The kinetic study was executed placing 10 mg of the RACNTs in 6 different test tubes containing 10 mL of a 50 mg L1 Pb2þ solution prepared in an acetate buffer (0.002 mol L1, pH 5.70). The tubes were agitated during 10, 25, 40, 55, 70 and 90 min and centrifuged during 10 min at 700g. For each tube, the Pb2þ concentration was immediately determined by flame atomic absorption spectrometry. The assays were carried out in triplicate.