Zhanglian Hong

Origin of Photocatalytic Activity of Nitrogen-Doped TiO2 Nanobelts

Experiments combined with the density functional theory (DFT) calculation have been performed to understand the underlying photocatalysis mechanism of the nitrogen-doped titania nanobelts. Nitrogen-doped anatase titania nanobelts are prepared via hydrothermal processing and subsequent heat treatment in NH(3). Both the nitrogen content and the oxygen vacancy concentration increase with increasing the NH(3) treatment temperature. Nitrogen doping leads to an add-on shoulder on the edge of the valence band, the localized N 2p levels above the valence band maximum, and the 3d states of Ti(3+) below the conduction band, which is confirmed by DFT calculation and X-ray photoelectron spectroscopy (XPS) measurement. Extension of the light absorption from the ultraviolet (UV) region to the visible-light region arises from the N 2p levels near the valence band and from the color centers induced by the oxygen vacancies and the Ti(3+) species. Nitrogen doping allows visible-light-responsive photocatalytic activity but lowers UV-light-responsive photocatalytic activity. The visible-light photocatalytic activity originates from the N 2p levels near the valence band. The oxygen vacancies and the associated Ti(3+) species act as the recombination centers for the photoinduced electrons and holes. They reduce the photocatalytic activity although they contribute to the visible light absorbance.

Visible light photocatalytic activity of nitrogen-doped La2Ti2O7 nanosheets originating from band gap narrowing

AbstractApproximately 15 nm thick nitrogen-doped lanthanum titanate (La2Ti2O7) nanosheets with a single-crystalline perovskite structure have been prepared by hydrothermal processing and subsequent heat treatment in NH3 at 600 °C. Doping nitrogen into the La2Ti2O7 nanosheets results in the narrowing of the band gap, extending the light absorption into the visible light region (∼495 nm). The nitrogen-doped La2Ti2O7 nanosheets not only show significant visible light photocatalytic activity toward the decomposition of methyl orange but also exhibit enhanced the ultraviolet light photocatalytic activity. The enhancement of photocatalytic activity originates from the narrowing of the band gap of La2Ti2O7 nanosheets. The results obtained show that the desirable route to extend the photocatalytic activity of a semiconductor from the ultraviolet to the visible light region is to narrow the band gap rather than to create localized mid-gap states.

Photocatalytic, sonocatalytic and sonophotocatalytic degradation of Rhodamine B using ZnO/CNTs composites photocatalysts

A series of ZnO nanoparticles decorated on multi-walled carbon nanotubes (ZnO/CNTs composites) was synthesized using a facile sol method. The intrinsic characteristics of as-prepared nanocomposites were studied using a variety of techniques including powder X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM), transmission electron microscope (TEM), scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX), Brunauer Emmett Teller (BET) surface area analyzer and X-ray photoelectron spectroscopy (XPS). Optical properties studied using UV-Vis diffuse reflectance spectroscopy confirmed that the absorbance of ZnO increased in the visible-light region with the incorporation of CNTs. In this study, degradation of Rhodamine B (RhB) as a dye pollutant was investigated in the presence of pristine ZnO nanoparticles and ZnO/CNTs composites using photocatalysis and sonocatalysis systems separately and simultaneously. The adsorption was found to be an essential factor in the degradation of the dye. The linear transform of the Langmuir isotherm curve was further used to determine the characteristic parameters for ZnO and ZCC-5 samples which were: maximum absorbable dye quantity and adsorption equilibrium constant. The natural sunlight and low power ultrasound were used as an irradiation source. The experimental kinetic data followed the pseudo-first order model in photocatalytic, sonocatalytic and sonophotocatalytic processes but the rate constant of sonophotocatalysis is higher than the sum of it at photocatalysis and sonocatalysis process. The sonophotocatalysis was always faster than the respective individual processes due to the more formation of reactive radicals as well as the increase of the active surface area of ZnO/CNTs photocatalyst. Chemical oxygen demand (COD) of textile wastewater was measured at regular intervals to evaluate the mineralization of wastewater.

Single crystalline La0.5Sr0.5MnO3 microcubes as cathode of solid oxide fuel cell

The efficiency of solid oxide fuel cells (SOFCs) is heavily dependent on the electrocatalytic activity of the cathode toward the oxygen reduction reaction (ORR). In order to achieve better cathode performance, single crystalline La0.5Sr0.5MnO3 (LSM) microcubes with the {200} facets have been synthesized by the hydrothermal method. It is found that the LSM microcubes exhibit lower polarization resistance than the conventional polycrystalline La0.8Sr0.2MnO3 powder in air from 700 °C to 900 °C. The ORR activation energy of the LSM microcubes is lower than that of the conventional powder. The ORR kinetics for the microcubes is limited by the charge transfer step while that for the conventional powder is dominated by the oxygen adsorption and dissociation on the cathode surface.

