Enhanced adsorption of fluoride from aqueous solutions by hierarchically structured Mg-Al LDHs/Al2O3 composites

Hierarchically structured layered double hydroxides (LDHs)/Al2O3 composites were fabricated from waste paper fibers using a two-step method. In the first step microscaled Al2O3 fibers were prepared by template-directed synthesis employing waste paper fibers as templates; and in the second step nanoscaled LDHs platelets were fabricated into hierarchical architectures based on crystal growth on Al2O3 fibers surface. The morphology and structure of asprepared samples were characterized by scanning electron microscopy (SEM), N-2 adsorption/desorption analysis and X-ray diffraction (XRD) analysis. The SEM results revealed that the inorganic fibers were covered by LDHs platelets, forming the hierarchical structures with micro- to nanoscales. The BET analysis showed that the surface area was increased from 76.66m(2)/g (Al2O3 fibers) to 165.0m(2)/g (composites) by the growth of LDHs platelets on the surfaces of Al2O3 fibers. As compared to bare LDHs particles and Al2O3 fibers, the LDHs/Al2O3 composites show a high fluoride adsorption capacity, and the maximum adsorption capacity can reach up to 58.7mg/g. The Langmuir isotherm model was found to agree well with the equilibrium data, while the pseudo-second order model provided the highest correlation of the kinetic data for fluoride adsorption. The as-prepared LDHs/Al2O3 composites and corresponding design strategies developed herein are expected to be applicable to the synthesis of other LDHs based composites for the removal of pollutants from water.