Preparation Of Modified Mg-MOF Carbonization Derived Materials And Their CO₂ Adsorption Properties

A large amount of carbon dioxide(CO₂)emission causes tremendous harm to human beings and the ecosystem,so it is urgent to control the amount of CO₂.One of the most effective ways to reduce the amount of CO₂is to use solid adsorbents for adsorption.There are some features in magnesium oxide(MgO),such as high theoretical CO₂ adsorption capacity,low actual adsorption capacity and slow adsorption rate.In this paper,due to the adjustable characteristics of metal nodes and ligands in metal-organic framework materials(MOFs).MOFs tend to form metal oxide and carbon composites during in-situ carbonization.Form the perspective of MOFs derived materials and doped metal oxides to improve the CO₂ adsorption capacity of MgO.The effects of Mg-MOF carbonized derivative material MgO@C and modified Mg-MOF carbonized derivative materials MgO@C/CeO₂ on the adsorption properties of CO₂ were studied.The specific research contents are as follows:(1)The Mg-MOF was synthesized by solvothermal method.When the carbonization temperature was 700?,the heating rate was 5?/min,and the carbonization time was 2 h,the derivative material MgO@C-700-5-2with the best CO₂ adsorption performance was obtained.MgO@C-700-5-2possesses mesoporous structure and weak alkaline adsorption active sites on the surface.Mg-MOF was modified by doping cerium dioxide(CeO₂).When the amount of CeO₂ was 5%,the carbonization temperature was 600?,the heating rate was 2?/min,and the carbonization time was 1 h,the derivative material 5MgO@C/CeO₂-600-2-1 with the best CO₂ adsorption performance was obtained.There are both mesopores and macropores in5MgO@C/CeO2-600-2-1,but it is mainly mesopore.There are weak alkaline and medium strength alkaline adsorption active sites on the surface.(2)The adsorption capacity of 5MgO@C/CeO₂-600-2-1 at the optimal adsorption temperature of 300? was 2.3283 mmol/g,and the CO₂adsorption capacity of commercial MgO was 0.8373 mmol/g.After10 cycles,the adsorption capacity of MgO@C-700-5-2 showed a regular decreasing trend.The adsorption capacity of 5MgO@C/CeO₂-600-2-1 was 5.8765mmol/g at the optimal adsorption temperature of 350?.When the adsorption temperature was 300?,the CO₂ adsorption capacity of commercial MgO/CeO₂ and 5MgO@C/CeO₂-600-2-1 were 0.9659 mmol/g and 4.3508 mmol/g,respectively.It shows that the doped CeO₂ modified derivative material 5MgO@C/CeO₂-600-2-1 has a significant superiority in CO₂ adsorption capacity.After the 4th cycle,the adsorption capacity of5MgO@C/CeO₂-600-2-1 remains constant.Even after 10 cycles,the material still maintains excellent CO₂ adsorption capacity,indicating that doping CeO₂ effectively improves the cyclic stability of MgO.Compared with mesoporous MgO prepared by other methods,the two derivative materials exhibit higher CO₂ adsorption capacity under the same adsorption conditions.(3)The adsorption process of 5MgO@C/CeO₂-600-2-1 and MgO@C-700-5-2 for CO₂ in the whole temperature range accords with the pseudo-second-order adsorption kinetic model,indicating that the adsorption process of the two materials is controlled by chemical adsorption.At the same time,the adsorption processes of CO₂ by MgO@C-700-5-2 and5MgO@C/CeO₂-600-2-1 were both affected by the membrane diffusion and intra-particle diffusion resistance.Three forms of salt were produced on the surface of the two materials after 10 cycles,namely bicarbonate,bidentate carbonateand monodentate carbonate.Three forms of bicarbonate,bidentate carbonate and monodentate carbonate were produced on the surface of the two materials after 10 cycles adsorption.