Published on Web Date: September 15, 2010 r2010 American Chemical Society 2881 DOI: 10.1021/jz101137m | J. Phys. Chem. Lett. 2010, 1, 2881–2885 pubs.acs.org/JPCL Controlling Phase, Crystallinity, and Morphology of Titania Nanoparticles with Peroxotitanium Complex: Experimental and Theoretical Insights Manaswita Nag, Sutapa Ghosh, Rohit Kumar Rana, and Sunkara V. Manorama* Nanomaterials Laboratory, Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad-500 607, India ABSTRACT This Letter presents a detailed experimental and theoretical study to unravel the unique role of hydrogen peroxide in controlling phase and thereby shape and crystallinity of nanocrystalline titania. Analysis of all reaction para- meters revealed that the H 2 O 2 /Ti ratio (r p ) is the predominant factor to obtain crystalline titania with different phase composition. Evolution of phase and crystallite size of the materials is determined from X-ray diffraction and Raman spectroscopy. Transmission electron microscopy images showed phase-related morphology, that is, truncated anatase and rod-like rutile. The solution Raman and Fourier transform infrared spectroscopy study confirmed different bonding pat- tern in the reaction medium. Complexation of titanium with -O-O- in bidentate manner with C 2v symmetry in the reaction mixture is confirmed by the strong Raman band at ∼630 cm -1 . Quantum mechanical calculations are performed using density functional theory with B3LYP/LANL2DZ to provide all possible intermediate structures and to predict the probable mechanism leading to the formation of different phases of titania under different experimental conditions. SECTION Nanoparticles and Nanostructures T itania with desired phase is of great importance be- cause of its wide-ranging potential application in the areas of photocatalysis, solar cells, functional coatings, and so on. 1,2 Current research focuses on synthetic routes adopting green methodologies to obtain the required phase. From an environmental viewpoint, water-soluble complexes of titanium have proved to be very promising in titania synthesis, but the role of the complexing ligand and the reaction pathway to control the phase and morphology of the formed TiO 2 is yet to be understood. 3-7 We have made an attempt to use peroxo titanium complex (PTC) as a precursor to obtain titania by a convenient wet chemical method, predict the final structure and phase of TiO 2 depending on the route adopted, and support the theoretical calculation. In our study, the stabilization of highly reactive titanium(IV) isopropoxide (TIP) is attained by complexation with H 2 O 2 in water by formation of an orange-colored water-soluble PTC at pH ∼3 that prevents spontaneous uncontrolled hydrolysis. 8-11 PTC is a robust complex in aqueous solution and is used as an analytical reagent for H 2 O 2 through a fast reaction to form peroxotitanate intermediates. 12 This precursor allows one to minimize the presence of impurity ions in the solution. 8-10 As an improvement over the existing method to obtain the desired TiO 2 phase starting with PTC by using additional acid, base, or other reagents, 3-7 the present method is a clean process with only concentration of H 2 O 2 as the controlling factor. Our strategy is to control the reaction parameters to obtain titania of pure anatase and mixed anatase-rutile phase. The samples have been named as TH, TPH, and TP depending on the H 2 O 2 concentration. To trace the progress of the reaction, the starting mixture is monitored by Raman and FTIR analysis before autoclaving. Solution Raman study showed the pre- sence of titanium peroxo complex with C 2v symmetry (Ti-O-O, ∼630 cm -1 ) 13-16 along with peaks for peroxide group (∼880 cm -1 )(Figure 1). In addition, the presence of CH 3 -CH-CH 3 ,O-H, C-O, and -CH 3 groups from H 2 O 2 , H 2 O, and IPA present in the system are also identified. Because of the complexation and consumption, peaks at 880 and 825 cm -1 are found to change their intensity compared with the blank. FTIR confirms the formation of complex (e.g., O-H of chelated complex, 2400 cm -1 ; free -O-O- group, 940-980 cm -1 ; Ti-O-C, 1000-1200 cm -1 ; and Ti-O- Ti/Ti-O-O, 700 cm -1 ) 6,17 (Supporting Informa- tion (SI), Figure S5). After ascertaining the nature of complex, the PTC is sub- jected to autoclaving, and the resulting product was isolated for further characterization (XRD, Raman, and TEM). The XRD (Figure 2)(comparison with the standard data, anatase JCPDS card no.: 21-1272, rutile JCPDS card no.: 21-1276) and Raman Received Date: August 12, 2010 Accepted Date: September 10, 2010