Shape transformation of silver nanospheres to silver nanoplates induced by redox reaction of hydrogen peroxide

In this paper we demonstrate a simple and rapid shape transformation of silver nanospheres (AgNSs) to silver nanoplates (AgNPls) using the oxidation and reduction capabilities of hydrogen peroxide. AgNPIs having tunable surface plasmon resonance across the visible region with average size of 40-100 nm and thickness of 10-15 nm can be fabricated within 2 min simply by adding H2O2 into a colloid of AgNSs with average particle size of 7 nm. The efficiency of H2O2 as a shape-transforming agent depends strongly on its concentration, pH of the AgNS colloid, and the employed stabilizers. H2O2 oxidizes AgNSs to silver ions while concertedly reduces silver ions to silver atom necessary for the growth of AgNPIs. The shape transformation reaction was conducted at a relatively low concentration of H2O2 in order to minimize the oxidative dissolution while facilitating kinetically controlled growth of AgNPls under a near neutral pH. Polyvinyl-pyrrolidone is an effective steric stabilizer preventing aggregation while assisting the growth of AgNPIs. Trisodium citrate inhibits the formation of AgNPls under the H2O2 reduction as it forms a stable complex with silver ions capable of withstanding the weakly reducing power of H2O2. After a complete consumption of AgNSs, large nanoplates grows with an expense of smaller nanoplates. The growth continues until H2O2 is exhausted. A high concentration H2O2 promotes catalytic decomposition of H2O2 on the surface of AgNSs and oxidative dissolution of AgNSs without a formation of AgNPIs. (C) 2015 Elsevier B.V. All rights reserved.