The critical role of oxidative debris in the adsorption and desorption of Pb(II) to graphene oxides under alkaline groundwater conditions

The application of graphene oxide (GO) and its derivatives as adsorbents to remove heavy metal contaminants from industrial wastewaters has attracted increasing attention worldwide. Here, we investigated the role of oxidative debris (OD) on GO surfaces in the adsorption of Pb(II) under natural conditions. OD attached to GO surfaces can be removed under alkaline conditions, and plays a critical role in the adsorption of Pb(II) by GO. Specifically, the maximum adsorption capacity of Pb(II) on GO decreased from 926.50 to 357.64 mg·g-1 after OD removal. Under simulated natural alkaline groundwater conditions, some adsorbed Pb(II) was released with OD that was stripped from spent GO adsorbents (i.e., GO-Pb(II)). Further, batch experiments indicated that 1.30-1.43% of adsorbed Pb(II) could stably disperse in water as dissolved PbCO3 and OD-Pb(II) complexes, at a pH of ~8.3. The stripping and dissociation of OD under alkaline conditions promoted the mobility of Pb(II) on GO adsorbents. This study enhances our understanding of heavy metal transport in natural alkaline groundwater environments that contain GO particles.