Controllable synthesis of alumina nanofibers with tunable crystal phases via a facile and cost-effective dealloying process

Owing to their unique mechanical properties and excellent thermal and chemical stability, Al₂O₃ nanofibers are highly desirable for practical applications as functional and structural building blocks. However, the scalable production of Al₂O₃ nanofibers has always faced significant challenges, namely, high cost and complicated processes. This work explores a feasible and straightforward dealloying strategy for the batch synthesis of Al₂O₃ nanofibers. When a binary Al‒Li alloy is immersed in alcohol, the alkoxide nanofibers spontaneously grow following the mechanism of boundary strain energy minimization. The results indicate that by dissolving Li in Al‒Li alloys, the continuous exposure of a fresh Al surface renders the remaining unsaturated bonds of Al sufficiently reactive, providing the conditions for the subsequent reaction with alcohols and thus inducing the formation of alcohol‒aluminum compounds. These nanofibers were calcined in air to obtain monocrystalline α-Al₂O₃ and polycrystalline γ-Al₂O₃ nanofibers. We investigated the evolution of the alloy into nanofibers in dry ethanol and the influence of different Al‒Li alloy compositions and calcination temperatures on the crystal structure and morphology of the resulting Al₂O₃ nanofibers. The study revealed that γ-Al₂O₃ with diameters of approximately 50–80 nm and lengths of approximately 20–30 μm and α-Al₂O₃ with diameters of approximately 100–150 nm and lengths of approximately 15–20 μm were successfully prepared via this technique route. The approach reported in this study is anticipated to open new paths for the efficient and economical synthesis of advanced metal oxide nanofibers and lay the foundation for their extensive application in current industrial sectors.