Titanium dioxides (TiO2) nanoarchitectures including microspheres surrounded by nanosheets were synthesized using simple, quick and effective hydrothermal method with moderate temperature (150 °C). We systematically investigated how reaction time affected final morphologies of TiO2. At reaction times equal to 4 and 8 hours (named as TS-4 and TS-8, respectively), TiO2 formed with morphology of irregular microspheres. At longer reaction times (12 hours, named as TS-12), urchin-like TiO2 nanocrystals formed. Photocatalytic activities of the formed TiO2 with different morphologies were evaluated against decomposition of methylene orange and blue (MO and MB, respectively) as well as rose-bengal (RB). Urchin-like TiO2 demonstrated high degradation ratio similar to the commercial catalyst PS 25 on MO (96%). Degradation ratios of samples synthetized for 4 and 8 hours were much lower: 60 and 80%, respectively. During 30 minutes reaction time, TiO2 with urchin-like morphology showed much higher selectivity towards neutralization of MB (99.5%) than towards MO (73%) and RB (88.7%).

Crystallization of well-defined anatase nanoparticles (5 nm) in the mesopore (6 nm) of SBA-15 over 400 °C, results the high photocatalytic activity for decomposition of acetic acid compared with other commercial titanium dioxides.

Mesoporous titanium dioxides nanoparticles (TiO2 NPs) were synthesized using activated carbon (AC) as templates after the decomposition of AC. All results indicated that TiO2 NPs with the small grain size presented the anatase phase structure. Mesoporous TiO2 NPs showed the high surface area and the surface area decreased with the TiO2 content. The removal of methylene blue (MB) indicated that the photocatalytic decomposition efficiency of mesoporous TiO2 NPs increased up to 92% for three-times doping with the TiO2 content, and then decreased. This should be attributed to the synergistic effect from the MB adsorption of mesoporous-structure and the photocatalysis of TiO2 NPs. Therefore, the higher MB concentration near TiO2 NPs from the mesoporous-structure increased the touch chance and the MB photocatalytic decomposition was promoted greatly.

The facet-specific interaction between molecules and crystalline catalysts, such as titanium dioxides (TiO2), has attracted much attention due to possible facet-dependent reactivity. Using surface-sensitive sum-frequency vibrational spectroscopy, we have studied how methanol interacts with different common facets of crystalline TiO2, including rutile(110), (001), (100), and anatase(101), under ambient temperature and pressure. We found that methanol adsorbs predominantly in the molecular form on all of the four surfaces, while spontaneous dissociation into methoxy occurs preferentially when these surfaces become defective. Extraction of Fermi resonance coupling between stretch and bending modes of the methyl group in analyzing adsorbed methanol spectra allows determination of the methanol adsorption isotherm. The isotherms obtained for the four surfaces are nearly the same, yielding two adsorbed Gibbs free energies associated with two different adsorption configurations singled out by ab initio calculations. They are (i) ∼−20 kJ/mol for methanol with its oxygen attached to a low-coordinated surface titanium, and (ii) ∼−5 kJ/mol for methanol hydrogen-bonded to a surface oxygen and a neighboring methanol molecule. Despite similar adsorption energetics, the Fermi resonance coupling strength for adsorbed methanol appears to depend sensitively on the surface facet and coverage.