Boosting Ethylene/Ethane Separation within Copper(I)-Chelated Metal-Organic Frameworks through Tailor-Made Aperture and Specific π-Complexation.

The development of new materials for separating ethylene (C2H4) from ethane (C2H6) by adsorption is of great importance in the petrochemical industry, but remains very challenging owing to their close molecular sizes and physical properties. Using isoreticular chemistry in metal-organic frameworks (MOFs) enables the precise design and construction of target materials with suitable aperture sizes and functional sites for gas separations. Herein, it is described that fine-tuning of pore size and π-complexation simultaneously in microporous copper(I)-chelated MOFs can remarkably boost the C2H4/C2H6 adsorption selectivity. The judicious choice of organic linkers with a different number of carboxyl groups in the UiO-66 framework not only allows the fine tuning of the pore size but also immobilizes copper(I) ions onto the framework. The tailor-made adsorbent, CuI@UiO-66-(COOH)2, thus possesses the optimal pore window size and chelated Cu(I) ions to form π-complexation with C2H4 molecules. It can rapidly adsorb C2H4 driven by the strong π-complexation interactions, while effectively reducing C2H6 uptake due to the selective size-sieving. Therefore, this material exhibits an ultrahigh C2H4/C2H6 selectivity (80.8), outperforming most previously described benchmark materials. The exceptional separation performance of CuI@UiO-66-(COOH)2 is validated by breakthrough experiments for 50/50 v/v C2H4/C2H6 mixtures under ambient conditions.

Introduction

Purification of olefins alone accounts for 0.3% of global energy consumption. Olefin/paraffin separation has been thus highlighted as one of seven most important chemical separations.1 Ethylene (C2H4), as the most important olefins, is the mainstay of petrochemical industry, with a global annual production of exceeding 170 million tonnes per year. “Polymer‐grade” specification of ethylene is required for the manufacture of polyethylene plastic. The industrial separation of ethylene from ethylene/ethane (C2H4/C2H6) mixtures highly relies on the repeated distillation–compression cycling at the temperature as low as −160 °C.1, 2 Such heat‐driven separation involving in the phase change of isolated fractions, is highly energy‐ and capital‐intensive. Finding energy‐efficient alternatives to distillation would widely lower global energy consumption, carbon emissions, and pollution. It is feasible in principle to separate C2H4/C2H6 mixtures based on porous solid materials via the energy‐efficient and environmentally friendly adsorption technology. In this context, development of suitable porous adsorbents for ethylene/ethane separation is of highly commercial significance.

A number of porous materials including zeolites,3 carbon molecular sieves,4 and alumina,5 have been explored for the separation of ethylene and ethane. However, the limits on deliberately designing the structure of such purely inorganic materials make them hardly meet the requirement of industrial implement. As an emerging class of microporous materials, metal–organic frameworks (MOFs) hold particular promise for the separation of light hydrocarbons,6, 7, 8, 9, 10, 11, 12, 13, 14, 15 because of their powerful reticular chemistry that enables them more readily tuning of their pore aperture and functionality.16, 17, 18, 19, 20, 21, 22 The most popular cases of C2H4/C2H6 separation at present have been mostly achieved by thermodynamic driven separation. One of the effective strategies is to immobilize the metal ions (such as Cu(I) and Ag(I)) on the pores to form the selective π‐complexation with ethylene, which has been well proved by porous materials.23, 24 Another analogous π‐complexation effect is typically contributed from open metal sites (OMSs) among MOFs.25 Such effect is capable of discriminating ethylene from ethane, and thus perform well for the separation of ethylene and ethane. Unfortunately, coadsorption of ethane commonly exists in these materials, originated from dynamic diffusion in oversize apertures and/or polarization of OMSs, thus delimiting the separation performance in most cases. On the other hand, C2H4/C2H6 separation can also be achieved by the controlled size‐sieving effect.6 However, considering their nearly identical sizes (only 0.028 nm difference in kinetic diameter), a few MOFs show the selective separation of C2H4/C2H6 based on this strategy with moderate high selectivities,26 and only one MOF (UTSA‐280) reported so far has shown the complete exclusion of ethane from C2H4/C2H6 mixtures with benchmark selectivity.27 Therefore, it still remains very challenging for MOF materials to separate ethylene from ethylene/ethane mixtures with a satisfied high selectivity based on a single separation mechanism. We speculate that if we combined the effect of π‐complexation and aperture sieving into a single MOF material, the resulting adsorbent may exhibit a superior separation performance for C2H4/C2H6. However, such synergistic effect has yet to be systematically studied within MOFs for this challenging separation.

