Synthesis Of ZIF-8 Derived Carbon Hybrid Carbonous Materials And Their CO₂ Adsorption And Separation Performance

As the development of industry and the continuous progress of human social activities,CO₂ emission gained a great more attention all over the world owing to its green house effects.Nowadays,CO₂ capture and separation technology has been utilized to reduce the concentration of CO₂ in the atmosphere.Porous carbon materials have potential application in CO₂ capture and separation due to their controllable nanostructure,designable chemical properties,developed pore structure,high thermal and chemical stability and low cost.Although porous carbon materials has been widely studied these days,the design of novel porous carbon materials is still an issue for precisely caught and separate CO₂ in an efficient way.Fine structure design will provide a new idea for the synthesis of high performance adsorption and separation materials.In addition,hybridization as a promising strategy,which not only could highlight the advantages of a single material and avoid its disadvantages,but also combine the advantages of two or more materials,providing an unexpected synergistic effect for CO₂ capture.The detial contents and results are as follows:（1）To solve the problems of low CO₂ absorption capacity and high regeneration energy of current CO₂ capture materials,N-doped porous carbon solid adsorption materials with good CO₂ adsorption performance,high cycle stability and high regeneration performance were constructed by using hybrid and post-synthesis thermal treatment methods.In detail,the cellulose was loaded on the surface of ZIF-8 to prepare ZIF-8/cellulose composite by simple coating method,and then the ZIF-8/cellulose composite was co-carbonized treatment to obtain hierarchical N-doped porous carbon.The cellulose coating method in favor of pores structure regulation and nitrogen protection of ZIF-8 during the carbonization process,and thus showed synergetic absorption of CO₂.When the carbonization temperature was 600°C,the obtained N-doped porous carbon showed the highest CO₂ capture capacity of 2.45mmol/g and 3.68 mmol/g at 25°C under 1 bar and 0°C under 1 bar,respectively.More importantly,N-doped porous carbon exhibited almost constant CO₂ uptake in 10 consecutive adsorption-desorption cycles,indicating the great stability and recyclability.（2）Membrane separation technology as one of the most promising technologies for CO₂emissions reduction due to its low investment cost,high efficiency and easy large-scale application.Carbon molecular sieve membrane with good gas separation performance,high thermal and chemical stability,but the trade-off between the gas permeability and selectivity of the membrane material limits its application in the gas separation field.To improve the gas separation performance of the carbon molecular sieve membrane,we induced ZIF-8nanoparticles as a doping agent to construct a series of phenolphthalein-based cardo poly（arylene ether ketone）（PEK-C）-based hybrid carbon molecular sieve mixed natrix membranes for CO₂/N₂ separation via an oxidation and a carbonization process with pyrolysis temperature in the range of 500–700°C.The carbonized ligand and metal centre of ZIF-8 offered additional pores of carbon matrix,which tailored the ultramicropores of ZCMS membranes for both excellent CO₂ permeability and selectivity.By treating with the temperature of 600°C,ZCMS-600-15（ZIF-8 derived carbon hybrid carbon molecular sieve mixed natrix membranes membrane based on 15 wt%of ZIF-8-doped PEK-C）exhibited the highest CO₂permeability of 8902 Barrer,which was 1.8 times higher than that of CMS-600（carbon molecular sieve membrane based on naked PEK-C）.ZCMS-600-15 showed an ideal CO₂/N₂ selectivity of 42.2,which is also higher than that of other samples.Moreover,ZCMS-600-15 also showed a superior CO₂ permeability of 8285 Barrer and the highest CO₂/N₂ selectivity of 24.08 for an equimolar mixture of CO₂ and N₂,far exceeding the 2008Robeson upper bound.Our results suggest that incorporating MOFs into polymer precursors to prepare hybrid carbon molecular sieve membranes by carbonization process could solving the trade-off problem between permeability and selectivity,introducing new possibilities for industrial application.（3）The dispersion,particle size,stability,hydrophobicity and morphology of functional fillers will significantly affect the gas separation performance of carbon molecular sieve mixed matrix membranes.On the basis of the research in the third part,we incorporating three different sizes of ZIF-8 crystals（～45 nm,450 nm and 900 nm）as doping agents to prepare a series of ZIF-8 derived carbon-based hybrid carbon molecular sieve mixed natrix membranes for CO₂/N₂ separation via an oxidation and a carbonization process,we studied the effect of the size of functional fillers on the gas separation of ZIF-8 derived carbon hybrid carbon molecular sieve mixed matrix membrane.It was found that three different size ZIF-8 derived carbon hybrid carbon molecular sieves mixed matrix membrane had excellent CO₂/N₂ separation performance.Among them,the ZIF-8-S（～45 nm）derived carbon doped ZIF-8 derived carbon hybrid carbon molecular sieve mixed matrix membranes（ZCMS-S）had the highest S_BET,resulting in higher CO₂ permeability and selectivity than the ZIF-8-M（～450 nm）and ZIF-8-L（～900 nm）doped ZIF-8 derived carbon hybrid carbon molecular sieve mixed matrix membranes（ZCMS-M and ZCMS-L）.In addition,the CO₂/N₂ mixed gas separation performance of the ZCMS-S and ZCMS-M far exceeding the 2008 Robeson upper bound.