The potential of direct air capture using adsorbents in cold climates.

The increasing concentration of carbon dioxide (CO2) in the atmosphere has compelled researchers and policymakers to seek urgent solutions to address the current global climate change challenges. In order to keep the global mean temperature at approximately 1.5 °C above the preindustrial era, the world needs increased deployment of negative emission technologies. Among all the negative emissions technologies reported, direct air capture (DAC) is positioned to deliver the needed CO2 removal in the atmosphere. DAC technology is independent of the emissions origin, and the capture machine can be located close to the storage or utilization sites or in a location where renewable energy is abundant or where the price of energy is low-cost. Notwithstanding these inherent qualities, DAC technology still has a few drawbacks that need to be addressed before the technology can be widely deployed. As a result, this review focuses on emerging trends in direct air capture (DAC) of CO2, the main drivers of DAC systems, and the required development for commercialization. The main findings point to undeniable facts that DAC's overall system energy requirement is high, and it is the main bottleneck in DAC commercialization.

Direct air capture (DAC) of CO2 complements traditional carbon capture technologies to achieve zero- or negative-carbon emissions. One of the most promising DAC technologies is moisture-swing adsorption due to its low regeneration costs and easiness of operation, particularly when using amine-based anion-exchange resins (AER) as sorbents, but the limited CO2 sorption capacity and desorption efficiency of current AERs are still critical challenges hindering the large-scale implementation of DAC. For the first time, this work developed a novel diamine-based double quaternary ammonium anion-exchange resins (Diamine-DQ-AER) by modifying commercial resins with tertiary diamines. The significantly improved quaternary ammonium content in Diamine-DQ-AER (68–81 %) compared to diamine-based single quaternary ammonium anion-exchange resins (Diamine-SQ-AER) resulted in an unprecedented moisture-swing DAC capacity of 3.41 mmol/g under DAC conditions, nearly doubled that of Diamine-SQ-AER. Diamine-DQ-AER also showed a stable capacity in the 6-cycle test, outperforming most moisture-swing DAC sorbents reported in the literature. Moreover, a complete desorption kinetic curve was obtained using an optimized testing protocol. It found that the CO2 adsorption/desorption process involves two stages, and the material exhibited fast desorption kinetics in the 1st stage.

Highly efficient catalytic direct air capture of CO2 using amphoyeric amino acid sorbent with acid‐base bi‐functional 3D graphene catalyst

Direct air capture of CO2 in designed metal-organic frameworks at lab and pilot scale

Amino acids make up a promising family of molecules capable of direct air capture (DAC) of CO2 from the atmosphere. Under alkaline conditions, CO2 reacts with the anionic form of an amino acid to produce carbamates and deactivated zwitterionic amino acids. The presence of the various species of amino acids and reactive intermediates can have a significant effect on DAC chemistry, the role of which is poorly understood. In this study, all-atom molecular dynamics (MD) based computational simulations and vibrational sum frequency generation (vSFG) spectroscopy studies were conducted to understand the role of competitive interactions at the air-aqueous interface in the context of DAC. We find that the presence of potassium bicarbonate ions, in combination with the anionic and zwitterionic forms of amino acids, induces concentration and charge gradients at the interface, generating a layered molecular arrangement that changes under pre- and post-DAC conditions. In parallel, an enhancement in the surface activity of both anionic and zwitterionic forms of amino acids is observed, which is attributed to enhanced interfacial stability and favorable intermolecular interactions between the adsorbed amino acids in their anionic and zwitterionic forms. The collective influence of these competitive interactions, along with the resulting interfacial heterogeneity, may in turn affect subsequent capture reactions and associated rates. These effects underscore the need to consider dynamic changes in interfacial chemical makeup to enhance DAC efficiency and to develop successful negative emission and storage technologies.

The direct air capture (DAC) of CO2 using aqueous solvents is plagued by slow kinetics and interfacial barriers that limit effectiveness in combating climate change. Functionalizing air/aqueous surfaces with charged amphiphiles shows promise in accelerating DAC; however, insight into these interfaces and how they evolve in time remains poorly understood. Specifically, competitive ion interactions between DAC reagents and reaction products feedback onto the interfacial structure, thereby modulating interfacial chemical composition and overall function. In this work, we probe the role of glycine amino acid anions (Gly-), an effective CO2 capture reagent, that promotes the organization of cationic oligomers at air/aqueous interfaces. These surfaces are probed with vibrational sum frequency generation spectroscopy and molecular dynamics simulations. Our findings demonstrate that the competition for surface sites between Gly- and captured carbonaceous anions (HCO3-, CO32-, carbamates) drives changes in surface hydration, which in turn tunes oligomer ordering. This phenomenon is related to a hierarchical ordering of anions at the surface that are electrostatically attracted to the surface and their ability to compete for interfacial water. These results point to new ways to tune interfaces for DAC via stratification of ions based on relative surface propensities and specific ion effects.

Direct air capture (DAC) of CO2 is considered one of the most promising carbon capture methods to reduce ambient CO2 concentration for climate change mitigation. Biochar represents an attractive adsorbent for DAC because it is environmentally friendly and cost-effective. In this work, KOH-activated bamboo biochar shows the CO2 capture capacity of 3.49 mmol g−1 (25 °C, 1 bar), and it is used as an adsorbent to perform direct air capture using a fixed-bed reactor with an ambient CO2 capture capacity of up to 51.74 μmol g−1. Furthermore, the effect of relative humidity on CO2 adsorption by biochar was investigated and exhibited promising stability under 2.7% relative humidity. However, the biochar activity for CO2 capture is reduced to 63.88% under 67.1% humidity after 50 cycles.

