Use of two-dimensional covalent organic framework materials as rn capture materials in humid air

Abstract

The application discloses application of a series of two-dimensional covalent organic framework materials as Rn capturing materials in humid air. The two-dimensional covalent organic framework materials are: linker108_C_linker87_C_kgm, linker108_C_linker93_C_bex, linker108_C_linker16_C_kgm, linker99_C_linker89_C_kgm and linker108_C_linker81_C_kgm. Since the two-dimensional COFs have relatively low cost and high water stability, the two-dimensional COFs can be used as practical candidate materials for Rn capturing. The linker108_C_linker87_C_kgm has the best capturing performance. The COFs provided by the application have relatively low cost and high water stability, and can be used as practical candidate materials for Rn capturing.

Description

Technical Field

[0001] The present invention belongs to the field of Rn capture materials and relates to the application of a series of two-dimensional covalent organic framework materials as Rn capture materials in humid air. Background Art

[0002] radon( 222 Rn) is a colorless, odorless, tasteless natural radioactive inert gas that emanates from soil and rocks and is concentrated in enclosed spaces such as basements, mines, houses and buildings. 222 Rn and its natural isotopes 220 Rn and 219 Rn is a decay product of radium, which originates from three primitive decay series 238 U. 232 Th and 235 Radon and its daughters are the largest contributors to the public's natural radiation dose. Radon decays radioactively by emitting alpha particles, and its daughters, polonium-218 and polonium-214, also decay by emitting alpha particles. When inhaled, radon is almost entirely exhaled, but its solid decay daughters tend to migrate and deposit in lung epithelial cells, exposing them to alpha radiation. This makes it the second leading cause of lung cancer, after smoking. Research on the epidemiological relationship between radon exposure and lung cancer has garnered widespread attention, sparking widespread concern about the removal of radon from air.

[0003] Using ventilation systems to remove radon is an effective control measure, but it is expensive, difficult to control pressure differentials, and can even lead to increased radon concentrations. Another adsorption method uses solid adsorbents, such as activated carbon and zeolites. In the early 20th century, Rutherford Laboratory pioneered the use of activated carbon to adsorb radon. Boyle et al. used a carbon canister system to adsorb radon from the air. In 1990, Nagarajan et al. used activated carbon canisters to monitor radon levels in the air. Hui Yang et al. introduced a method for microwave desorption and regeneration of activated carbon that adsorbs radon. However, activated carbon is susceptible to temperature and humidity and has poor regeneration capacity. Natural zeolites have some effect on reducing radon concentrations. A silver-exchanged zeolite has a reduced radon retention capacity and is more easily regenerated. However, due to the limited designability of pore structures in zeolite materials, the adsorption capacity of radon is relatively low. Furthermore, the harmful effects of radon exposure on the human body limit further research on the direct adsorption of radon using adsorbents.

[0004] In recent years, covalent organic frameworks (COFs) have attracted widespread attention as a novel porous material for gas separation and adsorption applications. COFs are porous crystalline networks formed by reversible covalent bonds between organic linkers. They are classified into two-dimensional (2D) and three-dimensional (3D) COFs, depending on the connection method of the organic structural units. They offer advantages such as low density, permanent porosity, tunable structure and pore size, large specific surface area, and good chemical and thermal stability. Due to their unique structural properties, COFs have been widely used in optoelectronics, catalysis, proton conduction, sensing, gas storage, and adsorption. Compared to 3D COFs, 2D COFs are layered materials with an ordered periodic skeleton and inherent polygonal pores connected to form dense one-dimensional channels. Furthermore, these one-dimensional open channels with uniformly small windows and no intersections or narrow junctions can avoid unfavorable path blockage and pore obstruction, making it easier to construct porous materials with fine porosity, discrete pore sizes, and polygonal shapes. Previous studies have shown that 2D COFs are excellent iodine vapor adsorption materials, but their separation and adsorption performance for radon gas has not been reported. Moreover, searching for excellent candidate materials with high radon capture efficiency in humid air from a large number of structural databases remains a huge challenge. Summary of the Invention

[0005] To address the shortcomings of the aforementioned background technology, the present invention utilized Grand Canonical Monte Carlo (GCMC) simulations to calculate the performance of 6,841 2D COFs in selective radon adsorption. Five 2D COF materials suitable for selective radon adsorption in humid air were selected for analysis to explore the radon adsorption performance of COFs. After studying the spatial distribution of the binding sites of these five candidate materials, linker108 (1,3,6,8-tetrabromopyrene) demonstrated superior adsorption performance. Furthermore, three rounds of performance comparisons were conducted under varying pressures, relative humidity, and Rn mole fractions. Linker108_C_linker87_C_kgm (composed of a topological network of 1,3,6,8-tetrabromopyrene, 1,4-dibromobenzene, and kgm) was found to have the best capture performance. This is because, under all test conditions, it exhibited the greatest Rn adsorption capacity compared to other candidate materials and also exhibited excellent Rn selectivity in most cases.

