Hierarchical porous Al2O3@ZnO core-shell microfibres with excellent adsorption affinity for Congo red molecule

Three-dimensional hierarchical Al2O3@ZnO core-shell composite was designed and fabricated by a multistep strategy, involving an initial hydrothermal reaction, a subsequent chemical bath deposition process and a final calcination treatment. Electron microscopy images revealed that the Al2O3@ZnO composite was uniform in size and possessed a structure constituted by an Al2O3 core and a shell of crumpled ZnO nanosheets on which numerous pores were found. The as-synthesized Al2O3@ZnO core-shell composite exhibited fast kinetics and outstanding adsorption capacity for Congo red (CR) due to its unique structure and highly porous texture, which was much superior to those of bare Al2O3 core and ZnO microspheres. The pseudo-second-order kinetic model could represent the adsorption kinetics for CR adsorption, whereas the Langmuir isotherm model was suitable for describing the adsorption isotherm. The as-synthesized hierarchical Al2O3@ZnO microfibres with maximal adsorption capacity of 714 mg g(-1) are highly competitive in terms of CR adsorption.