Comparative Adsorption of Phenanthrene, Bisphenol A, and Sulfamethoxazole on Humic Acid-Iron Oxide Nanoparticle Complexes

Abstract

Organo-mineral complexes are important components of soil and can greatly affect the behavior and fate of organic contaminants. Properties of organic components play important roles in organic coating on mineral surfaces. However, the dominant property and mechanism controlling organic contaminant behavior are still unclear. In this study, adsorption of various organic contaminants on humic acid-nano-Fe2O3 complexes with different properties were investigated. Nonpolar, aromatic, and high-molecular-weight fractions of humic acid (HA) were preferentially adsorbed on nano-Fe2O3, forming various HA-nano-Fe2O3 complexes with different properties. According to a correlation analysis between the adsorption of organic contaminants and properties of HA-nano-Fe2O3 complexes, the organic carbon content, aromaticity, and hydrophobicity, were believed to be the dominant properties controlling the organic contaminant adsorption. Organic carbon contents and π-π bonds might contribute to sulfamethoxazole (SMX) adsorption more than to bisphenol A (BPA) and phenanthrene (PHE) adsorption because the amino functional groups and N-heteroaromatic rings of SMX were strong π-acceptors. In comparison, hydrophobic interactions might contribute to BPA and PHE adsorption more than to SMX adsorption due to the higher hydrophobicity of BPA and PHE. The H-bond was not the dominant mechanism responsible for PHE and BPA adsorption, while it could not be ignored for SMX adsorption.