Surface properties of Ag nanoparticles may not be perturbed when they are filled with the relatively cheap Cu. To better understand how Ag can be coated on Cu, growth of the Cu and Ag bimetal during the temperature-programmed carbonisation (TPC) of Ag+- and Cu2+-β-cyclodextrin (CD) complexes having the Cu/Ag ratios of 0.5, 1 and 2 was studied by in situ synchrotron small angle X-ray scattering (SAXS) spectroscopy. The SAXS spectra provide the detailed structural changes corresponding to the growth of Ag and Cu nanoparticles as the Ag+- and Cu2+-CD complexes are carbonised at the temperature range of 363–513 K. It seems that Cu having a relatively high surface free energy is enriched in the core of the cherry-like Cu@Ag bimetal nanoparticles. The Cu@Ag bimetals are encapsulated in the carbon-shell formed from carbon unconsumed in the oxidation of CD during TPC. A rapid growth of the bimetal nanoparticles occurs at 393–423 K. As Ag+ and Cu2+ are reduced during the CD oxidation, the Ag nanospheres are filled with Cu, and eventually encapsulated in the carbon-shell. Note that the carbon-shell coated on Cu@Ag can be removed by steam reforming at 573 K.
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