Herein, we selected the UiO‐66 family from the abundant MOF gene pool for the study of C2H4/C2H6 separation due to their typically predictable and readily designable pore size and functionality.28, 29, 30 In this work, we carefully single out two organic linkers with different number of carboxyl groups, namely benzene‐1,2,4‐tricarboxylic acid (1,2,4‐BTC) and benzene‐1,2,4,5‐tetracarboxylic acid (1,2,4,5‐BTEC), to construct two different fcu‐MOFs (termed as UiO‐66‐COOH and UiO‐66‐(COOH)2) by using isoreticular chemistry (Figure ). The judicious choice of organic linkers in the UiO‐66 framework allows us to not only finely tune the pore size but also immobilize copper(I) ions onto the framework. The tailor‐made copper(I)‐chelated adsorbent, CuI@UiO‐66‐(COOH)2, thus possesses the optimal pore window size and specific π‐complexation for C2H4/C2H6 separation. Gas sorption studies show that CuΙ@UiO‐66‐(COOH)2 can rapidly capture ethylene via the strong π‐complexation affinity, while effectively reduce ethane adsorption due to its size‐sieving effect. As a result, its ideal adsorbed solution theory (IAST) selectivity for 50/50 C2H4/C2H6 mixtures at ambient conditions can reach up to 80.8, only lower than the benchmark UTSA‐28027 but outdistancing all the other previously top‐performing materials, such as Zeolite 13X (13.4),31 NaETS‐10 (14.7),32 NOTT‐300 (48.7),33 Co‐gallate (52)27 and FeMOF‐74 (13.5),34 PAF‐SO3Ag (26.9).24 Its exceptional separation performance was further validated by the breakthrough experiments on 50/50 v/v C2H4/C2H6 mixtures under ambient conditions.

Figure 1

X‐ray single crystal structure of UiO‐66‐type MOFs, indicating that 2‐connected linkers bridge 12‐connected [Zr6(µ3‐OH)8(O2C—)12] molecular building blocks (MBBs) to form the 3D fcu‐topology frameworks. The pore window size can be systemically modulated via the judicious choice of organic linkers, and it can be further contracted after the configuration of copper(I) ions.

