Thermal behavior and texture of mesoporous zirconia obtained from anionic surfactants

Thermogravimetric and differential thermal analyses of mesoporous zirconias obtained from anionic surfactants by a scaffolding mechanism reveal interesting differences between the samples prepared from long-chain sulfates or sulfonates, which lose their hydration water in two steps, and those obtained from long-chain phosphates for which dehydration occurs in one step. From the temperature of the tetragonal to monoclinic transition the molar volume of ZrO2 undergoing this transformation can be calculated. From the density and from the mesoporous volume (N2 adsorption), the thickness of the wall separating the elemental volumes of the mesoporous structure can be calculated as well as the pseudo-length of the pores. The calculated surface area of the mesopore fits nicely with the measured T-plot surface area for the sample calcined at 500 °C. For the sample dried at 140 °C, the agreement is not as good, probably because of a more disordered organization. The alkyl chain is tilted by about 57±10° with respect to the normal to the wall. Upon calcination the thickness of the wall increases to a point where crystallization in monoclinic zirconia occurs. At this point the mesoporous character is lost.