Template-Directed Synthesis of Porous Alumina Particles Via Atomic Layer Deposition

Highly porous alumina particles with precise wall thickness control were synthesized by atomic layer deposition (ALD) of alumina on highly porous poly(styrene-divinylbenzene) (PS-DVB) particle templates. Alumina ALD was carried out using alternating reactions of trimethylaluminum and water at 33 °C. The growth rate of alumina was ~0.3 nm per coating cycle. After deposition, the polymer was removed by air oxidation leaving a highly porous alumina skeletal structure. The wall thickness can be precisely controlled by adjusting the number of ALD coating cycles. Thermogravimetric analysis, X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and transmission electron microscopy were used to characterize the fabricated porous alumina particles. The effect of number of ALD coating cycles and calcination temperature on the mesoporous structure of the alumina particles was investigated. γ-alumina was formed at temperature above 600 °C. Porous crystalline alumina particles with a surface area of 80-100 m²/g were obtained and thermally stable at 800 °C. The pore volume of the porous particles can be as high as 1 cm³/g after calcination at 800 °C. Control of the wall thickness to within ~0.3 nm provides for ultimate control of surface area. Such porous alumina particles may find wide application in nanostructured materials fabrication, including novel catalyst supports.