CO2 Uptake Research Articles

Hexaazatrinaphthylene-Based Ultrastable Metal-Organic Frameworks Modulated by the Chelating Coordination Configuration for CO2 Capture.

Hexaazatrinaphthylene (HATN), a polyheterocyclic aromatic ligand, is ideal for constructing discrete functional coordination complexes. However, its conjugated rigidity has resulted in a great challenge in forming extended structures with only one 3D metal-organic framework (MOF) reported 24 years ago. Herein, by regulation of the dihedral angle between two chelating HATN planes, three new porous HATN-based MOFs (SNNU-231-233) with mononuclear metal centers were successfully synthesized. SNNU-231, a unique 2-fold interpenetrated MOF, was first assembled, but the interpenetration leads to the lost pores. By modulating coordination configurations, the pore channels were successfully opened in SNNU-232 and SNNU-233, leading to a new topology in SNNU-232 and breaking the interpenetration in SNNU-233. All HATN-based MOFs exhibit exceptional thermal stability above 500 °C, surpassing most reported MOF materials. At the same time, SNNU-233 can keep its structure in water from pH = 1 to 14. Specifically, SNNU-233 had outstanding CO2 uptake capacity and separation ability of CO2/N2 due to its strong affinity to CO2 molecules in specific pores with abundant hydrogen bonds and π-force adsorption sites. SNNU-233 also showed significant potential for the simulated low calorific value coal gases with five components of H2 (5.1%), CO (9.1%), CH4 (5.0%), N2 (66.3%), and CO2 (14.3%).

Mesoporous Silica-Polyethyleneimine Composites as High-Capacity Adsorbents for CO2 Adsorption: Isotherm and Thermodynamic Analysis

In this study, polyethyleneimine-mesoporous silica composite materials were prepared and the effectiveness of the promising sorbents in adsorbing CO2 was evaluated, along with the impacts of the silica support types (Mesoporous Silica Nanoparticles (MSN) and Mobil Composition of Matter No.48 (MCM-48)), polyethyleneimine (PEI) loading percentages (50 and 70 wt.%), calcination, surface functionalization by alkyl chains (CTMABr), and adsorption temperature (75 and 100 °C). The analysis’s results revealed that the pores of the sorbents were mostly covered with PEI molecules following PEI-functionalization, and the specific surface area and pore volume were also reduced with rising amine content. The highest CO2 adsorption capacities were achieved for UC-MCM-48–50 and UC-MSN–50 at 2.26 mmol/g and 3.31 mmol/g, respectively. The CO2 uptake capacities of CC-MSN–50 and CC-MCM-48–50, composed by dispersing CTMABr surfactant with the calcined materials before incorporating PEI, were remarkably similar to those of non-surfactant functionalized adsorbents. When the temperature’s influence on CO2 adsorption capacity was evaluated, the maximum holding capability adsorbent UC-MSN–50 had a slight increase in adsorption capacity (~ 3.6%), whereas UC-MCM-48–50 had a considerable drop (~ 23.9%) as the temperature elevated to 100 °C. Besides, Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms were used to model pure CO2 adsorption data, and a thermodynamic study was applied. In conclusion, a low-cost and more beneficial approach, which included less PEI handling and eliminating the calcination step, was implemented to enhance the CO2 sorption capacity of composites of PEI with the long alkyl chain template MCM-48 or MSN silica support materials.

Metabolic Versatility of acetogens in syngas Fermentation: Responding to varying CO availability.

Syngas fermentation using acetogenic bacteria offers a promising route for sustainable chemical production. However, gas-liquid mass transfer limitations and efficient co-utilization of CO and H2 pose significant challenges. This study investigated the kinetics of syngas conversion to acetate by Acetobacterium wieringae and Clostridium species in batch conditions under varying initial CO partial pressures (19 - 110kPa). A. wieringae strains, exhibited superior growth in all gas compositions, with a maximum growth rate of 0.104h-1. The distinct CO, H2, and CO2 consumption patterns revealed metabolic flexibility and adaptation to varying syngas compositions. Notably, A. wieringae strains and C. autoethanogenum achieved complete CO and H2 conversion, with C. autoethanogenum also exhibiting net CO2 uptake. These findings provide valuable insights into the distinct metabolic capabilities of these acetogens and contribute to the development of efficient and sustainable syngas fermentation processes.

