Facile tuning of plasmon bands in hollow silver nanoshells using mild reductant and mild stabilizer

Abstract

Hollow silver nanoshells with tunable plasmon bands have been synthesized using Ag₂O nanoparticles at an optimized temperature of 20 °C. The plasmon peak has been tuned in a wide range from 460 nm to 605 nm employing a combination of mild reductant and a mild stabilizer, hydrazine hydrate and sodium citrate, respectively. In contrast, the combination of strong reductant and strong stabilizer, NaBH₄ and hydrophilic thiols, resulted in limited plasmon tunability (455–510 nm). The differential behaviour is attributed to the change in dynamics of the diffusion–reaction process. For thiols, the effect of free end-groups was quite evident as plasmon peak shifted from 449 nm to 470 nm on replacing thioglycolic acid (HS–CH₂–COOH) with mercaptoethanol (HS–CH₂–CH₂–OH). Transmission electron microscopy (TEM) revealed that the aspect ratio [outer diameter (d)/shell thickness (t)] was 2.8 (d: 40.0 ± 1.6 nm, t: 14.0 ± 1.3 nm) and 5 (d: 84 ± 2.3 nm, t: 16.8 ± 1.9 nm) for the nanoshells exhibiting a plasmon peak at 460 nm and 605 nm, respectively. The crystal phase of nanoshells was found to be face centered cubic (fcc) as deduced from HR-TEM and electron diffraction data. Using the same Ag₂O template, morphological transformation from non-porous to mesoporous has also been achieved by simply reversing the order of addition.