Although chemically
synthesized gold nanoparticles (AuNPs) from
gold salt (HAuCl4) are among the most studied nanomaterials,
understanding the formation mechanisms is a challenge mainly due to
limited dynamics information. A range of in situ methods with down
to millisecond (ms) time resolution have been employed in the present
report to monitor time-dependent physical and chemical properties
in aqueous solution during the chemical synthesis. Chemical synthesis
of AuNPs is a reduction process accompanied by release of ions and
protons, and formation of solid particles. Dynamic information from
redox potential, pH, conductivity, and turbidity of the solution enables
distinct observation of reduction and nucleation/growth of AuNPs phases.
The dynamics of the electrochemical potential shows that reduction
of gold salt (HAuCl4 and its hydrolyzed forms) occurs via
intermediate [AuCl2]− to form Au atoms
during the early stage of the synthesis process. pH- and conductivity-dynamics
point further clearly to formation of coating layers on AuNPs and
adsorbate exchange between MES and starch.
Monodisperse platinum nanoparticles (PtNPs) were synthesized by a green recipe. Glucose serves as a reducing agent and starch as a stabilization agent to protect the freshly formed PtNP cores in buffered aqueous solutions. Among the ten buffers studied, 2-(N-morpholino)ethanesulfonic acid (MES), ammonium acetate and phosphate are the best media for PtNP size control and fast chemical preparation. The uniform sizes of the metal cores were determined by transmission electron microscopy (TEM) and found to be 1.8 ± 0.5, 1.7 ± 0.2 and 1.6 ± 0.5 nm in phosphate, MES and ammonium acetate buffer, respectively. The estimated total diameter of the core with a starch coating layer is 5.8-6.0 nm, based on thermogravimetric analysis (TGA). The synthesis reaction is simple, environmentally friendly, highly reproducible, and easy to scale up. The PtNPs were characterized electrochemically and show high catalytic activity for reduction of dioxygen and hydrogen peroxide as well as for oxidation of dihydrogen. The PtNPs can be transferred to carbon support materials with little demand for high specific surface area of carbon. This enables utilization of graphitized carbon blacks to prepare well-dispersed Pt/C catalysts, which exhibit significantly improved durability in the accelerated aging test under fuel cell mimicking conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.