Highly Efficient Adsorption and Reduction of Cr(VI) Ions by a Core–Shell Fe3O4@UiO-66@PANI Composite

Herein, we reported a simple solvothermal and chemical oxidation method to synthesize a magnetic core–shell composite (Fe3O4@UiO-66@PANI) for Cr(VI) removal from wastewater. Due to the porosity and stability of UiO-66 and stability, high acid resistance, and multiple active (reducing and chelating) groups of polyaniline (PANI), Fe3O4@UiO-66@PANI exhibited excellent efficiency, regeneration, and reusability performance for Cr(VI) removal. Its maximum adsorption capacity and removal rate were 474.42 mg·g–1 and 99.90%, respectively. The effects of initial pH values, contact time, and initial Cr(VI) concentration on Cr(VI) removal were investigated. The fitted data showed that the adsorption process was consistent with the pseudo-second-order kinetic model and Langmuir isothermal model. The study of the mechanism shows that the excellent efficiency of Fe3O4@UiO-66@PANI is due to the electrostatic adsorption and reduction of Cr(VI) and the chelation of Cr3+. The results demonstrate that Fe3O4@UiO-66@PANI is a promising adsorbent for the Cr(VI) removal.