Liquid-in-Aerogel Porous Composite Allows Efficient CO2 Capture and CO2/N2 Separation

The pursuit of efficient CO₂ capture materials remains an unmet challenge. Especially, meeting both high sorption capacity and fast uptake kinetics is an ongoing effort in the development of CO₂ sorbents. Here, a strategy to exploit liquid-in-aerogel porous composites (LIAPCs) that allow for highly effective CO₂ capture and selective CO₂/N₂ separation, is reported. Interestingly, the functional liquid tetraethylenepentamine (TEPA) is partially filled into the air pockets of SiO₂ aerogel with left permanent porosity. Notably, the confined liquid thickness is 10.9–19.5 nm, which can be vividly probed by the atomic force microscope and rationalized by tailoring the liquid composition and amount. LIAPCs achieve high affinity between the functional liquid and solid porous counterpart, good structure integrity, and robust thermal stability. LIAPCs exhibit superb CO₂ uptake capacity (5.44 mmol g⁻¹, 75 °C, and 15 vol% CO₂), fast sorption kinetics, and high amine efficiency. Furthermore, LIAPCs ensure long-term adsorption–desorption cycle stability and offer exceptional CO₂/N₂ selectivity both in dry and humid conditions, with a separation factor up to 1182.68 at a humidity of 1%. This approach offers the prospect of efficient CO₂ capture and gas separation, shedding light on new possibilities to make the next-generation sorption materials for CO₂ utilization.     

Facile Fabrication of Monodispersed Carbon Sphere: A Pathway Toward Energy-Efficient Direct Air Capture (DAC) Using Amino Acids

Direct removal of carbon dioxide (CO₂) from the atmosphere, known as direct air capture (DAC) is attracting worldwide attention as a negative emission technology to control atmospheric CO₂ concentrations. However, the energy-intensive nature of CO₂ absorption-desorption processes has restricted deployment of DAC operations. Catalytic solvent regeneration is an effective solution to tackle this issue by accelerating CO₂ desorption at lower regeneration temperatures. This work reports a one-step synthesis methodology to prepare monodispersed carbon nanospheres (MCSs) using trisodium citrate as a structure-directing agent with acidic sites. The assembly of citrate groups on the surface of MCSs enables consistent spherical growth morphology, reduces agglomeration and enhances water dispersibility. The functionalization-assisted synthesis produces uniform, hydrophilic nanospheres of 100–600 nm range. This work also demonstrates that the prepared MCSs can be further functionalized with strong Brønsted acid sites, providing high proton donation ability. Furthermore, the materials can be effectively used in a wide range of amino acid solutions to substantially accelerate CO₂ desorption (25.6% for potassium glycinate and 41.1% for potassium lysinate) in the DAC process. Considering the facile synthesis of acidic MCSs and their superior catalytic efficiency, these findings are expected to pave a new path for energy-efficient DAC.     

CO2 capture at high temperature using calcium-based sorbents

Calcium-based sorbents synthesized from CaO, CaCO₃, and Ca(OH)₂ precursors were demonstrated as high-temperature CO₂ capture materials. The effect on CO₂ capture capability of calcium-based sorbents receiving different activations was also investigated. After proper activation, the best carbon capturing material is CaO that captured 75% of available CO₂ in nine cyclic tests and captured 61% even after 40 cyclic experiments. The correlation of the structural difference in the three activated sorbents and CO₂ conversion has been discussed. The sintering effect is presumably a major cause for activity decline of calcium-based sorbents… after cyclic carbonation/decarbonation runs.     

A comprehensive overview of carbon dioxide capture: From materials,methods to industrial status

The separation and sequestration of anthropogenic CO₂ is one of the most effective steps to counter global warming by curtailing the excess CO₂ levels in the atmosphere. However, to achieve the global climate change targets, in addition to the capture of CO₂ from the point sources, complementary carbon-negative technologies that capture CO₂ directly from the atmosphere are also necessary. The most crucial aspect of any CO₂ capture technology is the selection of a suitable sorbent, which is the most efficient in a specific temperature, pressure, and moisture range. The urgent nature of the CO₂ crisis has led to overwhelming contributions from researchers globally in terms of different sorbents, measurement techniques, reactors, and processes. Additionally, to develop a commercially viable CO₂ capture technology, a detailed and holistic techno-economic analysis is also vital. In this review, we have documented the recent progress on CO₂ capture studies using different solid sorbents under various operational conditions, along with the methodologies and reactors used for these studies. Furthermore, this review presents a detailed account of the industrial status of various existing CO₂ capture technologies, including direct air capture and its techno-economic prospects. This review aims to provide a bird’s eye view of the status of CO₂ capture research with a particular emphasis on the most recent developments in this field.     