Differentiating low-carbon waste management strategies for bio-based and biodegradable plastics under various energy decarbonization scenarios.

Bio-based and biodegradable (bio-)plastics are heralded as a key solution to mitigate plastic pollution and reduce CO2 emissions. Yet, their end-of-life treatments embodies complex energy and material interactions, potentially leading to emissions through incineration or recycling. This study investigates the cradle-to-grave, emphasizing the waste management stage, carbon footprint for several types of bio-plastics, leveraging both GWP100a and CO2 uptake methods to explore the carbon reduction benefits of recycling over disposal. Our findings indicate that in scenarios characterized by carbon-intensive electricity, using polylactic acid (PLA) as an example, incineration with energy recovery (-1.6316kg CO2-eq/kg, PLA) yields a more favorable carbon footprint compared to chemical recycling (-1.5317kg CO2-eq/kg, PLA). In contrast, in environments with a high proportion of renewable energy, chemical recycling is a superior method, and compared to incineration (-1.4087kg CO2-eq/kg, PLA), the carbon footprint of chemical recycling (-2.0406kg CO2-eq/kg, PLA) are significantly reduced. While mechanical recycling presents considerable environmental benefits, its applicability is constrained by the waste quality, especially in the case of biodegradable plastics like PLA. In addition, the degradation of biodegradable plastics such as PLA was modeled during compost and anaerobic digestion processes. This enables us to quantify the specific biogenic carbon emissions released during these processing steps, revealing the direct emissions with dynamic degradation. This study highlights the importance of tailoring bio-plastic waste management strategies to support global energy decarbonization while understanding their life-cycle carbon metabolism to effectively tackle plastic pollution and climate change.

Carbon sink potential and the cost of afforestation in northwest China when accounting for ecosystem service value.

The cost effectiveness of mitigating climate change through afforestation needs to be evaluated for regions with a fragile environment and vulnerable ecosystems. This study develops an integrated geographic-economic-ecological framework to evaluate the cost-effectiveness of afforestation for carbon sequestration in Northwest China. It employs a spatial model of natural factors and a bioeconomic optimization model to identify marginal lands suitable for afforestation. Results indicate that nearly five million hectares of land are ecologically suitable and available for afforestation, but only some 215,000 to 583,000ha are economically feasible for afforestation, accounting for about one-eight of ecologically available land. The lands suitable for afforestation are primarily grasslands and other marginal lands distributed in Qinghai and Gansu provinces. Afforestation has the potential to remove 1.05-1.21 million tons of CO2 per year from the atmosphere in Northwest China. By 2060, this potential will cumulatively sequester 31.12-35.76Mt CO2 but contribute only 1%∼2% (depending on the level of incentives) of the region's CO2 uptake required to attain carbon neutrality. Further, compared with industrial emissions reduction and forestry activities in other jurisdictions, afforestation in Northwest China is not a cost-effective means for mitigating climate change. This conclusion likely relates to negligence in many studies regarding the inclusion of non-climate related ecological opportunity costs of potential candidate marginal lands for afforestation.

Life cycle assessment and industrial synergy for carbon reduction: A circular economy approach.

In the face of the climate change crisis, circular economy (CE) is put forward as a promising key to the sustainable development goals (SDGs) riddle. In this context that affects developed and developing countries alike, circular initiatives arise, such is the case for Morocco where an industrial synergy based on the CE concept of 'waste is food' can be envisioned between the local phosphate and cement industries. In order to support and guide this initiative, a life cycle assessment (LCA) was conducted to compare the environmental performance of the production of ordinary Portland cement (OPC), limestone calcined clay cement (LC3) and a phosphate waste-based cement known as calcined marl cement (CMC). In addition to a mass-based functional unit (FU), a performance-based FU was adopted to account for the 'longer service lives' concept of CE, which necessitated the estimation of cements' service lives and CO2 uptake potentials. Results show that CMC and LC3 production respectively reduce impacts on global warming by 23% and 60%, while the country aims for a 18.3% reduction by 2030; mineral resource scarcity is reduced by 30% and 48%; and other impacts by 10% and 40% compared with OPC. This is chiefly due to CMC and LC3's better durability performance and lower clinker content. Using LCA results, carbon tax was pre-estimated to drop by 9 and 18$/ton of cement for CMC and LC3. A life cycle costing and a social LCA must be conducted to comprehensively guide stakeholders in their decision-making process regarding a phosphate-cement synergy.

