Transformation of Freestanding Carbon-Containing Gold Nanosheets into Au Nanoparticles Encapsulated within Amorphous Carbon: Implications for Surface Modification of Complex-Shaped Materials and Structures

Freestanding metallic nanosheets (or 2D metals) have been attracting tremendous research interest because of their potential applications in numerous important fields, such as green energy, biomedical imaging, and nanodevices. However, thermal stability of 2D metals received much less attention and remains as an open issue to resolve. Here, we report the first synthesis of large-area freestanding carbon-containing gold nanosheets by polymer surface buckling-enabled exfoliation (PSBEE). Through a systematic study based on flash differential scanning calorimetry, we find that such 2D nanosheets tend to fragment upon heating, which are eventually transformed into nanoparticles of different sizes. Inspired by this interesting finding, we develop a facile method that enables scalable production of crystalline Au nanoparticles encapsulated with amorphous C by isothermally annealing the carbon-containing gold nanosheets. Compared to the traditional methods for the synthesis and deployment of nanoparticles, our nanosheet-based fabrication method is flexible and highly efficient, which can simultaneously synthesize and deploy nanoparticles on different materials regardless of their surface topologies, therefore appealing to various surface-related applications, especially the surface modification of complex-shaped electrodes and biosensors.