Renewable production of fuels and chemicals from direct air capture (DAC) of CO2 is a highly desired goal. Here, we report the integration of the DAC of CO2 with the thermochemical splitting of water to produce CO2, H2, O2, and electricity. The produced CO2 and H2 can be converted to value-added chemicals via existing technologies. The integrated process uses thermal solar energy as the only energy input and has the potential to provide the dual benefits of combating anthropogenic climate change while creating renewable chemicals. A sodium-manganese-carbonate (Mn-Na-CO2) thermochemical water-splitting cycle that simultaneously drives renewable H2 production and DAC of CO2 is demonstrated. An integrated reactor is designed and fabricated to conduct all steps of the thermochemical water-splitting cycle that produces close to stoichiometric amounts (∼90%) of H2 and O2 (illustrated with 6 consecutive cycles). The ability of the cycle to capture 75% of the ∼400 ppm CO2 from air is demonstrated also. A technoeconomic analysis of the integrated process for the renewable production of H2, O2, and electricity, as well as DAC of CO2 shows that the proposed scheme of solar-driven H2 production from thermochemical water splitting coupled with CO2 DAC may be economically viable under certain circumstances.

Feasibility Study of Combining Direct Air Capture of CO2 and Methanation at Isothermal Conditions with Dual Function Materials

Dual function materials (Ru+Na2O/Al2O3) for direct air capture of CO2 and in situ catalytic methanation: The impact of realistic ambient conditions

Piperazine-impregnated silica aerogel for direct air capture of CO2 for prevention of urea formation

Although Direct Air Capture (DAC) of CO2 is a potential technology for climate change mitigation, the cost, scalability, and efficiency of existing materials and techniques are severely limited. MXenes, a type of two-dimensional materials, have drawn interest due to their remarkable conductivity, enormous surface area, and adjustable chemistry, however, their potential for DAC has not yet been thoroughly investigated. Recent developments in MXene synthesis and functionalization are comprehensively reviewed, with an emphasis on how these characteristics might be used to enhance improve CO2 adsorption and capture efficiency. In addition, the difficulties of stability, scalability, and economic feasibility for real-world applications are evaluated. Our findings demonstrate the great potential of MXenes for DAC and offer fresh perspectives on how their special qualities might overcome current constraints. This study presents a new viewpoint on MXenes as a feasible CO2 capture option, indicating new avenues for future research and development, even though further optimization is required.

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO2 (400ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO2 insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400ppm) CO2 from gas mixtures via O─C bond formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using 13C-labeled CO2 sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40kJmol-1 between CO2 and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO2 release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO2 insertion. The as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO2 in crystalline scaffolds.

Direct air capture (DAC) of CO2 has emerged as the most promising "negative carbon emission" technologies. Despite being state-of-the-art, sorbents deploying alkali hydroxides/amine solutions or amine-modified materials still suffer from unsolved high energy consumption and stability issues. In this work, composite sorbents are crafted by hybridizing a robust metal-organic framework (Ni-MOF) with superbase-derived ionic liquid (SIL), possessing well maintained crystallinity and chemical structures. The low-pressure (0.4mbar) volumetric CO2 capture assessment and a fixed-bed breakthrough examination with 400ppm CO2 gas flow reveal high-performance DAC of CO2 (CO2 uptake capacity of up to 0.58mmol g-1 at 298 K) and exceptional cycling stability. Operando spectroscopy analysis reveals the rapid (400ppm) CO2 capture kinetics and energy-efficient/fast CO2 releasing behaviors. The theoretical calculation and small-angle X-ray scattering demonstrate that the confinement effect of the MOF cavity enhances the interaction strength of reactive sites in SIL with CO2 , indicating great efficacy of the hybridization. The achievements in this study showcase the exceptional capabilities of SIL-derived sorbents in carbon capture from ambient air in terms of rapid carbon capture kinetics, facile CO2 releasing, and good cycling performance.

Direct air capture(DAC) of CO2 is a promisingstrategyfor mitigating global carbon emissions by removing CO2 fromthe atmosphere. A critical factor in enhancing the efficiency of DACis the design of functionalized materials with strong CO2 binding capabilities. This study screens a variety of amino-functionalizedmolecules, utilizing MP2 and density functional theory calculations,to identify promising candidates for CO2 capture underdry and humid conditions. The analysis determined the most stableconfigurations of CO2 and water with 15 amino-functionalizedmolecules. Amino acids such as arginine, 7-azaindole, 1,5,7-triazabicyclo-[4.4.0]­dec-5-ene,and melamine demonstrated the strongest CO2 binding energies,ranging from −17 to −19 kJ/mol. This is the result ofboth Lewis acid–base interactions between the electron-deficientcarbon of CO2 and a N atom and hydrogen bonding. Generally,all of the amino groups exhibited a stronger binding affinity withwater, attributed to the formation of stable hydrogen bonds betweenan electron-rich N atom and the hydrogen atoms of water. To guidethe design of porous host structures incorporating these moleculesas functional groups, the study was extended to hypothetical systemswhere multiple functional groups can essentially “sandwich”CO2, promoting simultaneous binding. In these scenarios,the repulsion between functional molecules emerged as a critical factorincreasing the overall CO2 binding energy to ca. −30to −40 kJ/mol. This analysis enabled the identification ofoptimal pore sizes for the design of functionalized frameworks tomaximize the CO2 capture efficiency.