Factors influencing the PVA polymer-assisted freeze-drying synthesis of Al2O3 nanofibers

Three-dimensional (3D) nanofibrous structured Al2O3 was successfully synthesized using the poly (vinyl alcohol) (PVA) polymer-assisted freeze-drying method, and a series of factors that influence fiber performance were investigated in depth. PVA nanofibers were also investigated for the first time. The surface morphology, structure, and other properties of PVA nanofibers, precursor Al2O3/PVA nanofibers, and calcined Al2O3 nanofibers were characterized by scanning electron microscopy, X-ray diffraction, and nitrogen adsorption measurements. The results showed that Al2O3 nanofibers with good performances could be obtained at the optimum conditions where the precursor solution was prepared by boehmite nanoparticles (0.01 wt%) and PVA (0.1 wt%, DP = 500) with a mass ratio of 7: 3, followed by the use of the rapid freezing method at −196 °C under liquid nitrogen in the pre-frozen process; subsequently, calcination was performed at 500 °C for 5 h to form Al2O3 nanofibers. The increasing calcination temperature (500 °C–1300 °C) enabled the transformation of the Al2O3 crystalline phase from γ-Al2O3 to α-Al2O3. It also improved the specific surface area from 44.5 m2 g−1 for the precursor Al2O3/PVA nanofibers to 263.4 m2 g−1 for the Al2O3 nanofibers calcinated at 500 °C. However, an excessive calcination temperature at 1300 °C was detrimental to the specific surface area, presumably due to sintering or blocking by metal particles. This work provides optimum conditions that make Al2O3 nanofibers valuable for further development, and it has the potential for industrial applications.