www.afm-journal.de FULL PAPER 2012 WILEY-VCH Verlag GmbH this was confi rmed with the corresponding SAXS pattern (Supporting Information, Figure S1). After solvothermal treatment of these pre- cursor spheres at 433 K and then calcination at 773 K the monodispersity (Figure 1 d) and smooth surface of the spheres were retained (Figure 1 d inset). The diameter of the spheres (780 40 nm) was not altered signifi cantly during the heating processes. The original worm-hole like mesostructure in the precursor spheres is retained in the calcined sample as worm-hole like mesopores throughout the microsphere (Figure 1 e and f). SAXS patterns of the samples after solvo- thermal treatment and calcination at 773 K show a broad refl ection for the calcined sam- ples prepared using less than 80% Ti con- tent ( Figure 2 a), indicating the presence of worm-hole like pore structuring. This refl ec- tion is no longer apparent with samples prepared using 80% Ti content as anatase crystals ( 40 nm) are formed in the sample, as discussed below, disrupting the mesostructure. The corresponding wide angle XRD patterns are shown in Figure 2 b. Anatase crystals were present in the samples pre- pared using 80% Ti content as there was insuffi cient ZrO 2 present to prevent crystal growth. As the amount of zirconia in the sample increased, the samples were amorphous even after calcination at 773 K. This would indicate that the Ti and Zr spe- cies were well distributed within the microspheres, preventing suffi cient size domains of either species to occur and therefore crystallize during calcination. 14 , 22 Taking the 50Zr50Ti oxide microspheres as an example, no crystal phases of either titania binary oxide microspheres with high surface areas ( 280 m 2 /g) and uniform mesopores ( 5.5 nm) can be prepared when the Zr content ranges from 30 to 80%. In contrast, the Zr- or Ti- rich precursor microspheres ( 90% Zr or 25.40 mg/g, that is 0.49 mmol/g) for Cr (VI) anions in aqueous solution, showing a high potential for heavy metal ion sequestration applications. Table 1. Physical properties of the calcined mesoporous zirconium tita- nium oxide microspheres. a) Sample name S BET m 2 /g PSD nm V sp cm 3 /g Crystal phase TiO 2 108170.313Anatase TiO 2 10Zr90Ti oxide73230.406Anatase TiO 2 & Amorphous 20Zr80Ti oxide3046.20.356Anatase TiO 2 & Amorphous 30Zr70Ti oxide4134.90.389Amorphous 40Zr60Ti oxide3675.50.397Amorphous 50Zr50Ti oxide3155.60.345Amorphous 60Zr40Ti oxide3215.50.348Amorphous 70Zr30Ti oxide3065.60.327Amorphous 80Zr20Ti oxide2834.50.266Amorphous 90Zr10Ti oxide2124.80.201Tetragonal ZrO 2 ZrO 2 1047.00.161Monoclinic & Tetragonal ZrO 2 a) S BET = BET specifi c surface area obtained from N 2 adsorption data in the P / P 0 range from 0.05 to 0.20. PSD = pore size distribution determined by using the NLDFT method based on the oxide cylindrical pore model for N 2 at 77 K. V sp = single-point pore volume calculated from the adsorption isotherm at P / P 0 = 0.98. Figure 5 . Typical adsorption isotherms of the mesoporous zirconium titanium oxide microspheres with varying compositions. The solid lines are fi tted results using the Langmuir model. 05001000150020002500 0 5 10 15 20 25 30 30Zr70Ti 60Zr40Ti ZrO2 Cr(VI) Uptake (mg/g) Ceq (mg/L) TiO2 Table 2. Cr (VI) uptake capacity of the calcined mesoporous zirconium titanium oxide microspheres of varying compositions. a) Sample nameQ max mg/g R 2 Site density #Cr/nm 2 OH amount mmol/g OH density #/nm 2 #OH/#Cr (VI) mole ratio TiO 2 9.930.921.00.744.13.9 30Zr70Ti oxide29.460.960.82.063.03.6 40Zr60Ti oxide26.870.960.81.772.93.4 60Zr40Ti oxide25.540.980.91.753.33.6 80Zr20Ti oxide25.400.971.01.793.63.7 ZrO 2 17.170.941.91.076.23.2 a) Q max = maximum adsorption capacity obtained by fi tting with Langmuir model and refers to the total amount of Cr (VI) atom derived from HCrO 4 , CrO 4 2 and Cr 2 O 7 2 species. R 2 = correlation coeffi cient. Site density = (Q max 10 3 6.02 10 23 )/(52 S BET 10 18 ). OH densities of the resulting oxide microspheres were determined using a TGA method according to Ref-35. #OH/#Cr (VI) = mole ratio of the surface hydroxyl groups to the adsorbed Cr (VI) derived from HCrO 4 , CrO 4 2 and Cr 2 O 7 2 species. FULL PAPER 1970 www.afm-journal.de www.MaterialsV 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2012, 22, 19661971 charged anions. Cr (VI) adsorption isotherms on the mesoporous microspheres were obtained using batch contact methodology in which the powdered adsorbent was contacted with solutions containing the target species in a volume/mass ratio of 100 mL/g. That is 200 mg of the mesoporous microspheres were suspended in 20 mL Cr (VI) solution in a 28 mL screw-capped container with initial concentrations ranging from 50 to 2000 mg/L (0.96 to 38.46 mmol/L). The containers were wrapped with aluminium foil and shaken at 298 K for 48 h. Then the mesoporous microsp