Carbon dioxide and hydrogen adsorption study on surface-modified HKUST-1 with diamine/triamine

The present article intended to study the influence of post-synthetic modification with ethylenediamine (en, diamine) and diethylenetriamine (deta, triamine) within the coordinatively unsaturated sites (CUSs) of HKUST-1 on carbon dioxide and hydrogen storage. The as-sythesized adsorbent was solvent-exchanged and subsequently post-synthetically modified with di-/triamines as sources of amine-based sorption sites due to the increased CO2 storage capacity. It is known that carbon dioxide molecules have a high affinity for amine groups, and moreover, the volume of amine molecules itself reduces the free pore volume in HKUST-1, which is the driving force for increasing the hydrogen storage capacity. Different concentrations of amines were used for modification of HKUST-1, through which materials with different molar ratios of HKUST-1 to amine: 1:0.05; 1:0.1; 1:0.25; 1:0.5; 1:0.75; 1:1; 1:1.5 were synthesized. Adsorption measurements of carbon dioxide at 0 °C up to 1 bar have shown that the compounds can adsorb large amounts of carbon dioxide. In general, deta-modified samples showed higher adsorbed amounts of CO2 compared to en-modified materials, which can be explained by the higher number of amine groups within the deta molecule. With an increasing molar ratio of amines, there was a decrease in wt.% CO2. The maximum storage capacity of CO2 was 22.3 wt.% for HKUST-1: en/1:0.1 and 33.1 wt.% for HKUST-1: deta/1:0.05 at 0 °C and 1 bar. Hydrogen adsorption measurements showed the same trend as carbon dioxide, with the maximum H2 adsorbed amounts being 1.82 wt.% for HKUST-1: en/1:0.1 and 2.28 wt.% for HKUST-1: deta/1:0.05 at − 196 °C and 1 bar.

In the present study, we were inspired by amine-functionalized silicas with which our working group has many years of experience 30,31 . We applied a similar approach for MOF material (HKUST-1), which was postsynthetically modified with diamine (ethylenediamine, en) and triamine (diethylenetriamine, deta) on coordinatively unsaturated sites (CUSs) within HKUST-1 framework. Amines are known to have a high ability to capture CO 2 molecules, and therefore HKUST-1 has been functionalized with mentioned amines in different molar ratios. It is known that the calculated ideal pore size of material for efficient H 2 storage is 6-7 Å 32, 33 . We modified HKUST-1 by varying the concentration of amines to achieve maximum H 2 storage. The prepared materials were subsequently studied as CO 2 and H 2 adsorbents at 0 °C and − 196 °C, respectively. It was shown that the enhanced capacity of the materials towards the selected adsorptives increased with an decreasing amine molar ratio. In addition, it can be concluded that better results were observed for deta-modified materials compared to en-functionalized materials.

Experimental
Chemicals, synthesis and post-synthetic modification. All chemicals used to synthesise HKUST-1 and its subsequent post-synthetic modification were purchased in the highest available purity from Acros Organics and Sigma Aldrich.
HKUST-1. 1 g (4.76 mmol) of benzene-1,3,5-tricarboxylic acid (H 3 BTC) was dissolved in a 30 ml solvent mixture of ethanol and N, N′-dimethylformamide (DMF) (1:1, v:v). Subsequently, 15 ml of an aqueous solution of copper nitrate trihydrate (2.08 g, 8.6 mmol) was added to the H 3 BTC solution. The mixture was stirred for 10 min and finally allowed to react in an oven at 85 °C for 24 h. After a mentioned time, the resulting product was filtered off and dried. The weight of the prepared HKUST-1 was 2.088 g. Further, DMF (b.p. 153 °C) molecules located in the cavities of as-synthesized (AS) HKUST-1 were exchanged (EX) for ethanol (b.p. 78 °C) for subsequent easier activation at lower temperatures to obtain HKUST-1 in activated form (AC). The solvent exchange process was performed in a Soxshlet extractor for 48 h.
