### Carbon-Containing Functional Composites Based on Graphene
Graphene can be considered a molecule that can be chemically modified to obtain a new material with different chemical compositions and interesting properties [52,53]. Depending on the environment, the electronic configuration of the carbon atom (which has four valence electrons) can change significantly, allowing it to bond with other atoms. The combination of carbon atoms with oxygen forms graphene oxide (GO), which can be characterized as a single monolayer of graphite with randomly distributed sp\({}^{2}\) and sp\({}^{3}\) regions containing hydroxyl (-OH), epoxy (=O), carbonyl (-C=O), and carboxyl (-COOH) functional groups. The chemical composition and heterogeneity of GO are still widely discussed [52,54] (Figure 4). The optical, electrical, and mechanical properties of graphene are ideal for creating micro- and nanomechanical systems, transparent and conductive electrodes, and photonics. The chemical modification of graphene leads to materials with a wide range of functional properties, which depend on the type of modification and the degree of functionalization [55]. The synthesis of graphene and chemically modified graphene with various degrees of functionalization makes it possible to create a wide range of new materials that can be used in the rapidly developing field of printed electronics [25,26]. Next, we consider the features of using carbon compounds to obtain structural composite materials without considering graphene, which is practically not used in the production of structural materials. Figure 4: Structure of GO [54]. Figure 3: Layer-by-layer formation of a heterostructure based on graphene and other two-dimensional materials. Adapted by permission from Springer Nature [20], copyright © 2022. Carbon Nanotubes and Nanofibers Are Promising Solids for the Preparation of Structural Composite Materials with a Metal Matrix  
Currently, CNFs and CNTs are attracting a lot of attention not only because of their structural features and unique physical and mechanical properties but also because of their potential technological applications. The use of CNFs and CNTs can be divided into two groups: (i) the first group includes materials using ensembles of carbon nanostructures, such as composite materials (where CNTs and CNFs are used as reinforcing elements), materials for chemical power sources, adsorbents, catalysts, etc. Note that composites containing CNT/CNF have better mechanical properties [6]; (ii) the second group includes materials using individual CNTs due to their high mechanical and electrical properties [7]. CNTs and CNFs can be used to produce both structural and electrically conductive composites [55]. Due to their unique physical and chemical properties, even small additions of CNTs and CNFs to various materials can significantly improve their mechanical and electrical characteristics. Since the 1990s, works have been published suggesting the introduction of carbon nanostructures into a metal matrix in order to strengthen it, which has significantly improved the properties of composite materials and expanded their scope [56; 57; 58; 59; 60; 61; 62; 63; 64]. Theoretical and experimental studies of the mechanical properties of single-walled carbon nanotubes (SWCNTs) are described in many works [5; 62; 65; 66]. The value of the elasticity modulus of SWCNTs and double-walled CNTs (DWCNTs) has a wide range, from 80 to 140 and 140 to 190 GPa, respectively (Figure 5) [67]. Subsequently, the mechanical properties of CNTs were repeatedly confirmed [68]. Destruction experiments were carried out on SWCNT bundles [65]. The average tensile strength was 30 GPa with a range of values from 13 to 50 GPa. It was found that the load led to bundle separation, while the inner tubes of the bundle did not collapse but slipped relative to the outer tubes, which were subjected to destruction. In the case of MWCNTs, it was found that the elastic modulus average value of \(\sim\)1200 GPa [69]. The strength parameters varied from 20 to 90 GPa [70].