Amine‐Functionalized Triazolate‐Based Metal–Organic Frameworks for Enhanced Diluted CO2 Capture Performance

AbstractEfficient CO2 capture at concentrations between 400–2000 ppm is essential for maintaining air quality in a habitable environment and advancing carbon capture technologies. This study introduces NICS‐24 (National Institute of Chemistry Structures No. 24), a Zn‐oxalate 3,5‐diamino‐1,2,4‐triazolate framework with two distinct square‐shaped channels, designed to enhance CO2 capture at indoor‐relevant concentrations. NICS‐24 exhibits a CO2 uptake of 0.7 mmol/g at 2 mbar and 25 °C, significantly outperforming the compositionally related Zn‐oxalate 1,2,4‐triazolate – CALF‐20 (0.17 mmol/g). Improved performance is attributed to amino‐functions that enhance CO2 binding and enable superior selectivity over N2 and O2, achieving 8‐fold and 30‐fold improvements, respectively, in simulated CO2/N2 and CO2/O2 atmospheric ratios. In humid environments, NICS‐24 retained structural integrity but exhibited an 85 % reduction in CO2 capacity due to competitive water adsorption. Breakthrough sorption experiments, atomistic NMR analysis, and DFT calculations revealed that water preferentially adsorbs over CO2 due to strong hydrogen‐bonding interactions within the framework. Gained understanding of the interaction between CO2 and H2O within the MOF framework could guide the modification via rational design with improved performance under real‐world conditions.

Amine-Functionalized Triazolate-Based Metal-Organic Frameworks for Enhanced Diluted CO2 Capture Performance.

Efficient CO2 capture at concentrations between 400-2000 ppm is essential for maintaining air quality in a habitable environment and advancing carbon capture technologies. This study introduces NICS-24 (National Institute of Chemistry Structures No. 24), a Zn-oxalate 3,5-diamino-1,2,4-triazolate framework with two distinct square-shaped channels, designed to enhance CO2 capture at indoor-relevant concentrations. NICS-24 exhibits a CO2 uptake of 0.7 mmol/g at 2 mbar and 25 °C, significantly outperforming the compositionally related Zn-oxalate 1,2,4-triazolate - CALF-20 (0.17 mmol/g). Improved performance is attributed to amino-functions that enhance CO2 binding and enable superior selectivity over N2 and O2, achieving 8-fold and 30-fold improvements, respectively, in simulated CO2/N2 and CO2/O2 atmospheric ratios. In humid environments, NICS-24 retained structural integrity but exhibited an 85 % reduction in CO2 capacity due to competitive water adsorption. Breakthrough sorption experiments, atomistic NMR analysis, and DFT calculations revealed that water preferentially adsorbs over CO2 due to strong hydrogen-bonding interactions within the framework. Gained understanding of the interaction between CO2 and H2O within the MOF framework could guide the modification via rational design with improved performance under real-world conditions.

Nanoconfinement-Driven Energy-Efficient CO2 Capture and Release at High Pressures on a Unique Large-Pore Mesoporous Carbon.

