Mild Homogeneous Synthesis of Gold Nanoparticles through the Epoxide Route: Kinetics, Mechanisms, and Related One‐Pot Composites

• Published in: Chemistry : a European journal Vol. 26; no. 14; pp. 3157 - 3165
• Main Authors: Oestreicher, Víctor, Huck‐Iriart, Cristián, Soler‐Illia, Galo, Angelomé, Paula C., Jobbágy, Matías
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 09-03-2020
• Subjects: Chemistry; Chlorides; epoxides; Gels; Gold; Kinetics; Nanocomposites; Nanoparticles; Optical properties; Polyvinylpyrrolidone; Reaction kinetics; Room temperature; Small angle X ray scattering; Sol-gel processes; Spheroids; Stabilizers (agents); gold; nanoparticles; epoxides; kinetics; sol-gel processes
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201905335

A new one‐pot homogeneous methodology at room temperature to obtain Au nanoparticles (AuNP) on the basis of the epoxide route is presented. The proposed method takes advantage of the homogenous generation of OH− moieties driven by epoxide ring‐opening, mediated by chloride nucleophilic attack. Once reached alkaline conditions, the reducing medium allows the quantitative formation of AuNP under well‐defined kinetic control. A stabilizing agent, such as polyvinylpyrrolidone (PVP) or cetyltrimethylammonium chloride (CTAC), is required to maintain the AuNP stable. Meanwhile their presence dramatically affects the reduction kinetics and pathway, as demonstrated by the evolution of the UV/Vis spectra, small‐angle X‐ray scattering (SAXS) patterns, and pH value along the reaction. In the presence of PVP nanogold spheroids are obtained following a similar reduction mechanism as that observed for control experiments in the absence of PVP. However, if CTAC is employed a stable complex with AuIII is formed, leading to a different reaction pathway and resulting in ellipsoidal‐like shaped AuNP. Moreover, the proposed methodology allows stabilize the growing AuNP, by coupling their formation with nonalkoxidic sol–gel reactions, leading to nanocomposite gels with embedded metallic nanoparticles. The epoxide route thus offers a versatile scenario for the one‐pot preparation of new metal nanoparticles–inorganic/hybrid matrices nanocomposites with valuable optical properties.
Homogeneous alkalinization leads to the quantitative formation of gold nanoparticles at room temperature by means of epoxide ring‐opening. The new methodology takes advantage of the kinetically controlled generation of OH− in the reaction medium; under alkaline conditions spheroidal Au nanoparticles are formed. The required stabilizing agents affect the mechanism of growth and kinetics, as demonstrated by spectroscopic measurements.