Amine-Based Mof Synthesis for Enhanced Gas Capture Applications /

Abstract

Metal organic framework materials have been recently realized to have huge commercial potential with wide applications such as carbon capture to mitigate climate change, low-pressure gas storage for portable fuels and catalytic CO2 conversion and breakdown of toxic species to mention a few. The demand for MOF production at industrial scale is now increasing, However, there are still a few challenges that need to be addressed before reaching the maturity level of commercial technology these include enhancing carbon dioxide gas capture tendency, reducing cost of MOF production, increasing ease MOF of synthesis process, enhancing MOFs stability through various gas capture cycles. Present study was focused on the synthesis of various combinations of amine-based MOFs using various synthesis routes to meet the required challenges. Different synthesis schemes were used to produce MOFs for amine-based MOF materials synthesis including in-situ amine functionalization, post amine modification and amine-functionalized linker-based MOF synthesis. Prepared samples were fully characterized to analyze their structure, thermal stability and surface area using SCXRD, PXRD, SEM-EDS, Elemental analysis, FTIR and BET analysis. Obtained amine-based MOF materials were found highly crystalline and ordered structures (Mn-DOBDC CCDC #1948926, Mn-NH2-ABDC CCDC#1949695). These MOFs demonstrated required key features to be served as great sorbent. Highest surface area values (Langmuir 1780, BET 1453 m2/g) were recorded for Mn-NH2-ABDC. Amine-based MOF illustrated better carbon dioxide uptake capacities compared to analogous MOFs without amine functional groups. Highest CO2 capture (wt %) recorded for Mn-NH2-ABDC and EDA-Mn-DOBDC were found highest i.e., 90.4 and 70.4 at 273 K and 15 bar pressure, respectively. Amine incorporation into MOFs not only enhances CO2 uptake, it also stabilized coordination polymer structure than increasing its thermal stability of these coordination polymers. Targets of this study were successfully achieved xxiii by incorporation of amine molecules within MOF structure that provided additional binding sites in MOF framework and induce charge dispersion and electrostatic forces that enhanced CO2 gas adsorption. Moderate isosteric heat of CO2 adsorption (Qst values within 28-35 KJ/mol) for prepared MOFs is highly desirable because of the anticipated lower regeneration energy demand. All materials prepared represent good stability during six consecutive carbon dioxide capturing cycles. Amongst all materials studied here, Cu-BDC⊃HMTA showed least cost per mole carbon dioxide capture i.e., $ 9.05 and showed only 1% carbon dioxide capture tendency loss over six capture cycles. Not only low chemical cost, there was ease of amine group incorporation in Cu-BDC⊃HMTA MOF material. Using HMTA in commercial MOFs preparation as a cheap additive, would serve as a low-cost alternative to expensive amine-based ligands that are often custom-built to make MOFs for carbon dioxide capture.