Selective adsorption of CO2 in TAMOF-1 for the separation of CO2/CH4 gas mixtures

Article https://doi.org/10.1038/s41467-025-58426-w Selective adsorption of CO 2 in TAMOF-1 for the separation of CO 2 /CH 4 gas mixtures Santiago Capelo-Avilés 1,2,15 , Mabel de Fez-Febré 1,2,12,15 , Salvador R. G. Balestra 3 , Juanjo Cabezas-Giménez 1,2,13 , Raiana Tomazini de Oliveira 1 ,IreneI.GalloStampino 1 , Anton Vidal-Ferran 4,5 , Jesús González-Cobos 1,14 , Vanesa Lillo 1 , Oscar Fabelo 6 , Eduardo C. Escudero-Adán 1 , Larry R. Falvello 7 ,JoséB.Parra 8 , Paolo Rumori 9 , Gemma Turnes Palomino 9 , Carlos Palomino Cabello 9 , Stefano Giancola 10 ,SofiaCalero 11 & José Ramón Galán-Mascarós 1,4 TAMOF-1 is a robust, highly porous metal–organic framework built from Cu2+ centers linked by a L-histidine derivative. Thanks to its high porosity and homochirality, TAMOF-1 has shown interesting molecular recognition properties, being able to resolve racemic mixtures of small organic molecules in gas and liquid phases. Now, we have discovered that TAMOF-1 also offers a competitive performance as solid adsorbent for CO 2 physisorption, offering promising CO 2 adsorption capacity ( > 3.8 mmol g–1)andCO 2 /CH 4 Ideal Adsorbed Solution Theory (IAST) selectivity ( > 40) at ambient conditions. Moreover, the material exhibits favorable adsorption kinetics under dynamic conditions, demonstrating good stability in high-humidity environments and minimal degradation in strongly acidic media. We have identified the key interactions of CO 2 within the TAMOF-1 framework by a combination of structural (neutron diffraction), spectroscopic and theoretical analyses which conclude a dual-site adsorption mechanism with the majority of adsorbed CO 2 molecules occupying the empty voids in the TAMOF-1 channels without strong, directional supramolecular interactions. This very weak dominant binding opens the possibility of a low energy regeneration process for convenient CO 2 purification. These features identify TAMOF-1 as a viable solid-state adsorbent for the realization of affordable biogas upgrading. The presence of CO 2 in gas streams is deleterious to the environment as emissions, but also problematic as an undesirable impurity in industrial feedstocks and in methane-based gas mixtures such as biogas and natural gas1,2. The former is a green replacement for the latter, where methane is obtained from the anaerobic fermentation of biological residues, as a renewable fuel3. Its exploitation offers a functional solution for the conversion of biowaste into usable renewable energy while reducing greenhouse gases. Biogas upgrading into biomethane to be used as a fuel (high calorific value) which can meet pipeline grade requirements is of great environmental, economic, and technological interest4,5. However, the separation and capture of the carbon dioxide (typically around 50% in biogas) is an extremely challenging process as (i) the CH 4 and CO 2 molecules have similar kinetic diameters making the separation of mixture difficult by kinetic/size exclusion; (ii) low-pressure operations are preferred, close to 1 bar (low driving force) to avoid high energy-consumption from compression work; and iii) it needs very high efficiency in CO 2 removal (≥98%)6,7. Received: 2 September 2024 Accepted: 17 March 2025 Check for updates A full list of affiliations appears at the end of the paper. e-mail: [email protected];[email protected];[email protected] Nature Communications | (2025) 16:3243 1 1234567890():,; 1234567890():,; Gas-liquid absorption in chemical solvents (aqueous amine solution)8is the most mature technology for large-scale CO 2 capture9,10, including for methane purification11. However, this technology has three major drawbacks: high energy requirement for solvent regeneration, waste management (solid salts and traces of gaseous compounds due to amine degradation), and a large footprint. This calls for the development of alternative solutions based on novel and cutting-edge materials. In particular, the separation of CO 2 /CH 4 mixtures directly in the gas phase would be highly desirable. In this context, a promising process for gas separation is physisorption12,13. Due to the physical nature of the interactions involved, this process typically demands lower energy consumption during the regeneration step when compared to processes ruled by strong chemical interactions such as chemisorption in solid or liquid adsorbents. Different technologies based on physisorption are available, such as pressure swing adsorption (PSA)14,15, vacuum swing adsorption (VSA)16,and thermal swing adsorption (TSA)17. These technologies involve at least two consecutive steps. First, CO 2 is selectively adsorbed by the active component at high pressure and/or low temperature, and then the adsorbent is regenerated by CO 2 desorptionatlowerpressure/vacuum (PSA/VSA) or/and at higher temperature (TSA). Several types of porous materials have been investigated as physisorbents for CO 2 removal18. Benchmark zeolites typically exhibit competitive separation performance, characterized by high adsorption capacity and equilibrium selectivity19. However, while advantageous for CO 2 removal from dry emission or process streams, this