Synthesis of monolithic zirconia with macroporous bicontinuous structure via epoxide-driven sol–gel process accompanied by phase separation

Abstract

Monolithic macroporous zirconia was synthesized through a new method involving an epoxide-driven sol–gel method accompanied by a spontaneous phase separation. The sol–gel transition utilized inorganic salt ZrCl4 as primary precursor and propylene oxide as matrix former through a ring-opening reaction. Phase separation was induced with poly-(ethylene oxide) (PEO) and its tendency was adjusted by incorporating Mg2+/Y3+ and N-methylformamide (NFA) in starting solution. The morphology of the dried gel changed from a solid nanoporous structure through a phase separated macroporous bicontinuous structure to aggregates particles when varying Mg2+ or Y3+, NFA and PEO composition. An appropriate choice of the starting composition, by which the phase separation and gelation occurred parallel, allows the fabrication of macroporous zirconia monoliths in large dimensions (Φ = 30 mm, h = 8 mm). The skeleton of the monolithic macroporous zirconia gels possess a BET surface area of 271.7 m2/g. Accordingly, the effect and mechanisms of Mg2+, Y3+ and NFA during gelation process were proposed in detail. Moreover, Mg2+ or Y3+ might also act as stabilizer to form the magnesia or yttria stabilized tetragonal or cubic zirconia after the samples were heat-treated at high temperature (800 °C).