Results and Discussion

Encouraged by the successful construction of isoreticular UiO‐66 with deliberately fine‐tuned apertures,30 we elected to explore the promise of this fcu‐MOF platform for the adsorptive separation of ethylene form ethane. As shown in Figure 1, MOF materials with fcu topology hold a unique desired feature that the entrance into the inner pores of the frameworks is only via the ligand‐delimited triangular windows. Construction of isoreticular fcu‐MOF with relatively bulkier linkers will permit the anticipated contraction of pore apertures, and subsequently realize the efficient size‐sieving effect. With this in mind, we selected 2‐connected linkers with different number of carboxyl groups (1,2,4‐BTC and 1,2,4,5‐BTEC) to construct two different fcu‐MOFs (UiO‐66‐COOH and UiO‐66‐(COOH)2) by using isoreticular chemistry. Both of the synthesized MOFs have the prospective fcu topology as determined by the PXRD analyses (Figure b), in which the patterns of both UiO‐66‐(COOH)2 and UiO‐66‐COOH match well with the theoretical ones of UiO‐66 derived from the crystal structure. Topological analysis of the UiO‐66 series indicates that the carbon atoms from the coordinated carboxylates act the extension points of network, bridging the 2‐connected linkers and the 12‐connected [Zr6(µ3‐OH)8(O2C−)12] molecular building blocks (MBBs) to produce the 3D framework (Figure 1a,b). The window size of UiO‐66 was found to be around 6.0 Å. Obviously, both ethylene and ethane molecules can readily diffuse into the internal pores of UiO‐66. When using the bulkier linker of 1,2,4‐BTC instead of 1,4‐BDC, the resulting UiO‐66‐COOH shows a contracted pore window size of 5.3 Å. Further reduction in window size can be fulfilled by using 1,2,4,5‐BTEC to construct the framework. The corresponding size is reduced to be 4.8 Å for UiO‐66‐(COOH)2. In principle, such pore aperture is still much larger than the sizes of both C2H4 (4.1 Å) and C2H6 (4.4 Å), and cannot provide the obvious size‐sieving effect for C2H4/C2H6 separation. However, these functionalized linkers with free carboxyl groups provide us a platform to immobilize some targeted metal sites and thus to further reduce the pore window size (Figure 1c).

Figure 2

a) XPS for Cu(I) sites of CuΙ@UiO‐66‐(COOH)2 after the surface etching; b) The PXRD patterns for the synthesized UiO‐66 series MOF materials along with the simulated XRD pattern of UiO‐66 (black) derived from the simulated crystal structure; c) The pore size distribution of UiO‐66 series MOF materials; d) Element maps for Cuprum (Cu) of CuΙ@UiO‐66‐(COOH)2; e) N2 sorption isotherms at 77 K of UiO‐66 series MOF materials.

It has been well documented that the incorporated Cu(Ι) and Ag(Ι) ions into porous materials can form the specific π‐complexation with alkenyl units of olefin molecules to fulfill high separation performance.23, 24 Owing to the existing free carboxyl groups in CuΙ@UiO‐66‐COOH and CuΙ@UiO‐66‐(COOH)2, it is reasonable to speculate that the incorporation of such transition metals into these MOFs may be highly effective to discriminate ethylene and ethane significantly. On the other hand, this process can also reduce their pore window sizes and thus make them provide more efficient size‐sieving effect to further improve the separation performance. Therefore, we herein introduced the Cu(I) ions into the aforementioned fcu‐MOF materials by the coordination with bare carboxyl groups to form two Cu(I) immobilized materials, namely CuΙ@UiO‐66‐COOH and CuΙ@UiO‐66‐(COOH)2. First, we confirmed the presence of Cu(I) ions in these metalated materials by X‐ray photoelectron spectroscopy (XPS) analyses (Figure 2a; Figure S5, Supporting Information). There exists a characteristic signal from copper(I) at binding energies of 952.9 and 933.1 eV, corresponding to the peaks of Cu 2p1/2 and 2p3/2, respectively. Then, their phase purity of bulk materials was determined by the PXRD analysis (Figure 2b and S1, Supporting Information). FE‐SEM was performed to characterize the morphology of MOF materials (Figure S2, Supporting Information), all of which feature the homogeneous particles with a size of 100–200 nm. Apparently, the immobilization process shows no significant effect on the morphology of these robust MOFs. Fourier infrared spectrum analysis (FTIR) indicated that a strong band at 1715.7 cm−1 can be clearly observed in UiO‐66‐COOH and UiO‐66‐(COOH)2, mainly attributed to the C=O stretching vibration of uncoordinated ‐COOH groups (Figure S3, Supporting Information). After the metalation of two MOFs, this peak almost disappeared in CuΙ@UiO‐66‐(COOH)2 and CuΙ@UiO‐66‐COOH, further confirming the success of chelating the Cu(I) ions into carboxyl groups. The ICP‐MS (Table S1, Supporting Information) and energy‐dispersive X‐ray (EDS) analyses (Figure 2d; Figure S6, Supporting Information) comprehensively determined that there are ≈47% and ≈52% uncoordinated –COOH groups transformed into –COOCu for CuΙ@UiO‐66‐COOH and CuΙ@UiO‐66‐(COOH)2, respectively.

