Macroporous alumina monoliths prepared by filling polymer foams with alumina hydrosols

Abstract

Macroporous alumina monoliths have been prepared for the first time by filling polystyrene foam templates with alumina hydrosols which were prepared from pseudo-boehmite. Polystyrene foam templates were obtained by polymerization in highly concentrated water-in-oil (W/O) emulsions. The organic templates were subsequently removed by calcination. The effects of filling times of the alumina hydrosols, calcination temperature, and CTAB surfactant addition in the hydrosols on the properties of the monolith have been investigated. TG, FT-IR, SEM, TEM, N₂ adsorption–desorption, and XRD techniques were used for characterization. The so prepared monoliths are the replicas of the polystyrene foams and are characterized with hierarchically porous structure. The macropores are interconnected and the macropore walls contain many meso and/or micropores. The hierarchically macro-meso-microporous structure can be controlled and tailored by adjusting the preparation conditions stated above and by addition of surfactant, and the organic components can be eliminated by high temperature calcination. When the calcination temperatures are 600 °C and 900 °C, the γ-Al₂O₃ phases are obtained, with S_BET of 228 and 85 m² g⁻¹, respectively. When calcined at 1100 °C, the alumina monolith presents a single θ-Al₂O₃ phase with S_BET of 80 m² g⁻¹. The 1300 °C calcined sample takes on the single α-Al₂O₃ phase with S_BET of 5 m² g⁻¹ and compressive strength of 3.1 MPa.