A method for adjusting the pore patency of metal-organic framework materials to achieve isotope recognition

Abstract

The present invention relates to a method for endowing metal-organic framework materials with the ability to distinguish isotopes by modifying the pores of the metal-organic framework materials, belonging to the technical field of nanoporous materials. This method utilizes the characteristics of the uniform pores and rigid framework of the metal-organic framework materials. During the synthesis process, the regulator is directly doped into the pores of the metal-organic framework materials, which can affect the transport and diffusion rate of small molecules in the pores. At the same time, the characteristics of the crystal structure of the metal-organic framework materials allow for quantitative regulation of the pore blockers, thereby regulating the diffusion rate of small molecules in the pores. When the regulation of the diffusion rate reaches the limit value, the small differences in the physicochemical properties of similar small molecules can be amplified to effectively distinguish H2O and D2O. This simple regulation strategy can be widely applied to all reported metal-organic framework material systems at present, which cannot be achieved by traditional methods. It is believed that this will open up new possibilities for the enrichment / separation of hydrogen isotope water.

Description

Technical Field

[0001] The invention relates to a method for adjusting the pore patency of a metal organic framework material to realize isotope identification, in particular to a new adjustment method different from a traditional synthesis method, and belongs to the technical field of isotope separation. Background Art

[0002] Isotopes are atoms with the same number of protons but different numbers of neutrons. Protium (H) and deuterium (D) are the most common isotopes. Deuterated water (D2O) has played an important role in nuclear research since the discovery of deuterium in 1931.

[0003] However, due to their extremely similar physical and chemical properties, the effective separation of isotopes has always been challenging. The main methods for separating hydrogen isotope water in industry are: water electrolysis, high-temperature distillation, and proton exchange equilibrium. These methods are all based on the slight difference between H2O / D2O to achieve separation, such as bond energy, boiling point, etc., so the separation factor is extremely low, with a maximum of only 1.2 (1.0 means no separation effect), and it is extremely energy-consuming. The development of nanotechnology has provided new options for isotope separation. Among them, metal-organic framework materials (MOFs) are effective in the field of isotope separation due to their uniformly distributed and adjustable pores.

[0004] At present, the key to using MOF to distinguish hydrogen isotope water relies on the synthesis of ultra-fine narrow pores (<0.3nm). When hydrogen isotope water passes through ultra-fine narrow pores, the size restriction can effectively reduce their diffusion rate, amplify the difference in their diffusion rate through the nanopores, and allow one molecule to pass through the pore first, while the other passes through the pore later or even remains in the pore, thus achieving separation.

[0005] Since ultrafine narrow-pore MOFs are extremely difficult to synthesize, there is only one ultrafine narrow-pore MOF that has been reported and can distinguish hydrogen isotopes in water. Gu et al. (Separating water isotopologues using diffusion-regulatoryporous materials, Nature 2022, 611, 289) reported a new copper-based MOF with an ultra-small window. Compared with D2O, this MOF exhibits high selectivity for H2O at room temperature.

[0006] There are currently 20,000 known MOF materials. Usually, the pore size of these MOF materials is about 1nm, and they do not have the ability to distinguish isotopes. In view of the diversity of MOF systems, we proposed a simple strategy to add blockers to the pores of conventional MOFs to reduce the permeability of the pores and give them the ability to distinguish isotopes.

[0007] At the same time, in order to be able to monitor the effect of pore blockage on the diffusion rate of small molecules in situ, we chose to embed fluorescent molecules that are sensitive to microenvironmental changes into the pores. On the one hand, the diffusion rate of small molecules can be monitored in real time by a dwell spectrometer; on the other hand, the degree of blockage of the pores by fluorescent molecules can be quantitatively adjusted to quantify the relationship between the diffusion rate and the degree of blockage, which we call the throttle effect. Summary of the invention

[0008] The technical problem solved by the present invention is: a method for adjusting the pore patency of metal organic framework materials to achieve isotope recognition is proposed, and by adjusting the conventional MOF pore method, the conventional MOF-ZIF8, which originally does not have the ability to identify H2O / D2O, has the ability to identify H2O / D2O after the pore patency is adjusted. The characteristics of the metal organic framework material pore uniformity and skeleton rigidity are utilized. During the synthesis process, the regulator is directly doped into the pore of the metal organic framework material, which can affect the transport and diffusion rate of small molecules in the pore. At the same time, the characteristics of the crystal structure of the metal organic framework material allow the quantitative regulation of the pore blockers, thereby regulating the diffusion rate of small molecules in the pore. When the regulation of the diffusion rate reaches the limit value, the small gap in the physical and chemical properties of similar small molecules can be magnified, and H2O and D2O can be effectively distinguished.

