(352b) Nanoparticle Applications for Catalysis

The distinct optical, electronic and catalytic properties of colloidal gold nanoparticles (AuNPs) which are not seen in bulk gold have made them an attractive research subject in the past few decades. Oxidation of alcohols, reduction of nitroarenes, hydrogenation of quinolone and carbon - carbon coupling reactions are the reactions oxidized by colloidal (AuNPs). The preference for supported catalysts in industries over colloidal catalysts is due to their usability in continuous reactors and simplicity in recovery through simple separation methods like centrifugation, sedimentation and filtration for reuse. In comparison, recovery of colloidal catalysts is a bit complicated, employing methods like temperature or pH induced aggregation and redispersion, solvent extraction etc. However, the prospective advantages of colloidal (AuNPs) over supported catalysts lie in improved catalytic activity, selectivity and milder reaction conditions with applications in chiral catalysis. The colloidal (AuNPs) need to be stabilized with ligands to remain dispersed and be functional as catalysts. This also causes surface passivation of the nanoparticles thereby reducing their catalytic activity. We are exploring the effects of the organo thiol stabilizing ligands on the catalytic activity of colloidal (AuNPs). Reduction of 4-nitrophenol to 4 -aminophenol with sodium borohydride (NaBH₄) as a reducing agent catalyzed by colloidal (AuNPs) is our model reaction. Effects of the chain length of ligands and surface coverage of nanoparticles on catalytic activity are studied. Studying the relationship between the molecular structure of the stabilizing agents and the surface coverage of the nanoparticles is vital for understanding the mechanism of the catalytic rate of colloidal (AuNPs) for redox reactions. The use of pH sensitive ligands for pH triggered recovery and reusability of colloidal (AuNPs) catalysts is also studied.