Mechanistic Study of Citrate Affecting the Adsorption of Gold Nanoparticles by Goethite

The mechanism of regulating the interfacial behavior of gold nanoparticles (AuNPs) in environmental media is key to assessing their ecological risks. In this study, we break through the traditional one-factor adsorption research model and focus on the multiscale regulatory role of Citrate (Cit) in the nanoparticle-mineral interface, revealing for the first time the biphasic mechanism by which this molecule dominates the environmental behavior of AuNPs through pH-responsive coordination mode switching. By constructing the goethite-AuNPs- Cit ternary interface model, it was found that : under acidic conditions (pH < pHpzc), Cit competes for positively charged adsorption sites on the surface of goethite with the AuNPs and inhibits the adsorption significantly; whereas under alkaline conditions (pH > pHpzc ), Cit bridges the negatively charged clinoptilolite and AuNPs through charge-assisted hydrogen bonds (CAHBs) and Lewis acid-base interactions, promoting adsorption. This study innovatively established an organic ligand-mediated dynamic regulation model of nanoparticles (NPs) interface, clarified the mutation mechanism of NPs ‘retardation-migration’ behavior caused by pH oscillation in rhizosphere microenvironment, and provided a theoretical basis for the study of the interaction between NPs and minerals. Meanwhile, it will also bring new insights into the environmental fate of AuNPs, especially in the rhizosphere environment.