Adsorption and desorption of phenanthrene by magnetic graphene nanomaterials from water: Roles of pH, heavy metal ions and natural organic matter

Abstract

The adsorption of phenanthrene onto magnetic graphene oxide (MGO), magnetic chemically-reduced graphene (MCRG) and magnetic annealing-reduced graphene (MARG) were compared to examine their unique adsorption properties. The effects of environmental factors on the adsorption-desorption properties of phenanthrene e.g. pH, heavy metal ions, and natural organic matter were also investigated. MCRG had the highest adsorption capacity for phenanthrene, mainly due to the larger surface area and pore volume, and numerous wrinkles of MCRG. The π–π interaction was the predominant adsorption mechanism of MCRG. Coexisting Cd(II) and As(V) had a minor impact on phenanthrene adsorption by MCRG, while the adsorption capacity of phenanthrene decreased considerably with coexisting humic acids. Phenanthrene caused desorption hysteresis, which was largely suppressed by humic acids. The desorption hysteresis was ascribed to the entrapment of phenanthrene molecules derived from the generation of closed interstitial spaces caused by the rearrangement of graphene nanosheets onto MCRG. Steric hindrance was much larger with adsorbed humic acid molecules. Our findings on magnetic graphene nanomaterials (MGNs) and related adsorption-desorption properties highlight their potential applications as efficient adsorbents and their possible risks in natural aquatic environments.