Direct CO2 Capture Research Articles

On the synergy between Ru and K2CO3 supported on carbon nanofibers for the direct air capture and conversion of CO2

On the synergy between Ru and K2CO3 supported on carbon nanofibers for the direct air capture and conversion of CO2

Innovative Design of PEI-Modified AMO-Layered Double Hydroxide for Efficient and Stable Direct Air Capture of CO2.

Emerging as a critical technology for atmospheric carbon dioxide (CO2)removal, the mass deployment of direct air capture (DAC) demands breakthrough innovations in efficient and stable adsorbent materials that simultaneously achieve high capacity, oxidative durability, and low cost. Herein, a hydroxyl-rich Mg0.55Al layered double hydroxide (LDH) support is developed via aqueous miscible organic solvent treatment, circumventing energy-intensive calcination while engineering mesopores for efficient polyethyleneimine (PEI) loading. The optimized 60wt.% PEI modified Mg0.55Al-CO3 AMO-LDH achieves a CO2 uptake of 3.92mmol g-1 under simulated wet air at 25°C and retains 90.8% capacity over 20 cycles. Crucially, the abundant surface hydroxyls of uncalcined LDH, validated by 1H Nuclear Magnetic Resonance and in situ X-ray Photoelectron Spectroscopy, form hydrogen bonds with PEI, suppressing oxidative degradation. After 3h at 120°C in simulated air, PEI-LDH retains a CO2 capacity of 1.06mmol g-1, significantly outperforming PEI/mixed metal oxide and conventional silica-based adsorbents. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy further reveals that hydroxyl-mediated amine anchoring minimizes water co-adsorption. This work establishes a dual strategy of hydroxyl preservation and mesopore engineering to design cost-effective DAC adsorbents, achieving both high capacity and exceptional stability under realistic operating conditions.

Effect of Humidity on the Energy and CO2 Separation Characteristics of Membranes in Direct Air Capture Technology

Membrane-based direct air capture of CO2 (m-DAC) is a promising solution for atmospheric decarbonization. Despite growing interest, the impact of relative air humidity on the performance of m-DAC systems is often neglected in the literature. This study presents detailed parametric analyses that take into account humidity variability and several hypothetical scenarios regarding membrane selectivity toward water vapor. Specifically, cases were considered where the permeance of H2O relative to CO2 was assumed to be 0.5, 2, and 5 times higher, which allowed for a systematic assessment of the impact of relative humidity on process performance. The calculations were carried out both for membranes with assumed separation parameters and for the PolyActiveTM membrane, enabling a realistic evaluation of the influence of atmospheric conditions on the process. The results show that an increase in humidity in the analyzed range from 0 to 80% can lead to a rise in the energy intensity of the process by up to approximately 34%, and an increase in total power demand by around 29%. As humidity increases, key process parameters such as CO2 purity in the permeate and recovery rate decrease. The water vapor content in the permeate in a single-stage membrane separation process can reach up to 60%. It is recommended to use gas drying systems and to develop membranes with low H2O permeance in order to reduce the energy cost of the process. The potential location of m-DAC systems should preferably be in regions with low air humidity. The study highlights the necessity of considering local climate conditions and the need for further research on membrane selectivity.

Session 24. Oral Presentation for: Amine based liquid capture technology for direct air capture of CO2 – an overview on technology development

Presented on 29 May 2025: Session 24 The large-scale deployment of direct air capture (DAC) technologies is essential to meet the global target of limiting temperature increase to below 2°C. Amine-based liquid capture technology, as the leading method for point-source CO2 capture, holds promise as a low-cost and scalable solution for DAC. We previously reported that the cost of this technology could approach US$100/tCO2, using a non-volatile absorbent, inexpensive cooling towers as gas–liquid contactors, and scaling up to capture 1 million tonnes of CO2 per year. To further reduce CO2 capture costs, we developed a second-generation DAC system, named the mist contactor. This system atomises the absorption liquid into fine droplets, increasing the contact area between the liquid and air. The resulting lower liquid-to-gas ratio, reduced gas-side pressure drops, and potentially higher capture rates are expected to reduce CO2 capture costs even further. We developed an optimised process design and model as a baseline for the design and construction of a pilot-scale system capable of capturing approximately 100 tonnes of CO2 per year. For DAC to contribute to achieving net-zero emissions, the CO2 captured must be either stored underground or utilised. Integrating DAC with downstream processes can further reduce costs by sharing infrastructure between capture, storage, and utilisation. A preliminary assessment of the integration between DAC and downstream processes, such as CO2 compression and fuel production, has been conducted and will be presented. To access the Oral Presentation click the link on the right. To read the full paper click here

