Aqueous (co)polymer stabilisers for size-controlled 2–5 nm gold nanoparticle synthesis with tuneable catalytic activity

Abstract

Gold nanoparticles, or colloidal gold (AuNP), represent one of the most significant and established forms of sub-micron inorganic structures to be researched in recent years. AuNP physical and chemical properties are dictated by both their ligand surface chemistry and their size, which can be manipulated and tuned during their synthesis. In this study, aqueous linear and branched homo-polymers and (co)polymers are developed and used as surface stabilisers during AuNP synthesis. A library of such polymeric stabilisers were prepared using conventional free radical polymerisation techniques to incorporate units of varying AuNP surface binding affinity, using methacrylic acid (MAA) and oligo (ethylene glycol) methyl ether methacrylate (OEGMA) monomers and dodecane thiol (DDT) as the chain transfer agent. AuNPs were synthesised via HAuCl₄·3H₂O reduction in the presence of the prepared library of polymeric stabilisers. It was observed that variation of (co)polymer composition and architecture allowed for size-controlled gold nanoparticle synthesis, with AuNPs prepared ranging from 2.17 ± 0.07 nm to 4.83 ± 0.04 nm as determined by UV-vis spectroscopy. Varying (co)polymer composition and architecture also yielded variable catalytic behaviour in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH₄, with catalytic reaction rates ranging from 1.0 s⁻¹ to 45.3 s⁻¹ and induction times ranging from 0 seconds to 2070 seconds depending on the polymeric stabilisers employed during synthesis.