Self-assembly of a graphene oxide/MnFe2O4 motor by coupling shear force with capillarity for removal of toxic heavy metals

Abstract

Herein, we have developed an easy method for the fabrication of hollow three-dimensional (3D) graphene oxide/MnFe₂O₄ (GO/MnFe₂O₄) motors by mediating GO suspension with aniline and MnFe₂O₄via coupling shear force with capillarity. It is found that shear force helps the size breakup of GO/MnFe₂O₄ hydrogels and the formation of turbulent flow structures during their assembly. Furthermore, capillarity further shrinks their sizes and produces an asymmetric hollow Janus-like GO/MnFe₂O₄ motor at the millimeter scale during the drying process. In addition, the GO/MnFe₂O₄ motor demonstrates high efficiency as an adsorbent for the removal of heavy metals (i.e., Pb²⁺ and Cd²⁺) because of the rich oxygen-containing groups of GO. MnFe₂O₄ enables external magnetic control and functions as an engine decomposing H₂O₂ fuel for bubble-driven movement of motors in the target area. Typically, 20 mg GO/MnFe₂O₄ motor can fully remove 100 mg L⁻¹ Pb²⁺ and Cd²⁺ in 150 min and 180 min, respectively. Furthermore, the motor can be reused and retains 99.8% adsorption efficiency in the fifth cycle after chemical detachment of Pb²⁺ and Cd²⁺ with 0.2 M HCl from the surface of GO/MnFe₂O₄.