Homogeneous Synthesis of Gold Nanoparticles: kinetics, mechanisms, and related onepot composites

VICTOR OESTREICHER; HUCK-IRIART, CRISTIÁN; SOLER-ILLIA, GALO JUAN DE AVILA ARTURO; MATÍAS JOBAGGY; PAULA C. ANGELOMÉ

Encuentro; 30th LNLS Annual Users Meeting (RAU); 2020

Gold nanoparticles (AuNP) are among the most studied noble metal nanoparticles because of their key role in fundamental and applied nanoscience. Several morphologies and sizes could be obtained nowadays, that have been exploited for a great variety of applications, some of which are already available in the market. However, homogeneous synthesis of AuNP has been, by far, less exploited. This approach results excellent to ensure that both the nucleation and growth of the particles take place in the absence of any compositional inhomogeneity in the solution, leading to a more controlled reaction path. Moreover, this approach allows the combination with other chemical reactions to give rise to composites in one step. In this work, we introduce the homogeneous reduction of HAuCl4 into metallic AuNP through the epoxide route. The proposed method takes advantage of the homogenous generation of OH- and reductive 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. The homogeneous growth mechanism was comprehensively studied by means of in situ UV/Vis spectroscopy, small-angle X-ray scattering and pH measurements. The obtained results alert about the non-innocent role of the stabilizing agent in the chemical speciation of Au (III) and its reactivity. Finally, we present a particular application in which the reduction process is sequentially coupled with a non-alkoxidic sol?gel process, leading to nanocomposites (AuNP at inorganic hydrogels) of high optical quality on a one-pot basis. This work paves the way towards the generation of a wide variety of AuNP and composites by one-pot homogenous methods at room temperature. Moreover, it demonstrates the feasibility of using such methods to perform careful physicochemical characterization of the AuNP formation process.