Probing the Phytosynthesis Mechanism of Gold and Silver Nanoparticles by Sequential Separation of Plant Extract and Molecular Characterization with Ultra-High-Resolution Mass Spectrometry

Phytosynthesis of nanoparticles (NPs) has been regarded as a green and sustainable technology for future nanoscience. However, most of the studies focused on nanomaterial production and plant selection, whereas the underlying mechanism behind the phytosynthesis of NPs remains unclear largely due to the complex compositions and chemical diversity of plant extracts. Herein, a persimmon fruit extract was subjected to sequential solvent fractionation with hexane, n-butanol, chloroform, and water. The obtained fractions were then utilized to synthesize gold and silver NPs, which consequently had different morphologies and reaction kinetics. The molecular characterization was performed using ultra-high-resolution mass spectrometry, and a distinct compositional difference was observed among the isolated fractions. The capping agents on metal NPs were mainly unsaturated aliphatics with low oxygen content. The reduction of metal ions by plant extracts involved reducing agents with strong reducing ability like phenolic structures and weak reducing ability like terpenoids, peptides, and reducing carbohydrates. The morphology control seemed to relate to compounds with cyclic and highly unsaturated structures. Further, clear differences were observed for the key compositions and formation process in the phytosynthesis of gold and silver NPs.