[0009] In order to solve the technical problem of the present invention, the proposed technical solution is: a method for adjusting the pore patency of a metal organic framework material to achieve isotope identification, the specific steps are as follows:

[0010] Step (1): by controlling the molar ratio of 2-methylimidazole to the blocking substance, the 2-methylimidazole is dispersed in deionized water to form a stable and uniform mixed solution; the blocking substance is sodium fluorescein;

[0011] Step (2): on the basis of step (1), a certain proportion of zinc acetate solution is added to the mixed solution, and the mixture is allowed to stand for 12 hours; 2-methylimidazole reacts with zinc acetate to generate a metal organic framework material ZIF8, and sodium fluorescein is directly embedded in the pores of the ZIF8 framework structure during its formation;

[0012] Step (3): After 12 hours of reaction, a large amount of precipitation is generated in the system; the precipitation is a composite sample of sodium fluorescein and ZIF8, that is, the product after the ZIF8 pores are adjusted by sodium fluorescein; the precipitation is repeatedly washed with methanol, ethanol, and N,N-dimethylformamide in sequence until the supernatant is clear and transparent;

[0013] Step (4): The metal organic framework material prepared in step (3) is used to distinguish H2O from D2O by tracking the fluorescence intensity change curve over time through a stopped-flow spectrometer.

[0014] Preferably, the molar ratio of 2-methylimidazole, zinc acetate and sodium fluorescein is 1203:60.2:1.

[0015] Preferably, the fluorescence intensity versus time curve is tracked by a stopped-flow spectrometer to monitor the relationship between the diffusion rate of small solvent molecules in the ZIF8 pores and the degree of blockage, and the diffusion rate difference is amplified to distinguish H2O from D2O.

[0016] Preferably, the specific steps are as follows:

[0017] Step (1): Since bound sodium fluorescein is very sensitive to changes in the microenvironment, the diffusion rate of small solvent molecules in the ZIF8 pores can be monitored by tracking the change in the fluorescence intensity of sodium fluorescein over time;

[0018] Step (2): The diffusion rate of small molecules in the solvent shows obvious bidirectional exchange asymmetry; the rate at which methanol exchanges ethanol is very different from the rate at which ethanol exchanges methanol. This difference is precisely because sodium fluorescein blocks the pores and regulates the diffusion pathway, amplifying the difference in the diffusion rate of small molecules.

[0019] Step (3): Based on the experimental results of step (2), we tested the exchange rates between H2O and methanol, and between D2O and methanol. Since the physicochemical properties of H2O and D2O are very similar, and the kinetic radius is exactly the same (0.264nm), ZIF8 and sodium fluorescein themselves do not have the function of recognizing H2O and D2O; however, after the pore diffusion pathway is regulated by sodium fluorescein, the rate of H2O exchanging methanol is 2.7 times the rate of D2O exchanging methanol, and the rate of methanol exchanging H2O is 1.8 times the rate of methanol exchanging D2O.

[0020] That is to say, when the mixture diffuses in ZIF8, D2O stays in ZIF8 longer, so H2O will come out of ZIF8 first. Therefore, the adjusted ZIF8 has the ability to distinguish and separate the two.

