Improving the visible light photocatalytic activity of mesoporous TiO2 via the synergetic effects of B doping and Ag loading

B-doped together with Ag-loaded mesoporous TiO₂ (Ag/B–TiO₂) was prepared by a two-step hydrothermal method in the presence of boric acid, triblock copolymer surfactant, and silver nitrate, followed by heat treatment. The obtained samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption. It was revealed that all samples consist of highly crystalline anatase with mesoporous structure. For Ag/B–TiO₂, B was doped into TiO₂ matrix in the form of both interstitial B and substitutional B while Ag was deposited on the surface of B–TiO₂ in the form of metallic silver. Compared with the single B-doped or Ag-loaded TiO₂ one, mesoporous Ag/B–TiO₂ exhibits much higher visible light photocatalytic activity for the degradation of Rhodamine 6G, which can be ascribed to the synergistic effects of B doping and Ag loading by narrowing the band gap of the photocatalyst and preventing the fast recombination of the photogenerated charge carriers, respectively.     

Preparation of TiO2 hollow spheres for DSSC photoanodes

High crystallinity mesoporous TiO₂ hollow spheres (MHS-TiO₂) were prepared using the mesoporous carbon hollow sphere template. The MHS-TiO₂ contains mainly nanostructured anatase. The mesopore of the MHS-TiO₂ has a pore opening in the range of 400–600 nm. The refined extended X-ray absorption fine structure spectra indicate that the MHS-TiO₂ possesses less the 1st-shell Ti–O coordination numbers than the nano-TiO₂. More surface active species (A₂ ((Ti=O)O₄)) on the MHS-TiO₂ are also observed by the component fitted X-ray absorption near edge structure spectroscopy. The MHS-TiO₂ photoanode has a better DSSC conversion efficiency than the nano-TiO₂ one by at least 40%. Note that the N3 dye molecules are accessible to the mesopores of the MHS-TiO₂, and the loading time for N3 can be reduced by at least 70% if compared with those of the nano-TiO₂.     

Synthesis and enhanced photocatalytic activity of NaNbO3 prepared by hydrothermal and polymerized complex methods

We prepared NaNbO₃ by several methods, namely solid-state reaction (SSR), hydrothermal (HT) and polymerized complex (PC) methods, and investigated the relationships between the photocatalytic activity and the particle size and morphology. The photocatalytic activity was evaluated by H₂ evolution from an aqueous methanol solution and pure water splitting in the presence of the Pt(0.5 wt%)/NaNbO₃ and RuO₂(1.25 wt%)/NaNbO₃, respectively. It is found that the sample prepared by PC with smallest particles exhibits the highest photocatalytic activity in both reactions. Moreover, the HT sample with the cubic and rectangular shape also shows the enhanced photocatalytic activity for H₂ evolution from an aqueous methanol solution in comparison with that of the sample prepared by SSR.     

Photophysical and enhanced daylight photocatalytic properties of N-doped TiO2/g-C3N4 composites

N-doped TiO₂/C₃N₄ composite samples were synthesized by heating the mixture of the hydrolysis product of TiCl₄ and C₃N₄ at different weight ratios. The samples were characterized by X-ray diffraction (XRD), Raman spectrum, UV–vis absorption spectrum, photoluminescence spectrum, X-ray photon electron spectrum (XPS) and surface photovoltage spectrum (SPS). The XRD and Raman results indicate that the introduction of C₃N₄ could inhibit the formation of rutile TiO₂. The composite samples show slight visible light absorption due to the introduction of C₃N₄. The XPS result reveals that some amount of nitrogen is doped into TiO₂, and C₃N₄ exists in the composite sample. The intensities of the SPS signal in the composite samples decrease with the rise in the amount of C₃N₄ in the samples. The photocatalytic activity was evaluated from the Rhodamine B (RhB) degradation under fluorescence light irradiation. The composite samples show significantly enhanced photocatalytic activities and the RhB self-sensitized photodegradation in this system was observed by measuring the photocurrent in the dye sensitized solar cell using the composite as the working electrode.     