Valuing Metal–Organic Frameworks for Postcombustion Carbon Capture: A Benchmark Study for Evaluating Physical Adsorbents

The development of practical solutions for the energy‐efficient capture of carbon dioxide is of prime importance and continues to attract intensive research interest. Conceivably, the implementation of adsorption‐based processes using different cycling modes, e.g., pressure‐swing adsorption or temperature‐swing adsorption, offers great prospects to address this challenge. Practically, the successful deployment of practical adsorption‐based technologies depends on the development of made‐to‐order adsorbents expressing mutually two compulsory requisites: i) high selectivity/affinity for CO₂ and ii) excellent chemical stability in the presence of impurities. This study presents a new comprehensive experimental protocol apposite for assessing the prospects of a given physical adsorbent for carbon capture under flue gas stream conditions. The protocol permits: i) the baseline performance of commercial adsorbents such as zeolite 13X, activated carbon versus liquid amine scrubbing to be ascertained, and ii) a standardized evaluation of the best reported metal–organic framework (MOF) materials for carbon dioxide capture from flue gas to be undertaken. This extensive study corroborates the exceptional CO₂ capture performance of the recently isolated second‐generation fluorinated MOF material, NbOFFIVE ‐1‐Ni, concomitant with an impressive chemical stability and a low energy for regeneration. Essentially, the NbOFFIVE ‐1‐Ni adsorbent presents the best compromise by satisfying all the required metrics for efficient CO₂ scrubbing.     

Improving Prediction Accuracy of a Rate-Based Model of an MEA-Based Carbon Capture Process for Large-Scale Commercial Deployment

Carbon capture and storage (CCS) technology will play a critical role in reducing anthropogenic carbon dioxide (CO₂) emission from fossil-fired power plants and other energy-intensive processes. However, the increment of energy cost caused by equipping a carbon capture process is the main barrier to its commercial deployment. To reduce the capital and operating costs of carbon capture, great efforts have been made to achieve optimal design and operation through process modeling, simulation, and optimization. Accurate models form an essential foundation for this purpose. This paper presents a study on developing a more accurate rate-based model in Aspen Plus^® for the monoethanolamine (MEA)-based carbon capture process by multistage model validations. The modeling framework for this process was established first. The steady-state process model was then developed and validated at three stages, which included a thermodynamic model, physical properties calculations, and a process model at the pilot plant scale, covering a wide range of pressures, temperatures, and CO₂ loadings. The calculation correlations of liquid density and interfacial area were updated by coding Fortran subroutines in Aspen Plus^®. The validation results show that the correlation combination for the thermodynamic model used in this study has higher accuracy than those of three other key publications and the model prediction of the process model has a good agreement with the pilot plant experimental data. A case study was carried out for carbon capture from a 250 MW_e combined cycle gas turbine (CCGT) power plant. Shorter packing height and lower specific duty were achieved using this accurate model.     

Multishelled CaO Microspheres Stabilized by Atomic Layer Deposition of Al2O3 for Enhanced CO2 Capture Performance

CO₂ capture and storage is a promising concept to reduce anthropogenic CO₂ emissions. The most established technology for capturing CO₂ relies on amine scrubbing that is, however, associated with high costs. Technoeconomic studies show that using CaO as a high‐temperature CO₂ sorbent can significantly reduce the costs of CO₂ capture. A serious disadvantage of CaO derived from earth‐abundant precursors, e.g., limestone, is the rapid, sintering‐induced decay of its cyclic CO₂ uptake. Here, a template‐assisted hydrothermal approach to develop CaO‐based sorbents exhibiting a very high and cyclically stable CO₂ uptake is exploited. The morphological characteristics of these sorbents, i.e., a porous shell comprised of CaO nanoparticles coated by a thin layer of Al₂O₃ (<3 nm) containing a central void, ensure (i) minimal diffusion limitations, (ii) space to accompany the substantial volumetric changes during CO₂ capture and release, and (iii) a minimal quantity of Al₂O₃ for structural stabilization, thus maximizing the fraction of CO₂‐capture‐active CaO.     