The effects of counter ion on CO2 capture performance of amino acid salt solutions for direct air capture applications

The effects of counter ion on CO2 capture performance of amino acid salt solutions for direct air capture applications

Understanding the Role of Hydroxyl Functionalization in Linear Poly(Ethylenimine) for Oxidation‐Resistant Direct Air Capture of CO2

Abstract Aminopolymer‐based adsorbents are a prominent class of materials being used for direct air capture of CO2 at the industrial scale. However, improving their working lifetime, specifically by increasing their resilience to oxidative degradation, remains an ongoing challenge. Toward this end, functionalization of aminopolymers with non‐amine functionalities such as hydroxyls has emerged in recent years as a promising strategy toward improving adsorbent lifetime. Although there is a growing body of work demonstrating the effectiveness of this approach and investigating the origin of this improved stability, studies to date have primarily focused on branched aminopolymer systems such as branched poly(ethylenimine). In this work, hydroxyl‐functionalized linear poly(ethylenimine) is used to continue to probe the underlying protective mechanism of this strategy. A combination of thermogravimetric analysis, NMR relaxometry, differential scanning calorimetry, and computational simulations is used to better understand the relationship between the extent of chemical functionalization, physical properties, and adsorbent performance.

Nanoscopic structure of polyethyleneimine thin films evaluated using positron annihilation lifetime technique

Abstract Polyethyleneimine (PEI)-loaded porous materials show considerable promise for direct air capture of CO2. The energy-variable positron annihilation lifetime (PAL) technique has been employed to assess the nanoscopic free volume of PEI thin films, a key factor influencing gas transport properties. The PAL results showed that free-volume size decreases slightly due to carbamation and significantly due to amidation, as compared to the macroscopic properties derived from FT-IR and spectroscopic ellipsometry. In addition, these reductions in free volume become more pronounced with decreasing film thickness. This highlights PAL as a valuable method for characterizing the nanostructure of PEI films, subsequently enhancing the gas transport performance of high-efficiency CO2 capture materials.

Comparative study of modified Cu-BTC and ZIF-8 adsorbents for stable and enhanced direct air capture of CO2

Comparative study of modified Cu-BTC and ZIF-8 adsorbents for stable and enhanced direct air capture of CO2

Techno-economic and environmental life cycle analysis of renewable-based combined potassium - calcium looping cycle for direct air CO2 capture

Techno-economic and environmental life cycle analysis of renewable-based combined potassium - calcium looping cycle for direct air CO2 capture

Evaluating the performance and kinetics of amine-modified NaY zeolites from rice husk for direct air CO2 capture

Evaluating the performance and kinetics of amine-modified NaY zeolites from rice husk for direct air CO2 capture

Integrated direct air CO2 capture and solid oxide electrolyzer for sustainable chemical production: Case studies of methanol and synthesis fuel

Integrated direct air CO2 capture and solid oxide electrolyzer for sustainable chemical production: Case studies of methanol and synthesis fuel

Investigation of microwave-assisted regeneration of zeolite 13X for efficient direct air CO2 capture: a comparison with conventional heating method

