Removal of heavy metals from contaminated water using ethylenediamine-modified green seaweed (Caulerpa serrulata)

► Modified seaweed using ethylenediamine (EDA) was applied for removal of copper, lead and cadmium. ► Adsorption capacities for Cu, Cd and Pb were 5.27 mg g−1, 2.12 mg g−1 and 2.16 mg g−1, respectively. ► Modified seaweed showed reduced dissolved organic carbon content by 50% and no green colouration. ► Improved thermal stability of adsorbent; at 1000 °C more than 80% of the adsorbent was not degraded.