Ionic liquid assisted hydrothermal fabrication of hierarchically organized γ-AlOOH hollow sphere

Hierarchically organized γ-AlOOH hollow spheres with nanoflake-like porous surface texture have been successfully synthesized via an ionic liquid-assisted hydrothermal synthesis method in citric acid monohydrate (CAMs). It was found that ionic liquid [bmim]+Cl− played an important role in the morphology of the product due to its strong interactions with reaction particles. The samples were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM). The results show that the product has narrow particle size distribution (500–900 nm particle diameter range), high specific surface area (240.5 m2/g) and large pore volume (0.61 cm3/g). The corresponding γ-Al2O3 hollow spheres can be obtained by calcining it at 550 °C for 3 h. The proposed formation mechanism and other influencing factors of the γ-AlOOH hollow sphere material, such as reaction temperature, reaction duration, CAMs and urea, have also been investigated.

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► The γ-AlOOH hollow spheres were synthesized via an ionic liquid-assisted hydrothermal treatment.
► Ionic liquid plays an important role in the morphology of the product.
► Ionic liquid can be easily removed from the product and reused in next experiment.
► A “aggregation–solution–recrystallization” formation mechanism may occur in the system.