cr) and DES/NH2-MIL101(Cr) was investigated at temperatures of 288.15-303.15 K and pressures up to 1 bar. The obtained results indicate that the adsorption capacity of the MOF increases by 1.7 and 3 times with the impregnated DES for CO2 and N2, respectively. Nevertheless, the pore volume of the MOF decreased after impregnation, but the adsorption capacity of the MOF increased due to the interaction of the adsorbate with the confined DES in pores. The contribution of the impregnated DES to adsorption capacity is explained according to Henry's law. Also, high heats of adsorption are attributed to the strong interaction between modified NH2-MIL101(Cr) and CO2. Also, the sample was refined at 298 K and vacuum and was reused without considerable reduction of the CO2 capture capacity after 6 times. Moreover, the impregnation of ChCl:urea into NH2-MIL101(Cr) nanostructures was studied using density functional theory-based approaches.

Alkylimidazolium-based ionic liquids with tailored anions and cations for CO2 capture

A systematic investigation was conducted in the present study to determine how various cations and anions affected the solubility of CO2. To investigate the influence of different cations and anions on the solubility of CO2, twelve ILs were synthesized, characterized, and utilized. These ILs comprised five distinct anions (dioctylsulfosuccinate [DOSS], triflouromethanesulfonate [TFMS], dodecylsulfate [DDS], 3-sulfobezoate [SBA], and benzene sulfonate [BS]), and four distinct cations (1-butyl-3-propanenitrile imidazolium [C2CN Bim], 1-hexyl-3-propanenitrile imidazolium [C2CN Him], 1-octyl-3-propanenitrile imidazolium [C2CN Oim], and 1-decyl-3-propanenitrile imidazolium [C2CN Dim]). The synthesized ILs were characterized using NMR and elemental analysis. Their moisture and halide contents were determined. The gravimetric method (MSB) was employed to determine the solubility of CO2 at various pressures (20, 15, 10, 5, and 1 bar). In addition, the effects of temperature on the solubility of CO2 were investigated. The constant of Henry's law (kH) was also calculated, along with thermodynamic properties including standard enthalpy (H0), entropy (S0), and Gibbs free energy (G0).

Feasibility study of storing CO2 in the ocean by marine environmental impact assessment

Since the industrial revolution, which was accompanied with the use of fossil fuels as an energy source, the content of carbon dioxide (CO2) in the atmosphere has increased. To mitigate global warming, industries that utilize fossil fuels have continuously explored new approaches to reduce CO2 emissions and convert it to alternative fuels. The ocean is a vast source of absorbed CO2 on Earth, and various studies have been conducted on the use of the ocean to reduce global CO2. This study focused on reducing CO2 in the atmosphere by storing it as bicarbonate, a form of CO2 that exists in the ocean. The optimum condition for the conversion of CO2 into bicarbonate was investigated by considering the dissolved inorganic carbon (DIC; HCO3-, CO32-, H2CO3) concentration and pH. To confirm the biological impact of this conversion, biological impact experiments were conducted under various DIC concentrations using Skeletonema japonicum, a phytoplankton present in most areas of the sea. Based on the DIC concentration (2.09 mM) of the seawater, the DIC concentrations used in the Lab-scale experiment ranged from 2.5 mM to 18.75 mM, and the concentration with the highest conversion rate (< 6.38 mM) was applied in the pilot plant. Marine environmental impact modeling was performed to observe the effect of discharge to the ocean and its movement. The results revealed a slight growth inhibition of phytoplankton at DIC concentrations higher than the base concentration. Nevertheless, the change in the DIC concentration exerted no effect on the phytoplankton growth except at extremely high concentrations. Moreover, the high DIC concentration can be diluted by the ocean current flow rate, thus counterbalancing the growth inhibition effect. The results obtained in this study demonstrate the feasibility of CO2 storage in the form of DIC, and will be helpful for further development of CO2 mitigation.

