A novel bio-adsorbent was successfully synthesized by pyrolyzing Alternanthera philoxeroides (AP), one of the most widely used hydrophytes for eutrophic lake ecological restoration under O-2-limited condition at 600 degrees C. Compared with commercially active carbon (AC), the initial solution pH had a weak effect on the adsorption of Pb(II) by AP biochar (APB). The maximum adsorption capacity of APB for Pb(II) was 257.12 mg/g, which was 5.3 times of that of the AC. The adsorption process was fast, with only 2.5 h to reach adsorption equilibrium. The adsorption mechanism of Pb(II) by APB involves the precipitation and complexation of Pb(II) with free carboxyl/hydroxyl functional groups and mineral carbonates of APB as well as ion replacement between Pb(II) and alkaline earth cations. These results suggest that using a low-cost APB adsorbent for heavy metals contaminated water treatment may have great ecological and environmental significance. (C) 2014 Elsevier Ltd. All rights reserved.