Synthesis and hydrogen absorption of high-specific-surface ultrafine theta-Al2O3 nanowires

Abstract Ultrafine theta -Al 2 O 3 ( θ -Al 2 O 3 ) nanowires with average diameters of sub-10 nm and lengths up to several micrometers have been successfully synthesized via a novel two-stage method. With temperature gradually elevated, θ -Al 2 O 3 was generated from the slow transformation of gamma -phase Al 2 O 3 ( γ- Al 2 O 3 ), and its ultrafine nanowire structure was formed from the recrystallization of γ -Al 2 O 3 nanowire. By means of nitrogen adsorption–desorption isotherm at 77 K and the multipoint Brunauer–Emmett–Teller (BET) method, the specific surface area of the ultrafine θ -Al 2 O 3 nanowires is found to be up to~120 m 2 /g. With the high surface area, the material displays excellent gas absorption ability. Hydrogen absorption capacities could be measured to be~5.57 wt% at 77 K (liquid nitrogen), 1.51 wt% at 298 K (room temperature) and 0.81 wt% at 557 K, when a pressure of 30 atm (~3 MPa) is applied. The crystal or chemical nature of metastable θ -Al 2 O 3 phase may play a vital role in the observed excellent gas storage capacity.