Advancements in Gas Separation for Energy Applications: Exploring the Potential of Polymer Membranes with Intrinsic Microporosity (PIM)

Membrane-based Polymers of Intrinsic Microporosity (PIMs) are promising candidates for energy-efficient industrial gas separations, especially for the separation of carbon dioxide over methane (CO2/CH4) and carbon dioxide over nitrogen (CO2/N2) for natural gas/biogas upgrading and carbon capture from flue gases, respectively. Compared to other separation techniques, membrane separations offer potential energy and cost savings. Ultra-permeable PIM-based polymers are currently leading the trade-off between permeability and selectivity for gas separations, particularly in CO2/CH4 and CO2/N2. These membranes show a significant improvement in performance and fall within a linear correlation on benchmark Robeson plots, which are parallel to, but significantly above, the CO2/CH4 and CO2/N2 Robeson upper bounds. This improvement is expected to enhance the credibility of polymer membranes for CO2 separations and stimulate further research in polymer science and applied engineering to develop membrane systems for these CO2 separations, which are critical to energy and environmental sustainability. This review aims to highlight the state-of-the-art strategies employed to enhance gas separation performances in PIM-based membranes while also mitigating aging effects. These strategies include chemical post-modification, crosslinking, UV and thermal treatment of PIM, as well as the incorporation of nanofillers in the polymeric matrix.

Porosity as a Design Element for Developing Catalytic Molecular Materials for Electrochemical and Photochemical Carbon Dioxide Reduction

The catalytic reduction of carbon dioxide (CO2 ) using sustainable energy inputs is a promising strategy for upcycling of atmospheric carbon into value-added chemical products. This goal has inspired the development of catalysts for selective and efficient CO2 conversion using electrochemical and photochemical methods. Among the diverse array of catalyst systems designed for this purpose, 2D and 3D platforms that feature porosity offer the potential to combine carbon capture and conversion. Included are covalent organic frameworks (COFs), metal-organic frameworks (MOFs), porous molecular cages, and other hybrid molecular materials developed to increase active site exposure, stability, and water compatibility while maintaining precise molecular tunability. This mini-review showcases catalysts for the CO2 reduction reaction (CO2 RR) that incorporate well-defined molecular elements integrated into porous materials structures. Selected examples provide insights into how different approaches to this overall design strategy can augment their electrocatalytic and/or photocatalytic CO2 reduction activity.

Impregnation of amine functionalized deep eutectic solvents in NH2-MIL-53(Al) MOF for CO2/N2 separation

To improve the CO2/N2 separation performance of metal-organic frameworks (MOFs), amine functionalized deep eutectic solvents (DESs) (choline chloride/ethanolamine (DES1), choline chloride/ethanolamine/diethanolamine (DES2), and choline chloride/ethanolamine/methyldiethanolamine (DES3)) confined in the NH2-MIL-53(Al). NH2-MIL-53(Al) impregnated with DES was synthesized and characterized using N2-sorption analysis and Fourier transform infrared (FTIR) spectroscopy. Morphology of the synthesized MOFs was investigated using scanning electron microscopy (SEM). Also, elemental analysis was determined by energy-dispersive X-ray spectroscopy (EDX). CO2 adsorption isotherms of amine-functionalized DESs impregnated NH2-MIL-53(Al) were measured at temperatures range of 288.15-308.15 K and pressures up to 5 bar. The results reveal that the impregnated MOF with functional group of amine DES improves separation performance NH2-MIL-53(Al). CO2 adsorption capacity of DES1/NH2-MILS-53(Al) was twofold respect to of pristine NH2-MIL-53(Al) at 5 bar and 298.15 K; which helps to guide the logical design of new mixtures for gas separation applications. Also, the heat of adsorption for the synthesized NH2-MIL-53(Al) and DESs/NH2-MIL-53(Al) were estimated. Most importantly, CO2 chemisorption by NH2 group in the sorbent structure has a significant effect on the adsorption mechanism.