selectivity is often compromised in the presence of water. Water molecules preferentially coordinate with exposed metal sites, outcompeting CO 2 20. Furthermore, these materials necessitate high regeneration energy19,21,22, which consequently increases the operational expenditure (OPEX) in industrial plants striving for high CO 2 15,20. Carbon-based materials offer the advantage of low cost and easy regeneration, although they are limited by a lower adsorption capacity and selectivity. Nowadays, the limitations of the adsorbents are also limiting the commercial use of carbon capture (CC) technologies just to niche applications, where there is no alternative. Suitable materials combining high adsorption capacity at low/moderate working pressures, able to discriminate CO 2 against molecules with similar dimensions (e.g., CH 4 and N 2 ) with high selectivity, with low-energy regeneration and fast adsorption/desorption kinetics would offer plausible opportunities to realize CC not only for biogas upgrading but also in many additional fields. Especially if CC becomes economically competitive with current CO 2 emission rights. Metal-organic frameworks (MOFs) are crystalline and porous materials23,24 prepared by the self-assembly of metal ions or clusters with organic ligands or linkers to form reticular structures25,26.Dueto their exceptional properties27 such as high accessible surface areas (up to 6200 m2g–1)28, extra high porosities (up to 90%)29, tunability in pore dimensions and morphology30, versatile functionality31 as well as thermal and chemical stability32, MOFs are recognized as promising materials for selective gas separations potentially able to overcome intrinsic limitations of common adsorbents33–35. Even though nowadays morethan70000 MOFs have been discovered, just a few of them have shown promising features into adsorption/desorption protocols or as membrane components for CO 2 capture23,36. Some of the most remarkable candidates include CALF-20, a Zn-based oxalate-bridged framework with high performance inCO 2 capturefrom flue gas, andan extraordinary robustness under humid conditions37;orMg 2 (dobpdc), a Mg-based tetramine-functionalized framework with extraordinary cyclability and stability during CO 2 capture from flue gas. However, this last material is characterized by chemical CO 2 adsorption and needs a high operating temperature (100°C)38.InthecaseofCO 2 /CH 4 separations for biogas upgrading, the most relevant example is MUF16 (Co(Haip) 2 , Haip = 5-aminoisophthalic acid)39.ThisMOFisableto capture carbon dioxide from hydrocarbons with exceptional selectivity although with moderate CO 2 adsorption capacity40.Moreover,the low isosteric heat of adsorption allows for an easy regeneration step. Another interesting MOF is Qc-5-Cu-sql, a Cuquinoline-5-carboxylic acid supramolecular network, also showing excellent CO 2 /CH 4 selectivity via the molecular sieving mechanism. However, also in this case moderate CO 2 adsorption capacity isreported41.Moreover,a thorough explanation of the selectivity of MOFs to adsorbCO 2 isusually missing. Whereas chemisorption is easier to evaluate from structural data, the physisorption mechanism remains difficult to assess. In situ experiments are very rare to discriminate between: (i) size-exclusion principles, (ii) kinetically controlled processes, or (iii) thermodynamically controlled processes42. TAMOF-1 is the first in a series of homochiral MOFs based on natural amino acid derivatives, by transformation of the α-amino unit into a triazole group43,44. TAMOF-1 ([Cu(S-TA) 2 ].xH 2 O, S–HTA = (S)-3- (1H-imidazol-5-yl)-2-(4H-1,2,4-triazol-4-yl)-propanoic acid) is easily synthesized at large scale from low-cost raw materials just by reaction of a copper(II) salt with L-histidine derivative (imidazole-5-ylmethyl)- (1,2,4–triazol-4-yl)acetate (L 1 ) in water. This material has a 3D network, made from 10 Å wide, helicoidal, intercommunicated channels, decorated with multiple dangling functional groups carboxylate, triazole, and imidazole (Fig. 1) exhibiting a BET-specific surface area of 980 ± 50 m2g–1and a micropore volume of 0.38 cm3g–1.TAMOF-1 exhibits exceptional water stability, withstanding both hydration/ dehydration cycles without structural degradation or porosity loss44. Moreover, activation for gas separation is achieved under mild conditions (353–393 K under a sweep gas flow), preserving the MOF crystallinity—a rare feat for Cu-based MOFs and surpassing the requirements of typical MOFs and zeolites45,46. In previous reports, we disclosed the performance of TAMOF-1 as a stationary phase for the chromatographic separation of racemic mixtures of organic substances thanks to its porosity and homochirality47. The latter was further exploited for the kinetic resolution of chiral substrates by catalytic coupling. Moreover, the characteristic shape and size of its channels and pores, as well as the Cu metal center, make TAMOF-1 a good candidate for separating also a wide variety of volatile organic compounds such as benzene−cyclohexane system and xylene isomers (positional isomers reconnection). The separation of these molecules has been proved in both the liquid and gas phases48. Furthermore, TAMOF-1 has been reported to be capable of separating C 2 H 2 /C 2 H 4 and C 2 H 2 /CO 2 mixtures49. Fig. 1 | Crystal structure of TAMOF-1. Representation of the crystal structure of TAMOF-1, showing the network of open 10 Å-wide channels. Color code: Cu, deep blue; O, red; N, light blue; C, black. Hydrogen atoms omitted for clarity. Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 2 Here, we report that TAMOF-1 is a highly promising physisorbent to resolve CO 2 /CH 4 mixtures and, in a broader context, aiming to capture CO 2 . In particular, this material has highly promising CO 2 adsorption capacity and CO 2 /CH 4 selectivity. Moreover, it allows for a low energy (ambient temperature) regeneration. When compared with other available adsorbents, including other MOFs, the TAMOF-1 performance appears very promising also in terms of operation costs. We anticipate that this material may help to bridge the gap between effective adsorption and affordable regeneration. Noteworthy, the adsorption/desorption performance remains durable over time, even in the presence of water, with only a small reduction observed when exposed to highly concentrated H₂S. By combining specificexperimental (neutron diffraction and IR spectroscopy) and theoretical tools (Monte Carlo and molecular dynamics), we have thoroughly elucidated the molecular mechanism of the physisorption and transport properties of gas molecules within the TAMOF-1 network at the origin of its promising performance. Results and discussion Gas adsorption Single gas (CO 2 ,CH 4 ,andN 2 ) adsorption isotherms of TAMOF-1 powder up to 10 bars were measured in the 293–353K temperature range (Fig. 2a). As a function of temperature, all isotherms maintain their characteristic shapes, with gas uptake increasing as the temperature decreases, typical of a physisorption process. Type I isotherms are obtained for CO 2 , without reaching a plateau (saturation) in the investigated pressurerange. For example, at 298 K, CO 2 adsorption capacities of 3.8 and 6.5 mmol g–1are obtained at 1 and 10 bars, respectively. Linear isotherms are obtained for both CH 4 and N 2 ,with adsorption capacity following the order CO 2 >>CH 4 >N 2 , indicating selective preferential uptake of carbon dioxide. From the different adsorption models available (See SI), the dualsite Langmuir-Freundlich model shows the best fitting for the CO 2 adsorption isotherms(SupplementaryFigs. 7–11). See, for instance, the comparison with the single-site Langmuir-Freundlich model in the logq vs. logPplot (Supplementary Fig 12). This indicates that at least two different adsorption sites are responsible for dominant CO 2 uptake. Supplementary Tables 16, 17 show the isotherm parameters and regression coefficients. The CO 2 /CH 4 selectivity calculated by the ideal adsorption solution theory are reported in Fig. 2c and in the Supplementary Table 18. At 293 K and 1bar,45.9, 40.9, and 38.30 selectivity values are obtained for respectively 30:70, 50:50, and 70:30 CO 2 /CH 4 gas mixtures (in the typical biogas composition range). Interestingly, data indicate that TAMOF-1 is capable of separating CO 2 /CH 4 mixtures over a wide temperature range. Forexample, at 1 bar and 353K,TAMOF-1 hasa CO 2 sorption capacity and 50:50 CO 2 /CH 4 ideal selectivity of 1.8 mmol g–1 and 18, respectively. Another important feature is the complete adsorption/desorption reversibility obtained for all the gases (Fig. 2b) with no hysteresis observed. This behavior aligns with the physical nature of the gas adsorption phenomena within the TAMOF-1 network and underscores the structural rigidity of this material. The isosteric enthalpy of adsorption, ΔH ads was estimated via an indirect approach from the CO 2 adsorption isotherms at the different temperatures using the Clausius-Clapeyron equation (for a detailed description of the calculations, see SI). Supplementary Fig. 13 shows the evolution of –ΔH ads with CO 2 uptake. A high –ΔH ads is found at low pressure (zero coverage, –ΔH0 ads=0 ), and then it rapidly decreases as CO 2 uptake increases, approaching the bulk-phase sublimation heat of CO 2 ,26–27 kJ mol–1, at an adsorption capacity higher than 2mmolg –150. This energy range points to a physical gas adsorption behavior and denotes a heterogeneous adsorption process occurring at multiple adsorption sites with different surface energies51. Sahoo et al.42 conducted a preliminary comparison of mixed gas phase CO 2 sorption capacity and separation selectivity for various MOFs using IAST (Fig. 2d). While many studies report only single gas sorption capacity (which is typically higher than the mixed gas capacity), the review focused on those that provided mixed gas CO 2 data. Among the MOFs examined, MUF-16 and Qc-5-Cu-sql-βdemonstrated bothhighCO 2 sorption capacity (1.8 and 1.6 mmol g–1,respectively) and high CO 2 /CH 4 separation selectivity (6690 and 3300, respectively). Interestingly, TAMOF-1 (this study) exhibited an even higher mixed CO 2 sorption capacity (~ 3.1 mmol g–1)withacceptableseparation selectivity (> 40). Given the lack of established performance benchmarks for industrial-scale biogas separation, it is premature to definitively assess the potential of these MOFs. We have also to