Permanent porosity studies of these four UiO‐66‐type MOFs were performed by nitrogen (N2) sorption at 77 K, and all isothermals show typically reversible type‐I isothermals (Figure 2c,e). The Brunauer–Emmett–Teller (BET) surface area was estimated to be 712.8 and 622.3 m2 g−1 for UiO‐66‐COOH and UiO‐66‐(COOH)2 respectively, notably lower than that of the parent UiO‐66 (1110 m2 g−1) due to the bulkier linkers.35 With the copper ions chelated into the MOFs, the porosity can be further reduced and the BET surface area of CuΙ@UiO‐66‐COOH and CuΙ@UiO‐66‐(COOH)2 decreased to be 437.7 and 319.7 m2 g−1, respectively. The variation of pore sizes among these MOFs, determined by Horvath–Kawazoe method, corresponds well to the results of the porosities. As shown in Figure 2c, the pore size is also gradually reduced from 5.6 Å in UiO‐66‐COOH to 4.1 Å in CuΙ@UiO‐66‐(COOH)2, with the increased number of functional carboxyl groups and the chelation of copper ions. These experimental results are consistent well with the aforementioned pore sizes calculated from the crystal structures. The optimal aperture (4.1 Å) of CuΙ@UiO‐66‐(COOH)2 just falls in the range of the kinetic diameter of C2H4 (4.1 Å) and C2H6 (4.4 Å), which may provide an efficient size‐sieving effect on C2H4/C2H6 separation.

Single‐component adsorption isotherms of C2H4 and C2H6 including low‐pressure adsorption data for all four UiO‐66‐type MOFs were collected and shown in Figure a,b; Figures S9 and S10 (Supporting Information). Evidently, both of UiO‐66‐COOH and UiO‐66‐(COOH)2 without Cu(I) ions show the very similar adsorption capacities toward C2H4 and C2H6, indicating that neither of them can discriminate the two gases due to their oversize aperture and the absence of specific recognition sites. Conversely, both copper‐chelated materials show distinct ethylene‐selective sorption behaviors. Especially, CuΙ@UiO‐66‐(COOH)2 adsorbs C2H4 rapidly at low‐pressure region, with an appreciable uptake capacity of 1.86 mmol g−1 at 298 K and 1.0 bar. This C2H4 uptake at 1.0 bar approaches the stoichiometric quantity (2.14 mmol g−1) expected if one gas molecule is adsorbed per Cu(I) sites, indicating that the Cu(I) ions mainly account for its C2H4 uptake. Besides the increased C2H4 uptake, CuΙ@UiO‐66‐COOH and CuΙ@UiO‐66‐(COOH)2 also prove the notably reduced ethane uptake, indicating an efficient size‐selective effect. CuΙ@UiO‐66‐COOH reduces ≈35.6% uptake for C2H6 at ambient conditions compared with UiO‐66‐COOH, and about 51.3%‐decreased uptake of C2H6 occurs on CuΙ@UiO‐66‐(COOH)2 at the same conditions. As illustrated in Figure 3c, when the pore size of fcu MOFs gradually decreases from UiO‐66‐COOH to CuΙ@UiO‐66‐(COOH)2, the uptake capacity of C2H6 at 0.01 bar becomes fewer and fewer. In contrast, the C2H4 uptake at 0.01 bar increases in the order of UiO‐66‐COOH < UiO‐66‐(COOH)2 < CuΙ@UiO‐66‐COOH COOH)2. Thus, the tailor‐made CuΙ@UiO‐66‐(COOH)2 features the highest C2H4 adsorption (0.71 mmol g−1) but the lowest CH6 adsorption (0.02 mmol g−1), thus offering an ultrahigh C2H4/C2H6 uptake ratio of 35.5 at 0.01 bar and 298 K. In comparison to other promising MOFs, both the C2H4 capture capacity and the low C2H6 uptake at low pressure are also very significant (Figures S11 and S12, Supporting Information). These results clearly indicate that the immobilization of Cu(I) ions into CuΙ@UiO‐66‐(COOH)2 can efficiently improve the C2H4 capture capacity via the strong π‐complexation interactions, while the contracted aperture size provides the size‐sieving effect to reduce C2H6 uptake simultaneously, thus affording the excellent C2H4/C2H6 separation.