Crystallization study of sol-gel un-doped and Pd-doped TiO2 materials

Sol-gel nanostructured titania materials have been reported to have applications in areas ranging from optics via solar energy to gas sensors. In order to enhance the photocatalytic activity, there are many studies regarding the doping of titanium dioxide (TiO₂) material with either non-metals (S, C, N, P) or metals (Ag, Pt, Nd, Fe). The present work has studied some un-doped and Pd-doped sol-gel TiO₂ materials (films and gels), with various surface morphologies and structures, obtained by simultaneous gelation of both precursors Ti(OEt)₄ and Pd(acac)₂. Their structural evaluation and crystallization behavior with thermal treatment were followed by DTA/TG analysis, infrared (IR) spectroscopy, Fourier transform infrared (FTIR), spectroellipsometry (SE), X-ray diffraction (XRD) and atomic force microscope (AFM). The influence of Pd on TiO₂ crystallization for both supported and un-supported materials was studied (lattice parameters, crystallite sizes, internal microstrains). The changes in the optical properties of the TiO₂-based vitreous materials were correlated with the changes of the structure. The hydrophilic properties of the films were also connected with their structure, composition and surface morphology.     

Sol-gel derived S,I-codoped mesoporous TiO2 photocatalyst with high visible-light photocatalytic activity

A mesoporous S,I-codoped TiO₂ photocatalyst with high visible light photocatalytic activity was synthesized through the hydrolysis and condensation of titanium isopropoxide with thiourea and iodic acid as the precursors. The as-prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-vis diffuse reflectance (DRS), X-ray photoelectron spectroscopy (XPS), Fourier translation infrared spectroscopy (FT-IR), and N₂ adsorption. The results showed that the cations of S⁶⁺ and I⁵⁺ could substitute for some of the lattice titanium (Ti⁴⁺). The S,I-codoping forms the new bands above the valence band and narrows the band-gap of the TiO₂, then shifts the absorption edge from UV light region to visible light range. The activity of the catalyst was examined by photodegradation of methylene blue in an aqueous solution under visible light irradiation. The activity of the S,I-codoped catalyst is far superior to that of single S or I-doped TiO₂ counterpart. The high visible light photocatalytic activity could be attributed to the strong absorption of light, well-crystalline anatase phase, and mesoporous microstructure.     

Effects of microwave drying on the microstructure and photocatalytic activity of bimodal mesoporous TiO2 powders

Bimodal nanocrystalline mesoporous TiO₂ powders with highly photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate as precursor, and then dried in microwave oven. The prepared samples were characterized by XRD, SEM, TEM, HRTEM and N₂ adsorption-desorption measurement. The photocatalytic activity was evaluated by the photocatalytic degradation of acetone in air under UV light irradiation at room temperature. The effects of microwave drying on the microstructures and photocatalytic activity of the TiO₂ powders were investigated and discussed. The results show that microwave drying not only promotes the growth of the pores but also greatly reduces the state of agglomeration within the powders. All the microwave-dried TiO₂ powders show higher photocatalytic activity than Degussa P-25 (P25) and the TiO₂ powders dried by conventional method.     

Synthesis and crystallographic studies of garnet-type AgCa2Mn2V3O12 and NaPb2Mn2V3O12

High-purity powder specimens of AgCa₂Mn₂V₃O₁₂ and NaPb₂Mn₂V₃O₁₂ have been successfully synthesized by solid-state chemical reaction. The Rietveld refinements from X-ray powder diffraction data verified that these compounds have the garnet-type structure (space group , No. 230) with the lattice constant of a=12.596(2) Å for AgCa₂Mn₂V₃O₁₂ and a=12.876(2) Å for NaPb₂Mn₂V₃O₁₂. Calculation of the bond valence sum supported that Mn is divalent and V is pentavalent in these garnets. Estimation of the quadratic elongation and the bond angle variance showed that the distortions of the MnO₆ octahedra and the VO₄ tetrahedra are significantly suppressed. Our new results of AgCa₂Mn₂V₃O₁₂ and NaPb₂Mn₂V₃O₁₂ are compared to those of AgCa₂M₂V₃O₁₂ and NaPb₂M₂V₃O₁₂ (M=Mg, Co, Ni, Zn).     

