# Carbon Spheres as CO\({}_{2}\) Sorbents
## 1 Introduction  
The global economy requires a great amount of energy, which is produced primarily by the combustion of fossil fuels. Carbon dioxide emissions are a significant negative side-effect of this activity. Transportation also requires a great amount of petroleum and is responsible for significant emissions of greenhouse gases [1, 2]. The cumulative emission of CO\({}_{2}\) strongly contributes to climate change and is the greatest single contributor to the greenhouse effect [3, 4]. The average concentration of CO\({}_{2}\) in the earth's atmosphere in 2018 was 407 ppm, which is about 40% higher than in the preindustrial age [5]. The effort to develop technologies that will reduce CO\({}_{2}\) emissions is very important for both the global economy and the environment. Recently, methods of CO\({}_{2}\) capture from flue gas have been based on absorption into liquids (e.g., amines [6] or methanol [7]). These technologies are energy intensive and not environmentally sound. Solid sorbents offer an alternative solution. There are a number of criteria that must be met for a successful sorbent material, namely: high selectivity and adsorption capacity for CO\({}_{2}\), fast adsorption/desorption kinetics, efficient regeneration of sorbents, and low cost [8]. In recent years, a number of materials have been investigated as solid state adsorbents for CO\({}_{2}\), such as: zeolites [9], silica [10], porous polymer materials [11], metal organic frameworks [12], and carbon materials [13, 14, 15, 16]. The most efficient for CO\({}_{2}\) adsorption are carbon materials, which exhibit a high surface area, large porous volume, chemical stability, affinity for carbon dioxide, low cost, and the possibility of modification with heteroatoms [17]. The weak side of carbon sorbents is their poor selectivity. The application of carbon materials for CO\({}_{2}\) uptake has been widely investigated. There are many sources of carbon that can be used for the production of activated carbon: polymers, biomass, or resins. Some examples are shown in Table 1. Potassium compounds, namely potassium hydroxide or potassium oxalate, are most often used as chemical activators. Special attention should be paid to resins. Gradual growth of the polymer chain allows incorporating modificators into the carbonmatrix. Homogeneously distributed activator can improve not only the surface area of the material (impregnation), but its whole volume. A resorcinol-formaldehyde resin mixture could be a suitable carbon source for CO\({}_{2}\) adsorption. According to the results presented in Table 1, resins are very promising as a carbon source to produce solid sorbents for carbon dioxide capture. Among nanocarbon materials, spherical structures have been widely studied. The most popular method to obtain porous nanocarbon spheres is the method of Stober, using resins as a carbon source. The application of this method to produce carbon spheres was described in the work of [PERSON] et al. [26], where the source of carbon was a resorcinol-formaldehyde resin. Thanks to the development of the Stober method, researchers discovered a simple method to produce polymer beads. The product was in the form of spherical regular particles. Since then, the phenol derivatives were widely used as a carbon source [27; 28]. In work by [PERSON] and co-workers [28], using 3-aminophenol as a precursor, highly monodisperse material were obtained. They also proved that changing different parameters allowed for tuning spherical size in a very broad range. To enhance the surface area and porous volume, various processes of activation are employed, with two primary methods to activate carbon materials. First, physical activation carried out through carbonization in the presence of proper gases [29]. Second, chemical activation is induced by the addition of a strong base, i.e., potassium oxalate [19], potassium hydroxide [20; 30; 31], and potassium carbonate [32]. In the work of [PERSON] et al.