Yousong Liu

Photodegradation of Rhodamine B over unexcited semiconductor compounds of BiOCl and BiOBr

This study reported, for the first time systematically, photodegradation of Rhodamine B (RhB) in aqueous solution over BiOCl and BiOBr semiconductors. Under visible light irradiation (λ>400 nm, λ>420 nm and λ=550±15 nm), RhB adsorbed on the surface of BiOCl and BiOBr was photosensitized and decomposed effectively over unexcited BiOCl and BiOBr. The degradation of Methyl Orange (MO) and Methylene Blue (MB) over BiOCl and BiOBr was investigated as well, and the results were compared with RhB photodegradation. It was found that MB molecules having the lowest LUMO could not be degraded by this process. Utilizing the quantum chemical calculation (Gaussian 03 program), the relationship between frontier orbital energy of selected dye molecules and photodegradation rate was established for the first time in this study.

Rapid removal of bisphenol A on highly ordered mesoporous carbon

Bisphenol A (BPA) is of global concern due to its disruption of endocrine systems and ubiquity in the aquatic environment. It is important, therefore, that efforts are made to remove it from the aqueous phase. A novel adsorbent, mesoporous carbon CMK-3, prepared from hexagonal SBA-15 mesoporous silica was studied for BPA removal from aqueous phase, and compared with conventional powdered activated carbon (PAC). Characterization of CMK-3 by transmission electron microscopy (TEM), X-ray diffraction, and nitrogen adsorption indicated that prepared CMK-3 had an ordered mesoporous structure with a high specific surface area of 920 m2/g and a pore-size of about 4.9 nm. The adsorption of BPA on CMK-3 followed a pseudo second-order kinetic model. The kinetic constant was 0.00049 g/(mg x min), much higher than the adsorption of BPA on PAC. The adsorption isotherm fitted slightly better with the Freundlich model than the Langmuir model, and adsorption capacity decreased as temperature increased from 10 to 40 degrees C. No significant influence of pH on adsorption was observed at pH 3 to 9; however, adsorption capacity decreased dramatically from pH 9 to 13.

Enhancement photocatalytic activity of the graphite-like C3N4 coated hollow pencil-like ZnO

The pencil-like ZnO hollow tubes with 9-12 μm in length, 350-700 nm in width, 200 nm in wall thickness coating with g-C3N4 have been prepared via a chemical deposition process. As compared with uncoated ZnO or g-C3N4, these g-C3N4/ZnO composites showed the enhanced photocatalytic activity which can be attributed to the heterojunction structure. Furthermore, it is worth pointing out that the weight ratios of g-C3N4 to ZnO (g-C3N4/ZnO) played a significantly influence on the photodegradable properties. With increasing the mass ratio, the photocatalytic activity increased firstly and then decreased after reaching to an optimal photocatalytic performance. It can be inferred that the appreciation of g-C3N4 on the ZnO surface can improve the contact area which resulted in high separation of electrons and holes. However, excessive g-C3N4 may hinder the electrons transferring from the g-C3N4 to ZnO, and thus worse its photocatalytic performance. In our study, the g-C3N4/ZnO sample prepared with 10 wt% of g-C3N4 exhibited the optimal photodegradable efficiency which 94% of Rhodamine B (RhB) has been degraded just in 2 h.

The role of Sn in enhancing the visible-light photocatalytic activity of hollow hierarchical microspheres of the Bi/BiOBr heterojunction

Hollow hierarchical microspheres of Bi/BiOBr (SBB) with oxygen vacancies were prepared using a one step solvothermal method. It was found that the stannous chloride dihydrate played key roles in the formation of Bi, defects and the stacking mode of hierarchical construction units. Positron annihilation lifetime spectroscopy (PALS) was used to demonstrate the oxygen vacancies in Bi/BiOBr samples. The density of states (DOS) of the valence band of BiOBr can be modulated by the introduction of oxygen vacancies according to the valence band XPS and Density Functional Theory (DFT) calculations. Analyses of photoluminescence and BET demonstrated that SBB hollow hierarchical microspheres with higher specific surface area have a lower recombination rate of photo-generated electrons and holes. The photocatalytic and adsorptive performances showed that the samples exhibited stronger adsorption capacity toward rhodamine B (RhB) and highly efficient photocatalytic activity in the degradation of RhB, which were attributed to the higher adsorption ability and synergistic effect of oxygen vacancies and construction of the heterojunction structure (Bi/BiOBr).