[0021] Preferably, the fluorescence intensity versus time curve is tracked by a stopped-flow spectrometer to monitor the diffusion of solvent small molecules in the ZIF8 pores, and the specific steps are as follows:

[0022] Step (1): the molar ratio of 2-methylimidazole, zinc acetate and sodium fluorescein is (a) 4848:242.4:1; (b) 2432:121.2:1; (c) 1203:60.2:1;

[0023] The cleaned product was evenly dispersed in a methanol solution; a stopped-flow spectrometer was used to evenly mix it with an equal volume of water within a dead time of 1.1 milliseconds, and the diffusion process of water molecules exchanging for methanol molecules in the nanopores was monitored in real time at a resolution of 12.5 microseconds per step;

[0024] Step (2): the cleaned product (c) is uniformly dispersed in an aqueous solution; a stopped-flow spectrometer is used to uniformly mix the product with an equal volume of methanol within a dead time of 1.1 milliseconds, and the diffusion process of methanol molecules exchanging water molecules in the nanopores is monitored in real time at a resolution of 12.5 microseconds / step;

[0025] Step (3): the cleaned product (c) is uniformly dispersed in a methanol solution; a stopped-flow spectrometer is used to uniformly mix the product with an equal volume of D2O within a dead time of 1.1 milliseconds, and the diffusion process of D2O molecules exchanging methanol molecules in the nanopores is monitored in real time at a resolution of 12.5 microseconds / step;

[0026] Step (4): the cleaned product (c) is uniformly dispersed in a D2O solution; a stopped-flow spectrometer is used to uniformly mix the product with an equal volume of methanol within a dead time of 1.1 milliseconds, and the diffusion process of methanol molecules exchanging for D2O molecules in the nanopores is monitored in real time at a resolution of 12.5 microseconds / step;

[0027] Step (5): Use Fick's second diffusion model to fit the diffusion coefficient of all the above diffusion data; judge the rationality of the proposed diffusion scheme through the mean square error result;

[0028] Step (6): Compare the diffusion coefficients of the two processes in the above steps (1) and (3); it is found that within the same nanoparticle, the rate at which H2O exchanges methanol molecules is 1.8 times faster than the rate at which D2O exchanges methanol molecules;

[0029] Step (7): Compare the diffusion coefficients of the two processes in the above steps (2) and (4). Inside the same nanoparticle, the rate at which H2O exchanges methanol molecules is 2.7 times faster than the rate at which D2O exchanges methanol molecules;

[0030] Step (8): in the samples with the molar ratios of (a) and (b), the diffusion process of H2O / D2O and methanol exchange is repeated; and in situ tracking is performed using a dwell spectrometer;

[0031] Step (9): The comparison results show that, except for sample (c), the samples with other molar ratios do not have the ability to distinguish between H2O and D2O, which verifies the rationality of our proposed pore regulation strategy.

[0032] Beneficial effects:

[0033] (1) The pore adjustment method of the present invention is simple, and only requires directly embedding the blocking substance sodium fluorescein into the pores during the synthesis stage of the MOF material.

[0034] (2) The testing method of the present invention is simple and clear. Different from the traditional electrolysis, high temperature distillation and proton exchange, which consume a lot of energy, the present invention selects the fluorescent molecule sodium fluorescein as the blocker, and detects the change of fluorescence intensity in situ by the spectrometer, so as to realize the real-time monitoring of the diffusion rate of the isotope. Since the diffusion rates of the isotopes are different, H2O / D2O can be identified from the stopped-flow spectrum results.

[0035] (3) The MOF pore adjustment method of the present invention is significantly different from the ultrafine narrow pore MOF synthesis method, which will provide more possibilities for conventional MOFs in the field of similar small molecule recognition.

[0036] (4) Figure 1 This is a comparison of ZIF8 and the product after sodium fluorescein is embedded in the pores. Originally, ZIF8 is a white powder. After sodium fluorescein is embedded in the pores, ZIF8 appears orange, the color of sodium fluorescein. Figure 2 This is a transmission electron microscope comparison of ZIF8 and the pores after embedding sodium fluorescein. The morphology of the ZIF8 sample is a rhombic dodecahedron. The embedding of sodium fluorescein does not affect its morphology. Figure 3 Element distribution of ZIF8 after sodium fluorescein is embedded in the pores. The element distribution results show that O, the characteristic element of sodium fluorescein, is evenly distributed. Figure 4 This is a comparison of the UV excitation of ZIF8 and the sample after the pores were adjusted. Originally, ZIF8 did not produce any fluorescence under 365nm UV light excitation. But after the pores were embedded with sodium fluorescein, ZIF8 had fluorescent properties.

