Hexagonal tungsten oxide (hex-WO3) has the potential to separate Cs-137 and Sr-90 from nuclear power plant or fission Mo-99 production waste. This study aims to increase the capacity of hex-WO3 to adsorb Sr2+. Ta-doped hex-WO3 was synthesized by the hydrothermal treatment of sodium tungstate dihydrate and tantalum chloride in concentrated HCl, in the presence of ammonium sulfate. Incorporating Ta into the WO3 framework caused the interlayer spacing to expand, and the band gap to shift to higher energy. The Sr2+ adsorption capacity of Ta-doped hex-WO3 was significantly higher than that of hex-WO3. Sr2+ adsorption reached equilibrium within 2 h in acidic solution. Maximum Sr2+ removal occurred at pH 4. Sr2+ uptake by hex-WO3 was described better by the Freundlich model than by the Langmuir model. Sr2+ adsorption on hex-WO3 was spontaneous under the studied conditions. (C) 2013 Elsevier B.V. All rights reserved.