Synthesis of highly porous alumina-based materials

gamma-Alumina-based materials with high porous volume, tunable pore size, were synthesized by the addition of both PEO/PPO/PEO triblock copolymers (Pluronics (R) F127 and P123) and metal nitrates (Al3+, Mn2+, Cu2+) in a boehmite (AlOOH) nanoparticle hydrosol. During the subsequent thermal treatment, the surfactant was removed leaving a highly porous framework. The pore size distribution was strongly dependent on the metal nitrate added and its concentration. By this simple process it was possible to modify the porous volume in the range 0.3-2.6 cm(3) g(-1) and the median pore diameter in the range 5-40 nm. All these materials presented high surface areas in the range 300-500 m(2) g(-1). During the drying AlOOH particles aggregate to form linear objects (flat rods, laths) in order to minimize electrostatic repulsion. We think that the improvement of the textural characteristics of gamma-alumina could be explained by the adsorption of copolymer onto these fiber-like objects, preventing the compact rearrangement of the boehmite nanoparticles in a compact "card-pack" microstructure during the drying. The addition of electrolytes induces a reduction of electrostatic repulsions, leading to the formation of both fiber-like objects at lower AlOOH concentration, and a 3D network by bridging these 1D objects. This bridging is reversible since the gel returns to a sal state under shearing, but polymer adsorption can prevent the full collapsing of this network during the drying step and a huge porosity can be maintained after calcination. (c) 2013 Elsevier Inc. All rights reserved.