Mesoporous Oxides
Mesoporous oxides contain pores of roughly 2 to 50 nm, often made by templating an oxide precursor around surfactant micelles or block copolymers and then removing the template by heating. Evaporation-induced self-assembly (EISA), in which micelles organize as the solvent evaporates, is a common route. Their high specific surface area makes them attractive as catalysts and electrodes, but the thin pore walls can collapse or coarsen at the high temperatures needed to crystallize many oxides.
Mesoporous coatings formed inside porous supports (2011)
EISA templating survives confinement in micron-sized pores: HAADF STEM of LSM infiltrated five times into a commercial LSCF cathode showed an interconnected mesoporous framework with a mean pore radius of about 17 +/- 8 nm and walls of about 25 nm, much finer than the 100 to 200 nm features of conventionally impregnated LSM (Chao et al. 2011). The proposed mechanism is that CTAB micelles assemble on the pore walls once evaporation raises the surfactant above its critical micelle concentration, and leave mesopores when burned off during calcination; the surfactant also improves wetting of the backbone. The authors flag thermal stability of CTAB-templated coatings at operating temperature as an open question. Summary: chao2011.
EISA-templated (La,Sr)MnO3 and the area/stability trade-off (2012)
For LaMnO3 and (La,Sr)MnO3 prepared by EISA and calcined at 700 C, Chao and co-workers found that higher metal nitrate loading (up to the salt solubility limit), higher relative humidity during aging (60% versus 20%), and lower molecular weight surfactant (CTAB rather than P-123 or F-127) all raised the surface area, which BJH analysis traced to mesopores of about 5 to 50 nm. STEM showed a disordered interconnected network with 10 to 20 nm pores and 1 to 10 nm walls. Thermal stability ran the opposite way: in a 100 h, 750 C anneal the CTAB powder lost 35% of its area, while P-123 and F-127 powders lost 11% and 6%, which the authors attribute to thicker walls formed with the larger Pluronic templates (Chao et al. 2012). Summary: chao2012.