Successful Synthesis of Gold Nanoparticles through Ultrasonic Spray Pyrolysis from a Gold(III) Nitrate Precursor and Their Interaction with a High Electron Beam

Abstract

Herein, we report for the first time the successful preparation of a gold(III) nitrate [Au(NO3)3] water‐based precursor for use in a bottom‐up ultrasonic spray pyrolysis (USP) process. Due to its limited solubility in water, the precursor was prepared under reflux conditions with nitric acid (HNO3) as the solvent and ammonium hydroxide (NH4OH) as a neutralizer. This precursor enabled the USP synthesis of gold nanoparticles (AuNPs) and the in situ formation of low concentrations of NO2 − and NO3 − ions, which were caught directly in deionized water in a collection system. These ions were proven to act as stabilizers for the AuNPs. Investigations showed that the AuNPs were monodispersed and spherically shaped with a size distribution over three groups: the first contained 5.3 % AuNPs with diameters (2 r) <15 nm, the second contained 82.5 % AuNPs with 2 r between 15 and 200 nm, and the third contained 12.2 % AuNPs with 2 r>200 nm. UV/Vis spectroscopy revealed the maximum absorbance band of the AuNPs at λ=528 nm. Additionally, scanning transmission electron microscopy (STEM) observations of the smallest AuNPs (2 r<5 nm) revealed atomically resolved coalescence phenomena induced by interaction with the electron beam. Four stages of the particle‐growth process were distinguished: 1) movement and rotation of the AuNPs; 2) necking mechanism; 3) orientated attachment at matching facets; 4) reshaping of the AuNPs by surface diffusion. This provided important insight into the formation/synthesis process of the AuNPs.

Low-cost synthesis of AuNPs through ultrasonic spray pyrolysis

“…The lower surface tension affects the droplet formation by ultrasound, resulting in smaller droplets and consequently smaller AuNPs. Previously, we have shown comparisons between different precursor acids, such as the chlorides, acetates and nitrides used with USP [57,58]. However, the comparisons between different acidity levels of the same acid (chloride) have not yet been shown, nor are they readily available in literature.…”

Effect of Particle Size on the Corrosion Behaviour of Gold in the Presence of Chloride Impurities: An EFC-ICP-MS Potentiodynamic Study

“…This is of special importance in waste electrical and electronic equipment (WEEE), where Au is used in integrated circuits. Recently, also printing of gold nanoparticles has been gaining popularity [16][17][18]. It has been shown that these devices can fail in operation due to corrosion of Au [19].…”

Advances in Ultrasonic Spray Pyrolysis Processing of Noble Metal Nanoparticles—Review

“…Gold nitrate, HAu(NO 3 ) 4 , was chosen as an additional precursor for AuNP synthesis with USP, and for comparison of the produced nanoparticle morphology. Commercially available gold nitrate is poorly soluble in water, and an investigation was needed for preparing a soluble and chemically stable water-based gold nitrate precursor [34]. The preparation of a precursor solution required reflux boiling and additional steps to make it usable within the USP process.…”

“…In our long-term investigation and experimental work, we have used USP to produce several metallic and metal oxide particles with micron and nano sizes, ranging from Au (from Au salts and from gold scrap), Ag, Ag/TiO 2 , Au/TiO 2 , ZnO, Fe/Au, Co, Cr and rare earth metals. For Au nanoparticles (AuNPs) we have also investigated extensively the cytotoxic and immunomodulatory properties of these particles for biomedical applications [31][32][33], as well as their behaviour when exposed to in situ heating during TEM observation [34], and their use in printing inks for Electronics (not yet published). We have also applied Au and ZnO nanoparticles in PMMA composites for advanced dental materials for removable prostheses [35].…”