Transition metal doping of amorphous silica particles

Amorphous, homogeneously doped particles with 1–10 atomic percent (at%) nickel or zinc, smaller than 100 nm, were synthesized. Additionally, 20 at% nickel and zinc-doped silica particles were synthesized, although the particle size was > 300 nm. The coordination state of the metal in solution did not change with the ammonia or water concentrations used. Particle size was found to decrease with both increasing water and ammonia hydroxide concentrations. The NH₄OH concentrations of 4.5 and 6.5 M used allowed the formation of ammine–transition metal complexes and the zeta potential to remain in a stable range, allowing for spherical, nearly monodisperse particle formation at high metal dopant concentrations.