Role of Graphene Oxide in the Nucleation and Growth of Gold Nanoparticles Revealed by Operando Time-Resolved Studies

Understanding nanoparticle growth in complex composite systems remains a central challenge in materials chemistry. Herein, we elucidate the stepwise formation mechanism of gold nanoparticles (AuNPs) in graphene oxide (GO) aqueous systems under well-defined reductive conditions. Pulse radiolysis reveals that GO significantly accelerates AuCl₄ ^- reduction by hydrated electrons (e_aq ^-), thereby altering early-stage kinetics. Operando synchrotron small-angle x-ray scattering (SAXS) and time-resolved UV-vis absorption spectroscopy enable direct observation of AuNP nucleation and growth. Au(III) reduction precedes GO reduction, and nascent Au clusters preferentially anchor at GO edges through interactions with carboxyl groups, resulting in anisotropic, size-constrained growth. As GO becomes progressively reduced, depletion of oxygen-containing functional groups weakens interfacial stabilization and promotes nanoparticle coalescence. This stepwise mechanism integrates kinetic, spectroscopic, structural, and theoretical evidence, identifying GO as both a kinetic modulator and a spatial growth regulator. The insights provide general design principles for size-controlled nanoparticle growth in graphene-based composite systems.