# Polymeric and Crystalline Materials for Effective and Sustainable CO\({}_{2}\) Capture
## 4 Biobased Polymers
studied the CO\({}_{2}\) capture of palm shell activated chemically by ZnCl\({}_{2}\) leading to an uptake of 17.44 mmol g\({}^{-1}\) at 272.85 K at 20 bars [200]. Plastic waste can also offer opportunities as starting materials for CO\({}_{2}\) capture. A recent review from [PERSON] and coworkers highlighted the main utilization of commodity plastics for the preparation of functional materials for CO\({}_{2}\) capture [201]. One of those, polystyrene (PS), is a versatile material for creating polymeric adsorbents due to the susceptibility of its aromatic groups to electrophilic functionalization: its \(\pi\)-electron-rich phenyl groups enable induced-dipole interactions with CO\({}_{2}\) molecules. Hypercrosslinked polymers (HCPs),  
Figure 11: Bio-based polymers for CO\({}_{2}\) capture [183, 184, 185, 186, 187]. synthesized via Friedel-Crafts alkylation from waste-expanded polystyrene (EPS) with crosslinkers, like carbon tetrachloride, exhibited high CO2 adsorption capacity and selectivity. For instance, [PERSON] and coworkers reported the preparation of an HCP PS network by using a Friedel-Craft approach (dichloroethane, AlCl3) leading to a CO2 capture capacity of 1.987 mmol g\({}^{-1}\) at 273 K and 1.13 bars [185] (Figure 11). Hybrid HCPs, combining commercial PS with an octavinylsilesquisoxane (OVS) crosslinker, demonstrated tunable porosity and a CO2 uptake of 1.12 mmol g\({}^{-1}\) at 298K and 1.01 bars [202]. The latter were obtained by Friedel-Craft reaction between PS and OVS in the presence of AlCl3. Another example showcases a two-step synthesis involving the nitration of PS to give polynitrostyrene followed by a reduction in HCl/Sn condition to furnish PSNH2 polymer as reported by [PERSON] et al. [203]. The PSNH2 polymer showed a CO2 uptake of 1.05 mmol g\({}^{-1}\) at 273 K and 1 bar. At last, functionalizing chloromethylated PS with 2,6-bis-imidazo-1-yl-pyridine-4-carboxylic acid and imidazole at high temperature (403 K), led to the formation of the PS-BIMP polymer [186] (Figure 11). In addition to polystyrene (PS), waste polyvinyl chlorides (PVCs) are also a viable source for developing polymeric adsorbents for carbon capture and utilization (CCU) [201]. In this regard, [PERSON] et al. synthesized PVC-based/silica composites by introducing the aminated PVCs on mesoporous silica [204]. The ethylenediamine-treated PVC/SBA-15 composite exhibited an adsorption efficiency of 0.5 mmol g\({}^{-1}\) at 298 K. Moreover, these composites demonstrate increased hydrophobicity, indicating suitability for operation under humid conditions without deactivation by moisture. Beyond CO2 capture, recent research shows the potential of PVC for CO2 reduction and simultaneous dechlorination [205]. In a simulated aqueous environment containing HCO3\({}^{-}\) to replicate captured CO2 in an alkaline solution, polyvinyl chloride (PVC) demonstrated the capability to efficiently convert hydrogen carbonate into formate at 300 \({}^{\circ}\)C. The mechanistic studies suggest that PVC experiences dedchlorination and actively engages in redox reactions, leading to an impressive formate conversion of up to 16% and an almost complete dedchlorination efficiency nearing 100%. At last, polyethylene terephthalate (PET) is commonly utilized to produce activated carbon adsorbents due to the well-established infrastructure for recycling PET drink bottles. PET's high carbon content allows effective carbonization, and the presence of oxygen atoms creates polar sites in the resulting porous carbon materials, facilitating CO2 physisorption. Activation with potassium hydroxide (KOH) is necessary to generate micro and mesopores in PET for efficient CO2 adsorption at ambient conditions [206]. The activation process involves PET decomposition at a high temperature, releasing CO2 and CO, which then react with KOH to form K2 CO3. This compound further reacts with carbon precursors, enlarging the pores and improving CO2 binding by introducing oxygen-containing groups.