mention that IAST parameters are calculated under idealized equilibrium conditions and do not represent the actual separation performance of adsorbents in dynamic conditions such as those obtained from breakthrough curves. Nevertheless, IAST analysis is usually reported and used to compare the gas separation performance of adsorbents valuable insights into the relative adsorption capabilities of TAMOF-1 with respect to other adsorbents. Breakthrough measurements In Fig. 2e, we report methane/carbon dioxide breakthrough curves through a TAMOF-1 powder bed at 1 bar and 298 K at different CO 2 / CH 4 ratios. Gas separation parameters obtained from the breakthrough curves are reported in Supplementary Table 19 (See SI for details). Pure methane (≥99.9%) elutes first and speedily from the bed. Regular S-shaped curves were instead observed for CO 2 . Effective CO 2 / CH 4 separation is achieved in all cases as CO 2 is delayed. This confirms slower CO 2 diffusion through the TAMOF-1 bed. By reducing CO 2 molar flow, the related curves shift towards higher breakthrough times (Bt).Bt(CO 2 ) increases from 16.4to18.7 min g–1whentheCO 2 /CH 4 ratio is reduced from 50:50 to 25:75. In contrast, Bt(CH 4 ) is almost constant, independent of the CH 4 fraction. The CH 4 concentration overshoots its equilibrium value (C/C 0 > 1) before returning to equilibrium (C/ C 0 = 1). This roll-up effect indicates preferential adsorption of CO 2 , which displaces some of the initially adsorbed CH 4 . The precise shape of this overshoot depends on the methane flow rate, concentration, and adsorbent properties20. Adsorption capacities for both carbon dioxide and methane were also measured. Nitrogen is a gas that can be present in combination with CO 2 and CH 4 in many gas streams, thus we also evaluated CO 2 /CH 4 /N 2 separations through TAMOF-1 beds. For this purpose, fixed-bed column experiments were performed by varying the CH 4 /N 2 ratio at constant CO 2 concentration (50%) (Fig. 2f). Carbon dioxide breakthrough curves perfectly overlap independently of the CH 4 /N 2 ratio. This indicates that CO 2 diffusion through TAMOF-1 is not affected by the type of other gas components (CH 4 or N 2 ) in the inlet gas mixture. These gases do not affect the adsorption capacity, which depends directly on the CO 2 concentration, in agreement with isotherms measures (Fig. 2a). As a consequence, CO 2 adsorption capacities (Supplementary Table 19) are similar (q b = 1.7± 0.06 mmol g–1,q s = 2.5 mmol g–1,CO 2 = 50%). A similar CO 2 /CH 4 selectivity was also observed for a binary CO 2 /CH 4 (S s =6) or a CO 2 /CH 4 /N 2 ternary (S s = 4) inlet gas mixture with the same CO 2 concentration (i.e., 50%). It is important to mention that N 2 , when present, exits as the first component and almost immediately from the column with elution time almost coincident with the dead time. Breakthrough experiments at variable pressure conditions were also collected (Supplementary Table 19). By pressurizing the bed, Bt shifts to higher times with methane remaining always the first gas to elute. Increasing bed pressure from 1.2 to 6 bar at a constant flow rate, Bt(CO 2 ) increases from 34 to 122 min g–1, and Bt(CH 4 ) from < 4.7 to 32 min g–1.CO 2 adsorption capacities increase from 0.42 to 1.24 mmol g–1, but CH 4 adsorption also increases from < 0.06 to 0.33 mmol g–1. This results in a decrease in the CO 2 /CH 4 selectivity as Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 3 a function of increasing pressure, from > 7 to < 4 between 1.2 and 6 bar. Higher temperatures accelerate the gas elution, and the CO 2 concentration profiles sensibly shift toward lower Bt and lower adsorption capacity (Supplementary Table 19). This is in agreement with the weaker adsorbent-adsorbate interactions at higher temperatures, the faster molecular diffusion and the exothermic character of the adsorption process. A negligible temperature effect was instead observed for CH 4 , that speedily diffuses into the bed and almost immediately exits from the bed. Separation effectiveness decreases by increasing the temperature, and at temperatures similar to the activation one (393 K), CO 2 and CH 4 curves nearly overlap. Good Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 4 separation capability (S b >0.9)wasfoundupto353K,indicating applicability in a wide temperature range. Regeneration and stability assessment of TAMOF-1 The regeneration step of a TAMOF-1 bed after saturation appears to be quite simple, avoiding the need for thermal heating. TAMOF-1 can be completely regenerated at a constant temperature just by passing through a sweep gas (N 2 ). The corresponding CH 4 and CO 2 desorption curves after saturation by an N 2 sweep gas stream were collected for different flow rates, temperatures, and pressures (Fig. 3) CH 4 desorbs faster than CO 2 , as expected. The high CO 2 /CH 4 selectivity in desorption allows for the recovery of a high purity CO 2 fraction, which can be reused as a commodity. Moreover, the regeneration times are relatively short, when compared with the Bt times. Fig. 2 | Adsorption and desorption properties of TAMOF-1. a Adsorption/desorption isotherms of CO 2 ,CH 4 and N 2 in a TAMOF-1 powder sample at 298 K