Although microporous carbons can perform well for CO2 separations under high pressure conditions, their energy-demanding regeneration may render them a less attractive material option. Here, we developed a large-pore mesoporous carbon with pore sizes centered around 20-30 nm using a templated technical lignin. During the soft-templating process, unique cylindrical supramolecular assemblies form from the copolymer template. This peculiar nanostructuring takes place due to the presence of polyethylene glycol (PEG) segments on both the Pluronic® template and the PEG-grafted lignin derivative (glycol lignin). A large increase in CO2 uptake occurs on the resulting large-pore mesoporous carbon at 270 K close to the saturation pressure (3.2 MPa), owing to capillary condensation. This phenomenon enables a CO2/CH4 selectivity(SCO2/CH4,mol/mol) of 3.7 at 270 K and 3.1 MPa absolute pressure, and a swift pressure swing regeneration process with desorbed CO2 per unit pressure far outperforming a benchmark activated carbon (i.e., notably rapid decrease in the amount of adsorbed CO2 with decreasing pressure). We propose large-pore mesoporous carbons as a novel family of CO2 capture adsorbents, based on the phase-transition behavior shift of CO2 in the nanoconfined environment. This novel material concept may open new horizons for physisorptive CO2 separations with energy-efficient regeneration options.

Efficient CO2 Capture Using Nitrogen-Enriched Microporous Carbon Derived from Polybenzoxazine in a Single-Step Process for Environmental Sustainability

In this research, we successfully synthesized nitrogen-enriched microporous carbon through a meticulous process involving two different activation procedures. Initially, polybenzoxazine was carbonized at 800 °C to create a precursor material, which was then activated with two different activating agents (KOH and KMnO4) at the same temperature. This activation significantly enhanced the material’s porosity, increasing its specific surface area from 335 m2/g (KOH activated) to 943 m2/g (KMnO4 activated). XPS analysis confirmed the presence of nitrogen functionalities, including secondary-N, oxide-N, pyridone-N, and pyridine-N, which are critical for CO2 adsorption. Adsorption tests demonstrated a high CO2 uptake of 3.8 mmol/g at 25 °C and 1 bar, driven by a combination of physisorption (physical interaction with the surface area) and chemisorption (chemical interaction with nitrogen sites). This high adsorption capacity can be attributed to the carbon’s substantial surface area, significant micropore volume, and the interconnected network of pores, which together provide structural stability and facilitate the diffusion of CO2 molecules. These findings suggest that this nitrogen-enriched microporous carbon, derived from polybenzoxazine, holds significant promise as a highly efficient material for applications in CO2 capture and storage.

A Comparative Study of Mineral Carbonation Using Seawater for CO2 Utilization: Magnesium‐Based System Versus Calcium‐Based System with Low Energy Input

Mineral carbonation is promising for CO2 utilization and sequestration via capturing CO2 into stable solid carbonates. However, the effectiveness and price of the solvents, as well as the energy consumption of CO2 purification and pressurization of industrial flue gas, are hindering the development of this technology. Therefore, this study integrates two important concepts of seawater utilization and direct use of CO2 gas without purification and pressurization, investigating the mineral carbonation using seawater as an alternative solvent with low energy input. Carbonation of magnesium‐ and calcium‐based systems is investigated, and the behaviors as well as mechanisms of using seawater and distilled water are compared. The kinetics, conversion progress of compounds, and carbonation behavior are determined. The CO2 uptake capacities of seawater carbonation are higher in the Mg‐based system (1.16 g‐CO2/g‐MgO) than in the Ca‐based system (0.68 g‐CO2/g‐CaO); however, most CO2 in the Mg‐based system is captured in the solution phase. Insights into reaction optimization are provided. The potential assessment of mineral carbonation using seawater is provided. This study aims to facilitate the development of CO2 utilization and provide opportunities for mineral carbonation using seawater, through applying various alkaline wastes containing Ca and Mg from diverse industries.

A numerical assessment of ocean alkalinity enhancement efficiency on a river-dominated continental shelf—a case study in the northern Gulf of Mexico

