Anatase TiO 2 nanocrystals (aTiO 2 ) of a uniform size have been synthesized and were subject to a successive hydrogenation under a H 2 gas flow at elevated temperatures (500−700 °C). We found that the concentration of Ti 3+ defects, such as Ti 3+ interstitials and oxygen vacancies, and their distribution between surface and bulk varied significantly, depending on the hydrogenation temperature and time. Such changes in defects were found to be critical in enhancing the photoactivity of the hydrogenated TiO 2 (H-aTiO 2 ) by an order of magnitude. In our case, H-aTiO 2 nanocrystals hydrogenated at 600 °C for longer than 10 h showed 10 times higher photoactivity than aTiO 2 , which was explained from a high surface-to-bulk defect ratio and a nonuniform distribution of defects between bulk and surface due to a preferential diffusion of bulk defects to the surface. Our study showed that a kinetically controlled hydrogenation condition could be used not only to control the surface/bulk defects but also to enhance the photoactivity of oxide nanocrystals.

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Shape-controlled anatase TiO2 nanocrystals with large {001} facets are synthesized by a hydrothermal method using HF as a shape-controlling agent. The photoactivity of the TiO2 nanocrystals is evaluated from the photodegradation rate of methylene blue in aqueous solution under UV irradiation. Here, we observe higher photoactivities for the TiO2 nanocrystals with a {001} ratio of close to 60%, which is the shape effect in photoactivity. In addition, we observe that the photoactivity is further enhanced when the TiO2 nanocrystals are treated in a dilute NaOH (HF) solution. Our SEM, XPS, and EPR analyses reveal that the etching in the NaOH (HF) solution can induce significant changes in the surface defects as well as in the surface morphology. We find that the enhanced photoactivity is closely related to the changes in the surface defects, which favor the formation of surface O– species under ambient conditions.

The sandwich-like 2H MoS2 and unilaminar graphitic nanocarbon hybrid was synthesized via graphitizing threonic acid intercalated MoS2 precursor obtained using hydrothermal process. An excellent electrocatalytic efficiency of hydrogen evolution reaction with a remarkably small overpotential of 195 mV and a Tafel slope of 47 mV/decade is easily accessible for our hybridized catalyst in 0.5 M H2SO4 aqueous solution, much superior to that of pure 2H MoS2 and threonic acid intercalating MoS2 nanomaterials. Moreover, the detailed electrochemical activity surface area and electrochemical impedance suggest that the face-to-face stacking of unilaminar 2H MoS2 and graphitic nanocarbon at an alternating sequence accelerates the mass transport and electron transfer and, thus, enhances the efficiency for electrocatalytic water splitting. This work paves a neoteric and straightforward pathway for the fabrication of superlattice MoS2 and unilaminar graphitic nanocarbon hybrid, further improving the electrocatalytic efficiency of 2H MoS2 nanosheets via a synergistic modulation strategy.

Using the Gemini surfactant [C12H25N+(CH3)2-(CH2)2-N+(CH3)2-C12H25]·2Br- (abbreviated as C12-2 - 12) with the short spacer group (s = 2) as structure-directing agent and sodium silicate as precursor, high-quality ordered cubic mesoporous silica (space group Ia3d) was prepared through the S+I- route (S denotes surfactant, I precursor). The samples were characterized by small-angle X-ray diffraction, transmission electron microscopy, and N2 adsorption−desorption techniques. Results showed that the pore structure of the resulting mesoporous silica belonged to the cubic structure (space group Ia3d). The high-quality cubic mesoporous structure was formed at 1:0.33 (molar ratio of sodium silicate to C12-2 - 12), 2:1 (ethyl acetate to sodium silicate), and at 30 °C. The formation conditions of MCM-48 with C12-2 - 12 were milder than those with the corresponding monovalent surfactants, such as alkyltrimethylammonium bromide. N2 adsorption−desorption curves revealed type IV isotherms and H1 hysteresis loops; Brunauer−Emmet−Teller (BET) surface areas increased with the decrease of the molar ratio of sodium silicate to C12-2 - 12 and of ethyl acetate to sodium silicate as well as of the hydrothermal temperatures.