Photocatalytic abilities of gel-derived P-doped TiO2

P-doped TiO₂ nanoparticles were synthesized through hydrolysis and condensation of Ti(OC₂H₅)₄ with H₃PO₄ additions. Effects of [H₃PO₄]/[Ti(OC₂H₅)₄] molar ratios on the anatase-to-rutile phase transformation, crystallite sizes, surface areas, and photocatalytic abilities of the gel-derived P-doped TiO₂ were investigated. The P-doped TiO₂ nanoparticles prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 were composed of anatase monophase even at 900 ^oC and possessed very strong photocatalytic ability. Kinetic studies on the P-doped TiO₂ to photocatalytically decompose methylene blue under irradiation of 365 nm UV light found that the P-doped TiO₂ prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 and calcined at 800 ^oC had the specific reaction rates, at 25 °C, k_A,m=0.76 m³/(kg min) (based on the mass of P-doped TiO₂) and k_A,BET=46.2×10⁻⁶ m/min (based on the BET surface area of P-doped TiO₂), which is superior to the performance of a commercial product, P25 (k_A,m=0.22 m³/(kg min) and k_A,BET=4.8×10⁻⁶ m/min).     

Shape-controlled synthesis of Cu2O nano/microcrystals and their antibacterial activity

Uniform cuprous oxides with different morphologies have been successfully synthesized using polyvinylpyrrolidone (PVP) as a capping agent. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer, Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy were employed to characterize the structure and morphology of cuprous oxides. It was found that the reaction conditions such as PVP, reducing agent and complexing agent played important roles in the formation of regular cuprous oxide crystals. In addition, their antibacterial activity against Bacillus subtilis (B. subtilis), Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) was also investigated by the Oxford cup method. Results suggested that cuprous oxides are selective in their antibacterial action. They display effective antibacterial activity against S. aureus, B. subtilis and P. aeruginosa. There is no bactericidal ability against E. coli in the tested concentration range, which indicates that E. coli may be a Cu(I)-tolerant bacterium.     

Mesoporous TiO2-B nanowires synthesized from tetrabutyl titanate

Ultralong mesoporous TiO₂-B nanowires were synthesized via a hybrid hydrothermal-ion exchanging-thermal treatment using tetrabutyl titanate (TBOT) as a raw material. The phase transformations and porous structures of TiO₂-B nanowires were characterized and studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption-desorption measurement. Mesoporous TiO₂-B nanowires showed a length of several micrometers and diameter of about 25 nm. The porous structures of obtained TiO₂-B nanowires were demonstrated by BJH pore distribution measurement. The wirelike morphologies and porous structures of monodisperse nanowires calcined at 600 °C showed little change, which indicated that such nanowires possessed high thermal stability. The formation mechanism of TiO₂-B nanowires with mesoporous structures were also discussed based on our experimental results.     

Aqueous synthesis and enhanced photocatalytic activity of ZnO/Fe2O3 heterostructures

We report a facile synthesis of ZnO/Fe₂O₃ heterostructures based on the hydrolysis of FeCl₃ in the presence of ZnO nanoparticles. The material structure, composition, and its optical properties have been examined by means of transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and diffuse reflectance UV–visible spectroscopy. Results obtained show that 2.9 nm-sized Fe₂O₃ nanoparticles produced assemble with ZnO to form ZnO/Fe₂O₃ heterostructures. We have evaluated the photodegradation performances of ZnO/Fe₂O₃ materials using salicylic acid under UV-light. ZnO/Fe₂O₃ heterostructures exhibited enhanced photocatalytic capabilities than commercial ZnO due to the effective electron/hole separation at the interfaces of ZnO/Fe₂O₃ allowing the enhanced hydroxyl and superoxide radicals production from the heterostructure.     

