Lead oxide powder (oxidation degree = 72%), vanisperse A and Vulcan carbon XC-72R (VC-72) were provided by Leoch International Technology Co. Ltd. (Shenzhen, China). MWCNTs were bought from Nanjing XFNANO Materials Tech Co. Ltd. (Nanjing, China). Sulfuric acid (H2SO4, 98%), nitric acid (HNO3, 56%) and barium sulfate (BaSO4) were purchased from Sinopharm Chemical Reagents Co. Ltd. (Shanghai, China). All reagents were used as received without further purification, and distilled water was used throughout the experiments.
a-MWCNTs were prepared by refluxing MWCNTs in nitric acid for several hours to remove the impurities. In the meantime, the surfaces of MWCNTs were functionalized with abundance of oxygen-containing groups. After refluxing, the a-MWCNTs were washed by distilled water and centrifuged until a neutral pH. The a-MWCNTs were then re-dispersed in water to obtain an aqueous suspension of 5 mg mL−1.
a-MWCNTs were prepared by refluxing MWCNTs in nitric acid for several hours to remove the impurities. In the meantime, the surfaces of MWCNTs were functionalized with abundance of oxygen-containing groups. After refluxing, the a-MWCNTs were washed by distilled water and centrifuged until a neutral pH. The a-MWCNTs were then re-dispersed in water to obtain an aqueous suspension of 5 mg mL−1.