Adsorption based on weak interaction between phenolic hydroxyl, carboxyl groups and silver nanoparticles in aqueous environment: Experimental and DFT-D3 exploration

Abstract

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.