[0006] The technical solution adopted in the present invention is as follows:

[0007] A series of two-dimensional covalent organic framework materials are used as Rn capture materials in humid air. The two-dimensional covalent organic framework materials are: linker108_C_linker87_C_kgm, linker108_C_linker93_C_bex, linker108_C_linker16_C_kgm, linker99_C_linker89_C_kgm and linker108_C_linker81_C_kgm.

[0008] In the above technical solution, further, in humid air at 298K and 1 bar, and under relative humidity RH=0-1.0, any one of linker108_C_linker87_C_kgm, linker108_C_linker93_C_bex, linker108_C_linker16_C_kgm, linker99_C_linker89_C_kgm or linker108_C_linker81_C_kgm is used to capture Rn.

[0009] Furthermore, under the conditions of 298K and 1 bar in moist air with relative humidity RH=0-1.0, linker108_C_linker87_C_kgm with the best capture performance was used to capture Rn.

[0010] The beneficial effects of the present invention are:

[0011] This study, based on high-throughput computational screening, identified a series of two-dimensional covalent organic frameworks (COFs) that can be used to capture radon in moist air. The results also revealed the best material types for capturing radon under different conditions, effectively addressing the problem of radon removal in moist air. Due to their relatively low cost and high water stability, two-dimensional COFs are promising candidates for radon capture. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Scatter plots of (a) COF nitrogen selectivity, (b) COF oxygen selectivity, (c) COF water selectivity, and (d) COF radon adsorption, selectivity, and APS values. Humid air (mixed gas with a Rn / N2 / O2 / H2O molar ratio of 0.001 / 0.776 / 0.09 / 0.014 and a water vapor content of 50% relative humidity at ambient temperature (298 K) and 1 bar).

[0013] Figure 2(a) the radon adsorption density of linkers 108_C_linker87_C_kgm (consisting of 1,3,6,8-tetrabromopyrene, 1,4-dibromobenzene, and kgm topological network), (b) linkers 108_C_linker93_C_bex (consisting of 1,3,6,8-tetrabromopyrene, tris(4-bromophenyl)amine, and bex topological network), (c) linkers 108_C_linker16_C_kgm (consisting of 1,3,6,8-tetrabromopyrene, 4,4’-dibromo-[1,1’-biphenyl]-2,2’-diamine, and kgm topological network), (d) linkers 99_C_linker89_C_kgm (consisting of 3,3,5,5-tetrabromo-[1,1’-biphenyl], 2,7-dibromo-9,10-dihydrophenanthrene, and kgm topological network), (e) linkers 108_C_linker81_C_kgm (consisting of 1,3,6,8-tetrabromopyrene, 3,6-dibromopyridazine, and kgm topological network).

[0014] Figure 3 (a) the number of linkers ranked in the top ten in terms of selectivity greater than 5, (b) their number in the top 50 selectivity COFs.

[0015] Figure 4 The change in selectivity of COFs as a function of radon concentration at 1 bar and 298 K.

[0016] Figure 5 (a) the selectivity of 10 COFs for radon and (b) the adsorption capacity at X Rn = 0.001 and 298 K.

[0017] Figure 6 (a) the selectivity of 5 2D-COFs for radon and (b) the adsorption capacity at X Rn = 0.001, 298 K, 1 bar, and 0-80% relative humidity. DETAILED DESCRIPTION

[0018] The present application provides the use of a series of two-dimensional covalent organic framework materials as Rn capture materials in humid air. The detailed process of screening materials by the present application is shown below, and the performance of the screened materials in Rn capture is further shown.

[0019] 1. Screening Method

[0020] COF Database

[0021] Berend Smit et al. proposed 69,840 novel covalent organic frameworks assembled in silico from 666 different organic linkers and four established synthetic routes. This database contains 8,641 2dCOFs and 61,199 3dCOFs, and the present invention screened from a 2dCOF database consisting of 8,641 COFs. A COF with a 2D structure is a framework consisting of stacked 2D layers that are held on top of the next layer by dispersion interactions. In common with the naming scheme used in the study by Berend Smit and colleagues, the following naming scheme was used to identify the structures: linkerA_linkerB_net, where linkerA and linkerB represent the linker and its respective linker terminal, and net represents the topology. The corresponding IUPAC (International Union of Pure and Applied Chemistry) names of all linkers and their three-dimensional representations are available in previous literature.