Methods and characterization. Infrared spectra (IR) of the prepared materials were measured on a Nicolet 6700 instrument in the wavelength range of 4000-400 cm −1 using the ATR method. Elemental analysis was measured on a CHNOS Elemental Analyzer Vario MICRO instrument with a sample weight of ~ 2 mg. Thermoanalytical experiments, thermogravimetry with simultaneous different scanning calorimetry coupled with mass spectrometry (TG/DSC-MS) were performed using a SetsysEvolution (Setaram). The measurements were carried out with 16-19 mg of the sample using α-Al 2 O 3 crucible. TG-DSC curves were recorded in the inert atmosphere of Ar (20 cm 3 min −1 ) from 15-800 °C with a heating rate of 10 °C min −1 . Thermal analysis with simultaneous differential thermal analysis (TG/DTA) was carried out on a Netzsch STA 449 F1 Jupiter. The sample with the weight of ~ 20 mg was placed in a corundum crucible and heated from 30 to 900 °C with a heating rate of 10 °C min −1 in the air atmosphere with a flow rate of 60 cm 3 min −1 . Powder X-ray diffraction (PXRD) experiments were done in reflection geometry on a Rigaku MiniFlex 600 multipurpose diffractometer using Cu/Kα radiation (λ = 1.54056 Å) and 2θ continuous scan at 2° min −1 from 2 to 60°. Adsorption and desorption of Ar, CO 2 and H 2 were performed at − 186 °C, 0 °C, and − 196 °C, respectively, using the Autosorb iQ-XR (Quantachrome Instruments). Void volume was determined by a helium-free NOVA ® approach 34 . Samples were activated in a vacuum (20 h, 150 °C). The volume of micropores (V p, micro , pore diameter < 2 nm) and mesopores (V p, meso , pore diameter 2-50 nm) were calculated from pore size distribution curves obtained by fitting the Ar adsorption data by a Non-Local Density Functional Theory (NLDFT) adsorption kernel (ASiQwin software, Quantachrome Instruments) assuming cylindrical pores. BET area (S BET ) was calculated according to the procedure for microporous materials 35 , based on which adsorption isotherm points in the region of ca. 10 −3 -10 −2 of p/ p 0 (relative pressure) were used; 0.142 nm 2 as a cross-sectional area of Ar molecule was assumed.

Results and discussion
HKUST-1 structure and synthesis. HKUST-1 is one of the first MOF compounds, which attract scientists around the world in the preparation and application of metal-organic structures 36 . The crystal structure of HKUST-1 consists of two copper(II) cations with coordination number five, which form a paddle-wheel cluster with a square secondary building unit (SBU). Four carboxylate groups are coordinated to the cluster in syn-syn mode, forming a tetragonal base, and the fifth Cu(II) coordination position is occupied by coordinated water molecules to form a tetragonal pyramid-shaped polyhedron, as shown in Fig. 1a. The mutual combination of the mentioned building blocks results in the final 3D polymeric framework of HKUST-1 with bimodal pore size distribution, small cage with diameter 3.5 Å and large cage with diameter 9 Å (see Fig. 1b). The post-synthetic modification of HKUST-1 consisted of replacing coordinated water molecules in the paddle-cluster with amine molecules with different numbers of amine functional groups (ethylenediamine (en, diamine) and diethylenetriamine (deta, triamine)), see Fig. 1c. Water molecules were removed by heating the compound at 200 °C to form coordinatively unsaturated sites (CUSs) to which amines were attached via nitrogen donor atoms. Activation of the material was accompanied by a color change (from blue to purple, see Characterization. Infrared spectroscopy (IR), thermal analysis (TG / DSC) and powder X-ray diffraction (PXRD) methods were used to identify HKUST-1, monitor the post-synthetic modification process, thermal stability and characterization of prepared materials. The IR spectra of the materials are shown in Fig. 2a, Fig. S1 in ESI and the assignment of the characteristic vibration absorption bands are summarized in Table 1 in ESI. The comparison of IR spectra of as-synthesized (AS), solvent exchanged (EX) and activated (AC) HKUST-1 is shown in Fig. S1 in ESI and confirm successful ethanol exchange process and material's activation based on the presence/absence of characteristic solvent absorption bands. In