Unique lead adsorption behavior of ions sieves in pellet-like reduced graphene oxide

Hollow and pellet-like reduced graphene oxide (P-RGO) was synthesized by electrostatic assembly and acid-treatment. The average size and shell thickness of P-RGO were 65.9 nm and 4 nm, respectively. The adsorption capacity of P-RGO for lead ions was as high as 184.5 mg g(-1) and the adsorption equilibrium of lead ions (50 mg L-1) was achieved within 5 min. Lead ion removal by adsorption onto P-RGO increased with decreasing pH. Because P-RGO exhibited stronger affinity for lead ions than for water, lead ions could be drawn and stored into the cavity in the P-RGO, i.e., ions storage effect was observed. This led to high adsorption capacity and abnormal adsorption behavior. The adsorption mechanism was proposed as ions exchange and competitive process for layer RGO and P-RGO, respectively. This study suggested that structure reconstruction of materials could enhance the efficiency and capacity for unique metal removal.