An efficient visible light photocatalyst prepared from TiO<Subscript>2</Subscript> and polyvinyl chloride

An efficient visible light photocatalyst has been prepared from TiO₂ nanoparticles and a partly conjugated polymer derived from polyvinyl chloride (PVC). It was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The visible light photocatalytic activity of the as-prepared photocatalyst was evaluated by the photocatalytic degradation of Rhodamine B (RhB) under visible light irradiation. The XPS, FT-IR, and Raman spectra show that the partly conjugated polymer derived from PVC exists on the surface of the TiO₂ nanoparticles. The UV–Vis DRS, XRD, and TEM results reveal that the modification of the partly conjugated polymer can obviously improve the absorbance of the TiO₂ nanoparticles in the range of visible light and hardly affect their size and crystallinity. The visible light photocatalytic activity of the as-prepared TiO₂ nanocomposites is higher than that of commercial TiO₂ (Degussa P25) and comparable with those of visible light photocatalysts reported in the literature. Their visible light photocatalytic stability is also good. The reasons for their excellent visible light photocatalytic activity and the major factors affecting their photocatalytic activity are discussed.     

Functionalization of electrospun magnetically separable TiO<Subscript>2</Subscript>-coated SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers: strongly effective photocatalyst and magnetic separation

Magnetically separable TiO₂-coated SrFe₁₂O₁₉ electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO₂-coated SrFe₁₂O₁₉ fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant dye solution, MB in a photochemical reactor. In contrast to pure TiO₂ fibers, the TiO₂-coated SrFe₁₂O₁₉ fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe₁₂O₁₉ not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore, these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution of treated water.     

Photocatalytic degradation of methylene blue by Au-deposited TiO<Subscript>2</Subscript> film under UV irradiation

A TiO₂ photocatalytic film was prepared by the sol–gel and dip-coating methods. Au-loaded TiO₂ photocatalytic films were produced by the photodeposition method. The photocatalytic activity of the films under UV irradiation was evaluated by measuring the degradation of absorbance for a methylene blue (MB) aqueous solution. Au particles deposited on the TiO₂ film improved the photocatalytic activity under the O₂ bubbling condition. On the other hand, under N₂ or Ar bubbling, the doubly reduced form of MB, leuco-methylene blue (LMB), was formed at the beginning of UV irradiation, and then both MB and LMB were decomposed gradually by the photocatalytic reaction. In this process, Au particles on the TiO₂ film behave as electron traps.     

Hydrothermal synthesis of hemisphere-like F-doped anatase TiO<Subscript>2</Subscript> with visible light photocatalytic activity

Hemisphere-like F-doped anatase TiO₂ has been synthesized by hydrothermal treatment of TiF₄ aqueous solution in the presence of starch at 130 °C for 10 h, and then calcined at 450 °C for 2.5 h in air. The as-synthesized product has been investigated by photocatalytic reaction test and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV–Vis diffuse reflectance spectra (DRS). The results showed that fluorine was successfully doped into the TiO₂ hemispheres. The F-doped TiO₂ hemispheres showed high visible light activity in degradation of acid orange II, which could be attributed to the creation of oxygen vacancies and good crystallinity.     

Preparation of lanthanum-doped TiO<Subscript>2</Subscript> photocatalysts by coprecipitation