Carbon Capture Using Porous Silica Materials

As the primary greenhouse gas, CO₂ emission has noticeably increased over the past decades resulting in global warming and climate change. Surprisingly, anthropogenic activities have increased atmospheric CO₂ by 50% in less than 200 years, causing more frequent and severe rainfall, snowstorms, flash floods, droughts, heat waves, and rising sea levels in recent times. Hence, reducing the excess CO₂ in the atmosphere is imperative to keep the global average temperature rise below 2 °C. Among many CO₂ mitigation approaches, CO₂ capture using porous materials is considered one of the most promising technologies. Porous solid materials such as carbons, silica, zeolites, hollow fibers, and alumina have been widely investigated in CO₂ capture technologies. Interestingly, porous silica-based materials have recently emerged as excellent candidates for CO₂ capture technologies due to their unique properties, including high surface area, pore volume, easy surface functionalization, excellent thermal, and mechanical stability, and low cost. Therefore, this review comprehensively covers major CO₂ capture processes and their pros and cons, selecting a suitable sorbent, use of liquid amines, and highlights the recent progress of various porous silica materials, including amine-functionalized silica, their reaction mechanisms and synthesis processes. Moreover, CO₂ adsorption capacities, gas selectivity, reusability, current challenges, and future directions of porous silica materials have also been discussed.

Hybrid Polymer-Silica Nanostructured Materials for Environmental Remediation

Due to the ever-growing global population, it is necessary to develop highly effective processes that minimize the impact of human activities and consumption on the environment. The levels of organic and inorganic contaminants have rapidly increased in recent years, posing a threat to ecosystems. Removing these toxic pollutants from the environment is a challenging task that requires physical, chemical, and biological methods. An effective solution involves the use of novel engineered materials, such as silica-based nanostructured materials, which exhibit a high removal capacity for various pollutants. The starting materials are also thermally and mechanically stable, allowing for easy design and development at the nanoscale through versatile functionalization procedures, enabling their effective use in pollutant capture. However, improvements concerning mechanical properties or applicability for repeated cycles may be required to refine their structural features. This review focuses on hybrid/composite polymer-silica nanostructured materials. The state of the art in nanomaterial synthesis, different techniques of functionalization, and polymer grafting are described. Furthermore, it explores the application of polymer-modified nanostructured materials for the capture of heavy metals, dyes, hydrocarbons and petroleum derivatives, drugs, and other organic compounds. The paper concludes by offering recommendations for future research aimed at advancing the application of polymer-silica nanostructured materials in the efficiency of pollutant uptake.

Interplay between alkali-metal cations and silanol sites in nanosized CHA zeolite and implications for CO2 adsorption

Silanols are key players in the application performance of zeolites, yet, their localization and hydrogen bonding strength need more studies. The effects of post-synthetic ion exchange on nanosized chabazite (CHA), focusing on the formation of silanols, were studied. The significant alteration of the silanols of the chabazite nanozeolite upon ion exchange and their effect on the CO₂ adsorption capacity was revealed by solid-state nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR) spectroscopy, and periodic density functional theory (DFT) calculations. Both theoretical and experimental results revealed changing the ratio of extra-framework cations in CHA zeolites changes the population of silanols; decreasing the Cs⁺/K⁺ ratio creates more silanols. Upon adsorption of CO₂, the distribution and strength of the silanols also changed with increased hydrogen bonding, thus revealing an interaction of silanols with CO₂ molecules. To the best of our knowledge, this is the first evidence of the interplay between alkali-metal cations and silanols in nanosized CHA.

Implementation of a Core-Shell Design Approach for Constructing MOFs for CO2 Capture

Adsorption-based capture of CO₂ from flue gas and from air requires materials that have a high affinity for CO₂ and can resist water molecules that competitively bind to adsorption sites. Here, we present a core-shell metal-organic framework (MOF) design strategy where the core MOF is designed to selectively adsorb CO₂, and the shell MOF is designed to block H₂O diffusion into the core. To implement and test this strategy, we used the zirconium (Zr)-based UiO MOF platform because of its relative structural rigidity and chemical stability. Previously reported computational screening results were used to select optimal core and shell MOF compositions from a basis set of possible building blocks, and the target core-shell MOFs were prepared. Their compositions and structures were characterized using scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. Multigas (CO₂, N₂, and H₂O) sorption data were collected both for the core-shell MOFs and for the core and shell MOFs individually. These data were compared to determine whether the core-shell MOF architecture improved the CO₂ capture performance under humid conditions. The combination of experimental and computational results demonstrated that adding a shell layer with high CO₂/H₂O diffusion selectivity can significantly reduce the effect of water on CO₂ uptake.