Porous liquids as solvents for the economical separation of carbon dioxide from methane

Current CO₂ separation technologies by liquid solvents suffer from either high regeneration costs or low selectivity/capacity of the solvent. Dispersing ca. 12.5 wt% CO₂-selective zeolite rho solid into the commercial CO₂ capture solvent Genosorb® converts it into a porous liquid with at least 2.5 times greater CO₂ capacity and CO₂/CH₄ selectivity compared to Genosorb® itself. This is predicted to result in more economical separation processes, particularly for biogas upgrading.     

Development of CO2 Selective Poly(Ethylene Oxide)-Based Membranes: From Laboratory to Pilot Plant Scale

Membrane gas separation is one of the most promising technologies for the separation of carbon dioxide (CO₂) from various gas streams. One application of this technology is the treatment of flue gases from combustion processes for the purpose of carbon capture and storage. For this application, poly(ethylene oxide)-containing block copolymers such as Pebax^® or PolyActive™ polymer are well suited. The thin-film composite membrane that is considered in this overview employs PolyActive™ polymer as a selective layer material. The membrane shows excellent CO₂ permeances of up to 4 m³(STP)·(m²·h·bar)⁻¹ (1 bar = 10⁵ Pa) at a carbon dioxide/nitrogen (CO₂/N₂) selectivity exceeding 55 at ambient temperature. The membrane can be manufactured reproducibly on a pilot scale and mounted into flat-sheet membrane modules of different designs. The operating performance of these modules can be accurately predicted by specifically developed simulation tools, which employ single-gas permeation data as the only experimental input. The performance of membranes and modules was investigated in different pilot plant studies, in which flue gas and biogas were used as the feed gas streams. The investigated processes showed a stable separation performance, indicating the applicability of PolyActive™ polymer as a membrane material for industrial-scale gas processing.     

Assessing the carbon sequestration potential of magnesium oxychloride cement building materials

Magnesium oxychloride cement (MOC) boards have the potential to offset carbon emissions through carbon mineralization, a process whereby carbon dioxide (CO₂) is converted to carbonate minerals. Boards (0–15 years old) contained MOC phase 5 (21–50 wt%), brucite, primary (e.g., magnesite) and secondary (hydromagnesite and chlorartinite) carbonate minerals. Quantitative mineralogy, electron microscopy and carbon abundance data demonstrate that secondary carbonates form through the reactions of MOC and brucite with CO₂ within interfacial water layers after board manufacturing. Stable carbon isotopic data confirmed the source of sequestered CO₂ as being from the atmosphere. Average carbonation rates were approximately 0.07 kg CO₂/m² board/year or 9.8 kg CO₂/t board/year over 15 years, offsetting ∼20–40% of estimated carbon emissions. In experiments using 10% and 100% CO₂ gas, carbonation was accelerated by approximately 400 and 1600 times in comparison to the passive rate. Integration of carbonation reactions into MOC board production could provide significant carbon offsets.     

Optimal Bidding and Operation of a Power Plant with Solvent-Based Carbon Capture under a CO2 Allowance Market: A Solution with a Reinforcement Learning-Based Sarsa Temporal-Difference Algorithm

In this paper, a reinforcement learning (RL)-based Sarsa temporal-difference (TD) algorithm is applied to search for a unified bidding and operation strategy for a coal-fired power plant with monoethanolamine (MEA)-based post-combustion carbon capture under different carbon dioxide (CO₂) allowance market conditions. The objective of the decision maker for the power plant is to maximize the discounted cumulative profit during the power plant lifetime. Two constraints are considered for the objective formulation. Firstly, the tradeoff between the energy-intensive carbon capture and the electricity generation should be made under presumed fixed fuel consumption. Secondly, the CO₂ allowances purchased from the CO₂ allowance market should be approximately equal to the quantity of CO₂ emission from power generation. Three case studies are demonstrated thereafter. In the first case, we show the convergence of the Sarsa TD algorithm and find a deterministic optimal bidding and operation strategy. In the second case, compared with the independently designed operation and bidding strategies discussed in most of the relevant literature, the Sarsa TD-based unified bidding and operation strategy with time-varying flexible market-oriented CO₂ capture levels is demonstrated to help the power plant decision maker gain a higher discounted cumulative profit. In the third case, a competitor operating another power plant identical to the preceding plant is considered under the same CO₂ allowance market. The competitor also has carbon capture facilities but applies a different strategy to earn profits. The discounted cumulative profits of the two power plants are then compared, thus exhibiting the competitiveness of the power plant that is using the unified bidding and operation strategy explored by the Sarsa TD algorithm.     

