[en] Nanotubed titanic acid (H₂Ti₂O₄(OH)₂) is a novel kind of material. The electron spin resonance (ESR) and inter-related properties of its vacuum-dehydrated product were investigated by means of transmission electron microscopic, X-ray diffraction, ESR, diffuse reflectance spectra. The results showed that after treatment under vacuum (-0.1 MPa) at 100 degree sign C, single-electron-trapped oxygen vacancies (SETOV), characterized by a symmetrical ESR signal (g=2.003), were generated in nanotubed H₂Ti₂O₄(OH)₂ crystal lattice. The g=2.003 ESR signal intensity (I_ESR) increased with treatment time. SETOV played the role of F centers, the visible-light absorption power of vacuum-dehydrated H₂Ti₂O₄(OH)₂ was proportional to I_ESR. During vacuum dehydration at 100 degree sign C, the H₂Ti₂O₄(OH)₂ nanotubes shortened but its crystalline form kept unchanged. The formation mechanism of SETOV was discussed

[en] The formation mechanism of sodium titanate nanotubes via the morphological variation in particle-nanotube transition was investigated by means of TEM. The results show that the formation of sodium titanate nanotubes is carried out by self-assembling of dissolved fragments, the intermediate of TiO₂ reacted with NaOH. The formation process occurs spontaneously in concentrated NaOH solution. After reacting for 20 h, the inside diameters of nanotubes range from 3.9 to 6.8 nm and some straight nanotubes form bundles with hundreds of nanometers long

[en] A new method for preparing PtO_x-inserted sodium titanate nanotube was reported. By suction of H₂PtCl₆ ethanol solution into the nanotubes first and annealed at 653 K for 3 h afterwards, Pt nanoparticles formed in the nanotubes. The size of Pt nanoparticles is controlled by the dimensions of nanotubes. Some of them are spherical, some are nanorods. XPS and XRD results revealed that during annealing the following complex reaction happened:Na₁.1H₀.9Ti₂O₄(OH)₂+H₂PtCl₆+O₂ → TiO₂(anatase)+PtO_x(x=1,2)+NaCl+HCl↑

[en] A novel kind of nano-sized TiO₂ (anatase) was obtained by high-temperature (400-700 deg. C) dehydration of nanotube titanic acid (H₂Ti₂O₄(OH)₂, NTA). The high-temperature (400-700 deg. C) dehydrated nanotube titanic acids (HD-NTAs) with a unique defect structure exhibited a p-type semiconductor behavior under visible-light irradiation (λ≥ 420nm, E_photon=2.95 eV), whereas exhibited an n-type semiconductor behavior irradiated with UV light (λ≥ 365nm, E_photon=3.40 eV)

[en] The effect of N₂ treatment on the photocatalytic activity of Pt⁰/TiO₂ was investigated. The results showed that after treatment at 500 deg. C in N₂, 70% of the photocatalytic activity of 1.0 wt.% Pt⁰/TiO₂ was lost by the evaluation of photocatalytic oxidation reaction of C₃H₆. Transmission electron microscopy (TEM) and Ar⁺ ion sputtering tests revealed that in the course of high-temperature N₂ treatment, the size of Pt⁰ particles on TiO₂ increases and a strong interaction between metal and support, i.e. Pt⁰ particles encapsulated by Ti_xO_y, happens, which are the reasons for the deactivation of Pt⁰/TiO₂ photocatalyst treated by high-temperature N₂

[en] Nano-sized spinel lithium titanate (Li₄Ti₅O₁₂) was synthesized using sodium titanate nanotube as precursor via a facile solution ion-exchange method in association with subsequent calcination treatment at relatively low temperature. The influences of precursors, ion-exchange condition, and calcination temperature on the microstructure and electrochemical performance of the products were studied. Results indicate that pure-phase Li₄Ti₅O₁₂ can be harvested from sodium titanate nanotube precursor through an ion-exchanging at room temperature and calcination at 500 °C. The products exhibit a better performance as Li-ion battery anode material than the counterparts prepared from protonic titanate nanotube (H-titanate) precursor. The reason may lie in that sodium titanate nanotube is easier than protonic titanate nanotube to synthesize lithium titanate without TiO₂ impurity, resulting in reduced electron transfer ability and Li-ion transport ability. The capacity of Li₄Ti₅O₁₂ prepared from sodium titanate nanotube is 146 mAh/g at 10 C, and it has only 0.7 % decay after 200 charge/discharge cycles

