Template-free synthesis of mesoporous γ-alumina with tunable structural properties

Mesoporous γ-Al2O3 (MA) with agglomerated nanoparticles was successfully synthesized by using aluminum sulfate as inorganic Al resource, and hexamethylene tetramine (HMTA) as precipitant without using any surfactants, via a hydrothermal method. All the experimental processes experienced the hydrolysis, precipitation and calcination steps. The structural and morphological properties of uncalcined and calcined samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry differential thermal gravity (TG-DTG) and N2 adsorption–desorption. The bulk density of the sample is 0.682 cm3  g−1, and the specific surface area is 273.302 m2 g−1. The pore diameters (7.1 nm and 9.7 nm) indicate that a typical bimodal mesoporous structure was formed within MA. In order to tune the structural properties of MA, various kinds of inorganic aluminum sources and precipitating agents were employed to carry out contrast experiments, which leaded to regular variations in the specific surface area (200.898–273.302 m2 g−1), pore volume (0.121–1.327 cm3 g−1) and pore size (3.7–35.9 nm). At the same time, the experimental results also demonstrated that the various kinds of Al resources and precipitants had no effects on the crystal structure of MA. However, the morphologies of samples, such as nanoparticles, short fibers, flower-like and block-shaped, can be controlled effectively. The present study provides a simple and effective approach for preparing MA, and the structural properties of MA can be controlled precisely by carefully choosing aluminum sources and precipitants. The approach of this work not only allows us to investigate the growth mechanism of the final product, but also reduces cost and the environmental pollution effectively than other template methods.