Bimetallic Au//Ag alloys inside SiO2 using a solid-state method

Abstract

Bimetallic Au/Ag nanostructures have been included inside SiO2 by pyrolysis of the macromolecular complexes Chitosan·(MLn/M′Ln)n·SiO2 and PSP-4-PVP·(MLn/M′Ln)n·SiO2 with MLn = AuCl3 and M′Ln = Ag(CF3SO3). The structural characterization was performed by XRD (X-ray diffraction of powder) and UV–Vis, and the microstructural characterization was done by SEM/EDS analysis HRTEM. The resulting products from the pyrolytic precursors PSP-4-PVP·(AuCl3/AgSO3CF3)n·SiO2 1:1 (1), PSP-4-PVP·(AuCl3/AgSO3CF3)n·SiO2 1:5 (2), Chitosan·(AuCl3/AgSO3CF3)n·SiO2 1:1 (3) and Chitosan·(AuCl3/AgSO3CF3)n·SiO2 1:5 (4) were Au/Ag//SiO2, Au//SiO2 and Ag//SiO2 as well as isolated Au and Ag, depending on the polymeric precursor. The Chitosan polymer precursor induces mainly Ag and Ag/SiO2 nanostructures, while PSP-4-PVP induces mainly Au/Ag//SiO2 nanostructures. This can be explained by the facility to link Ag+ to the NH2 and OH groups of Chitosan than to the pyridine of PSP-4-PVP. On the contrary, Au3+ exhibits most coordination ability to pyridine groups of PSP-4-PVP than NH2- and OH-groups of Chitosan. EDS mapping analysis indicates a uniform distribution of the Au/Ag nanostructure inside the SiO2 matrix. Using reflectance diffuse analysis, the plasmon is consistent with the Au/Ag alloys structure.