Abstract A robust high-resolution coupled hydrodynamic-biogeochemical model was applied to the northern Gulf of Mexico to assess the efficiency of river- and ocean-sourced ocean alkalinity enhancement (OAE). Sensitivity tests indicate that the effectiveness of OAE-induced CO2 uptake is primarily influenced by the amount of alkalinity introduced and local wind-driven mixing, with the former determining the overall uptake and the latter affecting short-term variability. Compared to ocean-sourced OAE (direct ocean release), river-sourced OAE (elevated river alkalinity) is more effective and sustainable. River-sourced OAE has higher CO2 uptake efficiency with reduced spatial and temporal uncertainty and greater overall CO2 uptake. For river-sourced OAE, surface pH increases pronouncedly near the mouths of the Mississippi River. The ideal OAE implementation time includes spring, early summer, fall, and winter. Mid and late-summer implementation is not recommended due to weak mixing, which results in less alkalinity dispersal and greater pH variability. In addition, while the aragonite saturation state generally remains below 6 around the Mississippi River plume, it increases pronouncedly during mid to late summer, risking alkalinity loss due to CaCO3 precipitation and reduced CO2 uptake efficiency near river mouths. Scaling OAE-induced CO2 uptake to the 25 largest rivers in the world indicates that increasing riverine alkalinity concentrations by 10% could remove 23.23 megatons of CO2 annually, meeting 0.37%–0.61% of the 2025–2030 CO2 removal target.

Unveiling the Potential of Room-Temperature Synthesis of a Mixed-Linker Zeolitic Imidazolate Framework-76 for CO2 Capture

A room-temperature synthesis was used to prepare ZIF-76 by combining the organic linker imidazole and 5-chlorobenzimidazole, with the addition of NaOH as a modulator. The synthesis process was optimized by modifying the existing method, which includes the introduction of heating, different types of solvent, and adjustment to the reactant ratio. The synthesized MOFs were characterized to evaluate their crystallinity, textural properties and surface morphology. The result demonstrated that the introduction of heat led to the formation of ZnO whereas the replacement of DEF–DMF with methanol resulted in the production of amorphous material. Moreover, a change in precursor ratio led to the production of ZIF-76 with a low yield and surface area. Meanwhile, CO2 adsorption was performed in a pressure range of 0–1.2 bar at 298.15 K. Notably, ZIF-76B with a low surface area exhibited a greater CO2 uptake capacity of 1.43 mmol/g compared to ZIF-76A, which recorded 1.29 mmol/g. Furthermore, the isotherm and kinetic models were applied to fit the experimental CO2 adsorption data. The analysis of the adsorption models indicated that the CO2 adsorption was primarily governed by a monolayer formation on a homogeneous surface. Nevertheless, there was a slight diversion in terms of predicted qm with experimental data, which could be attributed to the adsorption not yet reaching equilibrium. Additionally, the kinetic model was applied to the initial stage of adsorption in the pressure range of 0–0.24 bar. The Elovich model was found to fit better with the CO2 uptake capacity data of ZIF-76A and ZIF-76B suggesting that the adsorption process may involve multiple mechanisms.

Synthesis and Assessment of Metal-Organic Frameworks (MOFs) Adsorbents for CO2 Capture: A Comparative work of the CO2 Adsorption Capability of Mono- and Bimetal-based MOFs Adsorbents

Adsorption utilising porous solid adsorbent has been considered a feasible option for conventional CO2 absorption over the past few decades. As a preliminary investigation towards obtaining Metal-Organic Frameworks (MOFs) adsorbent for CO2 capture, the CO2 adsorption efficiency using mono- and bimetal-based MOFs was assessed in this study. Among the numerous MOFs, Mg-MOF-74 exhibits the best CO2 uptake at low pressures because of its open metal sites. A strategy to incorporate Zn in Mg-based MOF as a co-metal node is required to enhance the CO2 adsorption performance of solid adsorbent. Selecting Zn as a metal node in MOF synthesis allows for the creation of stable, versatile, and functional materials for CO2 adsorption. Therefore, combining several metals in a structure to develop a new MOF with an improved gas uptake is quite a useful approach to further harness the immense potential of MOFs. This study aims to compare the performance of mono- and bimetallic-MOFs and select the most suitable adsorbent for CO2 capture. The performance of CO2 adsorption was conducted using three parameters: the effect of metal loading on MOFs, pressure (1–5 bar) and adsorbent dosage (0.2–0.5g). Based on the characterisation findings, the studies confirm the formation of Mg-MOF-74, Zn-MOF and 50wt.%Zn/50wt.%Mg-MOF. Overall, it was found that the bimetal adsorbent with 50 wt.%Zn/50wt.%Mg-MOF displayed the highest CO2 adsorption capacity (323 mgCO2/gadsorbent) when compared to the monometallic MOFs (Zn-MOF (134mgCO2/gadsorbent) and Mg-MOF-74) (122 mgCO2/gadsorbent) indicating a 50% increase in adsorption capacity over monometallic MOFs.

