Synthesis and characterization of monolithic ZnAl2O4 spinel with well-defined hierarchical pore structures via a sol-gel route

Hierarchically porous ZnAl 2 O 4 spinel monolith derived from ionic precursors has been successfully prepared via the sol-gel route accompanied by phase separation in the presence of poly (ethylene oxide) (PEO) and propylene oxide (PO). Appropriate amounts of PEO as a phase-separation inducer and PO as a gelation mediator allow the formation of the xerogel with bicontinuous macrostructure and a monolithic shape. The macropore size of the resultant dried gel is mainly distributed in the range of 0.2–1 μm, and the whole porosity is about 65%. The dried gel is constructed by crystalline Zn Al hydrotalcite, becoming amorphous after heat-treated at 300–500 °C in air, and is further transformed into single phase ZnAl 2 O 4 spinel with plate-like shape at 600 °C. The macroporous structure is well maintained while the porosity increases to 75% and the surface area rises to 109 m 2  g −1 after heat-treatment.