Preparation of LiCoO2 nanofibers by electrospinning technique

Using a sol-gel processing and electrospinning technique, extrathin fibers of PVA (polyvinyl alcohol)/lithium chloride/cobalt acetate composite were prepared. After calcinations of the above precursor fibers at 600°C, LiCoO₂ nanofibers with a diameter of 100-150 nm, were successfully obtained. Measurements of TG/DTA, IR, XRD, Raman, SEM, EDS, respectively, were performed to characterize the properties of the as-prepared materials. We observed a strong correlation between crystalline phase and morphology of the fibers and calcinations temperature.     

Preparation of nitrogen-doped titanium dioxide with visible-light photocatalytic activity using a facile hydrothermal method

Nitrogen-doped TiO₂ (N-TiO₂) nanoparticles have been successfully prepared via a direct and simple hydrothermal reaction of a commercial Degussa P25 with triethanol amine as solvent and nitrogen source. As-prepared N-TiO₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible light (UV-vis) absorption spectra, electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) techniques. The results confirm that hydrothermal reaction is an effective way to incorporate nitrogen into the TiO₂ lattice, especially nitrogen substitute for titanium. The nitrogen concentration in TiO₂ can be as high as 21% (molar ratio), which is described as Ti_1−yO_2−xN_x+y (in this paper, x=0.36, y=0.27, i.e., Ti_0.73O_1.64N_0.63). The chemical statuses of N have been assigned to N-Ti-O and O-N-O in the TiO₂ lattice as identified by XPS. Photocatalytic degradation of methyl orange has been carried out in both UV-vis (simulated solar light) and the visible region (λ>400 nm). N-TiO₂ exhibits higher activity than the Degussa P25 TiO₂ photocatalyst, particularly under visible-light irradiation. This study has developed a promising and practical pathway to new nitrogen-doped photocatalysts.     

Multicomponent GeSe2-CdI2-TeO2 (Bi2O3) systems: glass formation and properties

The glass-forming regions of the GeSe₂-CdI₂-TeO₂ (I), GeSe₂-CdI₂-Bi₂O₃ (II) and GeSe₂-TeO₂-Bi₂O₃ (III) systems have been determined. The obtained glassy phases have been characterized by their basic physicochemical parameters such as temperatures of glass transition, crystallization, and melting, density and microhardness. The phase T-X diagram of the GeSe₂-CdI₂ system, which is the basic joint line for systems I and II, has been specified. Three non-variant equilibria (two eutectic and one syntectic) have been observed at temperatures 350, 280 and 375 °C for compositions containing 15, 95 and 33.3 mol% GeSe₂, respectively. A new intermediate phase with probable composition of 2CdI₂·GeSe₂ has been formed.     

Synthesis and characterization of the SnO2-pillared layered titanate nanohybrid

SnO₂-pillared titanate nanohybrid has been prepared by reacting the exfoliated layered titanate sheets with the nanosized SnO₂ sol particles. The stable two-dimensional colloidal nanosheets could be obtained by intercalating tetrabutylammonium cation into the layered protonic titanate, H_xTi_2−x/4□_x/4O₄·H₂O (x=0.67) with a lepidocrocite-like structure, and by successive exfoliation process in an aqueous solution. Monodispersed SnO₂ nano sol particles were prepared by hydrolysis of SnCl₄·5H₂O in the presence of sodium hydroxide, and then the exfoliated titanate suspension was mixed with SnO₂ nano sol solution until the flocculated products formed. The final product was heated at various temperatures in order to complete the grafting reaction of intercalated SnO₂ nano sol on the interlayer surface of layered titanate. Inductive coupled plasma, X-ray diffraction, thermal analysis and N₂-adsorption-desorption isotherms were carried out to study the hybridizing process and the structure of SnO₂-pillared titanate nanohybrid.     