up to 10 bar. bAdsorption isotherms of CO 2 with a temperature range of293–353 K up to 10 bar. cIAST selectivity of different CO 2 /CH 4 gas mixtures with varying ratios at 25 °C up to 1 bar. dCO 2 sorptioncapacityversusCO 2 /CH 4 IASTselectivity forbinary 50:50v/v mixtures at 1bar and 293 K (IAST selectivity values> 20), adapted from ref. 42.eBreakthrough curves of CO 2 (solid line) and CH 4 (dashed line) for binary mixtures with different CO 2 /CH 4 ratios: 25:75(blue), 50:50(red), 75:25(green). fCO 2 breakthrough curves in different inlet gas mixtures: 50:50 CO 2 /CH 4 (red), 50:50 CO 2 /N 2 (cyan), CO 2 /CH 4 /N 2 =50/ 2 5/25 (magenta). Measures in (eand f)were performed with 0.7 g of activated TAMOF-1 powder. TAMOF-1 was activated under vacuum (10−1mbar) in both column top and bottom sides at 393K for 15h. gCO 2 / CH 4 (50:50) breakthrough curves for activated TAMOF-1 (7.7 g) at 72% relative humidity (RH). TAMOF-1 was activated under vacuum (10-1 mbar) in both column top and bottom sides at 393 K for 15 h. hCO₂/CH₄(50:50) breakthrough curves for activated TAMOF-1 (0.7 g) underacid gas conditions (0.9% H₂S, 2.5% H₂O). TAMOF1 was activated under N 2 flow (170 mil min–1g TAMOF –1) at 393 K for 15 h. All breakthrough experiments were performed at 298 K and 1.05bar. See Supplementary Tables 19–21 for detailed fixed-bed adsorption parameters. Fig. 3 | Gas desorption dynamics of TAMOF-1. TAMOF-1 desorption curves of CO 2 (full line) and CH 4 (dashed line) in a N 2 sweep gas flow to regenerate the TAMOF-1 after CO 2 -CH 4 breakthrough experiments for (a) different concentrations of equimolecularCO 2 -CH 4 mixtures, (b) different pressures, (c)different flow rates and (d) different temperatures. In all cases, the processes were performed at constant pressure, temperature, and overall flow rate during both, the breakthrough and desorption steps. TAMOF-1 (0.7 g) was activated under N 2 flow (170 mL min–1 g TAMOF –1) at 393 K for 15 h. Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 5 The regeneration time can be accelerated by increasing the nitrogen flow rate, or reducing the pressure, or increasing the temperature. All these data highlight the potential of TAMOF-1 as an adsorbent for pressure/vacuum/thermal swing adsorption processes. The presence of humidity is inherent in all raw biogas mixtures, typically reaching saturation levels underwater20.From anengineering perspective, and particularly when employing adsorbents under vacuum conditions, partial removal of water from the inlet stream becomes crucial. This necessity arises from the potential for water condensation within the column, leading to obstructions that can diminish vacuum pressure during the desorption phase52. However, it is important to acknowledge that a certain degree of water vapor will invariably persist in the biogas mixture entering the adsorbent column. Previous investigations have demonstrated the structural robustness of TAMOF-1 under humid conditions, even in liquid water, with the material exhibiting complete reactivation. Here, we evaluate the competitive adsorption behavior of CO 2 and H 2 O, as well as the adsorbent cyclic stability under dynamic adsorption conditions. As depicted in Fig. 2g, even in the presence of high humidity (~ 72% RH), TAMOF-1 retains its CO 2 adsorption capacity (2.3mmolg−1)withjusta 15% reduction compared to the dry inlet mixture. The CO 2 /CH 4 selectivity is also maintained within the range of 4–6. Subsequent to the adsorption step, regeneration was conducted under vacuum at a temperature of 80 °C. The separation performance of TAMOF-1 remained consistent over multiple adsorption-desorption cycles, as demonstrated by the overlapping CO 2 and CH 4 breakthrough curves (Supplementary Table 20). This stability indicates negligible degradation of the materialafter successive cycles andnear-complete recovery of working capacity under the operating conditions investigated. Hydrogen sulfide (H 2 S), a common impurity found in raw biogas (~ 0–100 ppm1), presents a significant challenge to biogas upgrading. H 2 S is a highly corrosive acid gas that can compromise the chemical stability of materials used in separation processes. For instance, H 2 S can disruptthecoordination bonds between organicligands and metal centers in the MOFs, leading to structural degradation53.Toassessthe separation behavior of MOFs in the presence of hydrogen sulfide is therefore crucial for their effective application in biogas upgrading. Analysis of TAMOF-1 in humid (2.5 mol% H 2 O) and acidic gas (0.9 mol% H 2 S) conditions (Fig. 2h) demonstrates its ability to separate CO 2 /CH 4 mixtures, even under these conditions. However, a reduction of adsorption capacities (16%) is observed between the first and the second cycle, while selectivity remains relatively constant (~ 3–5). We observed a reduction in the competitive adsorption between CO 2 and CH 4 , with negligible co-adsorption of CH 4 .Weassignthisdifferenceto the very high retention time found for H 2 S(noH 2 S was detected in the outlet stream not even after the CO 2 equilibrium regime), which competes for adsorption sites. Importantly, this analysis was performed under accelerated conditions, with very high H 2 S