(201j) Preparation of Monodisperse, Supported Nanoparticles with Switchable Surfactants

The preparation of monodisperse supported nanoparticle catalysts remains a non-trivial task. Organic surfactants are often required to limit growth and control the size of the nanoparticles during synthesis. Calcination is typically required following the deposition of the particles onto a catalyst support to remove the surfactant and activate the catalyst. In general, this calcination causes significant and unpredictable growth of the nanoparticle, undoing the monodispersity maintained during the synthesis. The undesired growth additionally leads to a decline in the catalytic activity of the nanoparticles due to a loss in surface area. We present the use of switchable surfactants (SwiS) for the preparation of monodisperse, supported nanoparticles. SwiS are molecules that undergo reversible, physical changes in response to an external stimulus. The SwiS can be “turned-on” to template nanoparticles during synthesis and then “turned-off” to release bare nanoparticles for deposition onto a catalyst support. The templating synthesis via a hypothesized reverse-micelle process allows for the production of monodisperse nanoparticles controllable by varying the size of the SwiS or the continuous phase. Nanoparticle size has shown to increase as the alkyl chain length of the SwiS is increased. The template is disassembled by reversal of the SwiS by simply heating the solution to drive off the CO₂ in the presence of a catalyst support. The deposition of bare nanoparticles allows for the formation of highly active supported nanoparticles that do not require calcination thus maintaining monodispersity as shown by analysis with transmission electron microscopy (TEM). Supported gold nanoparticles prepared using SwiS are more active in the hydrogenation of 4-nitrophenol than their traditionally prepared counter-parts while requiring less processing thus maintaining the size of the nanoparticle catalysts throughout the preparation. Additionally, supported nanoparticles prepared with SwiS are significantly more resistant to sintering than their traditionally prepared analogs.