γ-Al₂O₃ yolk–shell porous microspheres with superior Congo red removal performance

γ-Aluminum oxide (γ-Al₂O₃) yolk–shell meso–macroporous microspheres (AOYSs) were prepared using the glucose-assisted hydrothermal method followed by an annealing process, and were characterized by X-ray diffraction, scanning electron microscopy and Brunauer–Emmett–Teller nitrogen (N₂) adsorption–desorption analysis. The hierarchical AOYSs showed a high specific surface area (201 m²/g) with highly porous structures. Compared with solid and hollow microspheres, the hierarchical AOYSs showed an excellent adsorption performance toward Congo red, which can be attributed to their unique yolk–shell structures and hierarchical meso–macroporous structures with a high specific surface area. Furthermore, the Langmuir isotherm model and pseudo-second-order kinetic model well represented the adsorption of Congo red on the surface of hierarchical AOYSs. This study provides a new insight into the design and synthesis of yolk–shell nanostructures, which can offer various applications, such as those in adsorption, energy storage, catalysis and sensor fields.