Microwave-assisted adsorption of Cr(VI), Cd(II) and Pb(II) in presence of magnetic graphene oxide-covalently functionalized-tryptophan nanocomposite

Microwave (MW)-assisted remediation of heavy metals toxicity using a powerful environmental-friendly nanocomposite of magnetic graphene oxide functionalized tryptophan (MGO-Trp) was explored in this work. Magnetization of GO with Fe3O4 nanoparticles prepared in situ was uniformly achieved and then covalently bonded to Trp. The structural characterizations and thermal stability of synthetic MGO-Trp nanocomposite were investigated by FT-IR, XRD and TGA. A homogenous flake-like surface of well magnetized GO sheets was manifested by SEM and TEM images. The surface area measurements and BET method (adsorption/desorption curve) indicated a surface area = 10.157 m2 g−1 and mean pore diameter = 13.229 nm. MW-technique and MGO-Trp nanocomposite declared an efficacious sorption of Pb(II), Cd(II) and Cr(VI) ions with high adsorption capacity values. Different factors, MW-contact time, temperature, pH, nanocomposite dose and metal concentration affecting on the adsorption capacity, were followed up. The highest values of adsorptive capacities of Pb(II) and Cd(II) were observed to be 4800 and 5400 μmol g−1, respectively at pH 7 and MW-contact time of only 20s. The Cr(VI) species were efficiently extracted at pH 2 with capacity values = 3400 μmol g−1. Kinetic studies brought to light that the adsorption system was agreeing with pseudo-second order and Elovich than either pseudo-first order or intraparticle diffusion models. Thermodynamic parameters (ΔH°, ΔS° and ΔG°) were also evaluated and provided spontaneous exothermic adsorption for both Pb(II) and Cd(II) ions, while spontaneous endothermic adsorption behavior was observed for Cr(VI) species. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D-R) models and their parameters were investigated, confirming favorable and rapid adsorption processes. The potential applications of MGO-Trp as a felicitous and high performance nanocomposite of the mentioned metal ions in presence of other competing ions as well as from naturally contaminated water samples were successfully accomplished in fast effective operations with extraction percentages close to 100%. Graphical representation of MGO-Trp nanocomposite with Metal ions. [Display omitted] •Synthesis of magnetic graphene oxide functionalized tryptophan (MGO-Trp).•Microwave -assisted remediation of Pb(II), Cd(II) and Cr(VI) ions.•High capacities of Pb(II), Cd(II) and Cr(VI) ions at 20 s MW sorption time.•Kinetics-isotherm models fitting and thermodynamics evaluations.•Fa