Figure 3

a) Single‐component adsorption isotherms for C2H4 and C2H6 of UiO‐66‐COOH and CuΙ@UiO‐66‐COOH at 298 K; b) Single‐component adsorption isotherms for C2H4 and C2H6 of UiO‐66‐(COOH)2 and CuΙ@UiO‐66‐(COOH)2 at 298 K; c) Experimental C2H4 and C2H6 adsorption uptake of UiO‐66 series MOF materials at 0.01 bar; d) The isosteric heat (Q st) of C2H4 adsorption in the UiO‐66‐type MOFs; e) IAST calculations of activated UiO‐66‐type MOFs for the C2H4/C2H6 separation at 298 K; f) IAST calculations of representative materials explored for C2H4/C2H6 separation at room temperature.

Such C2H4 adsorption behavior of four fcu‐MOFs can be explained by the isosteric heat of adsorption (Q st), calculated by adsorption isotherms at different temperatures. As shown in Figure 3d and Figure S15 (Supporting Information), the Q st results are in good agreement with the experimental C2H4 uptakes. Higher Q st values of C2H4 were found in both Cu(I)‐chelated MOFs, thus validating that Cu(I) ions indeed enhance the binding affinity of C2H4. The Q st value (48.5 kJ mol−1) for C2H4 at close to zero loading in CuΙ@UiO‐66‐(COOH)2 is the highest, followed by CuΙ@UiO‐66‐COOH (32.9 kJ mol−1), UiO‐66‐(COOH)2 (27.4 kJ mol−1), and UiO‐66‐COOH (24.3 kJ mol−1). This C2H4 Q st value of CuΙ@UiO‐66‐(COOH)2 is even comparable to that of M2(dobdc)25 with high density of OMSs, implying the strong affinity between CuΙ@UiO‐66‐(COOH)2 and C2H4. We speculate that such strong C2H4 affinity is mainly attributed to the synergistic effect of the specific π‐complexation interactions and the smaller pores in CuΙ@UiO‐66‐(COOH)2. Instead, the incorporation of Cu(I) ions shows a negative effect on the affinity of ethane, in which the Q st values of C2H6 for CuΙ@UiO‐66‐COOH and CuΙ@UiO‐66‐(COOH)2 are even lower than the unmetalized MOFs. It is worth to note that the Q st value of C2H4 in CuΙ@UiO‐66‐(COOH)2 is much lower than that of most AgΙ‐chelated porous adsorbents, including PAF‐1‐SO3Ag (106 kJ mol−1)24 and (Cr)‐MIL‐101‐SO3Ag (12036/6337 kJ mol−1), affording a relatively low regeneration energy among these kinds of materials.

