Construction of novel maple leaf-like MnO2–SiO2@PDA composites for highly efficient removal of Cu(II), Cd(II) and Ni(II) from aqueous solution

The preparation of the maple leaf-like MnO 2 –SiO 2 @PDA biomimetic composites not only overcame the problem of easy agglomeration of nanoparticles, but also provided rich functional groups, large specific surface areas and good stability, achieving the efficient sorption of Cu(II), Cd(II) and Ni(II) from aqueous solution. The maximum sorption capacities of the MnO 2 –SiO 2 @PDA towards Cu(II), Cd(II) and Ni(II) attained from the Langmuir model were 218.788, 383.420 and 148.939 mg·g −1 , respectively. The sorption of Cu(II), Cd(II) and Ni(II) on the MnO 2 –SiO 2 @PDA were strongly affected by pH, but not by ionic strength, showing good resistance to salt interference. The main sorption mechanism of the MnO 2 –SiO 2 @PDA towards Cu(II), Cd(II) and Ni(II) was the strong surface complexation of the functional groups on the MnO 2 –SiO 2 @PDA with Cu(II), Cd(II) and Ni(II). Moreover, the radii of Cu(II), Cd(II) and Ni(II) ions and their complexation strength with the MnO 2 –SiO 2 @PDA jointly determined the order of the competitive sorption capacities as Cu(II) > Cd(II) > Ni(II). Given the above analyses, the maple leaf-like MnO 2 –SiO 2 @PDA biomimetic composites have excellent application prospects in practical wastewater treatment.