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

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 similar to 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 H-2 and He gas diffusion rates compared to silica glass.