Preparation Of Metal-Organic Frameworks MIL-101 And MOF-74 And Their Performance For CO₂ Adsorption

As global environmental standards are becoming ever more stringent regarding the emission of designated greenhouse gases,Substantial scale carbon capture and sequestration（CCS）is considered as one of the most promising strategies to mediate the atmospheric CO₂concentration for environmental remediation.Firstly,MIL-101（Cr）was synthesized by with different additives.Compared its structure,morphology and yield.MIL-101（Cr）synthesized by hydrofluoric acid as an additive has higher yield and smaller particle size due to different anion mineralization.Therefore,the experiment was followed by the hydrofluoric acid method to synthesis MIL-101（Cr）.The metal-organic framework MIL-101（Cr）was synthesized via hydrothermal process and then modified with pentaethylenehexamine（PEHA）through refluxing in ethanol.Various measures such as SEM,XRD,N₂ sorption,Elemental analysis and FT-IR were used to characterize the structure,morphology and properties of PEHA-grafted MIL-101（Cr）.Meanwhile,the performance of PEHA-grafted MIL-101（Cr）in CO₂ adsorption was investigated under 25℃.The results illustrate that the loading of PEHA in MIL-101（Cr）can conspicuously enhance the CO₂ adsorption capacity.PEHA-grafted MIL-101（Cr）with a PEHA loading of 0.24 mL exhibits the highest capacity for CO₂ adsorption;the adsorption capacity reaches 58.94 mg/g at 25℃and atmospheric pressure,which is 33%higher than that of the unmodified MIL-101（Cr）（44.21 mg/g）.In addition,the CO₂ adsorption capacities on both MIL-101（Cr）and PEHA-MIL-101（Cr）are greatly enhanced by increasing pressure,reaching1147.59 and 1256.74 mg/g at 1.1 MPa,respectively.These results suggest that PEHA modified MIL-101（Cr）could be a good candidate adsorbent for CO₂ capture at high pressure.Limit applications have been existed because hygroscopic property of MOFs,and atmospheric moisture also causes MOFs instability and low gases adsorption capacity.In order to overcome these problems,acid-functionalized multiwalled carbon nanotubes（MWCNTs）incorporated Mg-MOF-74 composite（CNT@Mg-MOF-74）has been successfully synthesized and characterized by XRD,FT-IR,TGA,SEM and BET analysis.Meanwhile,the performance of Mg-MOF-74,MWCNTs and CNT@Mg-MOF-74 in CO₂ adsorption were investigated under 25℃and ambient pressure.Tested regeneration performance of CNT@Mg-MOF-74and the moisture stability of Mg-MOF-74 and CNT@Mg-MOF-74 in moisture environment（at 33%relative humidity and 23°C）.The result indicating that CNT@Mg-MOF-74 obtained has the same crystal structure as that of virgin Mg-MOF-74,and has the same morphology both of the virgin Mg-MOF-74 and MWCNTs,but exhibited a much greater CO₂ adsorption capacity（increased from 59.75 to 79.88 mg/g,about a 34%increase in CO₂ storage capacity at 25℃and ambient pressure）,and an improved stability in moist conditions.The regeneration rate can maintain 100%in 5 repeat cycles.