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• Modified mesoporous silica structure with ethylenediamine group was synthesized. • Prepared ethylenediamine modified cubic mesoporous silica has high surface area. • Adsorption of mercury on prepared materials was studied at different conditions. • The mercury removal was studied via kinetics, isotherm and thermodynamic models. Studying the mercury removal from aqueous system using cubic mesoporous (Korea advanced institute of science and technology, KIT–6) and ethylenediamine functionalized KIT–6 (DA-KIT–6) silica materials were examined. The prepared KIT–6 and DA-KIT–6 were identified by FTIR, low–angle X-ray diffraction, Raman spectroscopy, 29Si NMR, BET, and HR-TEM. The removal of Hg2+ by adsorption was studied by applying various conditions such as the initial concentration of mercury ions, silica or modified silica amounts, contact time, and pH. Parameter optimization showed that the rate of Hg2+ adsorption of DA-KIT-6 is better than mesoporous KIT-6, which gave equilibrium adsorption rate of 95.9% and 82.5%, respectively, after 60 min at room temperature. The explanation of this behavior is due to the presence of ethylenediamine functionalized groups, –NH-(C 2 H 4)–NH 2, which have the ability to absorb Hg2+ ions from the aqueous solution. The thermodynamic calculations showed that the values of Δ G 0, Δ S 0 , and Δ H 0 were negative, which indicates that the adsorption of Hg2+ on the prepared silicas materials is exothermic and more energetically favorable sorption. The negative value of Δ S 0 considers a decrease in the randomness at the sorbents–solution/interface during the Hg2+ adsorption onto the pores of silica materials (KIT-6 and DA-KIT-6). [ABSTRACT FROM AUTHOR]