Selection Criteria for Metal Precursors and Solvents for Targeted Synthesis of Metallic Nanostructures Via Kinetic Control in the Polyol Process

Development of a technology for the synthesis of monometallic or multimetallic nanoparticles is exceptionally vital for the preparation of novel magnetic, optical. and catalytic functional materials. In this context, the polyol process is a safe and scalable method for preparation of metal nanoparticles with controlled sizes and shapes in large scales. However, there is no systematic investigation that discusses the criteria for the selection of metal salt and solvent type that determine the kinetics of reduction reaction that influences the morphology of the particles. Consequently, the design of metallic nanoparticles, which is controlled by the kinetics and thermodynamics of the reduction reaction, has become difficult. In this paper, the selection criterion for metal salt precursor is established based on the presumption that the ligand of the metal precursor promotes the formation of active species of the solvent, and the criterion for the selection of the solvent type is based on the highest occupied molecular orbital (HOMO) energy value estimated using molecular orbital theory. The results suggested that the dissociation constants of metal salt precursors and HOMO energy of the polyol solvent can be tuned to control the kinetics of the reduction reaction. The reduction potential of polyol depends on the number of carbon atoms and the location of hydroxyl ligands within the molecule. Among the polyols considered in this study, 1,4-butanediol had the highest reduction potential. The predictions have been experimentally verified by synthesizing metallic Co and Fe nanoparticles. The findings could be extended to other techniques such as thermal decomposition and alcohol reduction for the synthesis of noble metal-transition metal magnetic and catalytic nanoparticles with novel properties.