Controlling the Active Center of Gold Nanoreactors by Mediating the Metal-Polymer Interaction

V. Shah, C. Malardier-Jugroot, M. Jugroot
Royal Military College of Canada,

Keywords: polymeric nanoparticle, gold nanostructures, hybrid metal-polymer system


Nanomaterials have gained large interest from the scientific community due to the fact that materials at nanoscale exhibit unique electronic, magnetic and optical properties when compared to the bulk. The main advantage associated with nanostructures includes higher surface to volume ratio leading to an altered catalytic capability and the domination of molecular or atomic interactions at the nano-scale. Hybrid metal-polymer systems have showed great potential with their unique properties and many applications ranging from use in nano-devices such as nanowires or medical imaging agents to drug delivery agents. Gold nanoparticles (GNPs) in particular have been very commonly used because of their unique properties and many promising applications in the field of biomedicine. The new properties of gold nanoparticles have favoured their application in a variety of fields from catalysis to targeted drug delivery. Interestingly the non-reactive nature of gold in the bulk is altered at the nanoscale allowing its use as an active center for nanoreactors. Poly(styrene-alt-maleic acid) (SMA) is an amphiphilic alternating co-polymer which self assembles into highly organized nanostructures in water. These nanostructures include nanotubes or nanosheets creating hydrophobic cavities (~3nm) in the middle and hydrophilic domain on the outside. The nanoreactors generated by SMA are unsupported and induce a confinement effect due to the small size of the cavity, promoting reactions that are not thermodynamically favoured in bulk. Indeed, polymerization of pyrrole and the production of well dispersed and stable platinum nanoparticles (~2nm) have been observed under the confinement of SMA without any reducing agents. Moreover, it was also found that using the SMA-platinum system along with pyrrole led to faster kinetics of pyrrole polymerization and an overall threefold increase in the reaction rates. Therefore, using SMA as a template provides an option for environmentally friendly synthesis and reduction of metal salts under confinement effect without the use of any reducing agents. The size and the shape of the nanoparticles have proven to be important factors in determining the physical and electronic properties of the nanoparticles, it is therefore important to use a template for the synthesis of highly ordered gold nanoparticles. Gold when mixed with SMA was found to produce atomically thin gold crystals on the hydrophilic domain and gold clusters in the hydrophobic cavity produced by SMA. This paper will present the control of the interaction between SMA and gold in three ways including sonication, altering the nature of the polymer and by using thiophene to exploit the well-known gold-sulphur bond to draw the gold(I) chloride precursor into the confined regions of SMA. The ability to control the interaction of gold with the hydrophobic or hydrophilic cavity offers tremendous potential on tailoring the hydrophobic and hydrophilic reactive environment for many applications from drug delivery to nanocatalysis.