[0022] Calculation method

[0023] First, Grand Canonical Monte Carlo (GCMC) simulations were performed to investigate the Rn capture capabilities of all COFs in moist air (a mixture of Rn / N2 / O2 / H2O with a molar ratio of 0.001 / 0.776 / 0.209 / 0.014) at 298 K and 1 bar. Furthermore, the Rn capture at different total pressures (5–140 kPa) and humidity (relative humidity 0–80%), as well as at different radon concentrations (X Rn = 0.0001, 0.0005, 0.001). The universal force field (UFF) of COF was used, and the force field parameters for Rn, N2, H2O, and O2 were obtained from the study of AKRappe et al. 5000 initialization cycles were performed, and 5000 cycles were used to obtain the overall average of gas absorption. The cutoff distance was set to The LJ interactions were truncated. Long-range electrostatic interactions were described using the Ewald summation method. The charge balance method (Qeq) was used to assign atomic charges in COFs and is widely used for high-throughput screening of porous materials for gas separation performance. Furthermore, the surface area of ​​the linker molecules was quantitatively analyzed using the Multiwfn program.

[0024] The radon adsorption amount obtained by GCMC simulation is the absolute adsorption amount N Rn In the separation process, adsorption selectivity is an important parameter to measure the separation ability of the material. In a gas mixture, the selectivity S of gas i relative to gas j, k, and m is abs(i / (j+k+m)) is defined as:

[0025]

[0026] where x i , x j , x k and x m are the adsorbed amounts of gases i, j, k, m in the adsorbed phase, respectively; y i , y j , y k and y m are the contents of gases i, j, k, m in the bulk phase, respectively. In addition, an index called adsorbent performance score (APS) is introduced to evaluate the overall radon capture performance, which is defined as:

[0027] APS Rn = N Rn × S abs (R n / (N2+H2O+O2)) (2)

[0028] where S abs (Rn / (N2+H2O+O2)) is the selectivity of Rn over N2, H2O and O2.

[0029] 2. Rn capture capacity

[0030] Rn capture capacity of COFs in Rn / N2 / O2 / H2O

[0031] Moisture can have a significant impact on the adsorption of noble gases in porous materials. Therefore, the present invention discusses the Rn capture capacity of the quaternary gas mixture (Rn / N2 / O2 / H2O) to simulate radon adsorption in humid air. Two indices, including Rn selectivity and Rn uptake capacity, are used to evaluate the performance of 2D COFs, as adsorbent materials with high selectivity and adsorption capacity can achieve cost-effective gas separation processes. Figure 1 Figures (a) - (c) illustrate the relationship between Rn selectivity and the selectivity of 2D COFs for N2, O2 and H2O, respectively. From Figure 1 (a) and 1(b), it can be seen that COFs with Rn selectivity higher than 8.0 have very low selectivity for nitrogen and oxygen, with nitrogen and oxygen selectivity in the range of 0.1-0.4 and 0.4-1.0, respectively. In addition, Rn selectivity is typically negatively correlated with water selectivity, i.e. COFs with Rn selectivity higher than 8.0 have very low selectivity for water; while COFs with water selectivity around 5000.0 and above have Rn selectivity close to 0.0 Figure 1(c)). Therefore, among the three gas components, water has the greatest impact on the selective capture of radon, and the inverse correlation further suggests that hydrophobicity may largely contribute to the adsorption separation of radon from air by 2D COF. Figure 1 (d) shows the adsorption performance of all COFs for Rn. Blue, green, and red represent COFs that provide low (<0.05 mol / kg), medium (0.05 to 0.11 mol / kg), and high (>0.11 mol / kg) APS, respectively. Rn Based on this adsorption performance result, the top five APS were selected Rn The COF with the highest adsorption capacity (>0.11 mol / kg) was selected and their adsorption performance changes under different pressure, relative humidity and Rn molar volume conditions were analyzed. When the pressure was 1 bar, among the top five candidate COFs that adsorbed Rn components in humid air, APS Rn The order is linker108_C_linker87_C_kgm (about 0.21 mol / kg)>linker108_C_linker93_C_bex (about 0.14 mol / kg)>linker108_C_linker16_C_kgm (about 0.13 mol / kg)>linker99_C_linker89_C_kgm (about 0.12 mol / kg)>linker108_C_linker81_C_kgm (about 0.12 mol / kg).