The lanthanum-doped TiO₂ (La³⁺-TiO₂) photocatalysts were prepared by coprecipitation and sol–gel methods. Rhodamine B was used as a model chemical in this work to evaluate the photocatalytic activity of the catalyst samples. The optimum catalyst samples were characterized by XRD, N₂ adsorption–desorption measurement, SEM and electron probe microanalyses to find their differences in physical and chemical properties. The experimental results showed that the La³⁺-TiO₂ catalysts prepared by coprecipitation exhibited obviously higher photocatalytic activities as compared with that prepared by the conventional sol–gel process. The optimum photocatalysts prepared by the coprecipitation and sol–gel process have similar adsorption equilibrium constants in Rhodamine B solution and particle size distribution in water medium although there are larger differences in their surface area, morphology and pore size distribution. The pores in the sol-gel prepared catalysts are in the range of mesopores (2–50 nm), whereas the pores in the coprecipitation prepared catalysts consist of bigger mesopores and macropores (>50 nm). The morphology of the primary particles and agglomerates of the La³⁺-TiO₂ catalyst powders was affected by doping processes. The inhibition effect of lanthanum doping on the phase transformation is greater in the coprecipitation process than in the sol–gel process, which could be related with the different amount of Ti–O–La bonds in the precursors. This finding could be used for preparing the anatase La³⁺-TiO₂ catalysts with more regular crystal structure through a higher heat treatment temperature. The optimum amount of lanthanum doping is ca. 1.0 wt.% and the surface atomic ratio of [O]/[Ti] is ca. 2.49 for 1.0 wt.% La³⁺-TiO₂ catalysts prepared by the two processes. The obviously higher photocatalytic activity of the La³⁺-TiO₂ samples prepared by the coprecipitation could be mainly attributed to their more regular anatase structure and more proper surface chemical state of Ti³⁺ species. The optimum preparation conditions are 1.0 wt.% doping amount of lanthanum ions, calcination temperature 800 °C and calcination time 2 h using the coprecipitation process. As compared with the sol-gel process, the coprecipitation process used relatively cheap inorganic raw materials and a simple process without organic solvents. Therefore, the coprecipitation method provides a potential alternative in realizing large scale production.     

Hollow TiO2:Sm3+ spheres with enhanced photoluminescence fabricated by a facile method using polystyrene as template

Uniform hollow Sm³⁺-doped titania phosphors were prepared via a facile method using polystyrene spheres as template. After calcination at 500 °C for 3 h, hollow TiO₂:Sm³⁺ spheres with outer diameters of approximately 250 nm and a shell thicknesses ranging from 50 to 70 nm were obtained. A possible formation mechanism of the evolution process of the spheres was discussed in this paper. Photoluminescence (PL) results showed that the emission intensity of the as-prepared hollow TiO₂:Sm³⁺ spheres was 2.1 times higher than that of amorphous nanoparticles (NPs). We propose that this PL enhancement is due to the unique hollow structures obtained.     

Electrospun mesoporous W-doped TiO2 thin films for efficient visible-light photocatalysis

Mesoporous W⁶⁺-doped TiO₂ thin films photocatalysts were prepared via electrospinning and sol-gel chemistry, employing a triblock copolymer as structure-directing agent, and were characterized by SEM, TEM, XRD as well as N₂ adsoption/desorption isotherm. The photocatalytic activity of the films was investigated by employing the methylene blue (MB) as probe. In this study, 3% was the most suitable content of W⁶⁺ in TiO₂, at which the recombination of photoinduced electrons and holes could be effectively inhibited. In the mean time, making the photocatalysts at nanoscale and with mesopores in the films could produce more reactive sites to adsorbe and oxidize pollutants.     

Luminescence properties and electronic structure of Sm<Superscript>3+</Superscript>-doped YAl<Subscript>3</Subscript>B<Subscript>4</Subscript>O<Subscript>12</Subscript>

The luminescence properties of Sm³⁺ ions in YAl₃B₄O₁₂ were studied upon synchrotron excitation in the 3.8–11 eV region. In addition to the 4f → 4f excitation bands, the excitation spectra of the Sm³⁺ emission contain broad bands at 6.1 and ~7.0 eV. These bands are attributed to charge transfer transition in Sm³⁺–O²⁻ complexes and 4f → 5d transition of Sm³⁺ ions, respectively. The optical absorption edge of YAl₃B₄O₁₂ was determined at 7.3 eV. A comparison with the results of electronic structure calculations on YAl₃B₄O₁₂ is also made.     

