Facile synthesis of magnetic composite with reduced graphene oxide as apromising adsorbent for mercury removal

Mercury with high toxicity can be discharged into the atmosphere, soil and water, accumulate in the food chain and enter the human body via food consumption, posing a great threat to human health and ecological environments [۱-۳]. To reduce mercury emissions from power plants, the Mercury and Air Toxicity Standard (MATS) was issued by the United States Environmental Protection Agency (EPA) in ۲۰۱۱ and wasimplemented in ۲۰۱۲ [۴]. In April ۲۰۱۶, the ۲۰th meeting of the Standing Committee of the۱۲th National People's Congress of the People's Republic of China decided to ratify the Minamata Convention on mercury, requiring State parties to prohibit the production, importand export of mercury-containing products as of ۲۰۲۰. Coal combustion in thermal powerplants is one of the main sources of mercury pollution [۵, ۶]. However, Hg۰ is extremely difficult to remove using existing air pollution control devices (APCDs) because of its highequilibrium vapor pressure, low melting point and insoluble nature in water [۷, ۸]. Thus,finding an effective method to remove elemental mercury is the main research direction of new mercury removal technology. Our previous review has summarized the recent advances of graphene-based adsorbents for the decontamination of wastewater [۸]. Graphene has a large theoretical specific surface area (∼۲۶۳۰ m۲ g−۱) and graphene oxide(GO) has abundant functional groups, indicating their potentiality for the removal of heavymetal ions and organic pollutants [۹], [۱۰]. However, it is difficult to separate graphene orGO from aqueous solution via traditional centrifugation and filtration method because ofits small particle size [۱۲]. Therefore, magnetic graphene-based adsorbents that facilitateseparation by magnetic field have begun to be used in the field of environmentalremediation.In this work A magnetic composite consisting of few layers reduced graphene oxide (rGO) and Fe۳O۴ nanoparticles were fabricated by a facile one-step reaction route. Scanningelectron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize theFe۳O۴/rGO. Morphology, chemical structure and element analysis showed that theFe۳O۴/rGO was successfully synthesis. It was encouraging to find that the ternary Fe۳O۴/rGO nanohybrid exhibited excellent performance for Hg removal from aqueoussolution. The maximum adsorption capacity for Hg onto Fe۳O۴/rGO was ۳۶۵.۲۱ mg g−۱,which was much higher than that of Fe۳O۴/rGO. The removal process was pH dependence, exothermic and spontaneous. The adsorption of Hg species was facilitated through bothelectrostatic attraction and ion exchange process. The Fe۳O۴/rGO non-nanocomposite couldbe utilized as an efficient, stable, less toxic and magnetically separable adsorbent for environmental cleanup.