Synthesis and optical property of zinc aluminate spinel cryogels

• ZnAl2O4 cryogels were synthesized by sol–gel technology followed by vacuum freeze drying and annealing at 450 °C.
• The reflectance of the cryogels was about 70–80% at 400–2500 nm.
• The ZnAl2O4 cryogels have a potential application as thermal insulating materials at high temperature.

Zinc aluminate spinel cryogels with various molar ratio of Al/Zn are synthesized by sol–gel technology followed by vacuum freeze drying. The structures and optical properties are both found to be affected by the molar ratios of Al/Zn and annealed temperatures. The peaks of zinc oxide (ZnO) and zinc dialuminum oxide (ZnAl2O4) are both obtained for the samples with more Zn content annealed at 750 °C or upward. The composites have a large surface area (137 m2/g) with mesoporous structure after annealing at 750 °C. The SEM images reveal that the ZnAl2O4 crystals formed a multilayer structure with redundant ZnO particles which deposited on it. Furthermore, the maximum infrared reflectance is about 80% with an improvement of 35% in the infrared region after annealing at 950 °C compared with that of 450 °C, which indicates that these porous cryogels have a potential application as thermal insulating materials at a high temperature.