An investigation on synthesis and photocatalytic activity of polyaniline sensitized nanocrystalline TiO<Subscript>2</Subscript> composites

Polyaniline (PAn) sensitized nanocrystalline TiO₂ composite photocatalyst (PAn/TiO₂) with high activity and easy separation was facilely prepared by in situ chemical oxidation of aniline from the surfaces of the TiO₂ nanoparticles. The morphology, structure, and light absorption properties of composite photocatalyst were examined in term of its application to photocatalysis. The photocatalytic activity of PAn/TiO₂ nanocomposites for the degradation of methylene blue (MB) aqueous solution was investigated and compared with pure TiO₂. The spectra analyses illustrated that, when PAn deposited on the surface of TiO₂, the crystalline behavior of PAn was hampered and the degree of crystallinity decreased, and the characteristic peaks of the PAn were shifted indicating that there was a strong interaction between PAn and TiO₂ nanoparticles. PAn was able to sensitize TiO₂ efficiently and the composite photocatalyst could be activated by absorbing both the ultraviolet and visible light (λ = 190–800 nm), whereas pure TiO₂ absorbed ultraviolet light only (λ < 400 nm). Photocatalytic experiments showed that under natural light irradiation, MB could be degraded more efficiently on the PAn/TiO₂ than on the pure TiO₂, due to the charge transfer from PAn to TiO₂ and efficient separation of e⁻-h⁺ pairs on the interface of PAn and TiO₂ in the excited state. More significantly, the PAn/TiO₂ composite photocatalyst exhibited easy separation and less deactivation after several runs. The advantages of the obtained PAn/TiO₂ composite photocatalyst revealed its great practical potential in wastewater treatment.     

Synthesis of PANI/TiO<Subscript>2</Subscript>–Fe<Superscript>3+</Superscript> nanocomposite and its photocatalytic property

A convenient method for synthesizing highly photocatalytic activity PANI/TiO₂–Fe³⁺ nanocomposite was developed. The effect of calcination temperature on the phase composition of TiO₂ nanopowder was investigated. It was found that higher temperature could promote the formation of rutile phase. The nanocomposite was characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). The results indicated that the nanohybrid was composed of TiO₂, Fe³⁺ and PANI. The photocatalytic property of the nanocomposite was evaluated by the degradation of methyl orange. In the presence of this catalyst, the degradation rate of methyl orange of 95.2% and 70.3% could be obtained under the UV and sunlight irradiation within 30 min, respectively. The apparent rate constant was 5.64 × 10⁻² which is better than that of the Degussa P25.     

Conductivity of Sm<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Sm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The oxygen-ion conductivity of porous materials, the coarse-grained pyrochlore-like Sm₂Ti₂O₇ and fine-grained Sm₂TiO₅ compounds, produced by mechanical activation of initial oxides is studied at 400–1000 °C. The Sm₂TiO₅ samples contain ～15 wt % of the nanosized pyrochlore-like Sm₂TiO₅ phase in addition to the rhombic phase. As determined by impedance spectroscopy, the ionic conductivities of Sm₂TiO₅ and Sm₂Ti₂O₇ at 1000°C are 1.3 × 10^?3 and 1.8 × 10^?4 S cm^?1, and the activation energies of the bulk and grainboundary conductivities of the materials are 1.04 and 1.24 eV for Sm₂TiO₅ and 1.69 and 1.80 eV for Sm₂Ti₂O₇.     

Preparation of anatase F doped TiO<Subscript>2</Subscript> sol and its performance for photodegradation of formaldehyde

Anatase fluoride doped TiO₂ sol (F-TiO₂) catalyst was prepared by a modified sol-gel hydrothermal method, using tetra butyl titanate as a precursor. The influences of F doping, temperature of hydrothermal, values of medium pH on the morphology and crystallization were studied. The microstructure and morphology of sol sample were characterized by XRD, TEM, FTIR, UV–Vis–DRS, particle size distribution (PSD) and XPS. The results showed that F-TiO₂ particles in sol were spherical and partly crystallized to anatase structure, and dispersed in the aqueous medium homogeneously and that the average particle size was ca. 10.5 nm calculated from XRD and TEM results. It was also found that the addition of fluorine could improve the crystallization and adsorption of particles significantly, the photocatalytic activity for decomposition of formaldehyde were enhanced remarkably with the doping of fluorine. Possible mechanism of anatase F-TiO₂ formed under hydrothermal conditions was discussed.     

