Formation of nanofibrous alumina by polyvinyl alcohol assisted spray-freeze-drying technique

Abstract

In the experiment, three-dimensional net-structured alumina nanofibers were successfully prepared by spray-freeze-drying process for the first time with an average diameter below 100 nm. Alumina nanofibers were obtained from polyvinyl alcohol (PVA) and boehmite precursor nanofibers after calcination at 500 °C for 5 hours. At first, boehmite nanoparticles as a source of alumina were dispersed with 1 wt% PVA aqueous solution to form alumina nanofibers with different weight ratios of PVA and alumina. The best weight ratio of PVA and alumina (30:70) was selected on the basis of fiber morphology, nano diameter, thermal stability and precipitation of boehmite nanoparticles. This best weight ratio of PVA and alumina was applied again to form alumina nanofibers from PVA/boehmite precursor nanofibers which were prepared using 0.5, 0.1 and 0.01 wt% PVA aqueous solutions. The best alumina nanofibers were obtained when 0.1 wt% PVA solution was used. Here, average fiber diameter of alumina nanofibers was 79 nm along with more interconnected net-structure and higher specific surface area. Crystalline phase of alumina nanofibers was transferred from γ-alumina to α-alumina when calcination temperature increased from 500 °C to 1200 °C. Specific surface area and porosity of alumina nanofibers significantly decreased with the increase of calcination temperature.