Developing new strategies for template-free synthesis of penta-coordinated Al3+ γ-Al2O3 with different morphologies using glycothermal modification

Abstract

High surface area mesoporous γ-Al₂O₃ was synthesized using a robust template-free glycothermal process. The samples were prepared using inexpensive aluminium nitrate and two different precipitating agents (aqueous ammonia and urea), forming nanorods and nanosheets, respectively. The resultant material was calcined at 600 °C for 3 and 5 h to ensure the formation of the γ-Al₂O₃ with penta-coordinated Al³⁺. The surface and morphology of the synthesized material were characterized using ²⁷Al MAS NMR, N₂-physisorption, NH₃-TPD, TEM, SEM, and powder-XRD. ²⁷Al MAS NMR confirmed the presence of varying amounts of penta-coordinate Al³⁺ on the surface. The surface area of the synthesized material varied from 239 m² g⁻¹ to 492 m² g⁻¹, depending on thermal treatment. The TEM and SEM observations highlighted the different microstructures and morphology present for the synthesized materials, with distinct 3D surfaces present for the nanorod and nanosheet samples. The described methods provide a robust, scalable synthesis for penta-coordinate Al³⁺ γ-Al₂O_3, which can be used in industrial applications such as catalysis, energy storage, and nanocomposites.