Structural evolution of hierarchical porous NiO/Al2O3 composites and their application for removal of dyes by adsorption

Hierarchical porous NiO/Al 2 O 3 composites were successfully prepared by two-steps. First, the core-shell structured Al 2 O 3 microspheres were prepared via a template-free hydrothermal route using KAl(SO 4 ) 2 ·12H 2 O and Al 2 (SO 4 ) 3 ·18H 2 O as aluminum source. Then, the NiO/Al 2 O 3 composites with micro- and nano-hierarchical structures were prepared by a hydrothermal method combining the subsequent calcination process. The obtained characterization result presented that the morphology of hierarchical Al 2 O 3 microsphere tuned to irregular platelets by simply varying Ni/Al ratios. The BET analysis showed that the special surface area from 52.12m 2 g −1 to 214.8m 2 g −1 after two hydrothermal complex process. Effects of Ni/Al ratio, adsorbent dosage, Congo red (CR) concentration, coexisting ions, adsorption time and temperature were investigated. The obtained results indicated that NiO/Al 2 O 3 composite had the high adsorption efficiency (99.6%) and great adsorption capacity (186.9mg g −1 ) under the optimum conditions. The adsorption isotherm and kinetics data were found to be well fitted and in good agreement with the Langmuir isotherm model and pseudo-second order model, respectively. The hierarchical porous NiO/Al 2 O 3 composites presented remarkably higher adsorption efficiency during five recycling, which showed their potential as the highly efficient adsorbent for removal of CR in wastewater.