Design and synthesis of carbonaceous porous organic polymers for environmental applications

Abstract

In recent years, carbonaceous porous polymers have attracted significant interest due to their wide range of applications such as gas storage, drug delivery, catalysts, sensors, precursors of nanostructured carbon materials, and electrode materials for energy storage. Such wide applications have been possible due to the potential of carbonaceous porous organic polymers to converge the unique properties of both porous polymers and carbon materials. The unique properties include not only permanent porosity and high surface area, but also exceptional physicochemical and thermal stability and low density. Up to recently, various types of carbonaceous porous polymers have been synthesized using the diverse synthetic routes available. However, the incorporation of $sp^2-hybridized$ large aromatic groups have been challenging since they have low solubility as a monomer and tend to irreversibly aggregate into graphite-like structure. Although $sp^2-hybridized$ carbons have several exciting properties such as electrical and thermal conductivity, it has been challenging to introduce these into porous polymers. In order to address the solubility and stacking problems, I introduced a two-step bottom-up synthetic strategy

(1) direct polymerization reaction and (2) cyclodehydrogenation or cyclodeoxygenation reaction. Bottom-up synthetic approach allows the successful incorporation of $sp^2-hybridized$ extended aromatics within carbonaceous porous polymers and also, introduces chemical functionalities for the target applications. The dimensions and hybridization of carbonaceous porous polymers can be tailored by controlling combination of monomers and polymerization methods. In this dissertation, through bottom-up synthetic approach, carbonaceous porous polymers with various dimensions (2D or 3D), hybridizations ($sp^2-sp^3 or sp^2-sp^2$) and functional groups (H, OMe, $CF_3$, F or triazine) have been designed, synthesized, and characterized. In Chapter 2, bottom-up approach was utilized for the synthesis of Graphene Nanoribbon Frameworks (GNFs) and introduced an efficient, catalyst-free, low-cost C-C polymerization reaction, that is the Diels-Alder cycloaddition reaction between dicyclopentanedienone and areylacetylene derivative, followed by FeCl3-catalyzed intramolecular cyclodehydrogenation reaction for the preparation of these new-class of nanoporous polymers, incorporating GNRs up to ~2 nm in length and ~1.1 nm in width, that is being the largest aromatic subunit incorporated into nanoporous polymers to date. $sp^2-hybridized$ GNRs were successfully separated by permanent pores using sp3-hybridized carbon ‘spacer’, namely, tetraphenylmethane. In Chapter 3, functional groups are introduced into Graphene Nanoribbon Frameworks, namely, GNF-0, GNF-1, GNF-2, and GNF-3 (OMe, H, $CF_3$, and F, respectively). All GNFs were found to be extremely stable up to $400\circ C$ in air and exhibited high surface area up to $755 m^2 g^{-1}$. The ultra-micropores (~0.6 $\AA$) and large \pi-surface area resulting from graphene nanoribbons led to high affinity towards gases such as $CO_2$ (27.4-30.9 kJ $mol^{-1}$ at 1 bar), $CH_4$ (21.3-26.0 kJ $mol^{-1}$ at 1 bar), and $H_2$ (6.5-8.2 kJ $mol^{-1}$ at 1 bar). Moreover, GNFs showed promising $CO_2/CH_4$ breakthrough separation performance for natural gas sweetening and landfill gas separations. GNF-2 and GNF-3 substituted with $CF_3$ and F groups showed high affinity towards perfluorocarbons and chlorofluorocarbons, which are classified as ozone-depleting substances, showing its viability in CFCs uptake as a low-cost, efficient solid-sorbents. Chapter 4 focuses on the synthesis of graphene nanoribbon-incorporated covalent triazine framework (gCTF-1), which has nitrogen atom substituted within 2D $sp^2-sp^2$ hybridized network. The synthetic techniques involve two steps, namely, $ZnCl_2$-catalyzed ionothermal reaction and $FeCl_3$-catalyzed cyclodehydrogenation reaction. Incorporation of extended $\pi-conjugation$ and nitrogen-rich triazine rings showed potential as a catalyst for hydrogen evolution reaction. The oneset potential of gCTF-1 was found to be -410 mV with corresponding overpotential of 640 mV. Lastly chapter 5 develops fully-conjugated 3D carbon network (FCN-1), composed of fully $sp^2-hybridized$ carbons in 3D porous network. The synthetic techniques involve two steps

(1) the Diels-Alder polymerization and (2) acid-catalyzed cyclodeoxygenation reaction. The extension of incorporating $sp^2-hybridized$ carbon into three-dimensional networks can offer almost limitless structural possibilities.