Synthesis and Electrochemistry of 6 nm Ferrocenated Indium–Tin Oxide Nanoparticles

Abstract

Indium–tin oxide (ITO) nanoparticles, 6.1 ± 0.8 nm in diameter, were synthesized using a hot injection method. After reaction with 3-aminopropyldimethylethoxysilane to replace the initial oleylamine and oleic acid capping ligands, the aminated nanoparticles were rendered electroactive by functionalization with ferrocenoyl chloride. The nanoparticle color changed from blue-green to light brown, and the nanoparticles became more soluble in polar solvents, notably acetonitrile. The nanoparticle diffusion coefficient (<i>D</i> = 1.0 × 10^–6 cm²/s) and effective ferrocene concentration (<i>C</i> = 0.60 mM) in acetonitrile solutions were determined using ratios of <i>DC</i> and <i>D</i>^1/2<i>C</i> data measured by microdisk voltammetry and chronoamperometry. The <i>D</i> result compares favorably to an Einstein–Stokes estimate (2.1 × 10^–6 cm²/s), assuming an 8 nm hydrodynamic diameter in acetonitrile (6 nm for the ITO core plus 2 nm for the ligand shell). The ferrocene concentration result is lower than anticipated (ca. 1.60 mM) based on a potentiometric titration of the ferrocene sites with Cu­(II) in acetonitrile. Cyclic voltammetric data indicate tendency of the ferrocenated nanoparticles to adsorb on the Pt working electrode