Fig. 7
a Relationship between the removal efficiency and time for the adsorption of Pb(II) by Fe3O4@C (20 mg) at initial Pb2+ concentrations of 10, 30, and 50 mg L−1, respectively. b Pseudo-second-order kinetics for adsorption of Pb2+ on the Fe3O4@C sample (T = 30 °C; absorbent dose = 400 mg L−1; Pb2+ concentrations: a = 10 mg L−1, b = 30 mg L−1, c = 50 mg L−1)