Thermal behavior and texture of mesoporous zirconia obtained from anionic surfactants

Abstract

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.