Design and Validation of an Experimental Setup for Evaluation of Gas Permeation in Ceramic Membranes

An experimental setup for the evaluation of permeation of gaseous species with the possibility of simultaneously collecting electrochemical impedance spectroscopy data in disk-shaped ceramic membranes was designed and assembled. It consists of an alumina sample holder with thermocouple tips and platinum electrodes located close to both sides of the sample. Water-cooled inlet and outlet gas connections allowed for the insertion of the sample chamber into a programmable split tubular furnace. Gas permeation through a ceramic membrane can be monitored with mass flow controllers, a mass spectrometer, and an electrochemical impedance analyzer. For testing and data validation, ceramic composite membranes were prepared with the infiltration of molten eutectic compositions of alkali salts (lithium, sodium, and potassium carbonates) into porous gadolinia-doped ceria. Values of the alkali salt melting points and the permeation rates of carbon dioxide, in agreement with reported data, were successfully collected.

Multi-Scale Computer-Aided Design of Covalent Organic Frameworks for CO2 Capture in Wet Flue Gas

Discovery of remarkable porous materials for CO₂ capture from wet flue gas is of great significance to reduce the CO₂ emissions, but elucidating the most critical structure features for boosting CO₂ capture capabilities remains a great challenge. Here, machine-learning-assisted Monte Carlo computational screening on 516 experimental covalent organic frameworks (COFs) identifies the superior secondary building units (SBUs) for wet flue gas separation using COFs, which are tetraphenylporphyrin units for boosting CO₂ adsorption uptake and functional groups for boosting CO₂/N₂ selectivity. Accordingly, 1233 COFs are assembled using the identified superior SBUs. Density functional theory calculation analysis on frontier orbitals, electrostatic potential, and binding energy reveals the influencing mechanism of the SBUs on the wet flue gas separation performance. The "electron-donating-induced vdW interaction" effect is discovered to construct the better-performing COFs, which can achieve high CO₂ uptake of 4.4 mmol·g^-1 with CO₂/N₂ selectivity of 104.8. Meanwhile, the "electron-withdrawing-induced vdW + electrostatic coupling interaction" effect is unearthed to construct the better-performing COFs with superior CO₂/N₂ selectivity, which can reach 277.6 with CO₂ uptake of 2.2 mmol·g^-1; in this case, H₂O plays a positive contribution in improving CO₂/N₂ selectivity. This work provides useful guidelines for designing optimized two-dimensional-COF adsorbents for wet flue gas separation.

Ionic Liquids-Polymer of Intrinsic Microporosity (PIMs) Blend Membranes for CO2 Separation

Membranes with high CO₂ solubility are essential for developing a separation technology with low carbon footprint. To this end, physical blend membranes of [BMIM][Ac] and [BMIM][Succ] as Ionic Liquids (ILs) and PIM-1 as the polymer were prepared trying to combine the high permeability properties of PIM-1 with the high CO₂ solubility of the chosen ILs. Membranes with a PIM-1/[BMIM][Ac] 4/1 ratio nearly double their CO₂ solubility at 0.8 bar (0.86 cm³ (STP)/cm³ cmHg), while other ratios still maintain similar solubilities to PIM-1 (0.47 cm³ (STP)/cm³ cmHg). Moreover, CO₂ permeability of PIM-1/[BMIM][Ac] blended membranes were between 1050 and 2090 Barrer for 2/1 and 10/1 ratio, lower than PIM-1 membrane, but still highly permeable. The here presented self-standing and mechanically resistant blend membranes have yet a lower permeability compared to PIM-1 yet an improved CO₂ solubility, which eventually will translate in higher CO₂/N₂ selectivity. These promising preliminary results will allow us to select and optimize the best performing PIM-1/ILs blends to develop outstanding membranes for an improved gas separation technology.

