Multivariate synthesis optimization, comprehensive characterization, and surface ligand determination of palladium nanoparticles.

We present a high-throughput approach for synthesizing palladium nanoparticles (PdNPs), which are widely used as catalysts in industrial processes, employing an aqueous reaction medium and a commercial reaction platform that enables parallel reactions under identical conditions. The optimal synthesis conditions, including reaction temperature and the concentrations of Pd, thiol ligands (3-mercaptopropionic acid (MPA) and L-cysteine (Cys)), and reducing agent, were established using a Doehlert experimental design. The purified thiol-capped PdNPs were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and nanoparticle tracking analysis (NTA), confirming the formation of irregularly shaped PdNP-MPA and PdNP-Cys with polydispersity indices up to 0.270. Single particle-inductively coupled plasma-mass spectrometry (sp-ICP-MS) enabled determination of particle size and size distribution, demonstrating its suitability for characterizing polydisperse nanoparticles with irregular shapes and yielding results consistent with those obtained by TEM and NTA. Bulk ICP-MS was employed to determine the surface density of thiol ligands from the sulfur-to-palladium ratio. Overall, this study demonstrates the potential of multivariate experimental design for PdNP synthesis and the value of complementary analytical techniques for comprehensive nanoparticle characterization.