Preparation Of Cr（Ⅵ）@MOF-74（Ni）@γ-Al₂O₃ Composites And The Performance On Separation Of Hydrogen Isotope H₂/D₂

In this paper,MOF-74(Ni)with chemical affinity quantum sieving effect on hydrogen isotopes H2/D2 was loaded on γ-Al2O3 through liquid phase extension method,and MOF-74(Ni)@γ-Al2O3 composite was successfully synthesized.MOF-74(Ni)γ-Al2O3 composite was modified by dipping-evaporation to obtain Na2Cr2O7/Na2CrO4/NaCl@MOF-74(Ni)@γ-Al2O3,Na2Cr2O7@MOF-74(Ni)@γ-Al2O3,Na2CrO4@MOF-74(Ni)@γ-Al2O3,NaCl@MOF-74(Ni)@γ-Al2O3 and NaCl/Na2CrO4@MOF-74(Ni)@γ-Al2O3 composites.Gas chromatography was used to separate hydrogen isotope with the composites as chromatographic stationary phase,and its separation performance was analyzed.The main results as follows:(1)Preparation and Characterization of Chromatographic Stationary Phases:.MOF-74(Ni)@γ-Al2O3 composites was synthesized through liquid phase extension method,then MOF-74(Ni)@γ-Al2O3 was modified by dipping-evaporation method,and obtained Na2Cr2O7/Na2CrO4/NaCl@MOF-74(Ni)@γ-Al2O3,Na2Cr2O7@MOF-74(Ni.)@γ-Al2O3,Na2CrO4@MOF-74(Ni)@γ-Al2O3,NaCl@MOF-74(Ni)@γ-Al2O3 and NaCl/Na2CrO4@MOF-74(Ni)@γ-Al2O3 composites.The composites were characterized by IR,XRD,SEM,line scan,TG-DTA,Raman and BET.(2)The separation performance of hydrogen isotopes on the chromatographic stationary phase materials:Na2Cr2O7/Na2CrO4/NaCl@MOF-74(Ni)@γ-Al2O3,Na2Cr2O7@MOF-74(Ni)@γ-Al2O3,Na2CrO4@MOF-74(Ni)@γ-Al2O3,NaCl@MOF-74(Ni)@γ-Al2O33 and NaCl/Na2CrO4@MOF-74(Ni)&γ-Al2O3 composites were packed into a stainless steel column(1.0 m × 2.0 mm ID).Under the conditions that He as the carrier gas,the column temperature 77K,carrier gas flow rate 30 mL/min,injection volume 100 μL,the separation performance of hydrogen isotope H2/D2 were studied.The results show that the resolution of H2/D2 on MOF-74(Ni)@γ-Al2O3 composite material is 2.03,and the separation time is up to 17.1 min,and the trailing phenomenon is serious.The Na2Cr2O7/Na2CrO4/NaCl@MOF-74(Ni)@γ-Al2O3 composite material effectively improved the long separation time and serious peak trailing phenomenon,the resolution was as high as 2.87,the time was reduced to 7.15 min.In order to verify the effect of the modified substances in Na2Cr2O7/Na2CrO4/NaCl@MOF-74(Ni)@γ-Al2O3 on the separation performance of H2/D2,Na2Cr2O7@MOF-74(Ni)@γ-Al2O3,Na2CrO4@MOF-74(Ni)@γ-Al2O3,NaCl@MOF-74(Ni)@γ-Al2O3 and NaCl/Na2CrO4@MOF-74(Ni)@γ-Al2O3 composites were used as stationary phase materials,and study the performance of H2/D2 separation.The results showed that the separation time of H2/D2 on Na2Cr2O7@MOF-74(Ni)@γ-Al2O3 is 17.21 min,and the resolution is 2.25;the resolution of H2/D2 on Na2CrO4@MOF-74(Ni)@γ-Al2O3Na2CrO4 is 3.28,and the separation time is 8.64 min.The separation time of H2/D2 on NaCl@MOF-74(Ni)@γ-Al2O3 is reduced to 4.84 min,the resolution of H2/D2 is 1.85,and the peaks correspond to the gaussian distribution.Due to the presence of Na2CrO4 in the composite,the resolution of H2/D2 could be increased,while the presence of NaCl could shorten the separation time and improve the peak shape of the chromatographic peak.Therefore,Further optimize the ratio of NaCl and Na2CrO4 in the composites,the results show that when the ratio of NaCl/Na2CrO4 in the composites is 0.7:1,the separation performance of H2/D2 is better.When the carrier gas flow rate is 20 mL/min,injection volume is 100 μL,the resolution is 2.56,and the separation time is 5.91 min.(3)Repeatability test and quantitative analysis:Na2Cr2O7/Na2CrO4/NaCl@MOF-74(Ni)@γ-Al2O3 and NaCl/Na2CrO4@MOF-74(Ni)@γ-Al2O3 chromatographic packings were used for the repeatability and quantitative analysis of hydrogen isotope H2/D2 components.The relative standard deviations of the retention time of pure H2 and pure D2 was less than 1%,and the RSD of the peak height and peak area were all less than 5%,indicating that both columns have a good reproducibility and stability for H2/D2 separation.Repeated injection of H2/D2 mixed components,the RSD of the retention time was less than 1%,the peak area was lower than 5%,and the relative error between the experimental content and theoretical content was less than 0.05,indicating that the quantitative analysis is accurate.