Electrospun activated carbon nanofibers for supercapacitor electrodes

Porous activated carbon nanofibers have been prepared by electrospinning a H3PO4-containing polyacrylonitrile precursor. A small amount of H3PO4 (<1 wt%) serves as the activation agent during carbonization of the nanofibers. The activated carbon nanofibers have a large surface area (∼709 m2 g−1) and high porosity (0.356 cm3 g−1). A high specific capacitance of 156 F g−1 (at 0.5 A g−1) is obtained at a 1:10 mass ratio of H3PO4 to polyacrylonitrile. The energy density of the supercapacitor with the activated carbon nanofibers as the electrodes reaches 10.98 Wh kg−1 at a power density of 10 kW kg−1. This is ∼9 fold larger than that of carbon nanofibers without H3PO4 because the H3PO4-based activation process significantly increases both the micropore volume and the volume ratio of mesopores to micropores.

Conductive Carbon Nitride for Excellent Energy Storage

Conductive carbon nitride, as a hypothetical carbon material demonstrating high nitrogen doping, high electrical conductivity, and high surface area, has not been fabricated. A major challenge towards its fabrication is that high conductivity requires high temperature synthesis, but the high temperature eliminates nitrogen from carbon. Different from conventional methods, a facile preparation of conductive carbon nitride from novel thermal decomposition of nickel hydrogencyanamide in a confined space is reported. New developed nickel hydrogencyanamide is a unique precursor which provides self-grown fragments of ⋅NCN⋅ or NCCN and conductive carbon (C-sp2 ) catalyst of Ni metal during the decomposition. The final product is a tubular structure of rich mesoporous and microporous few-layer carbon with extraordinarily high N doping level (≈15 at%) and high extent of sp2 carbon (≈65%) favoring a high conductivity (>2 S cm-1 ); the ultrahigh contents of nongraphitic nitrogen, redox active pyridinic N (9 at%), and pyrrolic N (5 at%), are stabilized by forming NiN bonds. The conductive carbon nitride harvests a large capacitance of 372 F g-1 with >90% initial capacitance after 10 000 cycles as a supercapacitor electrode, far exceeding the activated carbon electrodes that have <250 F g-1 .

Luminescence behavior of terbium sulphosalicylic acid complexes in sol-gel derived host materials

The formation and luminescence behavior of terbium sulphosalicylic acid (TbSSA) complexes in sol-gel derived host materials have been investigated. The 5-sulphosalicylic acid (H{sub 3}SSA) was dissolved in ethanol in advance, and then the TbCl{sub 3} and ethanol containing H{sub 3}SSA were introduced into the initial precursor sol, respectively. The resulting sol exhibits intramolecular energy transfer from the coordinated sulphosalicylic acid to the terbium ion. The TbSSA complex has formed in the TbCl{sub 3} and H{sub 3}SSA codoped sol. The complexes were found to have notably higher fluorescence intensities than TbCl{sub 3} in both the sol and the gel. In the sol, the concentration quenching was a diffusion-controlled process due to aggregation and effective collision between molecules and the fluorescence was decreased with increase of H{sub 3}SSA concentration. On the other hand, the molecules in the gel were isolated in the pores of the silica network. The fluorescence intensities of TbSSA in the gel were increased with the increase of concentration ratio of H{sub 3}SSA/TbCl{sub 3}. Maximum fluorescence intensity was obtained at H{sub 3}SSA/TbCl{sub 3} = 2.

Molten salt assisted synthesis of black titania hexagonal nanosheets with tuneable phase composition and morphology

A facile, high yield ZnCl2/KCl molten-salt route is developed to fabricate black titania hexagonal nanosheets under atmospheric pressure and low temperature (400 °C). After post-annealing, the black titania possesses a tunable phase composition and enhanced visible light photocatalytic activity, accompanied with a controllable morphology transformation from hexagonal nanosheets to nanorods.

Formation of uniform nitrogen-doped C/Ni/TiO2 hollow spindles toward long cycle life lithium-ion batteries

Uniform nitrogen-doped C/Ni/TiO2 hollow spindles were successfully prepared with Ni nanoparticles encapsulated into the hollow N-doped TiO2/C matrix. This intriguing architecture not only exhibits favorable conductivity, but also provides a large quantity of accessible active sites for lithium ion insertion, thus contributing to superior lithium storage properties.

A facile citric acid assisted sol–gel method for preparing monolithic yttria-stabilized zirconia aerogel

A facile and general strategy for the synthesis of yttria-stabilized zirconia (YSZ) aerogels was developed by using citric acid as a gelation accelerator. This is a low-cost, nontoxic approach to prepare zirconia based aerogels which have important application potential in catalysis and insulation materials.