Fresh and Aged Chromite Ore Processing Residues (COPR): Weathering-Induced Alteration of Chemical Properties, Cr(VI) Mobility and Mineralogy At Open Dumpsites in Kanpur, India

Chromite ore processing residue (COPR) is a hazardous waste retaining relic Cr(VI). Large amounts are generated during the high-lime production of leather tanning salts in the region of Kanpur, India. Here, COPR is often deposited on open and uncontrolled landfills, leading to severe groundwater contamination. This study aimed at elucidating how ageing under these ambient conditions alters COPR properties and Cr(VI) mobility. For this, aged COPR obtained from surface and subsurface horizons of a visibly weathered open dumpsite was systematically compared to fresh high-lime COPR collected at two tanning salt factories. Elemental composition of the samples was characterized using X-ray fluorescence analysis while Cr(VI) mobility was assessed photometrically in alkaline and aqueous batch extracts. Mineralogical composition of the COPR was studied using X-ray powder diffractometry, scanning electron microscopy and thermogravimetry–mass spectrometry. The fresh COPR were highly alkaline and contained characteristic Cr(VI) host phases like calcium aluminum chromate hydroxide (CAC) and katoite. These were absent in the aged samples due to their lower pH of ~ 9. The pH drop was likely caused by uptake of atmospheric CO2, which was corroborated by elevated carbon and calcite levels. This carbonation coincided with vertical translocation of Cr(VI) to the subsurface of the landfill, where leachate concentrations in excess of 1.6 g · L−1 and chromatite (CaCrO4) precipitations were found. The results highlight the importance of carbonation as a key ageing process which will likely exacerbate Cr(VI) groundwater contamination at open COPR dumpsites.Graphical

Seasonal warming responses of the carbon dioxide sink from northern forests are sensitive to stand age

Northern forests (forests north of 30°N) are major terrestrial carbon dioxide (CO2) sinks, while rapid warming can disturb their CO2 sink function. Here we use multi-year net CO2 exchange observations from 65 northern forest sites to show that the increased net CO2 uptake during warmer springs was more pronounced in old forests (>90 years old) compared to young (<40 years old) and mid-aged (40–90 years old) forests. In addition, the decreased net CO2 uptake during warmer summers and autumns was more pronounced in young forests compared to mid- and old-aged forests. Annually, this resulted in an increase in net CO2 uptake due to seasonal warming for old forests (4.8 g C m−2 yr-1) and a decrease in young- and mid-aged forests (3.2 and 0.8 g C m−2 yr-1, respectively). In future projections, increasingly uneven seasonal warming may amplify the impacts of stand age on CO2 sinks of northern forests.

Wildfires offset the increasing but spatially heterogeneous Arctic–boreal CO2 uptake

The Arctic–Boreal Zone is rapidly warming, impacting its large soil carbon stocks. Here we use a new compilation of terrestrial ecosystem CO2 fluxes, geospatial datasets and random forest models to show that although the Arctic–Boreal Zone was overall an increasing terrestrial CO2 sink from 2001 to 2020 (mean ± standard deviation in net ecosystem exchange, −548 ± 140 Tg C yr−1; trend, −14 Tg C yr−1; P < 0.001), more than 30% of the region was a net CO2 source. Tundra regions may have already started to function on average as CO2 sources, demonstrating a shift in carbon dynamics. When fire emissions are factored in, the increasing Arctic–Boreal Zone sink is no longer statistically significant (budget, −319 ± 140 Tg C yr−1; trend, −9 Tg C yr−1), and the permafrost region becomes CO2 neutral (budget, −24 ± 123 Tg C yr−1; trend, −3 Tg C yr−1), underscoring the importance of fire in this region.