Covalent Organic Frameworks as a Decorating Platform for Utilization and Affinity Enhancement of Chelating Sites for Radionuclide Sequestration

The potential consequences of nuclear events and the complexity of nuclear waste management motivate the development of selective solid‐phase sorbents to provide enhanced protection. Herein, it is shown that 2D covalent organic frameworks (COFs) with unique structures possess all the traits to be well suited as a platform for the deployment of highly efficient sorbents such that they exhibit remarkable performance, as demonstrated by uranium capture. The chelating groups laced on the open 1D channels exhibit exceptional accessibility, allowing significantly higher utilization efficiency. In addition, the 2D extended polygons packed closely in an eclipsed fashion bring chelating groups in adjacent layers parallel to each other, which may facilitate their cooperation, thereby leading to high affinity toward specific ions. As a result, the amidoxime‐functionalized COFs far outperform their corresponding amorphous analogs in terms of adsorption capacities, kinetics, and affinities. Specifically, COF‐TpAb‐AO is able to reduce various uranium contaminated water samples from 1 ppm to less than 0.1 ppb within several minutes, well below the drinking water limit (30 ppb), as well as mine uranium from spiked seawater with an exceptionally high uptake capacity of 127 mg g^?1. These results delineate important synthetic advances toward the implementation of COFs in environmental remediation.     

Mixed waste ferrite as a novel sorbent for carbon dioxide derived from flue gases

Ferrite is a potential sorbent for flue gases such as CO₂, H₂S and SO₂. This paper discusses the adsorption and decomposition of CO₂ into carbon by hydrogen-activated waste ferrites prepared from Berkeley Pit acid mine water (Butte, MT). The decomposition effectiveness of these waste ferrites was studied at 300 °C and compared with the synthetic magnetite obtained from ferrous sulfate solution in our laboratory. The decomposition was measured by two methods: indirectly by measuring the adsorption rate of CO₂ and directly by analysing the carbon deposited on the samples. The results indicated that the mixed waste ferrite had good affinity for the adsorption and decomposition. The CO₂ decomposition data of both sorbents fitted the first-order reaction kinetics. Even though the surface area of the magnetite was higher than that of waste ferrite, the CO₂ decomposition rate of the waste ferrite was estimated to be 2.5 times higher than that of magnetite under identical conditions. The carbon analysis deposited on the sample indicated that the CO₂ was 100% decomposed into carbon and other carbon/hydrogen compounds by the waste ferrite, whereas the conversion was 43% by the magnetite. In terms of specific adsorption of carbon, ferrite was three to five times more efficient than magnetite.     

Field-emission characteristics of diamond-like amorphous carbon films deposited by mixed gas (N2 or H2) controlled i-C4H10 supermagnetron plasma

Diamond-like amorphous carbon (DAC) films were deposited for field-emission application using supermagnetron plasma by mixing N₂ or H₂ in i-C₄H₁₀ gas at the upper and lower electrode rf powers (UPRF/LORF) of 800 W/100-800 W. At an 800 W/800 W, the N₂ (0-80%) gas-mixed DAC films showed an emission threshold electric field (E_TH) of 19 V/μm. At the 800 W/100 W, the H₂ (20%) gas-mixed DAC film showed low E_TH's of 13 V/μm, respectively. The moderate reduction of CC and CN double bonds by the decrease of LORF from 800 W to 100 W was found to be effective to lower E_TH.     