Direct Air Capture of CO2 Using Poly(ethyleneimine)-Functionalized Expanded Poly(tetrafluoroethylene)/Silica Composite Structured Sorbents

The rapidly increasing atmospheric CO₂ concentration has driven research into the development of cost- and energy-efficient materials and processes for the direct air capture of CO₂ (DAC). Solid-supported amine materials can give high CO₂ uptakes and acceptable sorption kinetics, but they are generally prepared in powder forms that are likely not practically deployable in large-scale operations due to significant pressure drops associated with packed-bed gas-solid contactors. To this end, the development of effective gas-solid contactors for CO₂ capture technologies is important to allow processing high flow rates of gas with low-pressure drops and high mass transfer rates. In this study, we demonstrate new laminate-supported amine CO₂ sorbents based on the impregnation of low-molecular-weight, branched poly(ethyleneimine) (PEI) into an expanded poly(tetrafluoroethylene) (ePTFE) sheet matrix containing embedded silica particles to form free-standing sheets amenable to incorporation into structured gas-solid contactors. The free-standing sheets are functionalized with PEI using a highly scalable wet impregnation method. This method allowed controllable PEI distribution and enough porosity retained inside the sheets to enable practical CO₂ capacities ranging from 0.4 to 1.6 mmol CO₂/g_sorbent under dry conditions. Reversible CO₂ capacities are achieved under both dry and humid temperature swing cycles, indicating promising material stability. The specific thermal energy requirement for the regeneration based on the measured CO₂ and water capacities is 287 kJ/mol CO₂, where the molar ratio of water to CO₂ of 3.1 is achieved using hydrophobic materials. This is the lowest molar ratio among published DAC sorbents. A larger laminate module is tested under conditions closer to larger-scale operations (linear velocities 0.03, 0.05, and 0.1 m/sec) and demonstrates a stable capacity of 0.80 CO₂/g_sorbent over five cycles of CO₂ adsorption and steam regeneration. The PEI-impregnated ePTFE/silica composite sorbent/contactors demonstrate promising DAC performance derived from the amine-filled silica particles contained in hydrophobic ePTFE domains to reduce water sorption and its concomitant regeneration energy penalty.

Modeling Binary and Multicomponent Systems Containing Supercritical CO2 with Polyethylene Glycols and Compounds Relevant to the Biodiesel Production

The CPA equation of state is applied to model binary, ternary, and multicomponent mixtures that contain CO₂ with polyethylene glycols or compounds relevant to biodiesel production, such as glycerol and various triglycerides. Effort has been made to evaluate the model performance on correlating both the liquid and the vapor phase compositions, which is a demanding task, revealing the model’s and parameters’ limitations, due to the rather low concentrations of heavy compounds in the vapor phase. Initially the model’s binary parameters, which in all cases were temperature independent, were estimated using experimental data for binary systems. Those parameters were used to predict the phase behavior of supercritical CO₂ containing ternary and multicomponent mixtures. Since no parameter was adjusted to ternary or multicomponent systems’ data, the reported CPA results for such mixtures are considered as pure predictions. This is the final part of a series of studies [Tsivintzelis et al. Fluid Phase Equilibria 430 (2016) 75–92 and 504 (2020) 112337] that complete the parameterization of the CPA equation of state for systems relevant to the biodiesel production, which allows the application of the model to multicomponent mixtures of the relevant processes.

Synthesis and CO2 Capture of Porous Hydrogel Particles Consisting of Hyperbranched Poly(amidoamine)s

We successfully synthesized new macroporous hydrogel particles consisting of hyperbranched poly(amidoamine)s (HPAMAM) using the Oil-in-Water-in-Oil (O/W/O) suspension polymerization method at both the 50 mL flask scale and the 5 L reactor scale. The pore sizes and particle sizes were easily tuned by controlling the agitation speeds during the polymerization reaction. Since O/W/O suspension polymerization gives porous architecture to the microparticles, synthesized hydrogel particles having abundant amine groups inside polymers exhibited a high CO2 absorption capacity (104 mg/g) and a fast absorption rate in a packed-column test.

