Nucleation and Growth of Gold Nanoparticles Studied via in situ Small Angle X-ray Scattering at Millisecond Time Resolution

Abstract

Gold nanoparticles (AuNP) were prepared by the homogeneous mixing of continuous flows of an aqueous tetrachloroauric acid solution and a sodium borohydride solution applying a microstructured static mixer. The online characterization and screening of this fast process ( approximately 2 s) was enabled by coupling a micromixer operating in continuous-flow mode with a conventional in-house small angle X-ray scattering (SAXS) setup. This online characterization technique enables the time-resolved investigation of the growth process of the nanoparticles from an average radius of ca. 0.8 nm to about 2 nm. To the best of our knowledge, this is the first demonstration of a continuous-flow SAXS setup for time-resolved studies of nanoparticle formation mechanisms that does not require the use of synchrotron facilities. In combination with X-ray absorption near edge structure microscopy, scanning electron microscopy, and UV-vis spectroscopy the obtained data allow the deduction of a two-step mechanism of gold nanoparticle formation. The first step is a rapid conversion of the ionic gold precursor into metallic gold nuclei, followed by particle growth via coalescence of smaller entities. Consequently it could be shown that the studied synthesis serves as a model system for growth driven only by coalescence processes.

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…The main issue concerning SAXS is the detection limit; an attractive feature of SAXS is the time-resolved monitoring of the evolution of the structure. With adequate sample, the time resolution can reach the MS even with laboratory instruments [99], but it is typically on the order of a minute or longer using synchrotron sources for more environmentally relevant systems (0.1 mM Zn) [100].…”

Nanoscale Advances in Catalysis and Energy Applications

“…For example, transmission electron microscopy [89] and X-ray absorption spectroscopy [90] can monitor the growth of nanoparticles in solutions. The understanding of nanoparticle growth mechanisms may lead to large-scale and well-controlled nanoparticle synthesis processes.…”

Preparação de nanopartículas de prata e ouro: um método simples para a introdução da nanociência em laboratório de ensino

“…24 A pureza dos reagentes utilizados na síntese também é um fator de extrema importância, pois a presença de impurezas em quaisquer destes reagentes pode servir como sítio de nucleação das nanopartícu-las. Muitas referências descrevem que a pureza do nitrato de prata e do boroidreto de sódio deve ser maior que 99%, 8,9,27 porém, como descrito na Parte Experimental, o valor de pureza destes mesmos reagentes utilizados foi de 98%. Isso é um ponto muito importante, pois além da redução de custos com reagentes em relação a trabalhos anteriores, muitas vezes reagentes desse grau de pureza são mais acessíveis para aquisição.…”