Cr(vi) removal by mesoporous FeOOH polymorphs: performance and mechanism†
The mesoporous FeOOH polymorphs, i.e., goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhyte (δ-FeOOH) were synthesized and characterized before and after reaction with Cr(VI) by scanning electron microscopy (SEM), N2 adsorption–desorption isotherms, X-ray diffraction (XRD), saturation magnetization measurements, and X-ray photoelectron spectroscopy (XPS). The Cr(VI) removal efficiencies by these four FeOOH polymorphs were investigated. After reaction for 120 min, the Cr(VI) removal efficiencies by α-FeOOH, β-FeOOH, γ-FeOOH, and δ-FeOOH were 94.5%, 52.0%, 100%, and 84.6%, respectively. The Cr(VI) removal efficiencies by these four FeOOH polymorphs were influenced by their specific surface area. The XPS analysis indicated that the removal of Cr(VI) by these FeOOH polymorphs was a process of electrostatic attraction and ligand exchange. The study of this paper can reveal the reaction mechanism of FeOOH with Cr(VI) and the different behaviors of the four FeOOH polymorphs in the removal of Cr(VI).