Porosity, crystal phase, and morphology of nanoparticle derived alumina as a function of the nanoparticle's carboxylate substituent

Carboxylate-alumoxanes are a simple to prepare class of chemically functionalized alumina nanoparticles. The identity of the carboxylate group has a direct effect on the microstructure and temperature of phase conversion for their pyrolysis to alumina bodies. A series of carboxylate-alumoxanes with varying chain length of the organic substituent (organic content) have been investigated: acetic acid alumoxane (A-A), methoxyacetic acid alumoxane (MEA-A), methoxy(ethoxy)acetic acid alumoxane (MEA-A) and methoxy(ethoxyethoxy)acetic acid alumoxane (MEEA-A). The changes in porosity, surface area, pore volume, and pore size distributions, crystal phase and morphology of the alumina formed from each alumoxane have been studied between 600 and 1100 °C by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer, Emmett and Teller (BET). Alumina derived from A- and MEA-alumoxanes have a particulate morphology, while alumina derived from MA- and MEEA-alumoxane are composed of aggregates of smaller particles. The properties of the alumina at higher temperatures are dependent on the identity of the carboxylate periphery and hence the morphology of the alumina at the lower temperatures.