Zhensheng Jin

Study on composition, structure and formation process of nanotube Na2Ti2O4(OH)2

A nanotube material is obtained by the reaction of polycrystalline TiO2 with concentrated NaOH solution for 20 h at 110 °C. From the contents of Na, Ti and the structural water determined, it is concluded that the nanotube material is Na2Ti2O4(OH)2, rather than TiO2, TiOx or H2TiO3. After treating with an HCl solution of pH 1, nanotube Na2Ti2O4(OH)2 can be converted to nanotube H2Ti2O4(OH)2. The crystalline structure of such nanotube materials belongs to an orthorhombic crystalline system. TEM results indicate that nanotube Na2Ti2O4(OH)2 is formed in the reaction stage of TiO2 with concentrated NaOH solution. The formation process is discussed.

Morphological structure and physicochemical properties of nanotube TiO 2

Morphological structure and physicochemical properties of nanotube TiO2 were investigated. It was found that the TiO2 nanotube consisted of 2–5 monolayers of TiO2 molecules, and its inner diameter was between 4.2 and 5.9 nm. The nanotube TiO2 powder had high specific surface area and pore volume (379 m2/g and 1.431 cm3/g respectively) and its decolorization activity for Reactive Brilliant Red X-3B was 2 times higher than that of raw TiO2 (p-25). This new type of TiO2 was hopeful for application in photocatalysis and composite nanomaterial.

Photoactive centers responsible for visible-light photoactivity of N-doped TiO2

N-doped TiO2 (anatase) with high visible light photoactivity was obtained by the thermal treatment of nanotube titanic acid (denoted as NTA) in an NH3 flow and investigated by means of X-ray diffraction (XRD), transmission electronic microscopy (TEM), diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and photoluminescence (PL). With increasing NH3 treatment temperature at T = 400 to 600 °C, the anatase crystallinity of the N-NTA(400–600) samples was gradually enhanced, while at 700 °C a new phase, TiN, appeared in the N-NTA(700) sample. XPS results show that the doped N atoms incorporated into anatase TiO2 exist in the form of NO. A revised explanation for the triplet ESR signals obtained from the N-NTA(500–700) samples was put forward, i.e. the g = 2.004 main peak is contributed by single-electron-trapped oxygen vacancies (denoted as Vo˙), while two weak peaks (g = 2.023, 1.987) are contributed by chemisorbed NO in well-crystallized anatase TiO2. The visible light photoactivity is proportional to the height of the g = 2.004 main peak, which suggests that the photoactive centers are Vo˙-NO–Ti. The adsorbed NO molecule can effectively suppress the photoluminescence of Vo˙ defects, which facilitates photogenerated charge transfer to the surface reactive centers to conduct redox reactions. The higher the Vo˙-NO–Ti concentration, the better the visible light photoactivity. The highest photoactivity was obtained for the catalyst, NH3-treated at 600 °C. But the formation of TiN at T = 700 °C can readily destruct Vo˙-NO–Ti photoactive centers, and thus readily decreases photoactivity efficiency.

Coaction of Sub-band and Doped Nitrogen on Visible Light Photoactivity of N-Doped TiO2

We found in our previous work that the high photoactivity of N‐doped TiO2 for the oxidation of propylene under visible light was attributed to the photoactive center Vo•‐NO‐Ti and the formation of sub‐band originated from a large amount of single‐electron‐trapped oxygen vacancies (denoted as Vo•; C. X. Feng, Y. Wang, Z. S. Jin, J. W. Zhang, S. L. Zhang, Z. S. Wu, Z. J. Zhang [2008], New J. Chem. 32, 1038). In the present study, the structure of the sub‐band within Eg of a representative sample N‐NTA‐400 was investigated by means of photoluminescence (PL) spectrometry and ultraviolet‐visible light‐near infrared diffuse reflectance spectra. The coaction of the sub‐band and doped nitrogen on visible light photocatalytic activity of N‐doped TiO2 was also investigated. The electron spin resonance spectra measured under laser irradiation (λ = 532 nm) indicate that the doped nitrogen may contribute to stabilize the trapping electron center, i.e. surface oxygen vacancy (Vo••), and hence suppress the PL, enhancing the photocatalytic activity.

Study of blue electroluminescence from titania nanotubes doped into a polymeric matrix

The blue electroluminescence from titania nanotubes doped into poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) was studied. The results of absorption and photoluminescence demonstrated that the observed blue electroluminescence in the nanocomposites comes directly from band-to-band transitions of titania nanotubes. The relative intensity of the blue electroluminescence was enhanced by increasing the content of titania nanotubes. Moreover, polymer light-emitting diodes doped with titania nanotubes showed higher carrier transport ability and lower onset voltages. Electroluminescence from one-dimensional materials has potential applications in nanoscale electrical and optoelectronic devices.

Electrochemical lithium storage capacity of nickel mono-oxide loaded anatase titanium dioxide nanotubes

The NiO loaded anatase TiO2 nanotubes have been successfully synthesized. It was found that NiO nanoparticles could prevent the nanotubular morphology from destruction during the dehydration of interlayered –OH groups of NTA and improve the electronic conductivity of TiO2 nanotubes. Galvanostatic battery testing showed that the NiO loaded anatase TiO2 nanotubes electrode exhibit excellent rate capability and good cycle performance. The enhanced performances can be attributed to its favorable tubular morphology and the better electrical contact between NiO and TiO2 nanotubes.

Influence of dehydrated nanotubed titanic acid on polymer light-emitting diodes with phosphorescent dye

In this letter, we demonstrate that hole injection and transport in polymer light-emitting diodes with phosphorescent dye Ir(ppy)3 can be significantly enhanced by doping p-type conductive dehydrated nanotubed titanic acid into poly(vinylcarbazole) (PVK) films at 2wt.%. At the same time, both energy transfer and exciton recombination efficiency are improved because of the open and straight conformation of the PVK molecule in the nanocomposite. The performance of these devices was greatly improved, showing higher luminance, enhanced efficiency, and a lower turn-on voltage.

The Effect Of Crystal Form Of N-Doped Titanium Dioxide On Visible-Light Photocatalytic Activity

TiO2 samples with different crystal forms were treated in flowing NH3 at elevated temperatures to fabricate N-doped TiO2 photocatalysts with different crystal forms. The resulting N-doped TiO2 photocatalysts were characterized by means of X-ray diffraction, transmission electron microscopy, diffusion reflectance spectrometry, and X-ray photoelectron spectroscopy. The visible-light photocatalytic activity of the catalysts was evaluated by measuring the photocatalyzed removal rate of propylene. Results indicate that the visible-light activity of N-doped TiO2 photocatalysts is highly dependent on the crystal form. Namely, N-doped anatase TiO2 has the highest visible-light activity, while the visible-light activity of N-doped TiO2 photocatalysts decreases with decreasing content of anatase phase and increasing content of rutile phase. In addition N-doped rutile TiO2 has no visible-light photocatalytic activity.

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S2- to St- (stearateion). Chnracterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i.e. CdS particle inserts in the CdSt2, molecular layers to form a sandwirh-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.