This study investigates the regeneration of zeolite 13X for direct air CO2 capture by comparing microwave-assisted and conventional heating methods in a fixed-bed reactor. Zeolite 13X, a high-surface-area solid adsorbent, was tested over three adsorption/desorption cycles under ambient conditions with approximately 400 ppm of CO2. Microwave-assisted regeneration, optimized at 300 W for 10 min (350 °C), achieved a regeneration efficiency of 95.26%, with minimal loss in adsorption capacity (9%) across cycles. Conventional heating at 350 °C for 30 min achieved a comparable efficiency of 93.90% but required significantly more time and energy. The microwave technique operates via direct dielectric heating, selectively exciting polar species such as mobile Na⁺ ions within the zeolite framework. This localized and volumetric heating enhances CO2 desorption without requiring reactor preheating or carrier gas flow, unlike conventional methods that rely on slower conduction and convection. As a result, microwave regeneration demonstrated a tenfold reduction in energy consumption (0.06 kWh vs. 0.62 kWh for conventional heating). Statistical analysis using ANOVA identified microwave power and regeneration time as key factors, with microwave power exerting the greatest influence. The study highlights the advantages of microwave-assisted regeneration, including reduced energy demand, shorter regeneration times, and enhanced scalability. These findings emphasize its potential as a transformative approach for advancing direct air capture technologies. Compared to conventional methods, microwave-assisted regeneration offers a more energy-efficient and practical solution for CO2 removal from ambient air.

Amine based liquid capture technology for direct air capture of CO2 – an overview on technology development

The large-scale deployment of direct air capture (DAC) technologies is essential to meet the global target of limiting temperature increase to below 2°C. Amine-based liquid capture technology, as the leading method for point-source CO2 capture, holds promise as a low-cost and scalable solution for DAC. We previously reported that the cost of this technology could approach US$100/tCO2, using a non-volatile absorbent, inexpensive cooling towers as gas–liquid contactors, and scaling up to capture 1 million tonnes of CO2 per year. To further reduce CO2 capture costs, we developed a second-generation DAC system, named the mist contactor. This system atomises the absorption liquid into fine droplets, increasing the contact area between the liquid and air. The resulting lower liquid-to-gas ratio, reduced gas-side pressure drops, and potentially higher capture rates are expected to reduce CO2 capture costs even further. We developed an optimised process design and model as a baseline for the design and construction of a pilot-scale system capable of capturing approximately 100 tonnes of CO2 per year. For DAC to contribute to achieving net-zero emissions, the CO2 captured must be either stored underground or utilised. Integrating DAC with downstream processes can further reduce costs by sharing infrastructure between capture, storage, and utilisation. A preliminary assessment of the integration between DAC and downstream processes, such as CO2 compression and fuel production, has been conducted and will be presented.

Nature-based and geo-engineering climate mitigation technologies: Public acceptance and security prospects.

Climate change requires mitigation approaches, from nature-based to experimental geoengineering. We examined public attitudes toward six strategies-reforestation in previously forested areas, afforestation in new terrains, direct CO2 capture with underground storage, biomass energy with CO2 capture, stratospheric sulfate aerosols, and orbital mirrors-via a representative Czech survey (N= 3,007). Binary logistic regressions reveal how age, education, employment, and residence shape perceptions of efficacy, risks, and ethics. Results show strong favor for reforestation and afforestation due to ecological benefits and long-term promise; sulfate aerosols and orbital mirrors face skepticism. Surprisingly, participants with only primary education showed greater openness to geoengineering than university graduates. Older respondents favored biomass-based carbon capture but less so certain high-tech solutions. Our findings highlight the importance of policies aligned with diverse public views, ensuring both established and novel measures are harmonized into an effective climate mitigation strategy. These results indicate demographic contexts shape acceptance of climate interventions.

Amine-Functionalized Defective MOFs for Direct Air Capture by Postsynthetic Modification.

Amine-functionalized defective metal-organic frameworks (DM) showed promise for direct air capture (DAC) of CO2 under ambient conditions. In this work, chromium-based DM was functionalized via a two-step postsynthetic modification with ethylenediamine (EDA), tris(2-aminoethyl)amine (TAEA), and polyethylene-polyamines (PEPA). Characterization by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) confirmed successful synthesis and structural integrity. Among the samples, 1:1-PEPA-DM exhibited the best performance, with a CO2 adsorption capacity of 1.26 mmol/g, a regeneration energy of 75.1 kJ/mol, and only 26.62% capacity loss after 12 cycles in ambient air. In contrast, 1:1-TAEA-DM showed a high regeneration energy (158.61 kJ/mol) and a 95.17% capacity loss. Physically impregnating PEPA resulted in a lower capacity (0.94 mmol/g) and a loss of 76.32% after 12 cycles. These results highlight covalent PEPA grafting as a promising strategy for developing durable DAC sorbents.

