Platinum Nanoparticle Formation Kinetics and Mechanistic Studies: Evidence for an Alternative 4-Step Mechanism Involving Size-Dependent Growth and Chloride Anion and Room-Dust-Dependent Nucleation

Abstract

Platinum nanoparticles (NPs) are utilized extensively in myriad applications ranging from biotechnology and optoelectronics to industrial catalysis. However, precise control over their particle size, size distribution, and shape remains reliant on empirical approaches rather than on the desired kinetics, mechanism-based insight, and associated differential equations. The present study examines the synthesis and underlying mechanism of Pt NPs (Pt0 n ), emphasizing a second-generation system addressing the previously ill-defined nucleation rate constant (k 1) and its previous large (108) uncertainty. After testing nine pseudoelementary step mechanisms in the second-generation synthesis system, the best-fitting mechanism is found to be an alternative 4-step mechanism, X = PtII, as shown in the table-of-content graphic. That mechanism differs from the previously established, classic 4-step mechanism by replacing size-dependent aggregation (X = Pt0 n ) with size-dependent autocatalytic surface growth (X = PtII). Importantly, employing the alternative 4-step mechanism results in a 107 reduction in the uncertainty of k 1, thereby providing one line of evidence for that mechanism. The second-generation system and its kinetics also reveal a strong chloride anion-dependent slowing of the nucleation step as well as microfiltration-based evidence for room-dust-dependentand hence heterogeneousnucleation. As such, the present study and its disproof-based approach to the minimalistic Pt0 n NP formation mechanism advance our knowledge of Pt0 n NP syntheses and their condition- and impurity-dependent mechanisms.