concentration (9000 ppm), almost two order or magnitude higher than what is usually found in biogases. These data, therefore, demonstrate a relatively high robustness of the material also in strongly acid conditions. However,H 2 Sremovalisrecommended priortobiogasupgradingwith TAMOF-1 in order to increase material durability. Structure determination with adsorbed CO 2 We attempted to localize the preferential crystallographic position of the CO 2 molecules when adsorbed in the TAMOF-1 framework by X-ray diffraction analysis. A single crystal was dehydrated, exposed to a CO 2 stream, and then cooled down to 100 K. The analysis of the XRD structural data revealed residual densities in the channels that were compatible with the presence of CO 2 in the crystal matrix. However, the poor selectivity under X-ray diffraction conditions between oxygen and carbon, in addition to the possible presence of residual water, precluded the successful location of CO 2 molecules in the channels. For this reason, we turned to neutron diffraction54, where carbon and oxygen atoms can be properly identified thanks to their distinct neutron scattering lengths. The neutron diffraction structure analysis of an activated TAMOF1 single crystal confirms the crystal structure obtained by XRD (Fig. 4) with triangular empty channels running along the [111] direction, which is a 3-fold axis due to its cubic symmetry (Supplementary Tables 1–7). After exposure to CO 2 , and cooling down to 100 K, these channels are filled with CO 2 molecules exhibiting moderate disorder (Fig. 4), indicating that weak interactions with the TAMOF-1 network are dominant (Supplementary Tables 8–15). Adjacent to this channel, three copper atomsself-assembleintwo orientationsthatarerotatedapproximately 45° with respect to each other every 13.5 Å along the [111] axis, forming equilateral triangles of approximately 6.7 Å. This arrangement creates a narrower channel where CO 2 molecules align themselves with the oxygen’s lone pairs located between the Lewis sites of two of the copper atoms in the triangle. These CO 2 molecules are the only ones that exhibit a clear, directional interaction with any of the available TAMOF-1 sites. We associate this crystallographic position with the higher isosteric enthalpy of adsorption found at low coverage. The rest of the CO 2 molecules are located along the channels of the structure with apparently random orientations. The intermolecular interaction between CO 2 molecules located in the channel is consistent with London dispersion forces in agreement instead with the lowest isosteric enthalpy of adsorption approaching the bulk-phase sublimation heat of CO 2 . The oxygen atoms in the CO 2 molecules possess lone pairs that are directed toward the more positively charged carbon atoms, which are situated at distances ranging between 2.6 Å and 3.1Å. Similarly, the carboxylate groups of the TAMOFinteractinthesamewaywiththeCO 2 molecules,as theoxygen atoms in the carboxylate groups exhibit lone pairs that are directed towardsthecarbonatomsintheCO 2 molecule, whicharepositionedat adistanceof3.1Å. It is important to note that these neutron diffraction data were obtained at 100 K. Room temperature data collection resulted in a disordered model, indicating that room temperature is enough to break the dominant interactions between CO 2 and TAMOF-1. Spectroscopic analysis To further investigate the interactions between CO 2 and the TAMOF-1 framework at room temperature, we collected IR spectroscopy data. The IR spectra of CO 2 when adsorbed on TAMOF-1 (Supplementary Fig. 4) show a band at 2335 cm–1, which, according with previous reports55,56, can be ascribed to physisorbed CO 2 . The less intense band at 2324 cm–1has also been observed before and assigned to a combination band. These results suggest that there are not site-specificstrong interactions and CO 2 only physically interacts with the framework. To confirm the validity of these results, we also investigated CO adsorption for comparison. Supplementary Fig. 4b shows the C-O stretching region of carbon monoxide adsorbed on TAMOF-1. Interaction of the metal-organic framework with adsorbed CO resulted in the formation of an IR absorption band at 2139 cm–1,which,according to literature, is assigned to (non-localized) physisorbed carbon monoxide57, indicating that the metal-organic framework TAMOF-1 does not present accessible coordinatively unsaturated metal centers. Computational analysis and adsorption mechanism We calculated the single-component adsorption isotherms for CO 2 , CH 4 ,andN 2 molecules in TAMOF-1 in the 263–333 K, and 1–107Pa range. The good agreement between simulation and experiments validates our models (Fig. 5). Excess adsorption,following the protocol of Myers and Monson58, allows comparison with the experiment. Some energy parameters related to carbon capture were also calculated from the single-component isotherms of CO 2 and N 2 . We estimate that TAMOF-1 exhibits low parasitic energy, a volumetric working capacity of 23.46 kg m–3,andafinal CO 2 molar purity of the mixture of 0.904, Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 6 which are excellent features for carbon capture. The calculated adsorption