Cd(ii) removal by Fe(ii) surface chemically modified layered double hydroxide-graphene oxide: performance and mechanism.

Cd(ii) adsorption onto Fe(ii) modified Layered double hydroxide-graphene oxide (LDH-GO@Fe(ii)) was investigated using batch experiments. With the modification of Fe(ii), LDH-GO maintained its structure, while Fe(ii) species formed non-crystalline iron oxide clusters on the surface of the LDH/GO. A kinetics study indicated that adsorption obeyed a pseudo-second-order rate law. The equilibrium data were fitted well with the Langmuir isotherm model. The maximum adsorption capacity of LDH-GO@Fe(ii) was 28.98 mg g, higher those that of pure LDH-GO and LDH-GO@Fe(ii). The increased sorption capacities could be explained by the increased specific surface area. Modification with Fe(ii) would lead to the generation of amorphous Fe oxides and Fe could occupy the binding sites for Cd(ii), thus excess Fe in the structure will restrain the adsorption of Cd(ii). The XRD and XPS patterns revealed the formation of Cd(OH) after adsorption. Batch experiments indicated that precipitation and surface complexation were the main pathways for Cd(ii) removal.