_Applied_  
_sciences_  
_Article_  
**Understanding the Adsorption Capacity for CO2 in Reduced Graphene Oxide (rGO) and Modified Ones with Different Heteroatoms in Relation to Surface and Textural Characteristics**  
**[PERSON] 1,\({}^{\star}\), [PERSON] 2\({}^{\copyright}\) and [PERSON] 1,3**  
Footnote 11:  
non-combustion processes, including cement production. CO\({}_{2}\) has the most significant share in these emissions with a 72%, followed by CH\({}_{4}\) (19%), N\({}_{2}\)O (6%), and F-gases (3%). The five largest emitters of these gasses are responsible for 62% of the emissions globally. From these emitters, China has the largest share (26%), followed by the United States (13%), the European Union (more than 8%), India (7%), and the Russian Federation (5%) [5]. In 2018, an actual increase in greenhouse gasses emissions was shown in four of these countries: China (+1.9%), India (+5.5%), the United States (+2.7%), and the Russian Federation (+5.1%), whereas emissions somewhat decreased in the European Union (\(-1.5\%\)) [5]. CO\({}_{2}\) must be reduced, and currently, technologies and materials for capture CO\({}_{2}\) effectively should be improved. For the capture of CO\({}_{2}\), nowadays, there are several technologies available, such as solvent absorption, physical adsorption, membrane separation, cryogenic fractionation, and chemical looping. However, the lack of state-of-the-art materials with high performance and low costs of production prevents their full exploitation for CO\({}_{2}\) capture. The solid adsorbents are a unique category that can be used in adsorption-based technologies. A different class of porous solid sorbents is investigated. Some of them are already in practical application, as is the case with silica, zeolites, MOFs, mesoporous material, metal decorated phosphorene, nanostructured copolymer, and ionic liquids [6; 7]. Due to some limitations (not to be discussed in this manuscript), the abovementioned have not shown the best results, and research should focus on new ones with the idea of easiness in scale-up [8]. In the family of solid adsorbents, carbon-based materials (graphene, nanotubes, activated carbon, activated carbon fibers, and carbon spheres) are considered appropriate for CO\({}_{2}\) capture due to their high stability in cycle operation [8; 9]. Due to excellent characteristics (thermal and mechanical stability and the most important high surface area). Moreover, graphene can be prepared in a monolithic appearance that can help the adsorption due to a significant increase in the amount of active material per projected area and easiness of manipulation. The preparation of modified monolithic materials based on graphene oxide could improve their properties, including the adsorption capacity, selectivity, and stability in cycle operation. [8; 9]. Generally, graphene oxide can be functionalized covalently (carbon skeleton, hydroxyl, and carboxyl functionalization), non-covalently (p-p bond interaction, hydrogen bond interaction, ion interaction, and electrostatic interaction), and element doping [10]. Surface modifications have been performed using 12-molybdenum acid [11], polymer brushes [12], amine (-NH\({}_{2}\)) functionality (aliphatic and aromatic amines, amino acids, amine-terminated biomolecules, ionic liquids, small molecular weight polymers, and silane compounds) [13], diethylenetriamine [14], lysine [15], catecholamine reagent [16], and citric acid [17]. Reduced graphene oxide (rGO) 3D materials have been modified either with functional groups or elements. The majority of the modification reactions are based on the introduction of the N in the structure. Some of these examples are based on ethylenediamine, diethylenetriamine, triethylenetetramine (showing CO\({}_{2}\) adsorption of 2.0 mmol/g at 1 bar and 298 K [18], with urea (CO\({}_{2}\) adsorption at atmospheric pressure, and 25 \({}^{\circ}\)C of 2.40 mmol/g) [19], with hydrazine during reduction (for supercapacitors) [20] and ethylenediamine (1.1 mmol/g of CO\({}_{2}\) adsorption) [21].