| The separation of H2/D2 is of great significance because of the important uses of H2 and D2 in the industrial field.Therefore,it is necessary to develop the method of hydrogen isotope separation with economic benefits,and the separation method based on adsorption has become the main method of hydrogen isotope separation.Porous materials have broad application prospects in the field of gas adsorption and separation due to their large surface area,adjustable pore and flexible structure.Due to the infinite number of structures of newly synthesized and unsynthesized porous materials,it takes a lot of manpower and material resources to explore the hydrogen isotope separation performance of different skeleton materials only by experimental means.Therefore,in this work,we explored the adsorption and diffusion properties of hydrogen isotope H2/D2 in porous materials by grand canonical Monte Carlo（GCMC）molecular simulation method and molecular dynamic（MD）simulation method,and combined with gas chromatography experiments.The two kinds of materials in porous framework materials metal-organic frameworks（MOFs）and hydrogen-bonded organic frameworks（HOFs）were studied.（1）UTSA-280-Co is a three-dimensional MOF material in which Co atoms are coordinated with seven oxygen atoms from five different C4O42-ligands and one water molecule to form a pentagonal biconical cluster and bridged by organic ligands to form a one-dimensional infinite chain with one-dimensional pores of approximately 3.4?×3.4?.In contrast,after synthesizing UTSA-280and removing the guest water molecules,one-dimensional cylindrical pores with pore sizes of 3.2×4.5?and 3.8×3.8?can be obtained,and the open metal site Co is exposed.UTSA-280-Co with high open metal site density（9.23mmol/cm3）was synthesized for H2/D2 separation by in-situ crystallization method.The molecular simulation results showed that the adsorption selectivity of UTSA-280-Co for hydrogen isotope mixture（H2:D2=1:1）was 4.38 at 20 K and 2.70 at 77 K.The results showed that UTSA-280-Co had CAQS effect on hydrogen isotope separation due to the high density of open metal sites,and could be achieved effectively hydrogen isotope separation at higher temperatures.At the same time,the MD results showed that UTSA-280-Co has a KQS effect on the separation of hydrogen isotope H2/D2 when the temperature was lower than 60 K.With the increase of temperature,UTSA-280-Co had a good kinetic selectivity for hydrogen isotope H2/D2,and the kinetic selectivity was 1.35 at 77 K.After that,UTSA-280-Co was loaded onγ-Al2O3 by in-situ crystallization method,and the composite was used as stationary phase of gas chromatography.At 77 K,even 500μL of mixed hydrogen isotope H2/D2 could be separated,the resolution R was still 1.52,and the separation time was 10.14min with good reproducibility and accuracy.（2）The pore size of HOF-21-Co is 3.6?,which satisfies the requirement of KQS effect.Moreover,the central metal Co of HOF-21-Co is coordinated with two water molecules,and when the coordinated water molecules are lost,the central metal Co changes from six-coordinated to four-coordinated,and the existence of open metal sites is favorable to the separation of hydrogen isotopes by the CAQS effect.HOF-21-Co was synthesized for hydrogen isotope separation by in-situ crystallization method,which was the first time for HOF material to be used for hydrogen isotope separation.The Grand Canonical Monte Carlo（GCMC）simulation showed that the adsorption selectivity of HOF-21-Co for hydrogen isotope mixture（H2:D2=1:1）was 2.55 at 20 K and1.52 at 77 K.The results showed that the open metal site of HOF-21-Co had CAQS effect on the separation of hydrogen isotopes,and hydrogen isotopes could be effectively separated at higher temperatures.At the same time,the MD results showed that the diffusion coefficient of D2 was higher than that of H2 at the temperature below 70 K,indicating that there was kinetic quantum sieving（KQS）effect on hydrogen isotope separation by HOF-21-Co.The kinetic selectivity of HOF-21-Co for hydrogen isotope was 1.12 at 77 K.Therefore,the synergistic effect of CAQS effect and kinetic sieving effect can be played at the same time at higher separation temperature of HOF-21-Co,which effectively realized hydrogen isotope separation.Whenγ-Al2O3@4.53%-HOF-21-Co was used as stationary phase for gas chromatography,the resolution R reached 1.59and the separation time was 6.89 min at 77 K under the optimum chromatographic conditions.In conclusion,this work greatly improved the adsorption and separation performance of hydrogen isotope in HOF-21-Co through the synergistic action of the two effects,and expanded the application range of HOF materials.（3）UTSA-300-Co has a small pore size（2.4×3.3?2）and multiple potential binding sites,with each Co（II）metal center formed by four pyridine N atoms from four different 4,4′-dipyridyl sulfide ligands and two F atoms from two different hexafluoro silicates forming octahedral coordination sites.γ-Al2O3@UTSA-300-Co composite was synthesized by in situ crystallization method and used to separate H2 and D2.The molecular simulation results showed that the adsorption selectivity of UTSA-300-Co for hydrogen isotope mixture（H2:D2=1:1）was 3.12 at 77 K and 1.90 at 100 K.At 100 K,UTSA-300-Co showed CAQS and kinetic sieving effect on hydrogen isotope separation due to the existence of open metal sites and suitable pore sizes.Whenγ-Al2O3@8.17%-UTSA-300-Co was used as stationary phase for gas chromatography,the resolution R reached 1.52 and the separation time was 7.87min at 77 K under the optimum chromatographic separation conditions with good reproducibility and accuracy.（4）Using ZIF-67 and ZIF-8 as hydrogen isotope separation materials,the molecular simulation results showed that the adsorption selectivity of ZIF-67for hydrogen isotope（H2:D2=1:1）increased from 1.66 to 2.08 with the temperature decreasing from 77 K to 20 K.It showed that ZIF-67 have chemical affinity quantum sieving（CAQS）effect.MD results showed that the diffusion coefficients of H2/D2 in ZIF-67 were different.Below 72 K,ZIF-67 showed a kinetic selectivity of D2/H2with 4.41,indicating that ZIF-67 have kinetic quantum sieving（KQS）effect at low temperature.When the temperature was higher than 72 K,the diffusion coefficient of H2 was higher than that of D2.ZIF-67 exhibits a typical kinetic sieving effect,and the kinetic selectivity of ZIF-67for H2/D2 was 1.29 at 77 K.At 77 K,the adsorption capacity of D2 by ZIF-67was higher,and the diffusion coefficient of D2 was lower than that of H2.The combination of the two effects can effectively realize the separation of hydrogen isotopes.In contrast,ZIF-8,which has the same structure as ZIF-67,had no significant difference in adsorption of H2 and D2.Therefore,we thought that the excellent separation performance of H2/D2 by ZIF-67 came from the active metal site Co.（5）Cooperate with other students to design the composite material with two effects through the MOF-on-MOF strategy.The molecular simulation results showed that the adsorption selectivity of CAU-10-H for hydrogen isotope H2/D2was 1.33 at 77 K,and CAU-10-H had both CAQS effect and kinetic sieving effect while UTSA-16 only had kinetic sieving effect.UTSA-16 passivated the composite,enabling rapid elution of hydrogen isotope H2/D2 from the system.Both CAU-10-H and UTSA-16 promoted rapid diffusion of H2 through kinetic sieving effects.These addition effects enabled effective H2/D2 separation at 77K. |
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