Design of functionalized covalent-organic framework materials for utilization of carbon dioxide

Abstract

The rising carbon dioxide (CO2) concentrations in the atmosphere contribute to various environmental issues, including extreme weather, climate change, and global warming. As a result, it is essential to control growing CO2 levels by utilizing it as a C1 feedstock for generating value-added chemicals and fuels. However, the functionalization of CO2 under ambient conditions is challenging due to its high kinetic inertness and thermodynamic stability. Consequently, it is extremely desirable to synthesize effective catalysts capable of selectively capturing CO2 and converting it into commodity chemicals. However, to accomplish efficient chemical fixation of CO2, most catalysts require high temperatures and pressure conditions. On the other hand, green and sustainable chemistry practices prefer recyclable catalysts capable of transforming CO2 into value-added chemicals under eco-friendly mild conditions. In this context, covalent organic frameworks (COFs), a new family of porous organic polymers, have sparked widespread interest among researchers due to their modular nature facilitating the introduction of CO2-philic and catalytic sites. Motivated by the potential uses of COFs in the chemical fixation of CO2 to value-added chemicals, we sought to develop various functionalized frameworks suitable for environmentally friendly chemical fixation of CO2 into high-value compounds. The thesis work has been organized into five chapters. Chapter 1 presents importance of carbon capture utilization (CCU) and various strategies for converting CO2 into high-value chemicals or fuels. The advantages of COF-based materials in CO2 capture and utilization are also discussed. Thus, motivated by CO2 conversion to value-added chemicals to mitigate rising CO2 concentrations, we intend to develop functionalized COFs for effective CCU. In this context, Chapter 2 involves the rational construction of a polar functionalized COF with Brønsted acidic (-SO3H) sites decorated in the 1D channels and its investigation for metal/solvent-free cycloaddition of epoxide with CO2 to generate cyclic carbonates (CCs) under mild conditions. Further, the role of Brønsted acidic sites on the catalytic conversion of CO2 has been ascertained by utilizing a COF-H, which lacks acidic sites. In Chapter 3, synthesis of a highly CO2-phillic and thermally stable covalent triazine framework (bipy-CTF) and its functionalization to anchor non-noble metal Cu(I) for fixation of CO2 from dilute gas into value-added α-alkylidine cyclic carbonate (α-aCC) under mild conditions has been studied. Furthermore, considering the potential benefits of porphyrin-based linkers in selective CO2 capture and conversion, in Chapter 4, we developed Fe(III)-embedded porphyrin-based COF (P-COF) and its catalytic performance for one-pot synthesis of styrene carbonates (SCs) from readily available styrene and CO2 under ambient conditions. In Chapter 5, the application of silver nanoparticles (Ag NPs) anchored pyrene-based COF for carboxylation of terminal alkynes with CO2 to produce value-added alkynyl carboxylic acids via C-H bond functionalization and carboxylative cyclization of propargylic amines to generate bio-active oxazolidinones under atmospheric conditions is presented. Overall, the thesis work involves the rational synthesis and functionalization of porous covalent organic framework materials with CO2-philic and catalytic sites ideal for environmentally friendly chemical fixation of carbon dioxide, a greenhouse gas, into various value-added chemicals.