Abstract
Magnetic sulfonated graphene (MSG) composite was synthesized from polyethylene terephthalate bottle waste by using a facile and reproducible method in addition to two graphene-based nanomaterials, including highly reduced graphene oxide (HRGO) and sulfonated graphene (SG). Further, batch experiments were carried out to examine their adsorption efficiency in relation to two heavy metals ions, Cd(II) and Pb(II), in single metal and mixed-metal solutions. The synthesized materials were characterized by Fourier transform infrared, X-ray diffraction, transmission electron microscope, energy dispersive X-Ray spectroscopy, and Brunauer-Emmett-Teller analysis which indicated that HRGO was successfully decorated by sulfonic groups and magnetic nanoparticles. Operating parameters including time, initial concentration of metal and adsorbent dose on the adsorption process were investigated and optimized at a pH of 5.5 for both metals using a response surface methodology model; however, the optimum conditions for Cd(II) removal were 13.28 min contact time, 50 mg L-1 of Cd(II) initial concentration, and 0.012 mg of MSG at 25 degrees C while, at contact time 2.9 min, 100.7 mg L-1 of Pb(II) and 0.14 mg of MSG, complete removal was achieved. Adsorption process was obeyed pseudo-second-order and intra-particle diffusion kinetic models, while the calculated adsorption capacities of MSG for Cd(II) and Pb(II) ions at equilibrium fit perfectly with Langmuir and Freundlich isotherms models. The negative values of Delta G and positive values of Delta H and Delta S elucidate that the adsorption of Cd(II) and Pb(II) ions onto MSG is spontaneous, endothermic and random process. In addition, the adsorbents were easily regenerated and reused for five cycles with high adsorption capacity. This study indicates that the prepared MSG is a low-cost reusable adsorbent for the rapid and efficient removal of Cd(II) and Pb(II) ions from contaminated wastewater.