Amine Functionalization in Porous Adsorbents for Carbon Capture and Conversion

Metal-organic Frameworks (MOFs) are a class of crystalline porous materials with exceptionally high surface area, chemical tunability and stability. Due to alarming CO2 emission and global concern, research is focused on developing porous materials like MOFs for CO2 capture from the flue gas stream and direct air. Post-modification on MOFs with amines are widely studied for this application due to their high affinity for CO2. Amine functionalization is mainly carried on MOFs via appending small chain amines to the open metal sites (OMS) and by physical impregnation in the MOF pores. Such approaches have its advantages like high CO2 capacity and selectivity, however amine leaching in humid condition is a drawback, where water molecules displace the amines from the MOF pores and subsequently washes them off the pores. To avoid the amine leaching, two new approaches were developed, i) covalent amine grafting to the ligand of the MOF and ii) in-situ crosslinking of amines in the pores. This thesis focusses on the former approach of covalently grafting amines in the MOF pores for two primary applications, i) post-combustion carbon capture and ii) selective CO2 cycloaddition. In chapter 1, we briefly describe CO2 emission, its consequences and materials developed for CO2 capture. Chapter 2 showcase the developed new two-step post-modification strategy, which is employed on Zn based MOF, NH2-Zn-BDC. Here, for the first time we showed the feasibility of method and quantification of each step of post-modification via 1H-NMR. The chemistry associated with CO2 adsorption is probed via in-situ CO2 dossing coupled DRIFTS measurement. Chapter 3 reports the universality of the developed post-modification in different MOF, NH2-Cr-BDC for the practical applicability of CO2 capture from flue gas. Here, we used different spectroscopic techniques like XPS, XAS combined with molecular simulations to assess the extent of modification. The amine grafted MOF is subjected to simulated dry and wet flue gas stream and CO2 adsorption proprieties are assessed. Here we showed the advantage of amine grafting over traditional amine impregnation method. Chapter 4 shows the impact of using protic amine-salt functionalized Cr-MOF in CO2 cycloaddition reaction with epoxide. Here for the first time, we showed the polymerizing nature of Cr cluster in MOF. Moreover, we studied the resulted polymer species and their impact on catalyst reusability. Finally, we assessed the cause of the degrading catalytic performance via FTIR and TGA on the spent catalyst.