Glacial Southern Ocean deep water Nd isotopic composition dominated by benthic modification

The deep Southern Ocean (SO) circulation plays a key role in the storage and release of CO2 in Earth’s climate system. The uptake and release of CO2 strongly depend on the redistribution of well and poorly ventilated deep ocean water masses. Recently, evidence was found for possible stronger Pacific deep water overturning and subsequent intrusion into the SO during periods of reduced AMOC. Here, we present new authigenic neodymium isotope data (ɛNd) from two sites within the Atlantic sector of the SO to assess the distribution of water masses during the past 150 ka. PS 1768-8 (3299 m) and ODP 1093 (3624 m) feature unradiogenic interglacial ɛNd-signatures, which are typical for present-day Weddell Sea sourced Antarctic Bottom Water (AABW) (ɛNd ~ − 8.6). During peak glacial periods, radiogenic ɛNd-values ranging from ~ − 2.5 to − 3.5 are recorded. This may be the result of either a strong Pacific or benthic flux influence on the Nd budget in the Atlantic sector of the SO. However, an ocean circulation model indicates no stronger Pacific influence during glacials. Thus, we suggest that an increase in benthic flux influences the SO Nd budget, which is modulated by ACC strength. The more stratified and more sluggish deep water supports decreased vertical mixing and increased glacial carbon storage without the intrusion of poorly ventilated Pacific waters. The occurrence of highly radiogenic glacial bottom water or porewater signatures requires reassessment of the glacial Southern Hemisphere ɛNd-endmember for water mass sourcing reconstructions in the glacial Atlantic.

Exploring a Novel Adsorbent for CO2 Capture and Gas Separation.

The urgent need to mitigate carbon emissions has spurred research into small-pore zeolites as cost-effective options for CO2 capture by solid adsorbents, particularly in postcombustion and biogas separation applications. In this study we investigate levyne (LEV-type) zeolite, a largely unexplored material for CO2 adsorption, as a novel adsorbent for CO2 capture and gas separation. Using seed-assisted synthesis approaches and different synthesis conditions, nanosized and micron-sized LEV zeolites were synthesized and characterized in terms of synthesis pathways, morphology, crystal size, and chemical composition. The variation of the Si/Al ratios and chemical compositions of the synthesized LEV zeolites resulted in significant differences in their CO2 adsorption capacity and separation selectivity. Micron-sized LEV, with a lower Si/Al ratio = 3.5 and a higher Na+ content, exhibited superior CO2 uptake and stronger interactions with CO2 than the nanosized LEV (Si/Al = 6.6). Dynamic adsorption measurements using breakthrough curve analysis revealed that the micron-sized LEV exhibited twice the CO2 adsorption capacity of its nanosized counterpart, along with higher CO2/N2 and CO2/CH4 selectivities. This enhanced performance, including better cyclability, emphasizes the critical role of the zeolite Si/Al ratio in improving adsorption and separation properties. In situ FTIR measurements supported these findings, showing that the nanosized LEV predominantly adsorbs CO2 by physisorption, allowing efficient desorption using He flow only. In contrast, micron-sized LEV primarily physisorbs CO2 but also exhibited chemisorbed CO2, reflective of the more highly charged framework (higher Al content) and extra-framework cation content. These results highlight the importance of synthesis strategies in optimizing the properties of LEV zeolite, making them promising candidates as physical adsorbents for gas separation applications.

The Roles of Molecular Concavities in the Hierarchical Self-Assembly of Giant Tetrahedra for CO2 Uptake.

Giant tetrahedral molecules have sparked significant interest in the past decade due to their unique and diverse supramolecular nanostructures. The longer and bulkier peripheral substituents create deep molecular concavities and thus contribute to the different self-assembly behaviors compared to the conventional small tetrahedral molecules. In this study, a molecular giant tetrahedra, TetraNDI, was synthesized to investigate the important roles of the molecular concavities in the self-assembly mechanism. Single-crystal structural characterizations indicate that the TetraNDI takes its trigonal concavities to form 1D supramolecular columns, and its tetragonal concavities to reach close inter-columnar packing. The difficulty in occupying the concavities leads to the path-dependent phase behaviors of the giant tetrahedra. It is also found that the remaining molecular concavities in the supramolecular scaffolds affect the CO2 affinity of TetraNDI. With an understanding of the packing principles of molecular giant tetrahedra, the structure-property relationships could be better evaluated in the future and might broaden the horizon of porous materials.