isotherms were fitted to a dual-site (for CO 2 ) and single site (for CH 4 and N 2 ) Langmuir-Freundlich model using the RUPTURA software59 (solid lines in Fig. 5). Subsequently, we proceeded to compute the binary isotherms and determine the adsorption selectivity for CO 2 :CH 4 and 14 CO 2 :84N 2 mixtures (representing the composition of dry post-combustion flue gas). The resulting adsorption selectivities are depicted in Fig. 5d. In all cases, the adsorption of CO 2 surpasses that of CH 4 or N 2 , primarily due to the stronger interactions between CO 2 molecules and the adsorption surfaces. Simulation shows that at low values of pressure (1–500 Pa) the molecules of carbon dioxide are located in the narrow channels formed by the triad of Cu atoms. There is a dominant interaction between CO 2 and two Cu atoms (as shown in Fig. 4anddiscussedinthe SI, neutron diffraction analysis section), resulting in high values for the heat of adsorption, 50 kJ mol–1, in agreement with experimental results (Qst  Uhg DE +RT where Uhg DE is the mean interaction energy between the CO 2 and the TAMOF-1 at very low pressure). However, as the CO 2 pressure increases, the CO 2 -CO 2 interactions become strong enough to displace some of the adsorbed CO 2 molecules from these energetically favorable binding sites. This can be seen from radial distribution functions between CO 2 -CO 2 and CO 2 -Cu atoms, displayed in Fig. 6. Figure 6a shows that the interaction energy between the CO 2 molecule and the adsorption surface remains stable at around Fig. 4 | Crystal structure from neutron data showing the occupation of CO 2 molecules into the channels in TAMOF-1. a Detail of the CO 2 positions within the Cu 3 triangles in thelargest voidspace of TAMOF-1. The distances O1C-Cu1(zxy) and O2C-Cu1 are 2.7726(1) and 2.7068(1) Å, respectively. The view direction is along [111]. Cu1, Cu1(zxy) and Cu1(yzx) are related by a crystallographic three-fold axis, whichalsorelates theCO 2 moleculeatC1Ctotwoothers,which arenotshown.C1C/ O1C/O2C and its two congeners have site occupancy factors of 1/3 as a result of disorder about the symmetry axis. Color code: Cu, deep blue; O, red; N, light blue; C, gray; H, white. bView along [111] of the TAMOF-1 open framework (green stick representation) and the positions occupied by the guest CO 2 molecules (red van derWaals’radii representation) inthe TAMOF-1 channels, with the two components shown together (left) and individually (right). View along [100] (c)andviewalong [111] (d), of parts of the complex void structure that accommodates the guest CO 2 in TAMOF-1. The voids are represented as lighted areas for exterior surfaces and as shadowed areas for interior surfaces of the void boundaries. Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 7 –45 kJ mol–1up to 3 kPa and progressively decreases with pressure to –23 kJ mol–1.Although thistrendisqualitatively equivalentforCH 4 and N 2 , the range of energies and pressures differs, and the effect on adsorption is neglected. For example, for CH 4 , the interaction energy varies from –25 kJ mol–1(low pressure) to –12 kJ mol–1(high pressure). To conclude, the adsorption selectivity of CO 2 over CH 4 or N 2 at intermediate pressures (Fig. 5d) is mainly explained by two causes: the electrostatic interactions between CO 2 and the square planar Cu sites, and the confinement of CO 2 inside the TAMOF-1 pocket-cages. The narrow pores formed by the triad of Cu atoms contribute to decrease this selectivity at high pressures. The self-diffusivity coefficients (D)ofCO 2 and CH 4 were calculated using MD simulations at various temperatures and adsorption loadings (Fig. 7). CO 2 consistently exhibits lower diffusivity than CH 4 . At low loading (1 to 4 CO 2 molecules per unit cell), the molecules of CO 2 are confined in adsorption pockets formed by the triad Cu atoms, resulting in low diffusivity (i.e., D S CO2 ~10 –10 ms –1). As pressure increases, the molecules of CO 2 diffuse from the pocket adsorption site to the main channel. This leads to a maximum diffusivity at ~ 3 mol kg–1of adsorption loading for all temperatures (e.g., at 333 K, the self-diffusivity is approximately D S CO2 ~10 –9m·s–1). Beyond this loading(threemoleculesperCutriad),themoleculesofCO 2 are mainly adsorbed in the (chiral) channel, preventing transport and causing a progressively decreasing of diffusivity. In contrast to CO 2 ,for CH 4 molecules, self-diffusivity reaches its peak at infinite dilution for all temperatures (see Fig. 7b). The diffusion of CH 4 decreases with the increaseonadsorption.Asanexample, for 333K and for 1moleculeper unit cell, the self-diffusivity coefficient is D S CH4 ~6×10 –9ms –1. Breakthrough curves for CO 2 and CH 4 were computationally predicted to validate the experiments in a column bed length of 5.8 cm and a gas pressure of 1.05–1.3 bar at 298 K (Fig. 8). The fitted Langmuir-Freundlich parameters were used to predict this adsorption dynamic behavior. Helium was used as a carrier gas to ensure high gas velocity. Three distinct gas compositions were investigated: 95% He and 5% of a CO₂/CH₄mixture with ratios of 1.5:3.5, 2.5:2.5, and 3.5:1.5 (v/v). Initially, the column was fully saturated with helium. The void fraction