by placing 20 mg Fe3O4@SiO2–NH2 in 60-ml polytetrafluoroethylene-lined screw cap glass tubes receiving 50-ml Cu(NO3)2, Pb(NO3)2, or Cd(NO3)2 aqueous solutions
by placing 20 mg Fe3O4@SiO2–NH2 in 60-ml polytetrafluoroethylene-lined screw cap glass tubes receiving 50-ml Cu(NO3)2,Pb(NO3)2, or Cd(NO3)2 aqueous solutions