[0037] Figure 8 The diffusion rate curves of the mutual exchange of water / methanol and methanol / ethanol in samples (a) and (b) were tracked by stopped-flow spectroscopy. According to the β value, as the amount of sodium fluorescein embedded in the pore decreases, the asymmetry of the solvent exchange rate gradually decreases, that is, β gradually decreases.

[0038] Fig. 9 The diffusion rate curves of the mutual exchange of water / methanol and deuterated water / methanol in sample (c) were tracked by stopped-flow spectroscopy. Obviously, the diffusion rate of H2O is always faster than that of D2O. This obvious difference in exchange rate is not observed in samples (a) and (b).

[0039] Therefore, by simply adjusting the pore diffusion pathway, we can achieve a throttle effect for regulating the diffusion rate: by reducing the diffusion rate of similar small molecules in the pores, the difference in diffusion rates between the two can be amplified under a suitable throttling effect, so that one molecule passes through the separation first, while the other stays in the separation longer, thus achieving separation.

[0040] (5) ZIF8 and sodium fluorescein do not have the ability to identify H2O and D2O by themselves; however, after the pore diffusion pathway is regulated by sodium fluorescein, the optimal molar ratio of 2-methylimidazole, zinc acetate and sodium fluorescein is 1203:60.2:1. The rate of H2O exchanging methanol is 2.7 times that of D2O exchanging methanol, and the rate of methanol exchanging H2O is 1.8 times that of methanol exchanging D2O. The pore patency of the prepared metal organic framework material realizes the recognition of isotopic H2O and D2O, and the samples with other molar ratios do not have the ability to distinguish H2O from D2O. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be further described below in conjunction with the accompanying drawings.

[0042] Figure 1 This is a comparison of the product after ZIF8 and sodium fluorescein are embedded in the pore.

[0043] Figure 2 This is a transmission electron microscopy comparison of ZIF8 and the pores after embedding sodium fluorescein.

[0044] Figure 3 Element distribution diagram of ZIF8 after the pores are embedded with sodium fluorescein. (a) Morphology of the sample under transmission electron microscopy; in the area (a), element distribution diagrams of (b) carbon, (c) nitrogen, (d) zinc, and (e) oxygen are drawn respectively.

[0045] Figure 4 This is a UV excitation comparison of ZIF8 and the sample after pore adjustment.

[0046] Figure 5 This is a graph showing the change in fluorescence intensity of bound sodium fluorescein in different organic solvents.

[0047] Figure 6 The diffusion rate curves of water / ethanol exchange in sample 3 were tracked by stopped-flow spectroscopy. (a) Ethanol exchanged water, (b) water exchanged ethanol.

[0048] Figure 7 The diffusion rate curves of the mutual exchange of (a) water / methanol system, (b) methanol / ethanol system, and (c) methanol / water system in sample No. 3 were tracked by stopped-flow spectroscopy.

[0049] Figure 8 The diffusion rate curves of (a, c) water / methanol and (b, d) methanol / ethanol exchange in samples 1 and 2, respectively, were tracked using stopped-flow spectroscopy.

[0050] Fig. 9The diffusion rate curves of the mutual exchange of (a, d) water / methanol and (b, e) deuterated water / methanol in sample No. 3 tracked by stopped-flow spectroscopy, as well as the comparison diagrams of the two processes (c, f).

[0051] Fig.10 It is a diagram of the design and separation of the present invention. DETAILED DESCRIPTION

[0052] Example 1

[0053] In the invention, the patency of the ZIF8 pore can be adjusted by changing the amount of sodium fluorescein embedded. The specific method is to first mix 2-methylimidazole (1.6M) with sodium fluorescein (0.33mM (1), 0.66mM (2), 1.33mM (3) to successfully distinguish the concentration of water isotopes) to form a uniform and stable solution. Then mix it with zinc acetate (80mM) solution. The mixed solution quickly becomes turbid, indicating that ZIF8 nanoparticles begin to form. That is, samples No. 1, No. 2, and No. 3 are respectively the molar ratios of 2-methylimidazole, zinc acetate and sodium fluorescein are (a) 4848:242.4:1; (b) 2432:121.2:1; (c) 1203:60.2:1.

