This study reports a facile hydrothermal method to synthesize polyethylenimine-modified activated carbon derived from waste tires ( PEI-AC). The obtained material was characterized by Fourier transform infrared spectroscopy ( FTIR), Scanning Electron microscopy ( SEM) equipped with Energy-Dispersive Xray spectroscopy ( EDX), Thermogravimetric analyzer ( TGA), and Brunauer-Emmett-Teller ( BET) analyzer. The adsorption efficiency of the new adsorbent for the removal of Hg(II) was evaluated under the effects of its concentration, temperature, adsorption contact time, medium pH and re-usability. The optimum experimental conditions were found under response surface methodology ( RSM)using central composite design ( CCD). The results of the study show very good adsorption performance and high regeneration efficiency; the adsorption data fitted well into pseudo-second order model. The Langmuir monolayer capacity was determined to be 16.39 mg g (1). The exothermic enthalpy change ( DH) of 24.65 kJ mol (1) and negative Gibbs free energy change ( DG) assured the viability of the adsorption process. Therefore, the material leverages its cheap source and ease of regeneration in combination with its high and fast uptake capacities to offer a great promise for wastewater remediation. (C) 2017 Elsevier Ltd. All rights reserved.