Simple and low-cost production of magnetite/graphene nanocomposites for heavy metal ions adsorption.

It is challenging to produce economical magnetic graphene-based adsorbents on an industrial scale for heavy metal ions removal. Here, magnetite/graphene nanocomposite embedded in activated carbon matrix (magnetite/G-AC) was synthesized via in situ catalytic graphitization of iron-impregnated biochar to obtain graphene encapsulated iron nanoparticles (GEINs) embedded in biochar (BC) matrix, and followed by steam activation of GEINs-BC. Steam activation aimed to upgrade biochar to activated carbon with oxygen functional groups, crack encapsulated graphene shell to graphene nanosheets, and obtain magnetic Fe3O4 by oxidation of iron, thereby improving the adsorption capacity of magnetite/G-AC-800 (153.2 mg/g) four times higher than that of GEINs-BC. The parameters on the adsorption capacity were investigated using Pb(II) ions as a typical pollutant as a function of solution pH (3-7), contact time (5-300 min), initial Pb(II) concentration (50-400 mg/L), and adsorbent dosage (0.05-0.25 g). The fitted pseudo-second-order kinetic model and Langmuir model indicated that the main adsorption mechanism was chemical adsorption over monolayer. This research developed a low-cost magnetic adsorbent with the advantage of simple large-scale production and excellent adsorption capacity per unit cost for remediating wastewater.