[0054] After 12 hours of reaction, the system produced a large amount of orange precipitate, which was completely different from the white ZIF8 color. This indicated that sodium fluorescein was successfully embedded in the ZIF8 pores. The product was repeatedly washed with methanol until the supernatant was clear and transparent. Then, the product was thoroughly washed with ethanol and N,N-dimethylformamide ( Figure 1 ).

[0055] Transmission electron microscopy (TEM) results show that samples 1, 2, and 3 all have rhombic dodecahedral morphology, which is consistent with ZIF8. This indicates that the embedding of sodium fluorescein will not destroy the morphology of ZIF8 ( Figure 2 ). Sample No. 3 was subjected to elemental analysis. The elemental analysis results showed that Zn, C, and N elements were evenly distributed in the sample, and the characteristic element of sodium fluorescein - O element was evenly and clearly distributed ( Figure 3 ).

[0056] ZIF8 itself does not have fluorescent properties, such as Figure 4 As shown in the figure, ZIF8 has no fluorescence effect under UV excitation. However, after sodium fluorescein is embedded in the ZIF8 pores in situ, the sample exhibits obvious fluorescence.

[0057] Whether the sodium fluorescein embedded in the pores can distinguish different organic solvent environments is the key to in situ tracking of the diffusion rate of small molecules. We tested the fluorescence intensity of sample No. 3 in different organic solvent environments at the same concentration and compared them ( Figure 5 ).

[0058] The results showed that bound fluorescent molecules have a good ability to distinguish different organic solvents. This indicates that bound fluorescein sodium is very sensitive to changes in the microenvironment and is suitable as a fluorescent probe for monitoring the diffusion of small solvent molecules in the ZIF8 pores.

[0059] Next, we dispersed sample No. 3 evenly in water. The stopped-flow spectrometer quickly mixed it with an equal volume of methanol solution and tracked the fluorescence intensity of sodium fluorescein over time. The same process was repeated three times to evaluate the accuracy of exchange diffusion. Figure 6 As shown, Figure 6 The diffusion rate curve of water / ethanol exchange in (c) sample was tracked by stopped-flow spectroscopy. Each set of data was repeated three times to evaluate reproducibility. The diffusion trajectory was fitted using Fick's second diffusion law to obtain the corresponding diffusion coefficient.

[0060] The three independent test curves have good repeatability, indicating the reliability of the test data. ZIF8 is approximated as a spherical particle, and the data are fitted using Fick's second diffusion law. The corresponding diffusion coefficient is D = 2.0 × 10 -11 cm2 / s.

[0061]

[0062] In equation (1), ΔI t is the change in fluorescence intensity of the diffusion system at time t; ΔI ∞ V is the change in fluorescence intensity of the system when the diffusion is in equilibrium; t V is the volume change of the diffused molecules at time t; ∞ is the volume change of the diffusing molecules when the diffusion is in equilibrium; R0 is the average radius of sample No. 3 measured by TEM; D is the diffusion coefficient, the only unknown parameter in the equation.

[0063] Conversely, sample No. 3 was evenly dispersed in methanol, and the stopped-flow spectrometer quickly mixed it with an equal volume of aqueous solution and tracked the fluorescence intensity of sodium fluorescein over time. The same was repeated three times. The diffusion results were fitted using equation (1), and the corresponding diffusion coefficient was D = 1.3 × 10 -11 cm2 / s.

[0064] Using the same technique, the exchange diffusion rates of ethanol / water and ethanol / methanol in sample No. 3 were monitored ( Figure 7 ). Figure 7 The diffusion rate curves of the exchange of water / methanol and methanol / ethanol in the sample (c) were tracked by stopped-flow spectroscopy. The measurement was repeated three times, and the corresponding diffusion coefficients were fitted using the Fick model.

[0065] We summarize the corresponding diffusion coefficients in Table 1.

[0066] Table 1. Exchange diffusion rates between different solvent molecules of sample No. 3.

