PH-Controlled Assembly and Disassembly of Electrostatically Linked CdSe−SiO2 and Au−SiO2 Nanoparticle Clusters

Abstract

The effect of pH on the self-assembly and disassembly of nanoparticle aggregates (clusters) of amine modified silica spheres (50 nm) and carboxylic acid modified gold (7 nm) or cadmium selenide (6 nm) spheres was investigated using electron microscopy and infrared and electronic spectroscopy. 4-Mercaptobenzoic acid (MBA) ligated cadmium selenide nanoparticles were synthesized by ligand exchange on 6 nm trioctylphosphine oxide ligated CdSe nanoparticles in basic methanol solution at room temperature. Reaction of CdSe(MBA) and 11-mercaptoundecanoic acid (MUA) ligated gold nanoparticles with tetramethylammonium hydroxide in methanol or THF produced CdSe(MBA)-[N(CH3)4+] and Au(MUA)-[N(CH3)4+] as black solids. On the basis of signal integration in the 1H NMR spectra, organic groups occupy areas of 0.44 nm2 (MBA), 0.22 nm2 (MUA), and 0.69 nm2 (APS) on the nanoparticle surfaces. Combination of these modified colloids with solutions of 3-aminopropylsiloxane ligated colloidal silica in aqueous solution at various ...