# Polymeric and Crystalline Materials for Effective and Sustainable CO\({}_{2}\) Capture
## 2 Background
### MOFs, ZIFs, and Other Crystalline Materials for CO\({}_{2}\) Capture
It consists of zinc ions coordinated with benzene-1,4-dicarboxylate (BDC) linkers; HKUST-1 (also known as Cu-BTC) [76] is composed of copper ions coordinated with benzene-1,3,5-tricarboxylate (BTC) linkers; MIL-101 is a family of MOFs with various metal ions (e.g., aluminum, chromium, iron) coordinated with terephthalatic acid linkers, characterized by an exceptional porosity [77]; ZIF-8 is composed of zinc ions coordinated with imidazolate linkers, characterized by an excellent chemical stability and intensely studied in cancer-treatment therapy [78; 79]; MOF-74 consists of metal ions (e.g., magnesium, zinc) coordinated with 2,5-dihydroxyerephthalatic acid linkers, characterized by an exceptional CO\({}_{2}\) adsorption capacity [80; 81]; Ui-66 is composed of zirconium ions coordinated with terephthalatic acid linkers [82]; MOF-177 is constructed from octahedral Zn\({}_{4}\)O(-COO)\({}_{6}\) and triangular 1,3,5-benzetribenzoate (BTB), which possesses an exceptionally large pore size for microporous MOFs up to 1.8 nm [83]. MOF's pore surfaces can be readily fine-tuned to provide a highly selective bonding of CO\({}_{2}\)[84]. However, some MOFs were found to be unstable at high temperatures, under moisture conditions, or unable to meet industrial standards. A discussion on the subject was reported by [PERSON] et al., in which they reviewed the performances of a variety of microporous MOFs for CO\({}_{2}\) capture and separation while emphasizing the most important role in the CO\({}_{2}\) capture: capacity, selectivity, and regeneration [84]. Some of the novel trends for the chemistry of MOFs include the post-synthetic modifications, such as metal ions [85], ligand exchange [86], the introduction of novel functional groups [87], and surface functionalization with polymers [88] or nanoparticles to enhance the adsorption capacity of CO\({}_{2}\). [PERSON] and colleagues obtained MOFs with exceptional porosities and gas (hydrogen, methane, and carbon dioxide) uptake capacities using the concept of crystalline structure extension via the addition of secondary organic links [89]. These impressive materials demonstrated Brunauer-Emmett-Teller and Langmuir surface areas of up to 10,400 square meters per gram, the highest reported for crystalline materials, and a total carbon dioxide storage capacity of 2870 milligrams per gram (65 mmol CO\({}_{2}\) per gram of sorbent) at 50-60 bars. For the capture of CO\({}_{2}\) at atmospheric pressure, the best performance belongs to another MOF, namely TMU-42 {[Zn\({}_{2}\)(fum)\({}_{2}\)(4-bpdb)] :2H\({}_{2}\)O]n (fum = fumarate; 4-bpdb = 1,4-bis(4-pyridyl)-3,4-diaza-1,3-butadiene), which demonstrated an uptake of 320 milligrams per gram (7.29 mmol CO\({}_{2}\) per gram of sorbent) [90]. With the advancement in the synthesis of water and thermally stable MOF structures, some industrial-scale projects have recently emerged. The project titled MOF4 AIR is a European Commission's four-year initiative in the frame of the Horizon 2020 program, gathering 14 partners from 8 countries to develop and demonstrate the performances of MOF-based CO\({}_{2}\) capture technologies in power plants and energy-intensive industries, with a total budget of over EUR 11.1 M [91]. MOF4 AIR stands for metal-organic frameworks for carbon dioxide adsorption processes in power production and energy-intensive industries. Zeolites and zeolitic imidazolate frameworks (ZIFs) represent another important class of CO\({}_{2}\) adsorbents [64; 93; 94]. These two classes of porous materials share several common characteristics, such as a porous structure, high surface area, tunable pore size, high crystallinity, and the possibility to be functionalized via the surface and in-bulk modification [95]. While zeolites are crystalline aluminosilicate minerals that can be synthesized through hydrothermal or solvothermal methods [96], ZIFs belong to the class of MOFs composed of metal ions or clusters coordinated with imidazolate ligands and can be synthesized through hydrothermal, mechanochemical, or solvothermal methods [97].