Preparation and characterization of Cu2O-TiO2: Efficient photocatalytic degradation of methylene blue

A series of copper-deposited titania were prepared by photoreduction method under irradiation with a 125-W high-pressure mercury lamp. From XPS and AES results, the deposited-copper formed Ti-O-Cu bond on the surface of TiO₂, and the Cu species on the surface of copper-deposited TiO₂ can be identified as Cu(I). The photocatalytic degradation activity of methylene blue for the Cu₂O-TiO₂ series increased with increasing Cu₂O-deposited content, and then decreased. The highest photocatalytic degradation activity of methylene blue was obtained for 0.16% Cu₂O-TiO₂. When copper-deposited content reached to 0.32%, the photocatalytic activity was lower than that of pure TiO₂. It is shown that Cu₂O on the surface of TiO₂ can trap electrons from the TiO₂ conduction band, and the electrons trapped on the Cu₂O-TiO₂ site are subsequently transferred to the surrounding adsorbed O₂, thereby avoiding electron-hole recombination, and enhancing the photocatalytic activity. Excess copper loading may screen the photocatalyst from the UV source, so the photocatalytic activity diminishes with increasing Cu₂O.     

Photocatalytic properties of BiVO4 prepared by the co-precipitation method: Degradation of rhodamine B and possible reaction mechanisms under visible irradiation

Bismuth vanadate (BiVO₄) was synthesized by the co-precipitation method at 200 °C. The photocatalytic activity of the oxide was tested for the photodegradation of rhodamine B under visible light irradiation. The analysis of the total organic carbon showed that the mineralization of rhodamine B over a BiVO₄ photocatalyst (∼40% after 100 h of irradiation) is feasible. In the same way, a gas chromatography analysis coupled with mass spectroscopy revealed the existence of organic intermediates during the photodegradation process such as ethylbenzene, o-xylene, m-xylene, and phthalic anhydride. The modification of variables such as dispersion pH, amount of dissolved O₂, and irradiation source was studied in order to know the details about the photodegradation mechanism.     

Fabrication, structure, and enhanced photocatalytic properties of hierarchical CeO2 nanostructures/TiO2 nanofibers heterostructures

Combining the versatility of electrospinning technique and hydrothermal growth of nanostructures enabled the fabrication of hierarchical CeO₂/TiO₂ nanofibrous mat. The as-prepared hierarchical heterostructure consisted of CeO₂ nanostructures growing on the primary TiO₂ nanofibers. Interestingly, not only were secondary CeO₂ nanostructures successfully grown on TiO₂ nanofibers substrates, but also the CeO₂ nanostructures were uniformly distributed without aggregation on TiO₂ nanofibers. By selecting different alkaline source, CeO₂/TiO₂ heterostructures with CeO₂ nanowalls or nanoparticles were facilely fabricated. The photocatalytic studies suggested that the CeO₂/TiO₂ heterostructures showed enhanced photocatalytic efficiency of photodegradation of dye pollutants compared with bare TiO₂ nanofibers under UV light irradiation.     

Decomposition of the molecular precursor Bu4Sn6S6 on the surface of TiO2 to prepare semiconductor composite photocatalysts

In this work, the single source organometallic precursor Bu₄Sn₆S₆ was impregnated and decomposed on the surface of TiO₂ to produce semiconductor composites. ¹¹⁹Sn Mössbauer, Raman and ultra violet/visible spectroscopies, powder X-ray diffraction, temperature programmed reduction and surface area suggest for Sn contents of 1, 5 and 10 wt%, the formation of a highly dispersed unstable SnS phase which is readily oxidized by air at room temperature to form SnO₂ on the TiO₂ surface. The composite with Sn 30 wt% produced a mixture with the phases SnS/γ-Sn₂S₃ and SnO₂. Photocatalytic experiments with the composites SnX_n/TiO₂ using the textile dye Drimaren red as a probe molecule showed a first-order reaction with rate constants k_absorbance for the composites with Sn 1 and 5% higher than pure TiO₂ which was explained by the formation of the more active photocatalyst composite SnO₂/TiO₂.     

Effect of substitution in the scheelite-like series, AxBa1−xBi2Mo4O16 (A = Ca, Sr, Pb)

A new series of solid solutions of the type, A_xBa_1−xBi₂Mo₄O₁₆ (A = Ca, Sr, Pb) have been isolated. The domain of the solid solutions is very narrow and is in the range (0.01 ≤ x ≤ 0.10). All the phases were synthesized by the solid-state technique. The crystal structure is similar to that of the monoclinic scheelite type BaBi₂Mo₄O₁₆. The structure consists of layers of [Bi₂O₂] units separated by (Ba/AO)₁₀ units and isolated MoO₄ tetrahedra. Their semiconductor band gaps render them as potential materials for photocatalysis.     

