Atypical Catalytic Function of Embedded Gold Nanoparticles by Controlling Structural Features of Polymer Particle in Alcohol-Rich Solvents

Chemical transformation reactions generally require catalysts with large surface areas. In particular, metal-based colloidal nanoparticles have been extensively designed to serve as quasi-homogeneous catalysts in such reactions. To this end, many synthetic strategies for metal nanoparticles have been developed. However, most methods inevitably involve the use of stabilizing and capping agents that have a great influence on the final features of the nanoscale metal particles.  However, these stabilizing agents can greatly reduce catalytic performance by blocking or minimizing the active sites of the metal surfaces. Therefore, development of better synthetic approaches is highly desirable.

To this effect, Pascal Eyimegwu and Professor Jun-Hyun Kim from Illinois State University have prepared physically encapsulated gold nanoparticles within poly(N-isopropylacrylamide), PNIPAM, particles at room temperature. This in situ approach involves the reduction of gold ions under fluorescent light irradiation in the presence of PNIPAM particles, resulting in the incorporation of relatively large gold nanoparticles within the polymer particles. Subsequent purification and dispersion of the composite particles in alcohol-rich solvents greatly improved their overall stability while reducing the amount of stabilizing agents that were directly bound to the surface of the embedded gold nanoparticles. Thus, they aimed at fabricating stabilizing agent-free gold nanoparticles within the polymer particles exhibiting great colloidal stability. The work is published in the research journal, Nanotechnology.

It was necessary to examine the catalytic performance of the fabricated gold nanoparticles in a homocoupling reaction in both pure alcohol and alcohol-rich aqueous solvents under ambient conditions (shown in Figure), which resulted in unexpectedly high catalytic activity. In addition to the increased stability and readily accessible catalytic sites of the gold nanoparticles, the increased mass transfer capability for reactants and products in alcohol-rich solvents was also responsible for the highly improved yields in the coupling reactions. Furthermore, the gold nanoparticles exhibited great selectivity without the formation of any side products in pure alcohol solvents and were very stable, demonstrating multiple recyclability without losing their catalytic activity. As far as is known, this is the first incident for relatively large gold nanoparticles as quasi-homogenous catalysts to display unexpectedly high catalytic activity and selectivity at room temperature.

In summary, the Eyimegwu-Kim study successfully demonstrated atypical catalytic functions of embedded gold nanoparticles by controlling the structural features of polymer particles in alcohol-rich aqueous solvents. Based on their presented results, the study will pave the way for the design of practical and environmentally friendly catalytic reactions systems, particularly by using stabilizing agent-free metal nanoparticles.