all infrared spectra (see Fig. 2a), a broad absorption band at 3400 cm −1 is present, which can be assigned to the OH stretching vibration (ν(OH)) of the physisorbed water molecules. BTC linker in the materials is evident due to the presence of several characteristic vibrations: ν(COO − ) as about 1550 cm −1 , ν(COO − ) s  Table 1 in ESI). Thermal robustness and behavior of prepared materials were investigated by a combination of thermogravimetric (TG) analysis and differential scanning calorimetry (DSC) (see Fig. 2b). Unmodified HKUST-1 is thermally stable up to 50 °C, above mentioned temperature the compound desolvates in the temperature range Pyrolysis of the organic moiety occurred in the 220-450 °C temperature range, which is followed by exothermic effects on the DSC in the range of 220-370 °C. According to the changes in TG curves and colour change of materials with higher amine content, we assumed a phase change of these compounds, which was confirmed by PXRD measurements (see text below). The structural and thermal stability of HKUST-1 and materials after functionalization with en and deta in different molar ratios was monitored by PXRD measurements (see Fig. 2c, Figs. S2-S5 in ESI). In Fig. S2 in ESI the comparison of measured and calculated PXRD (Chui et al. 1999) patterns of HKUST-1 is presented, which are in good agreement and confirm the successful preparation of HKUST-1. Heating PXRD measurements studied the thermal stability of HKUST-1 at 50, 100, 150, 200, 250 and 350 °C (see Fig. S3 in ESI), which showed that HKUST-1 is stable after the activation process and its decomposition occurs at 350 °C. The obtained results are in good agreement with TG measurements (see Fig. 2b). From the PXRD patterns of HKUST-1: en materials (see Fig. 2c, left), it is evident that at molar ratios of 1:0.1 and 1:0.25 only the HKUST-1 phase is present. At a ratio of 1:0.5, in addition to the diffraction peaks corresponding to HKUST-1, novel diffraction lines appear, corresponding to the formation of a new phase. A further increase in the concentration of en completely eliminates HKUST-1, while only the diffraction peaks of the novel phase are present in the PXRD patterns. Similar changes were observed for deta-modified materials (see Fig. 2c, right). The HKUST-1 phase is stable up to a molar ratio Table 1. Obtained and calculated results of textural properties determined from Ar adsorption measurements @ − 186 °C and storage capacity of CO 2 and H 2 measured 0 °C and − 196 °C, respectively of prepared materials in different units. S BET BET area, V p pore volume, V adsorbed gas volume, w mass percent, n amount of substance, -undetecable, micro micropore, meso mesopore.

Material
Ar @ − 186 °C CO 2 @ 0 °C H 2 @ − 196 °C S BET (m 2 g −1 ) V p, micro (cm 3 g −1 ) V p, meso (cm 3 g −1 ) V (cm 3 g −1 ) w (wt.%) n (mmol g -1 ) V (cm 3 g −1 ) W (wt.%) n (mmol g −1 ) HKUST www.nature.com/scientificreports/ of 1:0.1, at a ratio of 1:0.25, a mixture consisting of HKUST-1 and a new phase is present, and at higher molar ratios, only a novel phase is present. The described phase changes were manifested visually by a colour change of prepared materials from blue to purple (see Fig. 1e). The thermal stability of selected en-modified materials at a low ratio, HKUST-1: en/1:0.25 represented by HKUST-1 phase (see Fig. S4 in ESI) and a high ratio, HKUST-1: en/1:1 characterised by novel phase (see Fig. S5 in ESI) was also studied. For the low ratio material, the same thermal stability as pure HKUST-1 was observed, and the high molar sample is thermally stable up to 100 °C, at higher temperatures, a phase change occurs, and at 350 °C the material decomposed.
