Finally, the AAO template was dissolved in a 1.5 M NaOH solution, and the NiFe2O4 nanotubes were collected.
2.2. Synthesis of NiFe2O4 nanoparticles
Nickel sulfate (NiSO4·6H2O, AR grade) and ferric chloride (FeCl3·6H2O, AR grade), purchased from Shanghai Reagent Co. of Chinese Medical were directly used as reactants. 0.25 M nickel sulfate solution of 20 ml and 0.5 M ferric chloride solution of 20 ml were mixed with stirring at 50 °C.