Dongxia Liu

Development and application of in situ surface vibrational spectroscopic methods to study adsorption of dendrimer-encapsulated metal nanoparticles

MELANIE SCHAAL

YARITZA LOPEZ

Dongxia’s primary research involves the development and application of in situ surface vibrational spectroscopic methods to study adsorption of dendrimer-encapsulated metal nanoparticles onto various substrates. She is also investigating the catalytic properties of these particles using a well-known liquid-solid phase hydrogenation reaction. 

Dendrimers are monodisperse, hyper-branched polymers that emanate from a central core with repetitive branching units. While possessing a very dense exterior, they contain hollow pockets that can be ideal for use as nanoscale containers. The use of dendrimers as templates/stabilizers for synthesis of encapsulated nanoparticles is a relatively new but active field. One of the more successful applications of this approach has been the synthesis of metal nanoparticles using poly(amidoamine) (PAMAM) dendrimers. Metal nanoparticles synthesized in this fashion have been demonstrated to exhibit interesting catalytic properties. The dendrimer can exert control over size and (in the case of multiple metal ions) composition of nanoparticles, which can allow for tuning of catalytic properties.

Most of the reported catalytic studies have been homogeneous, in that the dendrimer-metal nanoparticles have been used directly in solution. To design a heterogeneous analogue requires the ability to anchor these catalysts onto high surface area supports such as oxides. The goals of Dongxia's Ph.D. research are two-fold. First, the absorption of dendrimer stabilized metal nanoparticles on two different substrates, gold and alumina will be investigated. Gold is chosen as a model electrode material, while alumina is chosen as a model catalytic support.  Second, immobilized dendrimer encapsulated nanoparticles will be investigated as liquid-phase heterogeneous catalysts using a well-known hydrogenation reaction.

The proposed reaction is the hydrogenation of allyl alcohol, which has been shown to be effectively catalyzed by different kinds of transition metals such as platinum, palladium, copper, nickel. It will therefore provide an opportunity to study the bimetallic effect. The materials used for these studies will involve fourth generation hydroxyl-terminated poly(amidoamine) dendrimers (PAMAM G4OH) containing stable Pt_xM_y nanoparticles, where M is possibly Pd or Ru  and x+y =40.

In situ surface attenuated total reflection infrared (ATR-IR) spectroscopy and enhanced Raman spectroscopy (SERS) will be the primary tools used to probe adsorption and reactions on chosen surfaces. These studies will constitute the first in situ spectroscopic measurements of catalysis on the surfaces of dendrimers, as well as for the allyl alcohol hydrogenation reaction.