Adsorption of Pb2+ and Cd2+ on reduced graphene oxide hydrogel prepared from natural cryptocrystalline graphite

In this study, graphene hydrogel with small pore size and high specific surface area was prepared from unpurified natural cryptocrystalline graphite and was used to adsorb Pb2+ and Cd2+ from aqueous solution. The adsorption performance of reduced graphene oxide hydrogel under different pH, time, initial metal ion concentration and reuse time was investigated. It was experimentally found that the adsorption capacities of reduced graphene oxide hydrogel for Pb2+ and Cd2+ increased with the increase of pH. The adsorption of Pb2+ and Cd2+ followed the Langmuir monolayer adsorption model and pseudo second-order kinetic model. The maximum adsorption capacities of reduced graphene oxide hydrogel for Pb2+ and Cd2+ can reach 2503.62 mg/g and 1185.27 mg/g, respectively. The adsorption for metal ions can finish in about 5 min because of the existence of electrostatic attractive and cation-π interaction between them. The reduced graphene oxide hydrogel remained above 80% adsorption capacities for both Pb2+ and Cd2+ after 6 adsorption-desorption cycles. These results indicated that the graphene oxide prepared from unpurified natural cryptocrystalline graphite was an effective and stable adsorbent for the treatment of heavy metal ions in aqueous.