The new phase that forms at high amine concentrations (specifically HKUST-1: en/1:1.5) was studied through various physicochemical techniques in order to identify it and determine its chemical composition. By searching the CCDC (Cambridge Crystallographic Data Center) database, it can be concluded that two compounds containing Cu(II), BTC(-III) ions and a derivative of en ligand with the chemical composition Cu 4 (HBTC) 4 (tmen) 4 .12H 2 O (FUHYAJ 37 ) and Cu 3 (BTC) 2 (tmen) 3 (H 2 O) 2 ·6.5H 2 O (FEXSOR 38 ) were synthesized (see Fig. 3a). In their preparation, a N-tetramethyl-substituted en ligand (tmen-N,N,Nʹ,Nʹtetramethylethylenediamine) on nitrogen atoms was used. By comparing the PXRD pattern of HKUST-1: en/1:1.5 material and the mentioned compounds, a similarity with the compound Cu 3 (BTC) 2 (tmen) 3 (H 2 O) 2 ·6.5H 2 O can be observed (see Fig. 3b). Since it was not possible to clearly identify the newly formed phase by the PXRD comparison, we decided to study the exact chemical composition of the modified material HKUST-1: en/1:1.5. The presence of organic building blocks (BTC and en) was confirmed by IR spectroscopy. The IR spectrum (Fig. 3c) of compound contains characteristic absorption bands for the carboxylate group of the BTC linker (ν(COO − ) as 1563 cm −1 , ν(COO − ) as 1337 cm −1 and δ(COO − ) 723 cm −1 ) and the presence of en is confirmed by typical bands for aliphatic CH 2 (ν(CH) al 2970, 2947, 2927 and 2884 cm −1 ) and NH 2 groups (ν(NH) 3248 and 3148 cm −1 ; δ(NH) 1615 cm −1 ). By TG-MS, the thermal stability of the new phase was studied in an inert atmosphere of argon, through which the presence of en was also confirmed (see Fig. 3d). In the temperature interval 60-220 °C, the release of water molecules (dehydration) occurs, which was manifested on the MS spectrum by the signal m/z = 18. In the second step of thermal decomposition in the temperature interval 220-280 °C, a mass loss is observed, which corresponds to the release of coordinated en molecules with a signal of m/z = 60. Further heating in the temperature range of 280-350 °C results in pyrolysis of the polymer skeleton and further release of en. The mass spectra of gaseous products in the mentioned interval showed the signals with m/z = 18, 32, 44, 60 corresponding to H 2 O, CO, CO 2 and en, respectively. The above results show that the thermal decomposition of en and BTC cannot be clearly distinguished, and both decomposition steps take place simultaneously. As the thermal analysis was carried out in an inert atmosphere of argon, the sample did not fully decompose, and carbonized material was present in the resulting thermal decomposition product. For this reason, TG/ DTA measurements were carried out in an oxidizing air atmosphere to ensure complete thermolysis of the material, and based on weight losses and CHN elemental analysis results, it was possible to determine the exact chemical composition of the sample HKUST-1: en/1:1.5. TG/DTA curves of HKUST-1: en/1:1.5 measured in the air atmosphere are shown in Fig. 3e. In the first thermal decomposition step, in the temperature interval 40-150 °C, a mass loss of 10.18% was observed, which corresponds to the release of five water molecules (clcd. mass change 10.29%). Dehydration of the sample was manifested on the DTA curve by two endothermic effects at 96 and 118 °C. In the following two overlapping decomposition steps, the release of three amine molecules and the thermal decomposition of two BTC molecules occur. The total mass loss corresponding to the organic components was 61.77% (clcd. mass change 62.45%), and their decomposition/release was accompanied by three exothermic effects on the DTA curve at 244, 324 and 377 °C. PXRD identified the resulting thermal decomposition product as CuO (see PXRD pattern in Fig. 3f) with the experimental residual mass of 27.94% (clcd. residual mass 27.27%). Based on the described weight losses, it was possible to determine the exact chemical composition of the material HKUST-1: en/1:1.5 with the formula Cu 3 (BTC) 2 (en) 3 ·5H 2 O. The chemical composition was also confirmed by CHN elemental analysis, while the calculated and measured percentages of chemical elements in the compound are in good agreement (M r = 875.25 g mol −1 ; exp.: C 32.54%, H 4.51%, N 21.92%, clcd.: C 32.93%, H 4.61%, N 21.78%).

Texture and gas adsorption properties.
After successful preparation and characterization of the amine-modified compounds, the materials' textural properties (S BET area, micropore and mesopores volume) were studied by argon adsorption @ − 186 °C, and their storage capacities of carbon dioxide @ 0 °C and hydrogen @ − 196 °C were investigated. The results obtained from the adsorption measurements are shown in Fig. 4 and summarized in Table 1.