[en] The visible photocatalytic mechanism of nitrogen-doped novel TiO₂ was studied by means of electron spin resonance spectroscopy (ESR). It was found that, under visible light irradiation, the concentration of single-electron-trapped oxygen vacancy (SETOV, V_o^·) of novel TiO₂ remained unchanged, but that of nitrogen-doped novel TiO₂ increased and returned to original state when the light was turned off. This implies that, aside from V_o^· in bulk of nitrogen-doped novel TiO₂, oxygen vacancy without trapped electron (V_o^··) was formed on its surface. V_o^·· as a surface electron trap captured photogenerated electron from the bulk to generate extra V_o^·, carrying out photocatalytic reaction on the surface. At the same time, nitrogen doping product NO was chemically adsorbed on the vicinity of V_o^·· and inhibited the attack of oxygen, allowing V_o^·· to remain stable in air. The synergistic action of the two kinds of active structures, i.e., bulk V_o^·-NO-Ti and surface V_o^··-NO-Ti, accounted for the visible photocatalytic activity of N-doped novel TiO₂. - Graphical abstract: Synergistic action is realized between (V_o^·)_bulk and (V_o^··)_surf in the presence of active structures (V_o^·)_bulk-NO-Ti and (V_o^··)_surf -NO-Ti. Research highlights: → The origin of visible photocatalytic activity of the N-TiO₂ was studied by ESR. → (V_o^·)_bulk and (V_o^··)_surf formed in N-TiO₂. → (V_o^·)_bulk and (V_o^··)_surf show a synergistic effect in visible photocatalytic. → TiO₂ did not contain (V_o^··)_surf, so no visible photocatalytic activity.

[en] Titanium dioxide (TiO₂) nanotube with a large amount of single-electron-trapped-oxygen-vacancies (coded as T2) was obtained by annealing nanotube H₂Ti₂O₄(OH)₂ (coded as T1) at 400 deg. C in air. Silver nanoparticles with a diameter of about 30-50 nm were loaded onto the surface of T2 via deposition associated with photochemical reduction under ultraviolet irradiation. The resulting Ag/TiO₂ nanotube (coded as T3) was characterized by means of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible light diffusion reflectance spectrometry. It was found that C₃H₆ experienced unusual photo-induced adsorption-desorption on T3 under visible light irradiation. Namely, C₃H₆ was initially desorbed from T3 and then adsorbed on T3 under visible light irradiation. On the contrary, C₃H₆ was initially adsorbed on T3 in the dark, followed by desorption. The reason might lie in that two kinds of active sites exist on the surface of T3, corresponding to quite different rates of adsorption and desorption. It was found that oxygen vacancies in association with deposited silver particles, were responsible for the alternative adsorption-desorption of C₃H₆ on T3.

[en] X-ray photoelectron spectroscopy combined with Ar⁺ ion sputtering has been used to analyze the variation in the valence and concentration of Pt, Ti, and O of Pt⁰/TiO₂ reduced by H₂ at elevated temperature. It is confirmed that titanium oxide of low-valence is transferred onto the surface of Pt⁰ particulates to encapsulate the surface via a strong metal-support interaction under reducing atmosphere. It is also found for the first time that Pt⁰ atom is diffused into the lattice of TiO₂ to occupy the oxygen vacancy (V_O··) and accept one electron from adjacent Ti³⁺ forming a localized Pt^--Ti⁴⁺ bond. This differs from the strong metal-support interaction under oxidizing atmosphere. Namely, although the Pt⁰ atom is also diffused into the lattice of TiO₂ under oxidizing atmosphere, it replaces Ti atom and forms a Pt²⁺-O^2- bond. Moreover, the strong metal-support interaction under oxidizing atmosphere results in increased photocatalytic activity of Pt⁰/TiO₂, while the strong metal-support interaction under reducing atmosphere leads to decreased photocatalytic activity of Pt⁰/TiO₂.

[en] The strong interaction between Pt and TiO₂ under oxidizing atmosphere was studied by means of X-ray photoelectron spectroscopy (XPS) and Ar⁺ sputtering test. The results obtained show that under oxidizing atmosphere Pt⁰ atoms can thermally diffuse into TiO₂ lattice and be oxidized to Pt²⁺ to substitute for Ti⁴⁺ or form the interstitial ions at 673 K