Nitrogen adsorption isotherms were measured on a Micromeritics TriStar surface analyzer at liquid nitrogen temperature. Samples were degassed under vacuum at 110 °C for three h prior measurements. Surface areas were calculated using the BET method in the relative pressure range of 0.05-0.30. Pore size distribution was calculated using the BJH method using the desorption branch of the isotherm, following the literature procedure . Thermogravimetric analysis (TGA) was performed on a Perkin Elmer Pyris 1 TGA. Samples were heated from 30-650 °C at 20 °C min -1 in nitrogen.