Post-combustion CO2 capture via a variety of temperature ranges and material adsorption process: A review

Carbon dioxide (CO₂) emissions from fossil fuel combustion have been linked to increased average global temperatures, a global challenge for many decades. Mitigating CO₂ concentration in the atmosphere is a priority for the protection of the environment. This is a comparison of the three main technological categories available for CO₂ capture and storage. They include: oxy-fuel combustion, pre-combustion, and post-combustion. Each capture technology has inherent benefits and disadvantages in cost, implementation, and flexibility, but post-combustion CO₂ capture has demonstrated the most promising results in typical power plant configurations. This paper presents a review of different post-combustion CO₂ capture materials; solvents, membranes, and adsorbents, focusing on economical and environmentally safe low to high temperature solid adsorbents. Furthermore, the authors summarize the advantages and limitations of the materials investigated to provide insight into the challenges and opportunities currently facing the development of post-combustion CO₂ capture technologies. The solid sorbents currently available for CO₂ capture are also reviewed in detail, including physical and chemical properties, reactions, and current research efforts on improvement.

Copper and Iron Cooperation on Micro-Spherical Silica during Methanol Synthesis via CO2 Hydrogenation

A series of mono- and bi-metallic copper and iron samples were prepared by impregnation method on micro-spherical silica and used for the synthesis of methanol via CO2 hydrogenation. Compared with conventional carrier oxides, micro-spherical silica has obvious advantages in terms of absorption capacity and optimal distribution of active phases on its surface, also exhibiting excellent heat resistance properties and chemical stability. The prepared catalysts were characterized by various techniques including XRF, XRD, SEM, TEM, H2-TPR and CO2-TPD techniques, while catalytic measurements in CO2 hydrogenation reaction to methanol were performed in a fixed bed reactor at a reaction pressure of 30 bar and temperature ranging from 200 to 260 °C. The obtained results revealed that the mutual interaction of copper–iron induces promotional effects on the formation of methanol, especially on systems where Fe enrichment on the silica support favours the presence of a larger concentration of oxygen vacancies, consequently responsible for higher CO2 adsorption and selective methanol production. Surface reconstruction phenomena rather than coke or metal sintering were responsible for the slight loss of activity recorded on the catalyst samples during the initial phase of reaction; however, with no appreciable change on the product selectivity.

Experimental Investigation of Mass Transfer Intensification for CO2 Capture by Environment-Friendly Water Based Nanofluid Solvents in a Rotating Packed Bed

In this research, two intensification approaches for CO2 capture via a rotating packed bed (RPB) and nanofluids were examined simultaneously to maximize the experimental mass transfer coefficient. The two intensification approaches were done by using water as a green, environmentally friendly absorption solvent and as the base fluid for preparing nanofluids and also by using centrifugal acceleration in an RPB. Physicosorption of CO2 in an RPB was carried out by applying Al2O3, TiO2, and SiO2 nanofluids to intensify the mass transfer in water, and the operation parameters such as the angular speed of the rotor, concentration and type of nanoparticles, gas and liquid flow rates, and CO2 concentration in mass transfer intensification were evaluated and several nanofluids were selected to survey investigate how they affect the mass transfer at low pressure. The results show that the Al2O3 nanofluid was more effective than other nanofluids and that the 40 nm nanofluid of this type was more efficient than the 20 nm size. Therefore, a correlation is proposed in this paper for liquid volumetric mass transfer coefficient prediction that includes the microconvection of nanoparticles and surface tension.

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.

Metal Oxides as Catalyst/Supporter for CO2 Capture and Conversion, Review

Various carbon dioxide (CO2) capture materials and processes have been developed in recent years. The absorption-based capturing process is the most significant among other processes, which is widely recognized because of its effectiveness. CO2 can be used as a feedstock for the production of valuable chemicals, which will assist in alleviating the issues caused by excessive CO2 levels in the atmosphere. However, the interaction of carbon dioxide with other substances is laborious because carbon dioxide is dynamically relatively stable. Therefore, there is a need to develop types of catalysts that can break the bond in CO2 and thus be used as feedstock to produce materials of economic value. Metal oxide-based processes that convert carbon dioxide into other compounds have recently attracted attention. Metal oxides play a pivotal role in CO2 hydrogenation, as they provide additional advantages, such as selectivity and energy efficiency. This review provides an overview of the types of metal oxides and their use for carbon dioxide adsorption and conversion applications, allowing researchers to take advantage of this information in order to develop new catalysts or methods for preparing catalysts to obtain materials of economic value.