Analyzing the efficiency of nanostructured Sm3+- and Gd3+-doped TiO2 and constructing DSSCs using efficacious photoanodes

The rare earth elements, gadolinium and samarium, are doped with TiO₂ by hydrothermal synthesis technique to study the photoconversion performance of a photoanode in a dye-sensitized solar cell (DSSC). The obtained materials are subjected to the characterizations XRD, HR-TEM, UV–Vis spectroscopy, and XPS. DSSCs are fabricated using N719 dye, redox electrolyte, and platinum counter electrode. Charge-transfer ability was investigated using electrochemical impedance spectroscopy (EIS) on DSSCs. The efficiencies of DSSCs are influenced by the electron transport within the TiO₂–dye–electrolyte system. After the fabrication and simulation, among the two, Gd³⁺-doped TiO₂ gives the desired outcomes and higher efficiency (5.542%) than the pure and Sm³⁺-doped TiO₂ and thus it proves to be a superior solar cell anode material.

     

Hydrothermal synthesis and photoluminescence properties of Y<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript> phosphors

This article presents the synthesis and photoluminescence (PL) properties of Y₂Zr₂O₇:Tb³⁺. The Tb³⁺-doped Y₂Zr₂O₇ zirconates were successfully synthesized by a hydrothermal process at 200 °C for 20 h. X-ray diffractometer (XRD) patterns revealed that all of the products were phase-pure with the fluorite structure. PL study showed that the Y₂Zr₂O₇:Tb³⁺ phosphors exhibited obvious PL emission peaks which located at 490, 545, 585, and 623 nm; the dominant emission located at 545 nm is assigned to ⁵D₄ → ⁷F₅ transition. Furthermore, Tb³⁺-doping concentration strongly affected the PL properties, and the quenching concentration is 5 at.%.     

The synthesis and the magnetic properties of Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BiY<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>5</Subscript>O<Subscript>12 </Subscript>nanoparticles

Sm _x BiY_2–x Fe₅O₁₂ (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8) nanocrystals were fabricated by sol–gel method. Samples were characterized by powder X-ray diffraction (XRD), thermal gravity analysis (TGA) and differential thermal analysis (DTA), transmission electron microscopy (TEM), vibrating sample magnetometer(VSM). The samples were calcined at 850 °C and 1000 °C and the average size of the particles were determined by Scherrer’s formula . In this paper, we discussed the effect of Sm³⁺ substitution for Y³⁺ on magnetic properties of BiY₂Fe₅O₁₂. The magnetic properties of Sm _x BiY_2−x Fe₅O₁₂ are decreased with increasing content of Sm ion.     

Effect of Mn<Superscript>2+</Superscript> doping on the temperature coefficient of capacitance of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>-doped BaTiO<Subscript>3</Subscript> ceramics

The effect of Mn²⁺ on the temperature coefficient of capacitance (TCC) of TiO₂/SiO₂-doped BaTiO₃ ceramics has been investigated. The experiment has shown that the high temperature peak of TCC exhibited a continuous enhancement when Mn²⁺ concentration increased and X8R specification was gradually met. The secondary phase Ba₂TiSi₂O₈ was found in all samples. SEM and XRD analyses have proved that Mn²⁺ could depress the crystallization of TiO₂/SiO₂ in BaTiO₃ ceramics. The microstrain study through MAUD analysis depicted that the high temperature peak of TCC was dependent on the microstrain of samples to a certain extent. The Mn²⁺ could be a useful dopant for ameliorating the TCC of TiO₂/SiO₂-doped BaTiO₃ ceramics. The text was submitted by the authors in English.     

