# Polymeric and Crystalline Materials for Effective and Sustainable CO\({}_{2}\) Capture
## 4 Biobased Polymers  
Bioderived polymers and their related compounds offer abundant and sustainable options for CO2 fixation, chemisorption, and physiosorption [175; 176; 177]. Biobased polymers are defined as a type of polymer derived from renewable biological sources, such as plants, animals, or microorganisms, rather than from fossil fuels. These polymers can either be biodegradable or non-biodegradable. They are characterized by their low carbon dioxide footprint and are associated with sustainable practices [178]. For instance, the polysaccharide alongside polynucleotides and polypeptides, are the most prevalent naturally occurring biopolymer [179]. They are constituted of sugar monomers bound together by O-glycosidic bonds. By utilizing a catalytic system (i.e., DBU), epoxides, together with CO2, can be efficiently converted into cyclic carbonates, demonstrating high conversions and selectivity. As described in the upcoming paragraphs, biomass can be employed adequately to enhance the capture of CO2 [180] and its subsequent conversion into valuable compounds [181]. In their review, [PERSON] and coworkers detailed a variety of activated carbons such as cherry stones, corncob, cotton pulp, and wheat straw to name a few, with their corresponding adsorption data [182]. [PERSON] et al. reported the preparation of a bio-based polybenzoxazine through carbonization and activation [183]. Starting from paraformaldehyde, fufurylamine, and 4,4'-thiobisphenol, a TBP-fa intermediate was obtained. The latter was then cured at a high temperature (230 \({}^{\circ}\)C) followed by carbonization at 500 \({}^{\circ}\)C. The obtained material was finally activated at 800 \({}^{\circ}\)C in the presence of KOH to give a series of NSOPC derivatives (Figure 11). Among them, the NSOPC-1 derivative showed a CO2 uptake of 3.88 mmol g\({}^{-1}\) at 1 bar and 298 K.  
A fully bio-based epoxy thermoset (HMF-GU-Ep/DFA) has been reported as an efficient CO2 capture adsorbent by [PERSON] and coworkers [184] (Figure 11). They prepared the epoxy resin by curing 5-hydroxymethyl-2-furaldehyde-3, 5-diamino-1,2,4-triazole with 5,5'-methylenedifurfurylamine. They were able to reach a CO2 uptake of 2.15 mmol g\({}^{-1}\) at 298 K. Interestingly, the obtained epoxy thermoset was also effective as a flame retardant agent. Figure 10: Structures of several ionic polymers [170; 172; 173; 174]. Aerogels made from sustainable materials like starch, cellulose, alginate, chitosan, and lignin have also been used for CO\({}_{2}\) capture due to their high porosity [189]. For instance, maximum CO\({}_{2}\) adsorption has been reported for a series of cellulose-based aerogel composites such as cellulose-crosslinked polyethyleneenimine (2.32 mmol g\({}^{-1}\)) [190], cellulose-derived porous carbon (0.257 mmol g\({}^{-1}\)) [191], cellulose nanofibril grafted with amino silane (1.91 mmol g\({}^{-1}\)) [192], and cellulose silica composites (3.68 mmol g\({}^{-1}\)) [193]. The utilization of bio-based sorbents has retained attention as a cost-effective alternative to more traditional sorbents such as zeolite 13X [194, 195]. First, biomass waste materials are typically carbonized (600 \({}^{\circ}\)C) under an inert atmosphere. Then, activation is carried out by chemical means (alkaline or acid solution), physical activation (steam or other gases at 800 \({}^{\circ}\)C), or a self-activation technique (i.e., utilization of the gases evolved during the carbonization phase as activating agents) [196, 197]. For example, [PERSON] and coworkers have reported the use of coconut shell chars activated with a thermal annealing step at 450 \({}^{\circ}\)C, leading to a CO\({}_{2}\) adsorption of 3.60 mmol g\({}^{-1}\) at a temperature of 272.85 K at 2.5 bars [198]. Similarly, cherry stones were used as bio-based sorbent through a physical activation method (steam) giving a CO\({}_{2}\) uptake of 2.50 mmol g\({}^{-1}\) at 322.85 K at 2.5 bars [199]. At last, [PERSON] et al.