[0067]

[0068] By comparison, we found that there is a clear asymmetry between the two solvent exchange modes. For example, the rate of methanol exchange for ethanol in sample 3 (D = 1.0 × 10 -11 cm2 / s) is higher than the rate of EtOH→MeOH in the same batch of nanoparticles (D = 5.1×10 -13 cm2 / s) is about 20 times faster. In order to facilitate the comparison of the two-way exchange rate of solvents, we define β as their ratio (β=20). The exchange ratio is defined as:

[0069]

[0070] Among them, methanol, water and ethanol are abbreviated as m, w and e respectively; a, b and c represent three samples respectively. According to this definition, it is determined from Table 1 That is to say, among the three solvent combinations, two showed obvious exchange rate asymmetry.

[0071] We also conducted the same test on samples 1 and 2. We found that the asymmetry of the exchange rate decreases as the proportion of sodium fluorescein decreases ( Figure 8 ). This indicates that sodium fluorescein, as a blocker, successfully regulates the diffusion pathway of ZIF8.

[0072] Table 2. Exchange diffusion rates between different solvent molecules of samples No. 1 and No. 2.

[0073]

[0074]

[0075] *Indicates that it is difficult to track effective diffusion data due to the rapid diffusion rate.

[0076] According to Table 2, and and Therefore, the amount of blocking is the key to the asymmetry of exchange rates.

[0077] Based on the above experimental results, we monitored the diffusion process of H2O / D2O in sample No. 3. Fig. 9 As shown in a and b, all diffusion data were measured three times independently, and the results were highly reproducible and had small experimental deviations. In the same batch of NPs, the rate of H2O exchanging MeOH (D = 4.9 × 10-10 cm2 / s) is higher than the rate at which D2O exchanges MeOH (D = 1.8 × 10 -10 cm2 / s) is about 2.7 times faster ( Fig. 9 c). In turn, the rate at which MeOH exchanges H2O (D = 2.5 × 10 -11 cm2 / s) is also faster than the rate of MeOH→D2O (D=1.4×10 - 11 cm2 / s) 1.8 times faster ( Fig. 9 df).

[0078] In other words, D2O is always slower than H2O, and the difference is much larger than the experimental deviation. This difference is not observed in samples 1 and 2, indicating that high dye occupancy is the key factor. Therefore, by simply adjusting the pore diffusion pathway, we can achieve a throttle effect to adjust the diffusion rate: by reducing the diffusion rate of similar small molecules in the pore, the difference in the diffusion rates of the two can be amplified under a suitable throttling effect, so that one molecule passes through the separation first, and the other stays in the separation longer, achieving separation.

[0079] ZIF8 and sodium fluorescein do not have the ability to identify H2O and D2O by themselves; however, after the pore diffusion pathway is regulated by sodium fluorescein, the molar ratio of 2-methylimidazole, zinc acetate and sodium fluorescein is 1203:60.2:1, which is the optimal rate of H2O exchanging methanol is 2.7 times that of D2O exchanging methanol, and the rate of methanol exchanging H2O is 1.8 times that of methanol exchanging D2O. The pore patency of the prepared metal organic framework material realizes the recognition of isotopic H2O and D2O, and the samples with other molar ratios do not have the ability to distinguish H2O from D2O.

[0080] The present invention is not limited to the specific technical solutions described in the above embodiments, and all technical solutions formed by equivalent replacement are within the protection scope required by the present invention.

Claims

1. A method for adjusting the pore patency of a metal organic framework material to achieve isotope identification, characterized in that: The specific steps are as follows: Step (1): by controlling the molar ratio of 2-methylimidazole to the blocking substance, the 2-methylimidazole is dispersed in deionized water to form a stable and uniform mixed solution; the blocking substance is sodium fluorescein; Step (2): on the basis of step (1), a certain proportion of zinc acetate solution is added to the mixed solution, and the mixture is allowed to stand for 12 hours; 2-methylimidazole reacts with zinc acetate to generate a metal organic framework material ZIF8, and sodium fluorescein is directly embedded in the pores of the ZIF8 framework structure during its formation; the molar ratio of 2-methylimidazole, zinc acetate and sodium fluorescein is 1203:60.2:1; Step (3): After 12 hours of reaction, a large amount of precipitate is generated in the system; the precipitate is a composite sample of sodium fluorescein and ZIF8, that is, the product after the ZIF8 pores are adjusted by sodium fluorescein; the precipitate is repeatedly washed with methanol, ethanol, and N,N-dimethylformamide in sequence until the supernatant is clear and transparent; Step (4): The metal organic framework material prepared in step (3) is used to track the fluorescence intensity change curve over time through a stopped-flow spectrometer to evaluate the effect of channel adjustment on the diffusion rate of isotope molecules, thereby achieving the distinction between H2O and D2O.

