Experimental Study On Adsorption Of CO₂ By Modified MOF Materials

Carbon dioxide（CO₂）is widely recognized as the main greenhouse gas.The harmful effects of CO₂ on the environment have seriously affected human life.The excessive emission of CO₂ has led to the serious greenhouse effect.At present,the new energy utilization technology is not mature,and fossil fuels are still the main source of energy.Low carbon emission reduction is particularly urgent,adsorption method because of its low energy consumption,simple operation,easy to practical application and other characteristics hav e a good prospect.MOFs（Metal-Organic Frameworks）are emerging porous and large specific surface area materials in recent years,which are widely used in the adsorption field.Among them,U io-66shows good adsorption characteristics due to its large speci fic surface area and porous structure.In this paper,Uio-66 and Piperazine（PZ）modified Uio-66 were synthesized by solvothermal method,and CO₂ adsorbent was prepared by adjusting piperazine in different mole ratios.The effect of piperazine ratio on pore structure,crystal morphology and thermal stability was investigated.The adsorption heat curve of adsorbent was fitted to discuss whether the adsorbent was easy to desorption and its adsorption cycle stability was studied experimentally.1.In the screening of precursors,two sorbents,HKUST-1 and Uio-66,were selected to modify piperazine（PZ）.The performance and adsorption selectivity of the adsorbent in the HKUST-1 system decreased after loading PZ.The adsorption capacity and selectivity of carbon dioxide in Uio-66 system were improved.2.In this study,a novel piperazine（PZ）functionalized U io-66 was prepared by in-situ hydrothermal method.PZ was successfully loaded onto Uio-66 without damaging its crystal structure,porous morphology and thermal stability.When the molar ratio of PZ to zirconium chloride was 0.25（uio-0.25）,the specific surface area was up to 1350m2/g,and the adsorption capacity of CO₂ increased from35.18cm³/g STP to 42.67 cm³/g STP.More importantly,the adsorption selectivity of CO₂/N₂ increased significantly from 9.01 to 18.06.After 5 cycles of desorption and adsorption,the adsorption capacity basically remains unchanged and the cycle stability is good.In addition,the CO₂ adsorption heat of the prepared Uio-0.25adsorbent is low,which is 26.60 k J.mol^-1.The results show that the adsorption of CO₂ by PZ-loaded Uio-66 is mainly physical adsorption,which is beneficial to the energy saving desorption of CO₂.3.The Uio-66 adsorbent loaded with piperazine was characterized by FT-IR,thermogravimetric analysis and XRD.Uio-66 adsorbent loaded with PZ retained the octahedral structure of precursor and the crystal shape was intact.The pore size of the adsorbent decreased from 0.57cm³/g to 0.49cm³/g（Uio-0.25）,and the average pore size increased from 1.71nm to 2.16nm（Uio-0.25）.EDS analysis of elements can indicate the successful loading of piperazine.Thermogravimetric analysis shows that the thermal stability o f Uio-66 under PZ load is above 400℃.Uio-0.25 with high adsorption selectivity was synthesized by enhancing the chemical characteristics and porous morphology of the active site of MOF through PZ functionalization.The adsorbent has the advantages of thermal stability higher than 400℃,excellent adsorption cycle performance and low adsorption heat.