Decontamination performance of magnetic graphene oxide towards nickel ions and its underlying mechanism investigation by XAFS

In this paper, the decontamination performance and its underlying mechanism of magnetic graphene oxide (MGO) towards nickel (Ni(II)) ions were studied by batch technique and X-ray absorption fine structure (XAFS) analysis. The conditions that affect Ni(II) uptake, such as reaction time, pH, ionic strength, coexisting ions, humic/fulvic acid (HA/FA) and temperature were investigated by control variable method. The adsorption kinetics indicated that Ni(II) uptake on MGO was corresponded with pseudo-second-order rate equation, and it can reach equilibrium after ~4.0 h. The pH had ken speckle effect on Ni(II) uptake, while the ionic strength and coexisting ions had scant impact on Ni(II) uptake. The presence of HA/FA has a positive impact on Ni(II) uptake at pH < 7.0, while has a negative impact on Ni(II) uptake at pH > 7.0. The uptake of Ni(II) can be better described by Langmuir model than Freundlich model. The thermodynamic analysis suggests that Ni(II) uptake was an endothermic and spontaneous behavior. XAFS analysis indicate that Ni(II) was captured on the binding sites of MGO, and some Ni(II) can bind on the surfaces of the iron oxides coated on GO to form strong inner-sphere complexes with good thermodynamic stability. Results of this study indicate that MGO is a significant material for treatment of Ni(II)-bearing effluents and may also be an effective adsorbent for removing other metal ions from wastewater.