Surface display of carbonic anhydrase on Escherichia coli for CO2 capture and mineralization

Mineralization catalyzed by carbonic anhydrase (CA) is one of the most promising technologies for capturing CO2. In this work, Escherichia coli BL21(DE3) was used as the host, and the N-terminus of ice nucleation protein (INPN) was used as the carrier protein. Different fusion patterns and vectors were used to construct CA surface display systems for α-carbonic anhydrase (HPCA) from Helicobacter pylori 26695 and α-carbonic anhydrase (SazCA) from Sulfurihydrogenibium azorense. The surface display system in which HPCA was fused with INPN via a flexible linker and intermediate repeat sequences showed higher whole-cell enzyme activity, while the enzyme activity of the SazCA expression system was significantly higher than that of the HPCA expression system. The pET22b vector with the signal peptide PelB was more suitable for the cell surface display of SazCA. Cell fractionation and western-blot analysis indicated that SazCA and INPN were successfully anchored on the cell's outer membrane as a fusion protein. The enzyme activity of the surface display strain E-22b-IRLS (11.43 U·mL-1OD600 -1) was significantly higher than that of the intracellular expression strain E-22b-S (8.355 U·mL-1OD600 -1) under optimized induction conditions. Compared with free SazCA, E-22b-IRLS had higher thermal and pH stability. The long-term stability of SazCA was also significantly improved by surface display. When the engineered strain and free enzyme were used for CO2 mineralization, the amount of CaCO3 deposition catalyzed by the strain E-22b-IRLS on the surface (241 mg) was similar to that of the free SazCA and was significantly higher than the intracellular expression strain E-22b-S (173 mg). These results demonstrate that the SazCA surface display strain can serve as a whole-cell biocatalyst for CO2 capture and mineralization.

Adsorption of CO2 on ZSM-5 Zeolite: Analytical Investigation via a Multilayer Statistical Physics Model

In this paper, a synthesized zeolite (ZSM-5) is used as an adsorbent to analyze the adsorption phenomenon of carbon dioxide. This investigation, based on the statistical physics treatment, applied the multilayer model with saturation to understand the CO2 adsorption on four samples, namely M-ZSM-5 (M = Na+, Mg2+, Zn2+, La3+), at various temperatures T = 0 °C, 30 °C and 60 °C. The modeling results indicated that CO2 adsorption occurred via a non-parallel orientation on the ZSM-5 surface. The CO2 adsorption capacities varied from 26.14 to 28.65 cm3/g for Na-ZSM-5, from 25.82 to 27.97 cm3/g for Mg-ZSM-5, from 54.82 to 68.63 cm3/g for La-ZSM-5 and from 56.53 to 74.72 cm3/g for Zn-ZSM-5. Thus, Zn-ZSM-5 exhibits the highest adsorption amount. The analysis of the adsorption energies shows that the adsorption of CO2 on ZSM-5 zeolite is a physisorption phenomenon that could be controlled thanks to the energy parameters obtained via the numerical findings using the multilayer statistical model. Finally, the distribution of site energy was determined to confirm the physical character of the interactions between adsorbate/adsorbent and the heterogeneity of the zeolite surface.

Sensitivity Increase in Headspace Analysis of Hydrocarbons in Water by Using Online Selective Elimination of Gas Extractant

In this study, a novel approach in headspace gas chromatographic analysis using the selective absorption of the gas extractant during concentration of the analytes was developed. The carbon dioxide used as the gas extractant was removed from the sample flow by passing it through a column packed with microdispersed sodium hydroxide granules. The analytical capabilities of the suggested method were illustrated by the determination of aliphatic and aromatic hydrocarbons in water. We established that this method allows the preconcentration of analytes in the gas phase to be increased proportionally to the volume ratios of the gas extractant before and after absorption, while the analyte limits of detection decrease 30-fold. For example, benzene can be detected in water at a concentration of 0.5 μg/L.