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

We present a high-throughput sustainable chemistry approach for the synthesis of palladium nanoparticles (PdNPs), which are widely employed as catalysts in industrial processes, using a commercial reaction device to perform parallel reactions under identical conditions. The synthesis parameters assessed included reaction temperature, and the concentrations of Pd, thiol ligands (3-mercaptopropionic acid (MPA), L-cysteine (Cys)) and reducing agent. The optimization of these parameters was accomplished via a multivariate approach. A characterization of the thoroughly purified thiol-capped PdNPs by transmission electron microscopy (TEM), energy-dispersive X-Ray spectroscopy (EDS), dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) confirmed the formation of irregularly shaped particles with mean sizes of 96 ± 33 nm and 71 ± 30 nm for PdNP-MPA and PdNP-Cys, respectively, with polydispersity indexes up to 0.270. Subsequent analysis via single particle-inductively coupled plasma-mass spectrometry (sp-ICP-MS) enabled a direct size and size distribution determination comparable to those obtained by TEM and NTA. sp-ICP-MS also allowed the determination of particle number concentration (PNC). Bulk ICP-MS was applied for the determination of the thiol ligand surface density from the measured sulfur-to-metal ratio. Overall, our study demonstrated the potential of multivariate approaches for sustainable NPs synthesis, and application of complementary analytical tools for NPs characterization.