Exfoliated graphite with γ-Fe2O3 for the removal of oil and organic pollutants from the water surface: Synthesis, Mossbauer study, sorption and magnetic properties

Abstract

Exfoliated graphite (EG) is a promising sorbent for oil and organic pollutants, which has a high sorption capacity and hydrophobicity. Modifying the EG with ferrimagnetic compound allows EG with sorbed oil to be collected from the water surface with the use of a magnetic field. The aim of this work is to obtain a sorbent based on exfoliated graphite with ferrimagnetic maghemite (γ-Fe2O3) and investigate its structure and functional properties. The preparation of iron-containing EG includes the impregnation of expandable graphite with a FeCl3 water solution and the thermal treatment of impregnated expandable graphite at temperatures between 400 and 1000 °C. Mossbauer spectroscopy, X-ray diffraction analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy show the evolution of the iron-containing phase from FeOCl to the mixture of α-Fe2O3 and γ-Fe2O3, which grants magnetic properties to the samples. EG obtained at 1000 °C has a saturation magnetization of 22.7 emu g−1. High macropore and meso-/micropore volume investigated by mercury porosimetry and nitrogen adsorption-desorption method results in a high sorption rate and sorption capacity of EG up to 30 g g−1 toward oil and liquid hydrocarbons. At the same time, the EG sorption capacity toward water is ten times lower.