Restricting Lattice Flexibility in Polycrystalline Metal–Organic Framework Membranes for Carbon Capture

Although polycrystalline metal‐organic framework (MOF) membranes offer several advantages over other nanoporous membranes, thus far they have not yielded good CO₂ separation performance, crucial for energy‐efficient carbon capture. ZIF‐8, one of the most popular MOFs, has a crystallographically determined pore aperture of 0.34 nm, ideal for CO₂/N₂ and CO₂/CH₄ separation; however, its flexible lattice restricts the corresponding separation selectivities to below 5. A novel postsynthetic rapid heat treatment (RHT), implemented in a few seconds at 360 °C, which drastically improves the carbon capture performance of the ZIF‐8 membranes, is reported. Lattice stiffening is confirmed by the appearance of a temperature‐activated transport, attributed to a stronger interaction of gas molecules with the pore aperture, with activation energy increasing with the molecular size (CH₄ > CO₂ > H₂). Unprecedented CO₂/CH₄, CO₂/N₂, and H₂/CH₄ selectivities exceeding 30, 30, and 175, respectively, and complete blockage of C₃H₆, are achieved. Spectroscopic and X‐ray diffraction studies confirm that while the coordination environment and crystallinity are unaffected, lattice distortion and strain are incorporated in the ZIF‐8 lattice, increasing the lattice stiffness. Overall, RHT treatment is a facile and versatile technique that can vastly improve the gas‐separation performance of the MOF membranes.     

A Chemically Stable Hofmann-Type Metal−Organic Framework with Sandwich-Like Binding Sites for Benchmark Acetylene Capture

The realization of porous materials for highly selective separation of acetylene (C₂H₂) from various other gases (e.g., carbon dioxide and ethylene) by adsorption is of prime importance but challenging in the petrochemical industry. Herein, a chemically stable Hofmann-type metal−organic framework (MOF), Co(pyz)[Ni(CN)₄] (termed as ZJU-74a), that features sandwich-like binding sites for benchmark C₂H₂ capture and separation is reported. Gas sorption isotherms reveal that ZJU-74a exhibits by far the record C₂H₂ capture capacity (49 cm³ g⁻¹ at 0.01 bar and 296 K) and thus ultrahigh selectivity for C₂H₂/CO₂ (36.5), C₂H₂/C₂H₄ (24.2), and C₂H₂/CH₄ (1312.9) separation at ambient conditions, respectively, of which the C₂H₂/CO₂ selectivity is the highest among all the robust MOFs reported so far. Theoretical calculations indicate that the oppositely adjacent nickel(II) centers together with cyanide groups from different layers in ZJU-74a can construct a sandwich-type adsorption site to offer dually strong and cooperative interactions for the C₂H₂ molecule, thus leading to its ultrahigh C₂H₂ capture capacity and selectivities. The exceptional separation performance of ZJU-74a is confirmed by both simulated and experimental breakthrough curves for 50/50 (v/v) C₂H₂/CO₂, 1/99 C₂H₂/C₂H₄, and 50/50 C₂H₂/CH₄ mixtures under ambient conditions.     

Ultrathin Nitrogen-Doped Carbon Encapsulated Ni Nanoparticles for Highly Efficient Electrochemical CO2 Reduction and Aqueous Zn-CO2 Batteries

Electrochemical CO₂ reduction reaction (CO₂RR), powered by renewable electricity, has attracted great attention for producing high value-added fuels and chemicals, as well as feasibly mitigating CO₂ emission problem. Here, this work reports a facile hard template strategy to prepare the Ni@N-C catalyst with core–shell structure, where nickel nanoparticles (Ni NPs) are encapsulated by thin nitrogen-doped carbon shells (N-C shells). The Ni@N-C catalyst has demonstrated a promising industrial current density of 236.7 mA cm⁻² with the superb FE_CO of 97% at −1.1 V versus RHE. Moreover, Ni@N-C can drive the reversible Zn-CO₂ battery with the largest power density of 1.64 mW cm⁻², and endure a tough cycling durability. These excellent performances are ascribed to the synergistic effect of Ni@N-C that Ni NPs can regulate the electronic microenvironment of N-doped carbon shells, which favor to enhance the CO₂ adsorption capacity and the electron transfer capacity. Density functional theory calculations prove that the binding configuration of N-C located on the top of Ni slabs (Top-Ni@N-C) is the most thermodynamically stable and possess a lowest thermodynamic barrier for the formation of COOH^* and the desorption of CO. This work may pioneer a new method on seeking high-efficiency and worthwhile electrocatalysts for CO₂RR and Zn-CO₂ battery.     