Argon adsorption measurements @ − 186 °C studied the effect of post-synthetic amine-modification on the textural properties of HKUST-1. Figure 4a shows a comparison of the Ar adsorption/desorption isotherms of pristine HKUST-1, en-and deta-modified materials, and the selected textural properties calculated from the respective isotherms are summarized in Table 1. The materials show a typical type Ia isotherm classified by IUPAC 35 , characteristic for materials with narrow micropores below ca. 1 nm in diameter. This is in line with obtained micropore sizes that were the same for all studied materials and ranged from 0.6 to 1.2 nm. As can be seen from the obtained results, the S BET area of pristine HKUST-1 was 1468 m 2 g −1 , and after modification, the area of materials decreases with increasing amine concentration. The S BET area of modified materials decreased from HKUST-1: en/1:0.1 (656 m 2 g −1 ) to undetecable values for HKUST-1 : en/1:1.5 for en-modified samples, and in deta-functionalized materials from HKUST-1: deta/1:0.05 (1439 m 2 g −1 ) to undetecable values for HKUST-1: deta/1:1. The observed phenomenon can be explained by the reduction in the free pore volume/area of the modified materials due to the binding of a larger number of molecules and the bulk of amine molecules themselves. It can be seen that even a low molar ratio of en (1:0.1) in HKUST-1 structure leads to a halving of textural properties like S BET . On the contrary, the same content of deta leads to only a small decrease in texture www.nature.com/scientificreports/ parameters (1245 m 2 g −1 ). The observed difference can be explained based on the length of amines used and their coordination modes to coordinatively unsaturated sites (CUSs) within the HKUST-1 framework. The size of en molecule is 3.7 Å, and deta molecule is 6.3 Å (see Fig. S6a in ESI). Since the smallest distance between two Cu(II) ions within the HKUST-1 skeleton is 5.2 Å (see Fig. S6b in ESI), deta molecules can bridge and connect the two metal centres, while en can only bind terminally. The mentioned coordination modes of amine molecules are schematically drawn in Fig. S6c in ESI. Fig. S6c in EIS shows the entrance window to the HKUST-1 porous framework, where four Cu(II) cations are located inside the pore. When amines are coordinated to the metal centre, four molecules of en or two molecules of deta are coordinated within the entrance window, as shown in Fig. S6c in ESI. Thus, in the case of en coordination, the free pore volume is more efficiently filled, resulting in a lower surface area than bulkier deta molecules. To confirm the assumed theory, we prepared HKUST-1 modified , it can be concluded that in material HKUST-1: bapen/1:0.1 extended amine ligand also did not cause a significant decrease in S BET as in the case of en (see Fig. S7 in ESI). When reducing the textural properties of materials due to the increase in the concentration of amines, it is also necessary to consider the results of PXRD analysis. PXRD measurements revealed the formation of a new phase, which is present in the mixture at medium molar ratios and in pure form at the highest ratios. As is evident from the measured and calculated textural properties, the newly formed phase is non-porous, as the materials HKUST-1: en/1:1, HKUST-1: en/1:1.5, HKUST-1: deta/1:0.75 and HKUST-1: deta/1:0.75 adsorb only minimally amounts of argon. Moreover, on argon adsorption isotherms an increase in the Ar adsorbed volume at higher relative pressures is observed, as well as H4 hysteresis loop typical for aggregated crystals 35 indicating the presence of mesopores especially in the en-modified materials with ratios from 1:0.1 to 1:0.5 containing low concentration of en. Presence of mesopores or larger pores can be explained by formation of intraggregate voids 39 due to surface modification, or etching of the material caused by increasing the basicity of the environment during the modification process. As shown in Table 1, the percentage increase in mesopore volume (V p, micro /V p, meso ) rises with increasing amine concentration, and the values increase from 20 to 46% for HKUST-1: en and from 5 to 23% for HKUST-1: deta. Similar changes in textural properties were observed for other amine-modified MOF materials such as MOF-74 23 , MOF-177 39 and IRMOF-74 40 .
From the measured carbon dioxide adsorption/desorption isotherms, an increasing amount of stored CO 2 can be generally observed with the decreasing concentration of amines (see Fig. 4b, Table 1). The pristine www.nature.com/scientificreports/ HKUST-1 material can store in its framework 15.19 wt.% (3.45 mmol g −1 ) of CO 2 @ 0 °C and 1 bar. The maximum CO 2 storage capacity of en-modified materials was measured on HKUST-1: en/1:0.1 with a value of 22.31 wt.% (5.07 mmol g −1 ) and decreased to 0.61 wt.% (0.14 mmol g −1 ) for HKUST-1: en/1:1.5 @ 0 °C and 1 bar. For deta-modified materials, the highest CO 2 uptake of 33.09 wt.% (7.52 mmol g −1 ) was obtained for HKUST-1 : deta/1:0.05 and the lowest value of 1.06 wt.