Study of the preparation of γ-Al2O3 nano-structured hierarchical hollow microspheres with a simple hydrothermal synthesis using methylene blue as structure directing agent and their adsorption enhancement for the dye

• The γ-Al2O3 were prepared using methylene blue as structure directing agent.
• The microstructure of the prepared adsorbents can be effectively controlled.
• The mechanism of the enhanced adsorption can be explained by template synthesis.

The γ-Al2O3 nano-structured hierarchical hollow microspheres were prepared with a simple hydrothermal synthesis using methylene blue as structure directing agent and the structure directing agent was removed after the γ-Al2O3 samples were calcinated at 600 °C for 2 h. The microstructural and properties of the prepared γ-Al2O3 samples were characterized by X-ray diffraction (XRD), TEM, BET, FT-IR. The static adsorption of γ-Al2O3 for methylene blue was conducted. The results showed that when 20 mg (the molar ratio of Al3+ to structure directing agent was 56:1) of structure directing agent was used, the γ-Al2O3 samples were prepared with that the specific surface area increased by 31% and the maximum adsorption capacity for methylene blue was 8.38 mg/g, increased by 61%.In addition, the adsorption equilibrium isotherms model and adsorption kinetics model were investigated. The adsorption of γ-Al2O3 for methylene blue is best fitted with Langmuir adsorption model, the kinetic process of adsorption can be described by the pseudo-second-order kinetic model.This study demonstrates the microstructure of γ-Al2O3 can be effectively controlled and the adsorption properties of it is improved using template synthesis with a proper amount of methylene blue as structure directing agent.