[0032] Radon binding site analysis

[0033] In order to reveal the relationship between the structural characteristics of the best candidate COFs and the Rn separation performance, the spatial distribution of the top five candidate Rn binding sites was analyzed. Figure 2 As shown in Figure 2, there are two different types of Rn capture sites, one located in the channel of 2DCOF (Type I) and the other located in the interlayer (Type II). It is obvious that the channel with a smaller diameter corresponds to a high adsorption probability of the Type I binding site. Taking linker108_C_link87_C_kgm as an example, the adsorption probability of the small triangular channel is much higher than that of the large hexagonal channel (size The probability of about 0.95 is about The probability of about 0.05). The same behavior can be seen on other candidate materials, such as linker108_C_link93_C_bex and linker108_C_link81_C_kgm. This is mainly attributed to the stronger van der Waals (vdW) dispersion interaction between Rn atoms and the more matched channel size. For the interlayer binding sites (type II), we notice that the most dominant Rn capture site among the top five candidates is mainly composed of linker108 (linker108 is 4 / 5, linker99 is 1 / 5). This is reasonable, as the surface area of ​​the linker108 group is much larger than that of linker99 (linker108 is about linker99 about ), in addition, the lateral size of the former is much larger than that of the latter ( vs ). Therefore, the gap formed by the two linkers 108 is large enough to accommodate the Rn atom In addition, the hydrophobicity of this site can also endow it with a relatively high Rn selectivity relative to water.

[0034] Furthermore, the present invention also found that linker 108 is the largest linker among all other linkers, and COFs containing linker 108 may have better Rn adsorption performance. To verify this hypothesis, the structures of the top 50 COFs were further analyzed. The results showed that COFs containing linker 108 accounted for 54% of the total COFs, such as Figure 3 As shown in Figure 2, linker 108 has the best adsorption performance among all COFs and the top 50 COFs. Table 1 lists the IUPAC names and structures of the top ten linkers, ranked by the proportion of linkers with selectivities greater than 5.

[0035] Table 1: IUPAC names and structures of the top ten linkers. Carbon atoms are shown in grey, nitrogen in light blue, hydrogen in white, and bromine in light green.

[0036]

[0037]

[0038] Effect of radon mole percentage

[0039] In different scenarios, the concentration of Rn will vary greatly, which requires an ideal adsorbent to have good Rn capture performance at different Rn molar concentrations. Rn (X Rn=0.0001, 0.0005, 0.001) under GCMC simulation, where water is the content of 50% humidity at ambient temperature (X water =0.014), maintain the ratio like Figure 4 As shown, the Rn selectivity and absorption capacity of the five COFs all showed a positive correlation with the Rn molar concentration. Specifically, the order of Rn selectivity was linker108_C_linker87_C_kgm > linker108_C_linker81_C_kgm > linker108_C_linker16_C_kgm > linker108_C_linker93_C_bex > linker99_C_linker89_C_kgm. At the lowest Rn molar coefficient (XRn = 0.0001), the Rn absorption capacity of linker108_C_linker87_C_kgm and linker108_C_linker93_C_bex showed negligible differences, but was higher than the absorption capacity of the other three COFs, which also had very similar absorption capacities. When the Rn concentration is further increased to above 0.001, the performance differences of the five COFs gradually emerge, and the order of Rn absorption capacity is linker108_C_linker87_C_kgm>linker108_C_linker93_C_bex>linker99_C_linker89_C_kgm>linker108_C_linker16_C_kgm>linker108_C_linker81_C_kgm.

[0040] Effect of pressure

[0041] Considering their potential applications at different pressures (e.g., indoors, caves, and underground), a new round of comparisons of Rn capture performance at different pressures was conducted on the top five screened COFs. These tests were conducted at X Rn The results were carried out under the conditions of t = 0.001 and t = 298k, with the pressure varying from 5 to 140kPa. In general, their selectivity for Rn decreases with increasing pressure. Figure 5As shown, it is noteworthy that linker108_C_linker87_C_kgm has the most outstanding selectivity below 110 kPa. When the pressure is higher than 110 kPa, linker108_C_linker81_C_kgm shows the best selectivity, followed by linker108_C_linker87_C_kgm and linker108_C_linker16_C_kgm, and then linker108_C_linker93_C_bex and linker99_C_linker89_C_kgm. Interestingly, their Rn absorption capacity is positively correlated with pressure, with an almost linear relationship. The capture performance order (linker108_C_linker87_C_kgm>linker108_C_linker93_C_bex>linker99_C_linker89_C_kgm>linker108_C_linker16_C_kgm>linker108_C_linker81_C_kgm) remains almost unchanged under all test stresses.

