Modulated Triple-Material Nano-Heterostructures: Where Gold Influenced the Chemical Activity of Silver in Nanocrystals.

For efficient charge separations, multimaterial hetero-nanostructures are being extensively studied as photocatalysts. While materials with one heterojunction are widely established, the chemistry of formation of multijunction heterostructures is not explored. This needs a more sophisticated approach and modulations. To achieve these, a generic multistep seed mediated growth following controlled ion diffusion and ion exchange is reported which successfully leads to triple-material hetero-nanostructures with bimetallic-binary alloy-binary/ternary semiconductors arrangements. Ag2 S nanocrystals are used as primary seeds for obtaining AuAg-AuAgS bimetallic-binary alloyed metal-semiconductor heterostructures via partial reduction of Ag(I) using Au(III) ions. These are again explored as secondary seeds for obtaining a series of triple-materials heterostructures, AuAg-AuAgS-CdS (or ZnS or AgInS2 ), with introduction of different divalent and trivalent ions. Chemistry of each step of the gold ion-induced changes in the rate of diffusion and/or ion exchanges are investigated and the formation mechanism for these nearly monodisperse triple material heterostructures are proposed. Reactions without gold are also performed, and the change in the reaction chemistry and growth mechanism in presence of Au is also discussed.