Covalently Immobilized EDTA onto Graphene Oxide Using Ethylene Diamine as a Crosslinker for Cu(II), Pb(II), and Zn(II) Sorption

Abstract

This study introduces a novel method of EDTA immobilization onto graphene oxide (GO) using ethylene diamine as a crosslinker for heavy metal removal. GO was prepared from graphite via a modified Hummer method. Ethylene diamine was used as a novel crosslinker to immobilize EDTA onto GO via amide coupling. GO was functionalized with ethylene diamine to produce GO-NH2 onto which EDTA (H-form) was covalently immobilized producing GO-EDTA. FTIR and TGA show successful covalent immobilization of EDTA. Pb(II), Cu(II), and Zn(II) were tested for sorption from aqueous solutions onto GO-EDTA (Na-form). Initial pH 6.0 was found optimum for metal sorption. The kinetic sorption data were found to fit the pseudo-second-order model well with better performance as the temperature rises. The activation energy (Ea) of metal sorption was between 10.6 and 32 kJ/mol indicating metal physisorption. Equilibrium sorption data were found to fit well the Langmuir model with higher uptake as the temperature rises. The sorption capacity was 72.4, 46.5, and 28.0 mg/g at 25°C while it was 86.2, 56.8, and 31.95 mg/g at 35°C for Pb(II), Cu(II), and Zn(II), respectively. Metal sorption follows the order of GO-EDTA > GO-NH2 > GO and follows the order of Pb(II) > Cu(II) > Zn(II) from the metal mixture. Metal sorption is endothermic and spontaneous. GO-EDTA shows efficient recycle properties for metal sorption.