Pore-regulation Of Metal-organic Frameworks For Carbon Capture

Excessive CO₂ emissions have caused serious environmental issues.It is of great significance to research carbon capture to reduce CO₂.The adsorption method has been proven to have better CO₂ capture efficiency.Metal-organic frameworks（MOFs）show great potential for CO₂ capture,due to their extremely high specific surface area and porosity,adjustable pore structure,physical and chemical properties.Adsorption mainly depends on the pore size and properties of adsorbents.Based on this,MOFs were post-modified to adjust the pore structure and microenvironment and improve the ability of carbon capture.The staple contents and results are as follows:（1）A simple and environment friendly air-thermal processing（ATP）strategy was developed for activating and purifying MOF adsorbents.Through processing MOFs in closed space,the residual guest molecules and incomplete coordination linkers in MOFs can overcome the energy barrier of escape with assistance of the thermalized and pressurized air with high enthalpy.While ensuring the integrity of crystal,the obtained MOFs have a hierarchical micro/mesoporous structure,increased surface area（36%）and pore volume（72%）.By adjusting the processing temperature,the ATP strategy can be used to fabricate MOFs with hierarchically micro/meso/macro superstructure without modulator/template,which is beneficial to improve the adsorption capacity and selectivity of target molecules.At 298 K and 1.0 bar,the CO₂ adsorption capacity and CO₂/N₂（15:85）selectivity of MOF adsorbent increased from 3.7 mmol g^-1 and 9.1to 4.5 mmol g^-1 and 16.3,respectively.（2）A robust solvent vapor-assisted self-conversion strategy was developed to prepare nanoparticle/MOF composite adsorbents for improving the carbon capture capacity of MOFs.Based on the hydrolysis of the coordination bond triggered by water impurities in the solvent and the decarboxylation of the linker under thermal and alkaline conditions,the metal centers of MOFs could be converted to alkaline carbonate nanoparticles（BC）.Since the self-conversion was limited by the low content of water impurities and MOFs could be purified by excess organic solvents,the BC-MOFs maintain good crystallinity and even show excellent porosity.Especially the BET surface area and pore volume of BC-Cu BTC increased by 39%and 53%,respectively.Thanks to the increased specific surface area,open metal sites and additional alkalinity from the basic carbonate,the BC-MOF composites exhibit substantially improved CO₂capture performance with good balance between capacity and selectivity.For example,at 298 K and 1.0 bar,the the CO₂ adsorption capacity of BC-MOF adsorbent self-converted with ethanol solvent increased from 3.7 mmol g^-1 to 5.8 mmol g^-1,and the selectivity of CO₂/N₂（15:85）increased from 11.4 to 29.2.