Fabrication and photocatalytic properties of silicon nanowires by metal-assisted chemical etching: effect of H2O2 concentration

In the current study, monocrystalline silicon nanowire arrays (SiNWs) were prepared through a metal-assisted chemical etching method of silicon wafers in an etching solution composed of HF and H2O2. Photoelectric properties of the monocrystalline SiNWs are improved greatly with the formation of the nanostructure on the silicon wafers. By controlling the hydrogen peroxide concentration in the etching solution, SiNWs with different morphologies and surface characteristics are obtained. A reasonable mechanism of the etching process was proposed. Photocatalytic experiment shows that SiNWs prepared by 20% H2O2 etching solution exhibit the best activity in the decomposition of the target organic pollutant, Rhodamine B (RhB), under Xe arc lamp irradiation for its appropriate Si nanowire density with the effect of Si content and contact area of photocatalyst and RhB optimized.

Highly-active direct Z-scheme Si/TiO2 photocatalyst for boosted CO2 reduction into value-added methanol

In the present study, direct Z-scheme Si/TiO2 photocatalyst was synthesized via a facile hydrothermal reaction using tetrabutyl titanate and Si powder prepared from magnesiothermic reduction of SiO2 nanospheres. The Si/TiO2 nanospheres were composed of porous Si nanospheres with a diameter of ∼300 nm and TiO2 nanosheets with a diameter of 50 nm and thickness of 10 nm, and demonstrated superior visible light harvesting ability to either Si nanospheres or TiO2 nanosheets. CO2 photocatalytic reduction proved that Si/TiO2 nanocomposites exhibit high activity in conversion of CO2 to methanol with the maximum photonic efficiency of 18.1%, while pure Si and TiO2 catalyst are almost inactive, which can be ascribed to the integrated suitable band composition in the Si/TiO2 Z-scheme system for CO2 reduction. The enhanced photocatalytic property of Z-scheme Si/TiO2 nanospheres was ascribed to the formation of Si/TiO2 Z-scheme system, which improved the separation efficiency of the photogenerated carriers, prolonged their longevity, and therefore boosted their photocatalytic activity.

Hydrogenated Oxygen-Deficient Blue Anatase as Anode for High-Performance Lithium Batteries

Blue oxygen-deficient nanoparticles of anatase TiO2 (H-TiO2) are synthesized using a modified hydrogenation process. Scanning electron microscope and transmission electron microscope images clearly demonstrate the evident change of the TiO2 morphology, from 60 nm rectangular nanosheets to much smaller round or oval nanoparticles of ∼17 nm, after this hydrogenation treatment. Importantly, electron paramagnetic resonance and positronium annihilation lifetime spectroscopy confirm that plentiful oxygen vacancies accompanied by Ti(3+) are created in the hydrogenated samples with a controllable concentration by altering hydrogenation temperature. Experiments and theory calculations demonstrate that the well-balanced Li(+)/e(-) transportation from a synergetic effect between Ti(3+)/oxygen vacancy and reduced size promises the optimal H-TiO2 sample a high specific capacity, as well as greatly enhanced cycling stability and rate performance in comparison with the other TiO2.

Formation mechanism and magnetic properties of hollow Fe3O4 nanospheres synthesized without any surfactant

Hollow structured magnetite spheres were fabricated by a simple solvothermal process, with the assistance of various ammonium salts, where ethylene glycol was used as the solvent and reducing agent. The results of X-ray diffraction, scanning electron microscopy and transmission electron microscopy show that the as-synthesized products are pure single-phase Fe3O4 with good crystalline state, and all the samples are hollow structures except for the S-d sample, which was obtained by the assistance of NH4HCO3. The X-ray photoelectron spectrometry manifests that the Fe3+ ions on the surface of the hollow spheres exist in the form of Fe3O4, and Mossbauer measurements reveal that the hollow spheres are similar to the stoichiometric Fe3O4. The possible formation mechanism of hollow magnetite spheres with various sizes was discussed in detail. Meanwhile magnetic properties were determined by using a vibrating sample magnetometer at room temperature. The magnetic properties investigation showed that the Fe3O4 spheres were ferromagnetic with small hysteresis loops. The values of saturation magnetization are 82.989, 78.049 and 87.417 emu g−1 for the S-a, S-b and S-c samples, which decreases with increasing particle size. This phenomenon may be caused by the content of Fe3+ on A- and B-sites of the spinel ferrite. Based on experimental results, the relationship between their microcomponents also has been studied.

Gold-thickness-dependent Schottky barrier height for charge transfer in metal-assisted chemical etching of silicon

Large-area, vertically aligned silicon nanowires with a uniform diameter along the height direction were fabricated by combining in situ-formed anodic aluminum oxide template and metal-assisted chemical etching. The etching rate of the Si catalyzed using a thick Au mesh is much faster than that catalyzed using a thin one, which is suggested to be induced by the charge transport process. The thick Au mesh in contact with the Si produces a low Au/Si Schottky barrier height, facilitating the injection of electronic holes from the Au to the Si, thus resulting in a high etching rate.