Fabrication of boehmite and Al2O3 nonwovens from boehmite nanofibres and their potential as the sorbent

Abstract

Boehmite nonwovens with hierarchical texture could be fabricated by a simple procedure consisting of mixing a boehmite nanofibre sol with an organic solvent and filtering the mixture. However, whether the nonwovens were obtained or not depended on the solvents. High polar solvents such as methanol and ethanol caused gelation of the mixture, and low polar solvents such as toluene and ether yielded condensates in the mixture. The medium polar solvents with solubility parameters of 9–12.5, concretely, mixtures of butanol with methanol, ethanol and isopropanol, were favourable for obtaining the nonwovens. The nonwovens consisted of bundles of boehmite nanofibres, and the texture, pore volume, bulk density and porosity of the nonwovens roughly depended on the thickness of the bundles. Thus, thinner bundles and thicker bundles gave dense and loose textures, respectively. The bundles became thicker by increasing the butanol content in the mixed alcohols, and thinner by increasing the methanol, ethanol and isopropanol content. The nonwovens could be transformed from boehmite to θ-Al₂O₃via γ-Al₂O₃ in the crystal phase while maintaining seemingly the original texture when the calcination temperature was raised to 1000 °C stepwise. The nonwovens were tested as sorbents for polycyclic organics such as chromaqurol B, stilbazo and alizarin yellow R in water, and it was found that the nonwovens absorb chromaqurol B and stilbazo effectively, but alizarin yellow R slightly.