H2O2-triggered shape transformation of silver nanospheres to nanoprisms with controllable longitudinal LSPR wavelengths

Abstract

A novel approach for the synthesis of colloidal silver nanoprisms (AgNPrs) with controllable localized surface plasmon resonance (LSPR) via a chemical shape transformation of silver nanospheres (AgNSs) is presented. The shape conversion is carried out by feeding hydrogen peroxide (H₂O₂) solution into a starch-stabilized AgNS colloid under ambient conditions. Oxidative dissolution and the mild reducing action of H₂O₂ under alkaline conditions serve as the principal reactions for the shape transformation process. After addition of H₂O₂, the instantaneous shape transformation events can be visualized by the naked eye through the color change of the colloid. Initial concentration of AgNSs, molar ratio of H₂O₂ : AgNSs, H₂O₂ injection rate, and mixing efficiency are the key parameters for controlling the LSPR wavelengths of AgNPrs as the in-plane dipole plasmon resonance can be selectively tuned across visible and near infrared regions (i.e., 460–850 nm). The obtained AgNPrs exhibited mixed geometries e.g. hexagonal, truncated triangular, rounded-tip triangular prisms, and circular disks with average bisector lengths of 30 to 120 nm and the thickness of 10 to 20 nm. A colloid of highly concentrated AgNPrs having a final concentration up to 11 mM can be produced within 10 min.