Reactivity and mechanistic insights into multistep silane functionalization of oxo-graphene

Oxo-graphene (oxoG), an alternative form of graphene oxide with a low number of defects, is regarded as a versatile platform for covalent surface modification due to its abundant oxygen functional groups and a large surface area. Among the different functionalization strategies, epoxide ring opening is widely employed. However, reactions using bifunctional molecules like 3-aminopropyltriethoxysilane (APTES) often produce unpredictable outcomes, jeopardizing the characterization and hampering a clear identification of the chemical structure of the resulting conjugate. Here, we investigate the functionalization of oxoG with APTES in different solvents, providing unequivocal evidence that the amine group preferentially reacts via epoxide ring opening. The resulting oxoG-APTES was characterized using X-ray photoelectron spectroscopy and thermogravimetric analysis. Subsequent silanization with (3-glycidyloxypropyl)trimethoxysilane (GPTMS) confirmed the presence of terminal silane groups, and further nucleophilic ring-opening with 4-(trifluoromethyl)benzylamine (FMBA) validated the stepwise covalent modification. Simplified molecular model reactions analyzed via¹H NMR corroborated these findings and highlighted the critical influence of solvent and temperature on the outcomes of multistep reactions. This study provides a detailed mechanistic understanding of oxoG functionalization using silanes and demonstrates the importance of combining complementary analytical techniques to unambiguously characterize the different conjugates, enabling more predictable design of graphene-based nanomaterials for advanced applications.