Differing Plasmonic Intra-nanoparticle and Inter-nanoparticle Molecular Reaction Rates at the Three-Phase Contact Line of an Evaporating Sessile Droplet

Intra-nanoparticle and inter-nanoparticle heterogeneous chemical reaction pathways may involve different kinetic, dynamic natures and product selectivity like intramolecular and intermolecular counterparts in chemical synthesis and may involve rich chemistry. However, that is yet to be demonstrated. Herein, we utilized the phase change behavior of silver nanoparticles (AgNPs) from dispersion to deposition at the three-phase contact line (TPCL) in evaporating aqueous (H2O/D2O) droplet to experimentally monitor the plasmonic dimerization of 4-aminothiophenol (4-ATP) to 4,4´-dimercaptoazobenzene (DMAB) by surface-enhanced Raman spectroscopy (SERS). Raman signature of the solvent attached probe molecules in conjugation with density functional theory (DFT) calculations and DMAB formation in two steps suggested sequential intraparticle and interparticle DMAB formation, the former being ~3 times and ~1.5 times faster than the later in H2O and D2O, respectively.