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Numerous studies have shown that there are complex interactions between silver nanoparticles (AgNPs) and humic acid (HA) in the natural ecosystem. However, little is known about the interaction between AgNPs and HA in terms of molecular mechanisms. It is well-accepted that aromatics substituted by phenolic hydroxyl (Ar−OH) and carboxyl (−COOH) groups are primary constituents of HA. In this research, we proved that five benzene series (phenol, BA, OHBA, MHBA and PHBA) have different adsorption capacity sequences with AgNPs by experimental adsorption coefficient in UV–vis. Subsequently, FTIR analysis indicated the weak interaction in molecules is the main adsorption mechanism. Based on these facts, the weak interaction of Ar−OH and −COOH with silver nanoparticles (AgNPs) was systematically investigated by the first-principles calculations using density functional theory (DFT). The structure optimization and energy calculation demonstrated that the Ar−OH and −COOH groups on the benzene ring had the greatest influence on the AgNPs adsorption site, energy and deformation when they are in adjacent positions. Furthermore, the calculations of electronic structure, Density of states (DOS) and crystal orbital Hamilton population (COHP) provided evidence that the charges in C and H atoms were transferred to O atoms after the adsorption. Whereas, there was little charge transfer from AgNPs to benzene series. This study is hoped to provide a useful theoretical reference for the evaluation of HA and AgNPs in the water environment. [Display omitted] • The Ar−OH and −COOH groups affected adsorption site, energy and deformation. • Little charge transfer from silver to benzene series during the adsorption process. • Deformation and charge transfer mainly occur in the benzene series. • The Ar−OH and −COOH groups are active compared with the benzene ring. [ABSTRACT FROM AUTHOR]

A well-designed strategy utilizing H 2 O 2 as both oxidizing and reducing agent to synthesize multi-morphology silver nanoparticles (AgNPs) was developed to investigate the mechanism of anisotropic growth. At the initial stage, isotropic silver nanospheres were synthesized by pure reduction of H 2 O 2. Then a redox cycle was established, which consisted of mutual conversion between Ag+ and Ag0 caused by reduction and oxidization of H 2 O 2 , to induce anisotropic growth of the original nanospheres into popcorn-shaped AgNPs or silver nanoplates with the presence of different concentrations of poly(vinyl pyrrolidone) (PVP). The results indicated that the redox cycle provided a driving force of anisotropic growth by inducing the formation of defects, while PVP played a key role in controlling growth direction. This work provided a high-yield method to synthesize anisotropic AgNPs by combining reduction and oxidization and suggested a hypothesis of the mechanism of anisotropic growth. [Display omitted] • Redox cycle is established using H 2 O 2 as reducing and oxidizing agent simultaneously. • Anisotropic morphology of nanoparticles is tunable by controlling conditions. • No toxic agents are used and side products are environmentally friendly O 2 and H 2 O. • The yield rate is over 99% under ambient conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag0 and Ag+ were chemisorbed on silica surface via Ag O covalent bonds. • Adsorption energy of Ag+ on silica surface was higher than that of Ag0. • Ag0 was bonded with O4 of silica with 0.86 electrons transfer. • Ag+ was bonded with O1 of silica with few electrons transfer. • Adsorption mechanism depended on 2p–4d orbital hybridisation of O and Ag. 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 fixed-bed 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 SiO 2 /Ag+ and SiO 2 /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. [ABSTRACT FROM AUTHOR]