Competitive and multiple adsorption of humic and fulvic acids on spherical silver and gold engineered nanoparticles in aqueous media: A first-principles study

Abstract

Experimental studies have confirmed that engineered nanoparticles have different shapes such as cylindrical and spherical just to mention a few. The different shapes of engineered nanoparticles are likely to interact with natural organic matter in the aquatic environment. It is evident that when two or more different NOM’s adsorbed on molecules are going to compete for active sites. To understand the competitive and multiple adsorptions of humic acid (HA) and fulvic acid (FA) on spherical silver and gold engineered nanoparticles in aqueous media, dispersion-corrected density functional theory (DFT-D) has been used. For this purpose, HA and FA were used as model compounds for NOM. The results provide evidence of molecular interactions, competition for adsorption sites between NOM’s and Ag and Au spherical engineered nanoparticles, which are critical to understanding engineered nanoparticles behaviour and toxicity in the natural environment. The adsorption energy results of the mixtures of four HA and FA on Ag and Au spherical engineered nanoparticles have the highest adsorption energy of −1.94 eV and −3.40 eV respectively. Global reactivity descriptors such as ionization potential, electron affinity, chemical potential, hardness and electrophilicity index which give insights on adsorption of FA and HA on Ag and Au spherical engineered nanoparticles were calculated.