# Polymeric and Crystalline Materials for Effective and Sustainable CO\({}_{2}\) Capture
## 2 Background  
### General Principals of Carbon Dioxide (CO\({}_{2}\)) Capture and Sequestration  
To mitigate CO\({}_{2}\) accumulation in the atmosphere, its capture and sequestration are among the suggested techniques. They can be divided into three main processes: (1) capture, (2) transport, and (3) sequestration. The capture step is the most costly process and thus poses a serious challenge to the reduction of its operational costs. Indeed, several studies have suggested that CO\({}_{2}\) capture alone can contribute up to 75% of the overall capture and sequestration cost [18]. In particular, this step involves capturing CO\({}_{2}\) from industrial process emissions before they are released into the atmosphere. Various technologies are employed for carbon capture, including post-combustion capture, pre-combustion capture, and oxyfuel combustion [19; 20]. Among them, the most widely used is post-combustion capture due to its flexibility and ease of retrofitting to existing industrial processes, such as power plants and cement factories. It involves removing CO\({}_{2}\) from blue gases emitted during combustion processes using sorbents or solvents. Pre-combustion capture involves capturing CO\({}_{2}\) from the gasified feedstock or fuel before combustion occurs. Oxy-fuel combustion involves burning fuel in a mixture of oxygen and recycled blue gas, resulting in a concentrated stream of CO\({}_{2}\) that is easier to capture. Another novel alternative, namely chemical looping combustion, recently attracted interest because the use of a solid oxygen carrier (typically a transition metal oxide) provides the oxygen needed for combustion. This technique helps to avoid diluting the combustion effluent stream with the N\({}_{2}\) released from the air and, therefore, minimizes the requirement of CO\({}_{2}\) separation, a major cost of CO\({}_{2}\) capture [21]. While post-combustion capture is currently the most used method, ongoing research and development efforts are focused on improving all four capture technologies to make them more cost-effective, energy-efficient, and applicable to a wider range of industrial processes. As for sequestration, viable storage sites for technology encompass depleted gas fields, oceans, and saline aquifers [22]. However, it is important to point out that these locations require a geological stratum with a high impermeability to avert CO\({}_{2}\) leakage from the storage cluster [23]. Despite the significant progress in capture and sequestration, fundamental constraints endure. For instance, struggles with high energy consumption, suboptimal capture efficiency, and slow adsorption kinetics, the stability and longevity of storage sites, as well as safety concerns (i.e., leakage from storage sites) are the main barriers to overcome [4; 24]. Once captured, the CO\({}_{2}\) can be converted into valuable products through chemical, biological, or electrochemical processes. Carbon utilization pathways include the production of chemicals, fuels, building materials. Examples of carbon utilization technologies include the conversion of CO\({}_{2}\) into methane (methanation); the synthesis of chemicals such as methanol, ethylene oxide, or formic acid; the production of polymers and plastics; and the mineralization of CO\({}_{2}\) into inorganic carbonates for use in construction materials. CCU (carbon capture and utilization) offers several potential benefits, including carbon emission reduction, resource conservation, an important economic opportunity by generating revenue from the sale of carbon-derived products, diminution of the costs associated with carbon capture and storage (CCS), and waste reduction. In this regard,various large-scale multinational projects have been developed recently, including the CO2 EXIDE project, which was granted in 2018 by the European Commission in the frame of the Horizon 2020 program.