Decoupling Colloidal Stability and Catalytic Activity of Gold Nanocatalysts via In-Situ Sacrificial Physisorbed PEG...

Gold nanoparticles stabilized by sodium citrate (GNPs-citrate) are highly effective catalysts but often suffer from colloidal instability. Polymeric stabilizers can improve dispersion stability, yet chemisorbed polymer layers are canonically associated with suppressed catalytic activity. Herein, we evaluate an in situ sacrificial stabilizing system (ISSS) based on physisorbed hydroxyl-terminated poly(ethylene glycol) (PEG) on GNPs-citrate. GNPs-PEG were prepared using PEG (1.5, 4.0, and 6.0 kDa) at Au/PEG molar ratios of 1:2, 1:7, and 1:12. Dynamic light scattering showed substantially increased hydrodynamic diameter (D_h) and decreased magnitude of ζ-potential with increasing PEG loading, while UV-visible spectroscopy indicated invariant surface plasmon resonance (λ_SPR) features relative to GNPs-citrate. In the NaBH₄ reduction of p-nitrophenol to p-aminophenol, GNPs-PEG exhibited pseudo-first-order rate constants with no statistically significant difference to those of GNPs-citrate across the series; at 8.0 μM Au, the mean activity differed from the citrate control by only ∼3%, and no induction period was observed. Prolonged storage preserved D_h, ζ-potential, and λ_SPR, whereas stability tests under reaction conditions showed declining activity and increasing D_h over time, consistent with the expected loss of the physisorbed PEG layer. Collectively, these data support physisorbed PEG as a storage-stabilizing coating that is labile under reducing catalytic conditions, enabling stability without any sacrifice to initial catalytic performance.