Photocatalytic activity of polypyrrole/TiO<Subscript>2</Subscript> nanocomposites under visible and UV light

A series of polypyrrole (PPy)/titanium dioxide (TiO₂) nanocomposites were prepared in different polymerization conditions by ‘in situ’ chemical oxidative polymerization. The nanocomposites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectra (XPS), and UV–Vis diffuse reflectance spectra. The photocatalytic degradation of methyl orange (MO) was chosen as a model reaction to evaluate the photocatalytic activities of TiO₂/PPy catalysts. The results show that a strong interaction exists at the interface between TiO₂ and PPy, the deposition of PPy on TiO₂ nanoparticles can alleviate their agglomeration, PPy/TiO₂ nanocomposites show stronger absorbance than neat TiO₂ under the whole range of visible light. The obtained PPy/TiO₂ nanocomposites exhibit significantly higher photocatalytic activity than the neat TiO₂ on the degradation of MO aqueous solution under visible and UV light illumination. The reasons for improving the photocatalytic activity were also discussed.     

Ferroin adsorption on TiO<Subscript>2</Subscript>-based photocatalytic materials

We have studied ferroin adsorption on photocatalytically active nanocomposites based on TiO₂ doped with Fe³⁺, Nb⁵⁺, or W⁶⁺. The results demonstrate that the mass of an adsorbed organic substance correlates with the photocatalytic activity of the photocatalysts. High-temperature heat treatment of the nanocomposites increases manyfold the mass of an organic substance adsorbed from an aqueous solution for unit free surface area of the photocatalyst.     

TiO<Subscript>2</Subscript>/graphene composite from thermal reaction of graphene oxide and its photocatalytic activity in visible light

In this study, the P25 TiO₂ nanoparticles and graphene sheets (GSs) composite were prepared from a facile thermal reaction of graphene oxide. Its microstructures and photocatalytic properties were characterized and measured using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) specific area analysis, X-ray photoelectron spectroscopy (XPS), FT-IR spectra, and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy. Compared with pure P25 nanoparticles, the results reveal that (1) there is a red shift about 20 nm in the absorption edge of the P25/graphene composite; (2) the photocurrent of the composite is about 15 times higher than that of pure P25; (3) the visible light photocatalytic activity of the composite is enhanced greatly on decomposition of methylene blue (MB). The photocatalytic mechanism of the P25/graphene composite is also discussed.     

Photoinduced hydroxyl radical and photocatalytic activity of samarium-doped TiO(2) nanocrystalline

Sm(3+)-doped TiO(2) nanocrystalline has been prepared by sol-gel auto-combustion technique and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and also UV-vis diffuse reflectance spectroscopy (DRS). These Sm(3+)-doped TiO(2) samples were tested for methylene blue (MB) decomposition and *OH radical formation. The analysis of *OH radical formation on the sample surface under UV irradiation was performed by fluorescence technique with using terephthalic acid, which readily reacted with *OH radical to produce highly fluorescent product, 2-hydroxyterephthalic acid. It was observed that the presence of Sm(3+) ion as a dopant significantly enhanced the photocatalytic activity for MB degradation under UV light irradiation because both the larger specific surface area and the greater the formation rate of *OH radical were simultaneously obtained for Sm(3+)-doped TiO(2) nanocrystalline. The adsorption experimental demonstrated that Sm(3+)-TiO(2) had a higher MB adsorption capacity than undoped TiO(2) and the adsorption capacity of MB increased with the increase of samarium ion content. The results also indicated that the greater the formation rate of *OH radical was, the higher photocatalytic activity was achieved. In this study, the optimum amount of Sm(3+) doping was 0.5 mol%, at which the recombination of photo-induced electrons and holes could be effectively inhibited, the highest formation rate of *OH radicals was, and thereby the highest photocatalytic activity was achieved.