[0042] Effects of humidity

[0043] Considering that water has a high influence on the radon selectivity of 2D-COFs ( Figure 1 In (c), the present invention studies the effect of relative humidity on the radon selectivity and adsorption capacity of these five candidate materials, such as Figure 6As shown. Here, the molar ratio of Rn / N2 / O2 was maintained at 0.001 / 0.776 / 0.209, and the relative humidity was varied from 0 to 0.8. In general, the Rn selectivity of all five COFs decreased with increasing relative humidity. At low relative humidity (<0.5), 108_C_linker87_C_kgm performed best, and the performance of the other four COFs was approximately at a comparable level. However, when the relative humidity increased to the 0.6-0.8 range, linker108_C_linker81_C_kgm and linker108_C_linker16_C_kgm performed better than the other three COFs. Interestingly, when the relative humidity is below 0.5, the radon adsorption capacity of the five COFs is largely unaffected, with the order of performance being linker108_C_linker87_C_kgm > linker108_C_linker93_C_bex > linker99_C_linker89_C_kgm > linker108_C_linker16_C_kgm > linker108_C_linker81_C_kgm. When the relative humidity increases further to above 0.5, the radon adsorption capacity of all COFs decreases to varying degrees. Notably, 108_C_linker87_C_kgm exhibits the greatest radon adsorption capacity across the entire tested humidity range. In contrast, 108_C_linker81_C_kgm exhibits the most stable radon adsorption capacity, a characteristic that enables it to perform well under conditions of high relative humidity.

[0044] The present invention uses high-throughput GCMC simulation to separate the Rn capture performance of 8641 two-dimensional COFs under humid air conditions. First, the Rn capture ability of COFs in a quaternary gas mixture (the molar ratio of the mixed gas Rn / N2 / O2 / H2O is 0.001 / 0.776 / 0.209 / 0.014) at ambient temperature (298K) and 1 bar was compared, and five candidates were screened out (linker108_C_linker87_C_kgm (0.213mol / kg)> linker108_C_linker93_C_bex (0.143

[0045] mol / kg)>linker108_C_linker16_C_kgm(0.126

[0046] mol / kg)>linker99_C_linker89_C_kgm(0.124

[0047] mol / kg) > linker108_C_linker81_C_kgm(0.119 mol / kg).

[0048] These candidates were then further subjected to three rounds of performance comparison under different pressure, relative humidity, and Rn mole fraction conditions to select the ideal candidates with relatively stable Rn capture capacity under different working environments. Among the five COFs, 108_C_linker87_C_kgm was found to have the largest Rn adsorption capacity under all tested conditions, although its Rn selectivity can not always remain at the highest level, especially under high humidity. Considering the relatively low cost of COFs and their high water stability, two-dimensional COFs can be a practical candidate material for Rn capture.

Claims

1. Application of two-dimensional covalent organic framework materials as Rn capture materials in humid air, characterized in that: The two-dimensional covalent organic framework materials are: linker108_C_linker87_C_kgm, linker108_C_linker93_C_bex, linker108_C_linker16_C_kgm, linker99_C_linker89_C_kgm and linker108_C_linker81_C_kgm; The linker108_C_linker87_C_kgm is composed of 1,3,6,8-tetrabromopyrene, 1,4-dibromobenzene and kgm topological network; The linker108_C_linker93_C_bex is composed of 1,3,6,8-tetrabromopyrene, tris(4-bromophenyl)amine and bex topological network; The linker108_C_linker16_C_kgm is composed of 1,3,6,8-tetrabromopyrene, 4,4′-dibromo-[1,1′-biphenyl]-2,2′-diamine and kgm topological network; The linker99_C_linker89_C_kgm is composed of 3,3′,5,5′-tetrabromo-[1,1′-biphenyl], 2,7-dibromo-9,10-dihydrophenanthrene and kgm topological network; The linker108_C_linker81_C_kgm is composed of 1,3,6,8-tetrabromopyrene, 3,6-dibromopyridazine and kgm topological network.

2. The use of the two-dimensional covalent organic framework material according to claim 1 as a Rn capture material in humid air, characterized in that: Rn capture was performed using any of linker108_C_linker87_C_kgm, linker108_C_linker93_C_bex, linker108_C_linker16_C_kgm, linker99_C_linker89_C_kgm, or linker108_C_linker81_C_kgm at 298 K and 1 bar in humid air with a relative humidity of RH = 0-1.

0.

3. The use of the two-dimensional covalent organic framework material according to claim 2 as a Rn capture material in humid air, characterized in that: Rn was captured using linker108_C_linker87_C_kgm at 298 K and 1 bar in humid air with relative humidity RH = 0-1.0.

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