Enhanced removal of roxarsone by Fe3O4@3D graphene nanocomposites: synergistic adsorption and mechanism

Abstract

Roxarsone (ROX) is an emerging arsenic pollutant due to its potential degradation into highly toxic inorganic arsenic species in the environment. Adsorbents which can capture ROX with both high capacity and affinity are urgently needed. Herein, a nanocomposite of nano-Fe₃O₄ and three-dimensional graphene (Fe₃O₄@RGO) was designed, aiming to simultaneously attract arsenate and benzene groups in ROX. Characterization of the nanocomposite revealed that Fe₃O₄ nanoparticles (20–50 nm) with exposed (400) planes were highly dispersed on the graphene support. Adsorption experiments showed that Fe₃O₄@RGO had higher adsorption capacity, affinity, and adsorption rate towards ROX than pristine materials and efficiently removed ROX from both simulated natural and waste waters. The adsorption mechanism was confirmed as a synergetic interaction of As–Fe coordination, hydrogen bonding and π–π interaction. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) results suggested that the As–Fe complexes and hydrogen bonds between Fe₃O₄@RGO and ROX were stronger than those in pristine nano-Fe₃O₄, due to the greater number of surface hydroxyls and shorter As–Fe atomic distance in Fe₃O₄@RGO. The π–π interaction between ROX and the graphene part in Fe₃O₄@RGO was also enhanced. This study provided a novel idea for designing materials to remove pollutants with both inorganic and organic moieties, such as phenylarsonic acid compounds, from water.