of the adsorbent bed was 0.3. Simulation data are in agreement with the experimental results (Fig. 8). The simulated elution gas behavior remains qualitatively and quantitatively consistent with experimental data across the range of gas mixture compositions investigated (3.75%, 2.5%, and 1.25% v/v CH 4 ). Although a direct comparison with data reported in Fig. 2is not accurate, the rapid elution of CH 4 observed in this case may be attributed to its higher diffusivity at higher gas velocity (0.015 m s−1) and to its low gas partial pressure (Fig. 7b). In conclusion, TAMOF-1, a stable, robust, homochiral metalorganic framework (BET specificsurfacearea=980±50m 2g–1), has shown selective adsorption of CO 2 from CO 2 /CH 4 gasstreams, offering a promising performance. Although comparing breakthrough data across studies is often challenging due to inconsistencies in experimental details, the performance parameters exhibited by TAMOF-1 appear competitive for CO 2 /CH 4 separations when compared with state-of-the-art (Fig. 2d and Supplementary Table 22). As demonstrated by structural and theoretical data, CO 2 uptake is dominated by a variety of weak interactions. At low coverage, the preferred binding sites are the square planar Cu2+ centers. Once these positions are full, the TAMOF-1 open channels accommodate additional CO 2 molecules with weaker interactions with the dangling functional groups (carboxylate, triazole, imidazole) in the framework. Adsorption isotherms confirmtheCO 2 preferentialuptakewithrespecttoCH 4 orN 2 in a large pressure range, resulting in good separation parameters for CO 2 /CH 4 gas mixtures. CO 2 /CH 4 mixtures can be effectively separated with high selectivity in a wide CO 2 /CH 4 concentration (1–75%), pressure (1–6 bar), and temperature range (293–353 K). Elution behavior of CO 2 through the TAMOF-1 bed depends just on the CO 2 molar flow and it is not affected by the presence of the other gases investigated (CH 4 and/ or N 2 ). TAMOF-1 retains separation performance, even under high humid conditions (~72% RH) showing no degradation and high cycling stability. Separation capability is observed also in extremely acidic conditions (9000 ppm H 2 S) although a small performance degradation is observed. These data demonstrate TAMOF-1 robustness, also in harsh acidic environments although H 2 S removal is preferred to increase material durability. Fig. 5 | Computational modeling of gas-TAMOF-1 thermodynamic properties. a–cCalculated excess adsorption isotherm (empty circles) and experimental isotherms (solid points, see legend for more details) at 263.15, 303.15, 313, 323, and 333 K. Errors are estimated from the standard deviation in the adsorption processes. d,Selectivitysi j=qi=qj,whereiis CO 2 ,andjis CH 4 or N 2 . Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 8 These properties are crucial for industrial-scale CO 2 capture applications. TheweakCO 2 –TAMOF-1 interactions facilitate facile, lowenergy regeneration of the adsorbent bed. These attributes, coupled with high selectivity, render TAMOF-1’sperformanceinbiogas upgrading superior to other reported materials42. Consequently, TAMOF-1 appears well-suited for integration into pressure/vacuum/ thermal swing adsorption processes. A convenient regeneration protocol, adaptable to specific time and energy constraints through operationalparameter tuning, is readily achievable. Current efforts are focused on scaling and pelletization of TAMOF-1, advancing the development of a CO 2 capture and purification technology based on this promising material. Methods Materials All reagents were of commercial grade and used without further purification: L-histidine (≥98%, Iris Biotech GmbH), thionyl chloride (SOCl 2 ,≥99%, Sigma Aldrich), hydrazine monohydrate (NH 2 NH 2 ·H 2 O, reagent grade, 98%, Sigma Aldrich), sodium carbonate anhydrous (Na 2 CO 3 , ACS reagent, ≥99.5%, Sigma Aldrich). All solvents were of commercial grade and used without further purification: HPLC-grade ethanol, isopropanol, hexanes, acetonitrile and tert-butyl methyl ether (VWR, Chem-Lab and Sigma Aldrich), N,N-dimethylformamide (peptide grade, ≥99.9%, Iris Biotech GMBH) and diethyl ether (≥99%, VWR). Fig. 6 | Computational modeling of CO 2 -TAMOF-1 interactions. a Histogram for the CO 2 -TAMOF-1 interaction energy at several values of pressure. bRadial distribution function for (intermolecular) pairs, and atoms. Fig. 7 | Gas diffusion properties modeling. Self-diffusivity coefficient (D)forCO 2 (a)andCH 4 (b) at various temperatures and adsorption loadings. Solid lines are fitted to the data as guiding references to assist the reader (u.c.= unit cell). Fig. 8 | Experimental and computational breakthrough analysis. Calculated (lines) and experimental (square) breakthroughcurves for CO 2 andCH 4 at 1 bar and 298.15 K for three composition ratios: 25 CO 2 :75CH 4 (a),50 CO 2 :50CH 4 (b), and 75 CO 2 :25CH 4 (c). Experiments performed with helium as the carrier gas (95% v/v). Experiments performed using 7.7 g of activated TAMOF-1. TAMOF-1 was activated under vacuum (10−1mbar) in both column top and bottom sides at 393 K for 15 h. Article https://doi.org/10.1038/s41467-025-58426-w Nature Communications | (2025) 16:3243 9