% (0.24 mmol g −1 ) for HKUST-1 : deta/1:1 @ 0 °C and 1 bar. In the case of CO 2 adsorption, it is necessary to consider the competitive processes of chemisorption carried out on amine groups (R-NH 2 +CO 2 =R-NH 2 COO) and physisorption, which takes place in the void pore volume of materials. As already discussed in the context of Fig. S6, the void volume seems to be larger for materials modified by deta, than en, which is in line with the fact that deta-modified material (e.g. 1:0.1) exhibits larger CO 2 adsorption capacity compared to material modified by an equivalent quantity of en. In terms of concentration, although the number of active sites for the sorption of CO 2 molecules increases with the increasing concentration of coordinated amines, the free pore volume within the framework decreases due to the bulkiness of amines. The phenomenon described is clear from the measured results of CO 2 adsorption for amine-modified materials (see Fig. 4b, Table 1). Another fact that needs to be considered is the already mentioned phase change of materials at higher amine molar ratios, leading to non-porous materials' formation. A trend of decreasing CO 2 adsorption capacity with increasing amine concentration was also observed for MOF-177 functionalized with polyethyleneimine (PEI) and deta 39  . Because hydrogen is a nonpolar and the smallest known molecule, the storage of large amounts of H 2 is difficult, and for this reason, various MOF materials are intensively studied. It is known that efficient hydrogen storage can be achieved by the presence of alkali and alkaline earth metals within the framework, by the insertion of metal nanoparticles, or by post-synthetic modification 5,25,26 . Efficient hydrogen storage can also occur due to steric effects, as the calculated ideal pore size for hydrogen storage is 6-7 Å 32,33 . For this reason, the effect of different molar ratios of different bulk amines on the pore size in HKUST-1 was investigated to store H 2 efficiently. The measured hydrogen adsorption isotherms of the prepared materials @ − 196 °C are shown in Fig. 4c, and the achieved H 2 storage capacities in different units are listed in Table 1. As with Ar and CO 2 adsorption, the same trend and thus increasing in adsorbed amounts of H 2 with decreasing concentration of amines. The highest hydrogen uptakes were measured for HKUST-1 : en/1:0.1 and HKUST-1: deta/1:0.05 with 1.82 and 2.28 wt.%, respectively @ − 196 °C and 1 bar. The pore size can explain the increased affinity of H 2 for the prepared materials. Calculated pore size distributions (PSD) were obtained by fitting the Ar adsorption data using a NLDFT adsorption kernel assuming cylindrical pores. All materials contain pore sizes ranging from 0.6 to 1.2 nm, covering the ideal pore size range of 0.6-0.7 nm. The decreasing H 2 storage capacity of materials with increasing concentration of amines is due to the decreasing textural parameters like S BET and V p, micro . The formation of a non-porous phase cannot be neglected in materials with a higher concentration of amines, through which it is possible to explain the decreasing H 2 storage capacity of the compounds. According to the best of our knowledge, the effect of stored hydrogen on amine-modified MOFs has not yet been studied and the present study thus represents a pilot project. There are published articles dealing with the separation of H 2 /CO 2 on amine-modified Mg-MOF-74 or MIL-53 42,43 , but not for H 2 storage. In conclusion, however, it can be concluded that the measured highest storage capacities are in the range for top MOF materials 25,26 and are comparable, for example, with UiO-66(Zr) 44 , MOF-519 45 , Mg-MOF-74 46 with maximal H 2 uptakes of 1.87 wt.%, 2.13 wt.% and 2.20 wt.%, respectively @ − 196 °C and 1 bar.

Conclusion
The intention of present study was to increase the adsorption capacity of carbon dioxide and hydrogen in HKUST-1 through post-synthetic modification of amines with different numbers of amine groups. Ethylenediamine (en, diamine) and diethylenetriamine (deta, triamine) were chosen as amines in this study. At present, CO 2 capture is realized using liquid amines, which can efficiently bind CO 2 to form carbamates, but have many disadvantages (corrosivity, regeneration temperature). For this reason, a strategy of anchoring amines on porous support represented by the well-known MOF material, HKUST-1, was chosen. From the HKUST-1 stability point of view, it can be summarized that with increasing molar ratios of HKUST-1: amine, decomposition (1:2 for en and 1:2; 1:1.5 for deta), or a phase change (1:1.5; 1:1; 1:0.5 for en and 1:1; 1:0.75; 1:0.5; 1:0.25 for deta) were observed, which led to the formation of a non-porous materials, that have been thoroughly investigated. From the experimentally obtained adsorption measurements, it can be concluded that with the increasing concentration of amines, the CO 2 capacity of materials decreased and that the deta-modified materials showed higher stored amounts of CO 2 (probably due to their higher void volume) compared to en-modified compounds. The highest storage capacities were obtained for HKUST-1 : en/1:0.1 and HKUST-1 : deta/1:0.05 materials with 22.31 wt.% and 33.09 wt.% of CO 2 @ 0 °C and 1 bar, respectively. The same trend was observed in hydrogen adsorption measurements, H 2 storage capacity for HKUST-1: en 1:0.1 was 1.82 wt.% @ − 196 °C and 1 bar and for HKUST-1: deta 1:0.05 was 2.28 wt.% @ − 196 °C and 1 bar are comparable to other top MOF materials.

Data availability
The data are available on request, please contact corresponding author via e-mail (miroslav.almasi@upjs.sk).