Enhancing Sorption Capacities for Copper(II) and Lead(II) under Weakly Acidic Conditions by l-Tryptophan-Functionalized Graphene Oxide

Abstract

l-Tryptophan functionalized graphene oxide (GO/l-Trp) was successfully synthesized via the nucleophilic substitution reaction. Its structure was characterized and the performances of GO/l-Trp in the sorption of Cu(II) and Pb(II), including the influence of contact time, initial pH of solution, temperature of the system, and initial metal concentration, were explored. The studies indicated that GO/l-Trp exhibited enhanced sorption capacities for Cu(II) and Pb(II) at the initial pH of 5 and 4, respectively, due to the increased sorption sites. The sorption of Cu(II) and Pb(II) were nearly completed within 40 min and fitted better with Lagergren pseudo-second-order kinetic model, indicating that Cu(II) and Pb(II) sorption on GO/l-Trp were chemical interactions. Langmuir model was more suitable to describe the sorption processes and sorption capacities were 588 mg·g–1 and 222 mg·g–1 for Cu(II) and Pb(II), respectively. Thermodynamic studies revealed that sorption were exothermic and spontaneous. Moreover, it ...