Fig. 2 shows the FTIR spectra of the TOPO-capped Zr-doped TiO2 calcined at elevated temperatures. The C–H stretching absorption (2768–2981 cm1) which was obvious in the TOPO-capped samples disappeared after calcination at 250 8C. Instead, C C or C O stretching modes at 1320–1790 cm1 were observed [11], indicating thermal induced
partial oxidation and pyrolysis of TOPO. The carbonaceous absorptions were not detectable at 450 8C, indicating that the
surface carbons were almost completely removed by calcination. Meanwhile, the calcined samples began to show OH bending and stretching absorptions at 1613 and 3285 cm1, respectively [12]. Similar absorptions blue-shifted to 1625 and 3393 cm1, respectively, at 550 8C. The higher bonding strength after calcination at higher temperature reveals that reductive conditions resulted from dehydroxylation and/or deoxygenation. The OH absorptions diminished gradually for the samples calcined above 750 8C and disappeared at 950 8C. Two absorption bands at 1031–1082 and 1127–1192 cm1 corresponding to antisymmetric/symmetric O–P–O stretching modes appeared for the samples calcined above 450 8C [13,14]. The shifts of these bands suggest that different chemical environments existed around the phosphorus elements
after calcination at the various temperatures. To understand the chemical structures of the phosphorus species, we used XPS to further characterize the chemical states and relative elemental ratios of the calcined samples.