Electronic transfer through Langmuir–Blodgett layers of capped platinum nanoparticles: An electrochemical approach

Abstract

Amine functionalized platinum nanoparticles have been modified by over-grafting two different molecules, 2-thiophenecarbonyl chloride (Pt- 1) and 1-hexyl-4-(4-isothiocyanatophenyl)-bicyclo (2, 2, 2) octane (Pt- 2). Cyclic voltammetry was performed at gold electrodes coated with Langmuir–Blodgett (LB) mixed films of Pt- 1 and Pt- 2 nanoparticles, and behenic acid. From five layers the electrochemical response was essentially provided by the last LB component. The electrochemical responses towards the [Fe(CN) 6] 3−/4− couple were strongly influenced by the nature of the over-grafted molecules: films of Pt- 2 presented an almost complete blocking effect, while films of Pt- 1 allowed the redox reaction to occur on Pt nanoparticles. In order to understand the reasons for such different behaviors we built up hetero-nanostructures by superposing Pt- 1 and Pt- 2 LB layers in different ways, yielding different kinds of “sandwich” structures. The electrochemical response depended on the electrode ending. When Pt- 1 nanoparticles were in the outer layer, in contact with the electrolyte solution, the electrode was electroactive toward the redox probe, while when Pt- 2 layers were in the outer layer no electroactivity was detected. For sandwiches made of Pt- 1, with a variable thickness of an intercalated film of Pt- 2, the electrode response to [Fe(CN) 6] 3−/4− was modulated by the thickness of the inter-layer: the thicker the layer, the lower the response.