Formation of Ni nanoparticles in Al₂O₃–SiO₂ glass by reacting with hydrogen gas

Abstract

Metal nanoparticles (NPs) are precipitated on the surface or within the glass; such glass has attracted considerable interest because of its potential practical applications in optics, electromagnetics, and biosensing devices. Although such glass has been prepared via the deposition of separately synthesized NPs or via secondary heating of glass doped with metal ions, developing a well-designed NP-doped glass still remains a formidable challenge. Here, we succeeded in precipitating Ni NPs on the surface and within the glass by heating the Ni²⁺-doped Al₂O₃–SiO₂ glass under hydrogen gas. The Al₂O₃–SiO₂ glass prepared via melt quenching comprised two phases in which the Ni²⁺ ions were preferentially bound in the Al³⁺-rich phase. When hydrogen gas was loaded, it diffused in the glass; then, Ni²⁺ ions were reduced to Ni atoms, concurrently forming Al–OH bonds. The reduction of Ni²⁺ ions was discussed in relation to the hydrogen diffusion and reaction with the Ni²⁺ ions. The optical absorption band at ~ 350 nm wavelength could be assigned to the surface plasmon resonance of Ni nanoparticles. The precipitated Ni NPs moved toward the glass surface, which were removed using an acid solution. Thus, Ni-free glass exhibited fast H₂ and He gas diffusion rates compared to silica glass.