Preparation of discrete cage-like oxidized hollow carbon spheres with vertically aligned graphene-like nanosheet surface for high performance Pb absorption.

A novel oxidized hollow carbon sphere (OHCS) as absorbent for the removal of Pb was fabricated from the mixture of coal-tar pitch and aluminum isopropoxide followed by nitric acid oxidation. The as-prepared OHCSs were characterized by FESEM, TEM, BET, TG, FTIR and XPS, and meanwhile the effects of adsorption conditions on the Pb removal were investigated by batch experiments. Results show that the OHCSs prepared possess discrete cage-like structures and well-defined inner/outer surface features, exhibiting vertically aligned graphene-like nanosheets on their surfaces with mesoporous nature and high hydrophobicity. The maximum absorption capacity for Pb of the OHCSs can reach 280.79 mg g at the optimum condition. The adsorption kinetic of Pb onto the OHCSs was found to be well modeled by pseudo-second-order kinetic model, and the experimental equilibrium data were represented well by Langmuir isotherm model. Moreover, the OHCSs still exhibit excellent adsorption ability and stability after recycling 5 times, indicating its excellent reusability performance. Overall, the OHCS is a promising adsorbent for Pb removal.