Adsorption characteristics of silver atoms and silver ions on silica surface in silver nanoparticle hydrosol system

Previous studies have demonstrated that silver ions (Ag+) can be released from silver nanoparticles (AgNPs) to produce a system of silver atoms (Ag0) and Ag+ in equilibrium, which may affect the environment through adsorption on sediment. Here, the adsorption behaviour of Ag0 and Ag+ in a AgNP hydrosol system on a silica surface was systematically investigated using experimental evaluation and first-principles calculations based on density functional theory. The adsorption environment and performance were first analysed by batch and fixedbed experiments, which indicated that less adsorption occurred between silica and silver. Subsequent energy calculations and structural optimisation revealed that both Ag0 and Ag+ were more likely to be chemisorbed on the silica surface through covalent (Ag-O) bonds. The average adsorption energies of SiO2/Ag+ and SiO2/Ag0 were -5.445 and -3.61 eV, respectively. In addition, Ag0 lost an average of 0.86 electrons to the O4-silica bond. By contrast, only a few electrons, which bonded with O1, were transferred from silica to Ag+. Analyses of the density of states and crystal orbital Hamilton population revealed that O and Ag were hybridised with the 2p-4d orbitals after adsorption. In addition, the peak shifts in the high-resolution Ag 3d, O 1s and Si 2p X-ray photoelectron spectra after adsorption revealed changes in the chemical state. The presence of Ag-O bonds was confirmed by the surface-enhanced Raman scattering spectrum. Silica was selected as the main component of sediment in this study, and it is hoped that this work will motivate a simulation of the migration and transformation of silver by sediment in the water environment.

Automated summary

This study systematically investigated the adsorption behavior of Ag0 and Ag+ in a AgNP hydrosol system on a silica surface, showing that both Ag0 and Ag+ preferentially chemisorb onto the silica surface through covalent bonds, with Ag0 losing electrons more easily than Ag+.