Fig. 6: Controllable magnetic hydrogel rotors for environmental remediation.

a Schematic illustration of the fabrication procedure of the magnetic hydrogel. Before UV exposure, the KH570-modified Fe₃O₄ nanoparticles distributed in the hydrogel precursor are magnetized to assemble into chains. b Optical microscopy images of magnetic hydrogel rotor and Fe₃O₄ nanoparticles chains. c By removing or applying the magnetic field of a cuboid magnet, the magnetic rotor can be switched between rotation and stop. d By removing or applying the magnetic field of a cylindrical magnet, the magnetic rotor can be switched between rotation and revolution. e Three magnetic hydrogel rotors with the same concentration of Fe₃O₄ nanoparticles can revolve along the same orbit under the magnetic field of a cylindrical magnet. f Three magnetic hydrogel rotors with different concentrations of Fe₃O₄ nanoparticles (15 mg/mL in I, 40 mg/mL in II, and 65 mg/mL in III) can revolve along different orbits under the magnetic field of a cylindrical magnet. The revolution direction of the rotor can be switched by turning the rotor over. g Scheme of water purification. Magnetic hydrogel rotors contain a large number of amide groups, which can combine with copper ions. h Under the same conditions, the efficiency of capturing Cu²⁺ contaminants from water by magnetic hydrogel rotors revolving under magnetic field is higher than that by the rotors rotating in situ. Error bars denote the standard deviation of the measurements. The scale bars are 1 mm in b (left), 100 µm in b (right), 5 mm in (c–f).