Biochar from Alternanthera philoxeroides could remove Pb(II) efficiently

•A novel hydrophyte based biochar was synthesized and used for Pb(II) adsorption.•The maximum adsorption capacity of this biochar for Pb(II) was 257.12mg/g.•The adsorption mechanisms were fully discussed comparing with activated carbon. 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 O2-limited condition at 600°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 257.12mg/g, which was 5.3 times of that of the AC. The adsorption process was fast, with only 2.5h 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.