Preparation of magnetic composite sorbent based on exfoliated graphite with metallic iron, cobalt and nickel using melamine as a reducing agent

Abstract

Known preparation methods of the magnetic sorbents based on exfoliated graphite (EG) with metallic phase take several hours and requires the use of a large amount of reducing gas at a high temperature, which is not technologically advanced. The aim of the work is to obtain EG modified with iron, cobalt, and nickel using new simple method. This method includes the thermal treatment in nitrogen atmosphere of the mixture of expandable graphite, Mn+ nitrates (Mn+ = Fe3+, Co2+, Ni2+) and melamine. The thermal decomposition of melamine leads to formation of ammonia, which reduces the products of the Mn+ nitrates decomposition (α-Fe2O3, Co3O4/CoO, NiO) to metallic iron, cobalt and nickel. The use of different amount of melamine as reducing agent leads to the formation of mixtures with different compositions containing iron oxides Fe3O4, FeO, metallic iron α-Fe, Fe-C alloy γ-(Fe,C) and iron carbide Fe3C, which were confirmed by Mossbauer spectroscopy. Metallic Co and Ni on the EG surface is formed in nitrogen atmosphere by reduction with carbon even without melamine. Obtained EG/Fe has the highest saturation magnetization of 54.7 emu/g. EG/Co and EG/Ni have lower saturation magnetization of 40.1 and 12.0 emu/g, which is due to lower saturation magnetization of the individual metals.