BNF aerogel

In recent years, reports on ultralow density aerogels are increasing. Our boehmite nanofiber (BNF) aerogels are ultralight materials that have ultralow density and high visible-light transmittance.

Because the refractive index is very low, it seems as if the object on the AlOOH aerogel is floating. In fact, the idea of this research is that I wanted to create a model like a hover board by applying the optical properties.

The fabrication method of these materials is simple. Just add base to gelate a BNF dispersion sol (commercially available), exchange solvent, then do supercritical drying.

Water and oil are repelled well after simple surface treatment with perfluoroalkylsilane (FAS).

BNF cryogel

We succeeded in fabricating transparent porous cryogel beads like BNF aerogel by vacuum freeze drying. The boehmite nanofiber sol (in which the dispersion medium is tert-butyl alcohol) is dropped directly into liquid nitrogen to freeze instantly to prevent structural destruction caused by crystal growth of the dispersion medium and dried under vacuum.

The final product has ultralow density and highly transparent. Interestingly, it is possible to directly observe the state of drying.

By freezing a wet gel consisting of a diluted framework, it was also possible to obtain millimeter-thick transparent monoliths. It can be applied to light emitters with fluorescent molecules added.

Although there are some issues such as deterioration of optical properties and low yield when compared with aerogels by supercritical drying, It is an advantage that a transparent cryogels can be obtained by the simple process.


  • Hayase, G.; Nonomura, K.; Hasegawa, G.; Kanamori, K.; Nakanishi, K. Ultralow-Density, Transparent, Superamphiphobic Boehmite Nanofiber Aerogels and Their Alumina Derivatives. Chem. Mater. 2015, 27, 3–5. doi:10.1021/cm503993n (Open Access)
  • Hayase, G. Facile Fabrication of Ultralow-Density Transparent Boehmite Nanofiber Cryogel Beads and Their Application to a Nanoglue. ChemNanoMat 2017, 3, 168–171. doi:10.1002/cnma.201600360
  • Hayase, G.; Funatomi, T.; Kumagai, K. Ultralow-Bulk-Density Transparent Boehmite Nanofiber Cryogel Monoliths and Their Optical Properties for a Volumetric Three-Dimensional Display. ACS Appl. Nano Mater. 2018, 1, 26–30. doi:10.1021/acsanm.7b00097
  • Hayase, G.; Yamazaki, K.; Kodaira, T. Fabrication of Boehmite Nanofiber Aerogels by a Phosphate Gelation Process for Optical Applications. J. Sol-Gel Sci. Technol. 2022, 104, 558-565. doi:10.1007/s10971-022-05867-0 (ReadCube)