Preparation and CO_2 adsorption properties of porous carbon by hydrothermal carbonization of tree leaves

Porous carbon materials were prepared by hydrothermal carbonization(HTC) and KOH activation of camphor leaves and camellia leaves. The morphology, pore structure, chemical properties and CO_2 capture ability of the porous carbon prepared from the two leaves were compared. The effect of HTC temperature on the structure and CO_2 adsorption properties was especially investigated. It was found that HTC temperature had a major effect on the structure of the product and the ability to capture CO_2. The porous carbon materials prepared from camellia leaves at the HTC temperature of 240℃ had the highest proportion of microporous structure, the largest specific surface area(up to 1823.77 m~2/g) and the maximum CO_2 adsorption capacity of 8.30 mmol/g at 25℃ under 0.4 MPa. For all prepared porous carbons, simulation results of isothermal adsorption model showed that Langmuir isotherm model described the adsorption equilibrium data better than Freundlich isotherm model. For porous carbons prepared from camphor leaves, pseudo-first order kinetic model was well fitted with the experimental data. However,for porous carbons prepared from camellia leaves, both pseudo-first and pseudo-second order kinetics model adsorption behaviors were present. The porous carbon materials prepared from tree leaves provided a feasible option for CO_2 capture with low cost, environmental friendship and high capture capability.     

Evidence of Microporous Carbon Nanosheets Showing Fast Kinetics in both Gas Phase and Liquid Phase Environments

Despite the great advantages of microporous carbons for applications in gas phase separation, liquid phase enrichment, and energy storage devices, direct experiment data and theoretical calculations on the relevance of properties and structures are quite limited. Herein, two model carbon materials are designed and synthesized, i.e., microporous carbon nanosheets (MCN) and microporous carbon spheres (MCS). They both have nearly same composition, surface chemistry, and specific surface area, known morphology, but distinguishable diffusion paths. Based on these two types of materials, a reliable relationship between the morphology with different diffusion paths and adsorption kinetics in both gas phase and liquid phase environments is established. When used for CO₂ capture, MCN shows a high saturated CO₂ capacity of 8.52 μmol m⁻² and 18.4 mmol cm⁻³ at 273 K and ambient pressure, and its calculated first‐order rate constant is ≈7.4 times higher than that of MCS. Moreover, MCN shows a quick and high uptake of Cr (VI) and a higher‐rate performance for supercapacitors than MCS does. These results strongly confirm that MCN exhibits improved kinetics in gas phase separation, liquid phase enrichment, and energy storage devices due to its shorter diffusion paths and larger exposed geometrical area resulting from the nanosheet structure.     

Synergistic Functionality of Dopants and Defects in Co-Phthalocyanine/B-CN Z-Scheme Photocatalysts for Promoting Photocatalytic CO2 Reduction Reactions

The realization of solar-light-driven CO₂ reduction reactions (CO₂ RR) is essential for the commercial development of renewable energy modules and the reduction of global CO₂ emissions. Combining experimental measurements and theoretical calculations, to introduce boron dopants and nitrogen defects in graphitic carbon nitride (g-C₃N₄), sodium borohydride is simply calcined with the mixture of g-C₃N₄ (CN), followed by the introduction of ultrathin Co phthalocyanine through phosphate groups. By strengthening H-bonding interactions, the resultant CoPc/P-BNDCN nanocomposite showed excellent photocatalytic CO₂ reduction activity, releasing 197.76 and 130.32 µmol h⁻¹ g⁻¹ CO and CH₄, respectively, and conveying an unprecedented 10-26-time improvement under visible-light irradiation. The substantial tuning is performed towards the conduction and valance band locations by B-dopants and N-defects to modulate the band structure for significantly accelerated CO₂ RR. Through the use of ultrathin metal phthalocyanine assemblies that have a lot of single-atom sites, this work demonstrates a sustainable approach for achieving effective photocatalytic CO₂ activation. More importantly, the excellent photoactivity is attributed to the fast charge separation via Z-scheme transfer mechanism formed by the universally facile strategy of dimension-matched ultrathin (≈4 nm) metal phthalocyanine-assisted nanocomposites.