Adsorption of heavy metals from wastewater using reduced graphene oxide@titanate hybrids in batch and fixed bed systems

Wastewater contaminated by heavy metal ions poses serious threats to the ecosystem, needing to be well disposed of. In this study, reduced graphene oxide@titanate hybrids (rGOTHs) are synthesized to efficiently remove heavy metals from wastewater in batch and fixed bed systems. The size of prepared rGOTHs is large as hundreds of microns, which is beneficial for separation and application in batch and fixed bed system. In the batch studies, rGOTHs exhibits the fast adsorption rate and high adsorption capacity towards heavy metals, in which the adsorption kinetic and isothermal are best fitted to Pseudo-second-order kinetic model and Langmuir model, respectively. The maximum adsorption capacities of rGOTHs for Pb(II), Cd(II) and Cu(II) are 530.5, 201 and 130.5 mg/g at 298 K and pH 5, respectively. In addition, the exhausted adsorbent can be easily regenerated in alkaline hydrothermal process and the high removal efficiency is almost reserved after six cycles. Moreover, rGOTHs presents higher selective adsorption towards Pb(II) than other ions. Adsorption mechanisms are revealed to be ions exchange, electrostatic interaction, and coordination. In the fixed bed experiments, the effective treatment volume of rGOTHs-loaded column reaches to 2760 BV (15.45 L) for single Pb(II) polluted battery manufactory wastewater and 2280 BV (12.76 L) for multiple heavy metal polluted estuary effluent, before Pb(II) concentration exceeds the discharge limit of 1 mg/L. Our study demonstrates the great potential of rGOTHs to be applied in practical treatment of wastewater contaminated by heavy metal ions.