Catalytic activity of gold nanoparticles prepared with ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis (USP) is a scalable aerosol-based technique for the continuous synthesis of metallic nanoparticles; however, its potential for producing unsupported, colloidal gold nanoparticles (AuNPs) as room-temperature catalysts remains insufficiently explored. In this work, we demonstrate for the first time a direct comparison of the catalytic performance of USP synthesised AuNPs synthesised from chemically distinct precursors, including gold (III) chloride, gold (III) acetate, and a recycled aqua regia based gold precursor. For this study, the AuNPs were synthesised from pure gold (III) chloride, gold (III) acetate, and a recycled solution containing aqua regia recycled AuNPs. The catalytic activity of the different AuNPs was evaluated using the reduction of 4-nitrophenol to 4-aminophenol, monitored with UV–vis by the absorbance change in the range of 350–450 nm, and the oxidation of benzyl alcohol to benzyl aldehyde by the absorbance change in the range of 230–350 nm. Supporting characterisation using DLS, SEM, and NTA was also conducted, allowing turnover frequencies (TOF) and turnover numbers (TON) to be normalised per nanoparticle and per surface site. We show that all USP-produced AuNPs are catalytically active in the reduction reaction, while none exhibit detectable oxidation activity under the selected aqueous conditions. Notably, AuNPs synthesised from gold (III) acetate display exceptionally high particle and site normalised TOF and TON values, exceeding those of chloride derived and recycled AuNPs by up to two orders of magnitude. These findings reveal a potentially strong catalytic performance in USP synthesised AuNPs and highlight USP as a promising platform for nanoparticle catalyst synthesis.