In Pursuit of Carbon Neutrality: Progresses and Innovations in Sorbents for Direct Air Capture of CO2.

Direct air capture (DAC) is of immense current interest, as a means to facilitate CO2 capture at low concentrations (∼400ppm) directly from the atmosphere, with the aim of addressing global warming caused by excessive anthropogenic CO2 production. Traditionally, DAC of CO2 has relied on amine scrubbing and metal carbonate /hydroxide solutions. However, recent years have seen notable progress in DAC sorbents, with key advancements aimed at improving efficiency, capacity, and regenerability while reducing energy consumption. This review delivers an exhaustive analysis of contemporary developments in DAC sorbents, addressing the innovations in material design and consequent performance enhancement. The limitations of the sorbents have also been discussed, with future perspectives for improving sustainable CO2 capture strategies. We anticipate that this overview will help lay the groundwork for further development and large-scale implementation of sustainable sorbents and cutting-edge technologies toward attaining carbon neutrality.

Interfacial polymerization of poly(ethylenimine) on PAN hollow fibers for direct air capture of CO2

Interfacial polymerization of poly(ethylenimine) on PAN hollow fibers for direct air capture of CO2

Green synthesis of MIL-101(Cr) with enhanced direct air capture of CO2 through synergistic effects of polyethyleneimine and additives

Green synthesis of MIL-101(Cr) with enhanced direct air capture of CO2 through synergistic effects of polyethyleneimine and additives

Temperature-dependent kinetic analysis of direct air capture using a gravimetric approach in porous environments

Adsorption kinetics has been regarded as one of the most critical factors determining the productivity and economic feasibility of direct air capture (DAC) of CO2, but has received relatively little attention compared with adsorption thermodynamics. One commonly used method for kinetics investigation is thermogravimetric analysis (TGA) which suffers from gas diffusion limitations and often underestimates adsorption rates. Here, a modified TGA system equipped with a porous self-made crucible was employed to address the gas diffusion challenges and analyze the kinetic behaviors of three polymeric chemisorbents, including Lewatit VP OC 1065, for DAC. The obtained adsorption kinetics were successfully applied to simulate and describe the breakthrough behaviors in a fixed-bed column. The CO2 adsorption/desorption kinetics of chemisorbents with different amine structures or loadings were measured at various temperatures and described through the linear driving force model. The present work offers a reliable and fast kinetics analysis approach for DAC, paving the way for accurately collecting the kinetics parameters used for guiding further adsorbent and process design.Graphic abstract

C<sub>6</sub> to C<sub>17</sub> Organic Products from Artificial Photosynthesis Catalyzed by 2-Phenyl Indole (PI) Titanium Tetrachloride Complex (PI)<sub>2</sub>TiCl<sub>4</sub>: The Synergism of Hydroxyl Radicals

The newly discovered artificial photosynthesis process catalyzed by 2-phenyl indole (PI) and TiCl4 complexes, activated by visible light, produces long-chain oxygenated hydrocarbons up to C17. This process begins with the formation of α-carboxylic acid-ω-aldehyde compounds (C6 to C9), arising from a cascade of autocatalytic organotitanium complexes derived from (PI)2TiCl4. These complexes are formed via hydrolysis through ambient air humidity and the direct atmospheric capture (DAC) of CO2. Carbon chain growth utilizes system-generated formaldehyde as a feedstock. The initial C6 to C9 compounds can further couple into C12 to C17 derivatives through a radical mechanism initiated by hydroxyl radicals. A proposed mechanism explores the synergistic interaction between organotitanium catalysis and hydroxyl radicals. This development represents the only known heterogeneous catalytic system that autonomously captures CO2 and humidity from the atmosphere to subsequently produce long-chain oxygenated hydrocarbons using solar energy.