2. The method for adjusting the pore patency of a metal organic framework material to achieve isotope identification according to claim 1, characterized in that: The fluorescence intensity curve over time was tracked by stopped-flow spectrometer to monitor the relationship between the diffusion rate of small solvent molecules in the ZIF8 pores and the degree of blockage. By amplifying the difference in diffusion rate, it was used to distinguish H2O from D2O.

3. The method for adjusting the pore patency of a metal organic framework material to achieve isotope identification according to claim 1, characterized in that: The specific steps are as follows: Step (1): Since bound sodium fluorescein is very sensitive to changes in the microenvironment, the diffusion rate of small solvent molecules in the ZIF8 pores can be monitored by tracking the change in the fluorescence intensity of sodium fluorescein over time; Step (2): The diffusion rate of small molecules in the solvent shows obvious bidirectional exchange asymmetry; the rate at which methanol exchanges ethanol is very different from the rate at which ethanol exchanges methanol. This difference is precisely because sodium fluorescein blocks the pores and regulates the diffusion pathway, amplifying the difference in the diffusion rate of small molecules. Step (3): Based on the experimental results of step (2), the exchange rates between H2O and methanol, and between D2O and methanol were tested. Since the physicochemical properties of H2O and D2O are very similar, and the kinetic radius is exactly the same at 0.264 nm, ZIF8 and sodium fluorescein do not have the function of recognizing H2O and D2O. However, after the pore diffusion pathway is regulated by sodium fluorescein, the rate of H2O exchanging methanol is 2.7 times that of D2O exchanging methanol, and the rate of methanol exchanging H2O is 1.8 times that of methanol exchanging D2O.

4. The method for adjusting the pore patency of a metal organic framework material to achieve isotope identification according to claim 1, characterized in that : The fluorescence intensity was tracked over time by stopped-flow spectroscopy to monitor the diffusion of small solvent molecules in the ZIF8 pores. The specific steps are as follows: Step (1): the molar ratio of 2-methylimidazole, zinc acetate and sodium fluorescein is 1203:60.2:1; The cleaned product is evenly dispersed in the methanol solution; The stopped-flow spectrometer evenly mixed it with an equal volume of water within a dead time of 1.1 milliseconds, and monitored the diffusion process of water molecules exchanging methanol molecules in the nanopores in real time at a resolution of 12.5 microseconds per step; Step (2): uniformly dispersing the cleaned product in an aqueous solution; The stopped-flow spectrometer evenly mixed it with an equal volume of methanol within a dead time of 1.1 milliseconds, and monitored the diffusion process of methanol molecules exchanging water molecules in the nanopores in real time at a resolution of 12.5 microseconds per step; Step (3): uniformly dispersing the cleaned product in a methanol solution; The stopped-flow spectrometer evenly mixed it with an equal volume of D2O within a dead time of 1.1 milliseconds, and monitored the diffusion process of D2O molecules exchanging methanol molecules in the nanopores in real time at a resolution of 12.5 microseconds / step; Step (4): Evenly dispersing the cleaned product in a D2O solution; The stopped-flow spectrometer evenly mixed it with an equal volume of methanol within a dead time of 1.1 milliseconds, and monitored the diffusion process of methanol molecules exchanging D2O molecules in the nanopores in real time at a resolution of 12.5 microseconds / step; Step (5): Use Fick's second diffusion model to fit the diffusion coefficient of all the above diffusion data; judge the rationality of the proposed diffusion scheme through the mean square error result; Step (6): Compare the diffusion coefficients of the two processes in the above steps (1) and (3); it is found that within the same nanoparticle, the rate at which H2O exchanges methanol molecules is 1.8 times faster than the rate at which D2O exchanges methanol molecules; Step (7): Compare the diffusion coefficients of the two processes in the above steps (2) and (4); inside the same nanoparticle, the rate at which H2O exchanges methanol molecules is 2.7 times faster than the rate at which D2O exchanges methanol molecules.

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