Precision Covalent Chemistry for Fine-Size Tuning of Sandwiched Nanoparticles between Graphene Nanoplatelets.

The covalent functionalization of graphene for enhancing their stability, improving their electrical or optical properties, or creating hybrid structures has continued to attract extensive attention; however, a fine control of nanoparticle (NP) size between graphene layers via covalent-bridging chemistry has not yet been explored. Herein, precision covalent chemistry-assisted sandwiching of ultrasmall gold nanoparticles (US-AuNP) between graphene layers is described for the first time. Covalently interconnected graphene (CIG) nanoscaffolds with a preadjusted finely tuned graphene layer-layer distance facilitated the formation of sandwiched US-AuNPs (∼1.94 ± 0.20 nm, 422 AuNPs). The elemental composition analysis by X-ray photoelectron spectroscopy displayed an aniline group addition per ∼55 graphene carbon atoms. It provided information on covalent interconnection via amidic linkages, while Raman spectroscopy offered evidence of covalent surface functionalization and the number of graphene layers (≤2-3 layers). High-resolution transmission electron microscopy images indicated a layer-layer distance of 2.04 nm, and low-angle X-ray diffraction peaks (2θ at 24.8 and 12.5°) supported a layer-layer distance increase compared to the characteristic (002) reflection (2θ at 26.5°). Combining covalent bridging with NP synthesis may provide precise control over the metal/metal oxide NP size and arrangement between 2D layered materials, unlocking new possibilities for advanced applications in energy storage, electrochemical shielding, and membranes.