Morphology controlled Ag@SiO₂ core-shell nanoparticles by ascorbic acid reduction

Morphology controlled Ag@SiO₂ core-shell nanoparticles (NPs) were synthesized by using ascorbic acid as reductant, cetyltrimethylammonium bromide as stabilizer followed by silica coating with tetraethylorthosilicate. The effect of NaOH added amount on shape and size of Ag@SiO₂ core-shell NPs was investigated. X-ray diffraction result confirmed the formation of crystalline Ag core with amorphous silica shell. In the absence of NaOH, a mixed phase of Ag, Ag₂O and AgBr was formed due to incomplete reduction of Ag⁺ ions. Surface plasmon band of Ag NPs was blue-shifted with increasing NaOH amount, whereas red-shifted after silica coating. Transmission electron microscope analysis confirmed the formation of 25-55 nm Ag NPs with 4-35 nm silica shell in Ag@SiO₂ core-shell NPs. The size of Ag NPs was decreased while shell thickness increased with increasing NaOH amount. Higher amount (2.5 ml) of NaOH leads to multi core oval shape Ag@SiO₂ core-shell NPs. Graphical Abstract: [Figure not available: see fulltext.]