The present work investigated surface modification of activated carbon (CSC). The surface functionalization compromised solvothermal oxidation, plasma oxidation, reduction with lithium aluminium hydride (LiAlH4), silanization using 3-(aminopropyl)trimethoxysilane (APTMS), (3-glycidoxypropyl)trimethoxysilane (GPTMS), (3-mercaptopropyl)trimethoxysilane (SHMS) and 3-(trichlorosyiyl)propyl methacrylate (M-Cl), and the direct coupling of 4-fluorophenylhydrazine (FNP) and phenylhydrazine (BNP) onto oxidized surfaces. For the production of the functionalized CSCs, the first step included oxidation of the carbon via solvothermal and plasma-assisted oxidation with Ar and O2. In contrast to the standard surface modification methods, solvothermal and plasma-assisted oxidation are novel approaches for surface pre-activation in the functionalization of carbon materials. In general, it is demonstrated that solvothermal oxidation is shown to be a novel strategy that prioritises safety while handling, constant heating and stirring, and the prevention of solvent loss during the reaction period. The plasma-assisted oxidation process has the advantage of taking less time and the possibility to optimize the parameters of the process to minimise the hydrophobic recovery of the material. This refers to the preservation of the amount of oxygen units generated on the carbon surface maintained over a longer period. The following surface functionalisation was performed in two separate ways. The first experiment used LiAlH4 to obtain more hydroxyl groups (-OH) required for the reaction of coupling between inorganic carbon and organosilanes (APTMS, GPTMS, SHMS and M-Cl). In the second experiment, hydrazines are employed as coupling agents on carbonyl-rich surfaces produced by wet oxidation processes. An ultimate goal was to utilise organosilane-functionalized (APTMS and GPTMS) functionalized carbons. Therefore, a bisphenol A diglycidyl ether was added to the functionalized carbons to determine the lowest amount required to produce stable composites. The mechanical properties of the carbon/epoxy composites were analysed using the three-point bending test.