The IR spectrum of raw TiO2 spheres (black line) exhibits a feature typical of a carboxylate group bonded to a Ti atom at 1528 and 1442 cm-1 and CH stretching (2934 cm-1 for CH2; 2873 and 2960 cm-1 for CH3), indicating that a layer of carboxylate groups with long carbon chains surrounds the TiO2 spheres. The peak difference between asymmetric and symmetric COOH- stretching is 82 cm-1, because of bidentate chelation, which is one of the three vibration modes of the adsorbed carboxylate group.