The C2H4/C2H6 adsorption selectivity (S ads) of these UiO‐66 materials was calculated by IAST based on the measured sorption isotherms. Figure 3e shows the data obtained at 298 K. Due to the very similar C2H4 and C2H6 adsorption isotherms, the S ads value of UiO‐66‐COOH is as low as 0.9. Unlike UiO‐66‐COOH, the Cu(I)‐chelated CuΙ@UiO‐66‐COOH shows a significantly improved S ads value up to 14.5. With the tailor‐made apertures and Cu(I) ions, we found that CuΙ@UiO‐66‐(COOH)2 exhibits an ultrahigh S ads up to 225.7 at 0.01 bar and decreases down to 80.8 at 1.0 bar, which is orders of magnitude higher than all the other UiO‐66 materials. We note that this S ads value of CuΙ@UiO‐66‐(COOH)2 is only next to UTSA‐280,27 outperforming all the other benchmark materials including Zeolite 13X (13.4),31 NaETS‐10 (14.7),32 Co‐gallate (52),27 NOTT‐300 (48.7)33 (Figure 3f). In addition, it is also significantly higher than Ag(I)‐chelated adsorbents like PAF‐1‐SO3Ag (27)24 and (Cr)‐MIL‐101‐SO3Ag (1636/9.637). Considering its lower C2H4 Q st compared with these Ag(I)‐chelated adsorbents, the size‐sieving effect on CuΙ@UiO‐66‐(COOH)2 also contributes significantly to its exceptional selectivity apart from the π‐complexation interactions. Moreover, the sieving effect of C2H4/C2H6 separation in CuΙ@UiO‐66‐(COOH)2 can be strengthened at low temperature of 273 K, wherein the corresponding S ads value can be further enhanced to 110 at 1 bar (Figure S20, Supporting Information).

The strong C2H4 capture capacity and ultrahigh IAST selectivity of CuΙ@UiO‐66‐(COOH)2 prompted us to perform the breakthrough experiments in order to evaluate its actual separation efficiency. Such experiments were conducted in a packed column filled with the activated CuΙ@UiO‐66‐(COOH)2 powder, under 1.0 mL min−1 feed gas of equimolar C2H4/C2H6 mixture at 298 K (Figure ; Figure S27, Supporting Information). As shown in Figure 4a, efficient separation of C2H4 from 50/50 C2H4/C2H6 mixtures can be successfully fulfilled by using the activated CuΙ@UiO‐66‐(COOH)2. C2H6 gas was first eluted through the separation bed, while no C2H4 was detected until about 86 min. The adsorbed amount of C2H4, enriched from the equimolar C2H4/C2H6 mixtures, was calculated to be 1.92 mol per kg for a given cycle. Subsequently, the captured C2H4 gas in the column can then be recovered with high purity during the regeneration desorption step, which was carried out by the sweeping He gas (10 mL min−1) at 413 K. As shown in Figure 4b, the regeneration of CuΙ@UiO‐66‐(COOH)2 revealed that the adsorbed gas can be almost completely recovered within 15 min and no detectable C2H4 and C2H6 were found after 15 min, notably faster than that of Ag‐doped adsorbent (typically thousands of minutes).24 Moreover, high pure (92.5%) ethylene can be obtained during one cycle of the adsorption–desorption procedures. Multiple cycling column breakthrough tests under the same conditions showed that the breakthrough times of CuΙ@UiO‐66‐(COOH)2 for both C2H4 and C2H6 remains almost unchanged within three continuous cycles, confirming its good recyclability for C2H4/C2H6 separation (Figure 4c). Furthermore, CuΙ@UiO‐66‐(COOH)2 was proved to be insensitive to moisture, since its C2H4 adsorption is not affected after soaking it into oxygen‐free water (Figure S29, Supporting Information).

Figure 4

Multicomponent column breakthrough results for CuΙ@UiO‐66‐(COOH)2 at 298 K. a) The breakthrough curves of CuΙ@UiO‐66‐(COOH)2 for the C2H4/C2H6 (50/50, v/v) separation; b) The desorption curves of CuΙ@UiO‐66‐(COOH)2 under 10.0 mL min−1 sweeping He gas at 413 K; c) Multiple cycles of breakthrough tests of CuΙ@UiO‐66‐(COOH)2 for the C2H4/ C2H6 (50/50, v/v) separation.

