Study On CO₂/N₂ Adsorption Performance Of Flexible MOFs Synthesized By Low-toxic Solvents

Since the industrial revolution,environmental problems have become more and more serious,especially when excessive emissions of greenhouse gases such as CO2 have caused global warming,and low-carbon actions have gradually entered people’s field of vision,carbon capture and storage technology(Carbon Capture and Storage,CCS)is considered to be a viable way to reduce high CO2 emissions in the industry,and the key to this technology is the research and development of energy-saving,inexpensive,environmentally-friendly and recyclable adsorbents.As an emerging adsorbent,Metal-Organic Framework(MOF)has the advantages of high specific surface area,gas channel selectivity and controllability,and has become a hot topic in the research of adsorbents.Many MOF materials are suitable for C02.Has a strong adsorption capacity.The flexible MOF materials studied in this paper belong to a subset of the MOF category,and have a special feature of "gate adsorption" in gas adsorption.They exhibit a special"staircase" type for gas adsorption isotherms such as CO2 and CH4,which is high.The concentration of gas capture and utilization provides new ideas.In addition,many flexible MOF materials produce a "breathing effect" when the gas is adsorbed,and the skeleton expands.Thus,flexible MOF materials can also be applied to the design of the sensor.At the same time,the flexibility has a high CO2/N2 selective adsorption and is an ideal adsorbent for separating CO2 from flue gas.In this research,-three types of flexible MOFs in two ions such as Al3+and Cu2+,were successfully synthesized by using low-toxic solvent ethanol instead of the traditional organic solvents such as DMF,methanol and etherused in traditional synthesis.Three organic ligands of phthalic acid,4,4’-bipyridyl and 2,5-dihydroxybenzoic acid were synthesized into aluminum-based MIL-53(Al),copper-based ELM-11 and copper-based dual ligand Cu(dhbc)2(4,4’-bpy)material.XRD,thermogravimetric analysis,infrared spectroscopy,scanning electron microscopy and BET specific surface area analysis of flexible MOF samples synthesized by low-toxic solvent ethanol were carried out.The structure and properties of the samples were characterized,which proved the feasibility of ethanol instead of other solvents.In this study,the adsorption performance of CO2 and N2 under low pressure and high pressure was tested on three synthesized samples.The activation temperature,adsorption temperature and CO2 adsorption reproducibility of the material were controlled by Single variable method.The optimal activation temperature of MIL-53(Al)was 493 K,and the optimum activation temperature of ELM-11 and Cu(dhbc)2(4,4’-bpy)was 423 K.The adsorption temperature and regenerative test proved that the three materials adsorbed CO2 as a physical adsorption process,and the higher the adsorption temperature,the lower the adsorption amount,the higher the opening pressure,and the hysteresis loop became wider.As the adsorption temperature raised from 273 K to 303 K,the CO2 adsorption amount decreased from 3.3mmol/g to 2.7 mmol/g at I bar,and decreased from 9.2 mmol/g to 7.1 mmol/g at 10 bar.When ELM-11 was heated from 273 K to 303 K the CO2 adsorption amount was from 3.8 mmol/g decreased to 3.2 mmol/g at 1 bar,decreased from 10.5 mmol/g to 5.5 mmol/g at 12 bar;As the adsorption temperature of Cu(dhbc)2(4,4’-bpy)increased from 273 K to 303 K when CO2 adsorption amount was 3.1 mmol/g dropped to 1.8 mmol/g at 1 bar and decreased from 4.7 mmol/g to 3.1 mmol/g at 10 bar.In the regeneration performance,after five cycles,MIL-53(Al)adsorption performance retained 86.1%,ELM-11 adsorption performance retained 85.3%,Cu(dhbc)2(bpy)adsorption performance retained 87.1%,all three samples Can retain good regeneration performance.Finally,the kinetics of CO2 adsorption were studied by data fitting methods MIL-53(Al),ELM-11 and Cu(dhbc)2(4,4’-bpy).Three flexible MOFs were studied.The adsorption process is more in line with the Banham rate model,that is,the adsorption of CO2 on MIL-53(Al)is mainly due to its pore action and is a physical adsorption.