Preparation and characterization of nanofiber- and nanorod-like boehmite aerogels via ammonia vapor gelation method

Nanofiber-like and nanorod-like boehmite aerogels (BAs) were synthesized by using 1D boehmite nanofibers and nanorods as building units and chitosan as binder via sol-gel process and freeze-drying method. Two kinds of boehmite sols were both gelled via ammonia vapor gelation method. Nanofiber-like building units interconnect and tangle to form high-surface-area porous structures of BA-160, while nanorod-like ones self-accumulate and overlap to construct large-pore-diameter skeletons of BA-200. The compressive property of BAs mainly originates from the interaction of overlap joints between building units, and the overlap joints among nanofibers provide more anti-pressure positions than the ones among nanorods. The skeletons are further enhanced under the help of chitosan macromolecules due to the improved polycondensation between aluminoxane via ammonia vapor. With the increase of chitosan content, the mechanical properties of BAs increase, but the thermal conductivities decrease. All of ultralight BAs can be regarded as good thermal insulation materials. Nanofiber-like and nanorod-like boehmite aerogels (BAs) were synthesized by using 1D boehmite nanofibers and nanorods as building units and chitosan as binder via sol-gel process and freeze-drying method. Boehmite sols turning into gels were induced by ammonia vapor, which is beneficial to homogeneous gelation of boehmite sols. Two kinds of BAs possess different mechanical properties due to different porous structural characteristics. All of BAs present the features of ultralight and thermal insulation.