Porous SnO2 nanoflakes with loose-packed structure: Morphology conserved transformation from SnS2 precursor and application in lithium ion batteries and gas sensors

Porous SnO₂ nanoflakes with loose-packed structure were synthesized by calcination of SnS₂ precursors that were obtained through solvothermal method at low temperature. The as-obtained SnO₂ product had a three-dimensional porous structure with relatively high specific surface area. It was found that the SnO₂ nanoflakes inherited the morphology of precursor while numerous pores were formed after the annealing process. The combined techniques of X-ray diffraction, energy-dispersive spectrum, field emission scanning electron microscopy, and (high-resolution) transmission electron microscopy were used for characterization of the as-prepared SnO₂ product. Moreover, the porous SnO₂ nanoflakes with loose-packed structure could be used as gas sensors for detecting ethanol and acted as anode for lithium ion batteries. Our study shows that the as-prepared SnO₂ nanoflakes not only exhibit good response and reversibility to ethanol gas but also display enhanced Li-ion storage capability.     

P/Si-TiO2 transparent films with high anatase stability and photocatalytic activity

The anatase-TiO₂ transparent films, containing 3 mol% of Si and P elements (as dopants), were synthesized using a process combining the sol-gel method and spin-coating technique. Effects of relative ratio of dopants and calcination temperature on phase transformation, grain growth, surface morphology, light transmittance, band-gap energy and photocatalytic activity of the P/Si-TiO₂ films were examined and their results were compared with those of the undoped-TiO₂ and Si-TiO₂ films. The P/Si-TiO₂ films calcined at temperature between 600 and 900 °C adhered strongly to the surface of fused-silica substrate and were composed of anatase-TiO₂ monophase. The photocatalytic activities of the films were measured and represented using a characteristic time constant (τ) for the methylene blue (MB) photodegradation. The small τ stands for high photocatalytic ability of the film. The P/Si-TiO₂ film, containing equalmolar Si and P dopants, calcined at 800 °C gave the best performance in photocatalysis; this film had τ=5.7 h and decomposed about 90 mole% of MB in the water after 12 h of the 365-nm UV light irradiation.     

Preparation, characterization and electrochemical property of Sn-Fe-Mo-Al2O3 multi-phase composites

A novel technique has been developed to synthesize Sn-Fe-Mo-Al₂O₃, while nanoscale dispersion of a highly active tin phase was finely distributed in a stable inert multi-phase. The precursor was prepared by co-precipitation method with SnCl₄, FeCl₃, AlCl₃ and (NH₄)₆Mo₇O₂₄ as the raw materials. Sn-Fe-Mo-Al₂O₃ mixture was produced by reducing the precursor with H₂. The product was characterized by X-ray diffraction (XRD), ICP and scanning electron microscopy (SEM). The performance of the electrode was investigated. The Sn-Fe-Mo-Al₂O₃ electrode was found to have an initial charge capacity of over 461 mAh/g, and a reversible volumetric capacity of 2090 mAh/cm³, which is two times larger than that of graphite electrode (800 mAh/cm³). The coulomb efficiency in the first cycle was over 55%, but its cyclability was not improved significantly. In order to enhance the cycle performance, we investigated the anode after heat treated at 270 °C for 12 h. Under the same condition, the first charge-discharge characteristics were almost equivalent to the as-coated anode, and the retention capacity ratio after 20 cycles was improved from 41.1% to 86.5%. The heat-treated Sn-Fe-Mo-Al₂O₃ electrode exhibited better cycle life. The electrochemical reaction of the Sn-Fe-Mo-Al₂O₃ electrode with Li may obey the alloying-dealloying mechanism of Li_xSn(x?4.4) formation in the other tin-based electrodes.