We report synthetic methods to produce silver (Ag) or gold (Au) monodisperse nanoparticles with different loadings as well as Ag and Au nanorods with tunable aspect ratios and optical properties. This is achieved inside externally functionalized mesoporous SBA-15 material by utilizing a simple change of the type of metal complex that is reduced with imines or hemiaminals that were anchored within the channel walls of the mesoporous material. The imine and hemiaminal groups were produced by reacting grafted 3-aminopropyl groups with CH3CHO or HCHO, respectively. Upon using lower concentrations of aqueous AgNO3 or ammonical [Ag(NH3) 2]NO3 solution as the metal source, Ag monodisperse nanoparticles formed. Interestingly, when the concentration of ammonical [Ag(NH3)2]NO3 solution was increased, this resulted exclusively in nanoparticles with a higher loading and with no formation of nanorods; while increasing the concentration of aqueous AgNO 3 solution resulted in silver nanorods with higher aspect ratios and tunable optical absorption and color. A possible mechanism for the growth of nanoparticles versus nanorods in the mesoporous materials by using ammonical instead of aqueous silver complexes, respectively, was proposed. The synthesis of gold nanoparticles or tunable gold nanorods was also carried out by changing the concentration of aqueous HAuCl4 in the same material. The synthesis of Ag nanostructures with grafted imines and Au nanostructures with grafted imines and hemiaminals are to be reported for the first time. The functionalized mesoporous materials, the Ag and Au nanoparticles, and nanorods inside the mesoporous materials were characterized by UV-vis absorption and reflectance spectroscopy, small-angle and wide-angle X-ray diffraction, solid-state NMR spectroscopy, and transmission electron microscopy.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films