Synthesis of magnetite-graphene oxide-layered double hydroxide composites and applications for the removal of Pb(II) and 2,4-dichlorophenoxyacetic acid from aqueous solutions.

Magnetic composites consisting of magnetite (Fe3O4), graphene oxide (GO), and Mg3Al-OH layered double hydroxide (LDH), denoted as MGL composites, with varying GO contents (RGO) were synthesized by a mechano-hydrothermal (MHT) route using Fe3O4, Mg(OH)2, and Al(OH)3 as the inorganic starting materials. The application of the synthesized MGLs for removing the heavy-metal Pb(II) and the hydrophobic organic pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solutions was investigated. Chemical bonding among the GO, Fe3O4, and LDH components was observed in the MGLs. The MGL composites showed good water-dispersity, strong magnetic response, and high sorption capacities and removal efficiencies for both Pb(II) and 2,4-D pollutants. The sorption capacities of the MGL for the pollutants significantly increased with an increase in RGO. Increasing pH could increase the removal efficiency for Pb(II) but decrease that for 2,4-D. The MGLs showed more affinity for Pb(II) than for 2,4-D in the competitive sorption. In addition, the MGLs could remain almost constant removal efficiency for the pollutants after reuse over six cycles, indicating their potential use as sorbents in wastewater treatment. Furthermore, a Cs effect was observed in the sorption equilibriums, which could be described using the Langmuir-SCA and Freundlich-SCA isotherms. The removal mechanisms of the MGL for Pb(II) and 2,4-D were discussed. The MHT method provided a simple and environmentally friendly route for synthesizing GO-LDH composite materials.