Study On Interface Optimization And Gas Separation Mechanism Of Modified Cellulose Based Mixed Matrix Membranes

To reduce carbon emissions,a variety of technologies have been developed and applied to carbon capture and utilization processes.Among them,membrane separation technology stands out due to its advantages of simple process,simple operation,low energy consumption,and environmental friendliness.The commonly used gas separation membrane materials mainly include inorganic membranes,polymeric membranes,and mixed matrix membranes.Mixed matrix membranes can integrate the screening ability of inorganic membranes and the dissolution diffusion process of polymeric membranes,thus showing good application prospects.However,in the construction process of mixed matrix membranes,particle aggregation and membrane defects caused by interface mismatch are important obstacles that limit membrane separation performance.It is urgent to develop various interface engineering strategies to enhance the affinity of inorganic-organic interfaces and promote mixed matrix membranes to move towards more industrial application scenarios.This paper aims to enhance the CO₂ separation performance by preparing a mixed matrix membrane and optimizing the interfacial compatibility between the filler and the polymer,thereby improving the separation effect of the membrane.During the selection process of membrane substrate,the modified cellulose represented by cellulose acetate（acetylated cellulose,CA）was mainly investigated.In order to further improve the renewable performance of membrane substrates,the potential of natural green one-dimensional（1D）cellulose nanofibers（carboxylated nanocellulose,CNFs）as membrane substrates was also explored.During the selection process of inorganic fillers,emphasis was placed on metal organic frameworks（MOFs）that are easy to surface modify and graft,as well as the emerging two-dimensional（2D）MXene nanosheets.In the process of interface regulation,interface engineering strategies such as filler size optimization,amino grafting modification,and dimensional adjustment were adopted,effectively improving the separation performance of CO₂/N₂ and CO₂/CH₄.The main research was concluded as follows:（1）Exploring the effect of filler size on the interface properties and gas separation performance of cellulose acetate composite membranes.Zr based MOF（Ui O-66-NH₂）doped into CA networks and prepared by solvent casting method Ui O-66-NH₂@CA mixed matrix membranes（MMMs）.The introduction of Ui O-66-NH₂ with well-developed pore structure and rich amino groups provides an additional pathway for CO₂ transport,resulting in a high CO₂affinity for the membrane,greatly improving the separation efficiency of Ui O-66-NH₂@CA composite membranes.Characterization methods such as electron microscopy（SEM）and free volume testing（FFV）show that optimizing the particle size of Ui O-66-NH₂ can effectively suppress the problem of non-selective voids and particle aggregation in the composite membrane.The U-100@CA membrane（Ui O-66-NH₂:～200 nm）possesses the best separation performance,with a CO₂ permeability of 168.8 Barrer,and ideal selectivity for CO₂/N₂ and CO₂/CH₄ of 40.2and 51.3,respectively.The separation mechanism is mainly due to the presence of sufficient amino groups in the membrane matrix,high CO₂ solubility,and excellent inorganic-organic interface performance.The stability test shows that the separation capability of the membrane remained stable over a long period of time（120 h）,and the mixed gas test results show that the prepared mixed matrix membrane possesses excellent industrial application potential.（2）Exploring the effect of amino grafted ZIF-8 on the interfacial properties and gas separation performance of cellulose acetate composite membranes.In order to improve the interfacial compatibility between CA matrix and ZIF-8 crystals,this work proposes an interface design strategy of grafting polyethylene imine polymer（PEI）onto ZIF-8 particles.Introducing amino-rich PEI can regulate the surface properties of ZIF-8 crystals without damaging their pores.In addition,the amino groups in PEI can interact with the oxygen-containing hydroxyl/carbonyl groups on the CA chain,and PEI,as a flexible chain segment,can effectively repair interface voids and inhibit the generation of non-selective voids at the ZIF-8/CA interface.With the assistance of PEI,the interfacial compatibility between ZIF-8 and CA has been significantly improved.The PEI grafting ZIF-8@CA（PZIF-8@CA）membrane exhibits the separation performance with a CO₂ permeability of 150.3 Barrer and ideal selectivity of 44.2 and 53.7 for CO₂/N₂ and CO₂/CH₄,respectively.The separation mechanism is mainly due to the excellent interface properties of the CA matrix,the good dispersibility of PZIF-8 particles,the rich amino groups in PEI,and the high CO₂ solubility.（3）Exploring the effect of MXene intercalation modification on the interface properties and gas separation performance of nanocellulose composite membranes:2D materials exhibit excellent physical and chemical properties and broad application prospects in the field of molecular separation,but they face problems such as disordered stacking and interlayer defects.Compared to CA molecules,nanoscale CNFs possess advantages such as natural accessibility,abundant content,wide distribution,and environmental friendliness.Therefore,this work is based on the exfoliatibility of MXene nanosheets and the exchangeability of interlayer ion molecules.MXene nanosheets are used as building blocks,and 1D CNFs with negative charges are intercalated and exfoliated.CNFs are introduced to regulate the 2D channels of MXene,and prepared by vacuum assisted assembly method MXene@CNF composite membrane.Under the interaction between MXene and CNFs,the disordered stacking and interlayer defects of the original MXene membrane are repaired,which helps to form a continuous defect free membrane.CNFs are rich in carboxyl and hydroxyl groups,enhancing the dissolution diffusion behavior of CO₂ molecules.Therefore,the CO₂ permeance and the ideal selectivity of CO₂/N₂ and CO₂/CH₄are improved simultaneously.The results indicate that the MXene@CNF-3 membrane exhibites the best gas separation performance,with a CO₂ permeability of 156.7 Barrer and ideal selectivity of 42.6 and 47.8 for CO₂/N₂ and CO₂/CH₄,respectively.The main separation mechanism attributes to the construction of layered nanochannels and the high CO₂ solubility.