Conclusions

Herein, we precisely designed and constructed two copper(I)‐chelated metal–organic frameworks by using isoreticular chemistry, for the very challenging ethylene/ethane separation. The tailor‐made adsorbent, CuI@UiO‐66‐(COOH)2, possesses the optimal pore window size and specific π‐complexation. Our foregoing results indicated that this material can rapidly adsorb ethylene driven by the strong affinity of π‐complexation, while notably lessen ethane uptake due to its size‐sieving effect. This rare synergistic effect of the specific π‐complexation interactions and efficient size‐sieving effect in CuI@UiO‐66‐(COOH)2 thus led to an ultrahigh IAST selectivity of 80.8 at ambient conditions for 50/50 C2H4/C2H6 mixture, outdistancing most of previously benchmark porous materials reported. The exceptional separation performance was further confirmed by the detailed breakthrough experiments on 50/50 v/v C2H4/C2H6 mixtures. In light of its attractive design strategy and ultrahigh selectivity, we believe that CuΙ@UiO‐66‐(COOH)2 is placed among the best‐performing porous materials for the challenging C2H4/C2H6 separation, and this work may provide some guidance to develop new porous materials for boosting olefin/paraffin separation performance.

Experimental Section

Materials and Methods: All reagents and solvents including the organic ligands, 1,2,4‐BTC and 1,2,4,5‐BTEC, used to construct the UiO‐66‐type MOFs, were commercially available and used without further purification. Powder X‐ray diffraction (PXRD) patterns were collected in the 2θ = 5°–50° range on an X'Pert PRO diffractometer with Cu Kα (λ = 1.542 Å) radiation at room temperature. Inductively coupled plasma‐mass spectrometry (ICP‐MS) was performed on a Thermo Scientific XSERIES 2 ICP‐MS system. Fourier transform infrared (FT‐IR) spectrum was recorded on Thermo Fisher Nicolet iS10 spectrometer using KBr pallets in the 500–4000 cm−1 range. The morphology was investigated using a field‐emission scanning electron microscopy (FE‐SEM, Hitachi S4800). All gas sorption isotherms of UiO‐66‐type MOFs were obtained from the Micromeritics ASAP 2020 surface area analyzer and pore size analyzer. An ice‐water bath and water bath were used for C2H4 and C2H6 gases adsorption isotherms at 273 and 298 K, respectively.

Preparation of Cu: The activated UiO‐66‐(COOH)2 (≈200 mg, 0.09 mmol) and cuprous chloride (CuCl, about 108 mg, 1.08 mmol) were dispersed in acetonitrile (3 mL) in a 20 mL Teflon‐capped vial which was tightly wrapped with polytetrafluoroethylene sealing tape. The foregoing procedures were carefully operated in a glovebox with positive N2 pressure. Then, the vials were heated in an oven at 80 °C for two weeks to afford the resultant color‐changed powder CuI@UiO‐66‐(COOH)2. The preparation of CuI@UiO‐66‐COOH was referred to the preparation of CuI@UiO‐66‐(COOH)2, just the replace of the amount of cuprous chloride (≈62 mg, 0.62 mmol) and the activated UiO‐66‐COOH (≈200 mg, 0.10 mmol).

Activation of Cu: Before the gas sorption measurements, the obtained powder solids were directly solvent‐exchanged by methanol for at least ten times in a glovebox with positive N2 pressure. After solvent‐exchange, the powder materials were carefully transferred into in the adsorption tube, then were evaluated from the Micromeritics ASAP 2020 surface area analyzer at 373 K for 12 h and 413 K for another 12 h to yield the activated CuI@UiO‐66‐COOH and CuI@ UiO‐66‐(COOH)2.

Conflict of Interest

The authors declare no conflict of interest.

Supporting Information

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