Characterisation and photocatalytic activity of structure-controlled spherical granules of an anatase/hydroxyapatite composite

Materials that can purify the environments are desirable. Anatase (TiO₂) has received attention because it is stable and can decompose organic substances because of its photocatalytic activity. To make use of anatase effectively, we deposited nano-sized anatase particles on porous hydroxyapatite (HA) ceramics composed of rod-shaped particles. Spherical porous HA granules composed of rod-shaped HA particles were prepared using a hydrothermal process. The granules were soaked in a solution containing a water-soluble titanium complex and then hydrothermally treated. Nano-sized anatase particles were deposited on each rod-shaped HA particle. The anatase/HA granules composed of rod-shaped HA particles showed higher photocatalytic activity than those composed of globular HA particles. The granules are expected to be useful as an environment-purifying material with high manageability and photocatalytic activity.     

Crystallite, optical and photocatalytic properties of visible-light-driven ZnIn2S4 photocatalysts synthesized via a surfactant-assisted hydrothermal method

A series of ZnIn₂S₄ photocatalysts were synthesized via a surfactant-assisted hydrothermal method. The products were characterized with X-ray diffraction (XRD), UV-vis-near-IR diffuse reflectance spectra (UV-vis), photoluminescence spectra (PL) and field emission scanning electron microscope (FESEM). The results indicated that the CTAB-assisted ZnIn₂S₄ product had a wider band gap than the other three ZnIn₂S₄ products (CPBr-assisted, SDS-assisted and no-surfactant-assisted ZnIn₂S₄). The surfactant (especially CTAB) addition would greatly affect the crystal structure (i.e. d(0 0 6) along the c-axis) of ZnIn₂S₄. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic hydrogen production from water under visible light irradiation. The CTAB-assisted ZnIn₂S₄ product, with quantum yield (420 nm) determined to be 11.9%, had a much higher photocatalytic activity than the other three ZnIn₂S₄ products in our photocatalytic system. The energy conversion efficiency in the whole visible light region was determined to be 3.1% for the CTAB-assisted ZnIn₂S₄ photocatalyst.     

Crystal data and indirect optical transitions in Tl2InGaSe4 crystals

The room temperature crystal data and the optical properties of the Bridgman method grown Tl₂InGaSe₄ crystals are reported and discussed. The X-ray diffraction technique has revealed that Tl₂InGaSe₄ is a single phase crystal of monoclinic structure. The unit cell lattice parameters, which were recalculated from the X-ray data, are found to be a = 0.77244 nm, b = 0.64945 nm, c = 0.92205 nm and β = 95.03°. The temperature dependence of the optical band gap of Tl₂InGaSe₄ single crystal in the temperature region of 290–500 K has also been investigated. The absorption coefficient was calculated from the transmittance and reflectance data in the incident photon energy range of 1.60–2.10 eV. The absorption edge is observed to shift toward lower energy values as temperature increases. The fundamental absorption edge corresponds to indirect allowed transition energy gap of 1.86 eV that exhibited a temperature coefficient γ = −3.53 × 10⁻⁴ eV/K.     

Enhancement of photocatalytic H2 evolution on hexagonal CdS by a simple calcination method under visible light irradiation

An easy-handling calcination method has been used to eliminate the trap energy levels of hexagonal cadmium sulfide (CdS). The treated CdS exhibited extremely high photocatalytic activity for H₂ production under visible light irradiation. The rate of photocatalytic H₂ evolution has been dramatically enhanced by 55.8 times to 118 μmol h⁻¹ and further improved by 6.3 times to 749 μmol h⁻¹ after loading with 0.2 wt% Pt co-catalyst.     

Crystal structures of CdTi2O4(OH)2 and LaTiSbO6

The crystal structures of two PbSb₂O₆-type compounds containing titanium, CdTi₂O₄(OH)₂ and LaTiSbO₆ were refined by X-ray powder diffraction data. For both compounds structure refinements with the space group were successful and the R-factors were R_WP = 6.46% and R_P = 4.90% for CdTi₂O₄(OH)₂ and R_WP = 9.55% and R_P = 7.17% for LaTiSbO₆. These crystal structures were the same as that of the typical PbSb₂O₆-type compound in spite of the existence of protons in the interlayer or two different metal ions in the layer.     

Ligand-assisted hydrothermal synthesis of ZnWO4 rods and their photocatalytic activities

ZnWO₄ rods were prepared using a ligand-assisted hydrothermal method with ZnCl₂ and Na₂WO₄ in the presence of various amines as ligands for zinc ions. The choice of ligand was found to play an important role in the formation of ZnWO₄ rods. The aspect ratio of the ZnWO₄ rods increased with increasing ligand strength. XRD and HRTEM confirmed that the ZnWO₄ rods grow along the [1 0 0] direction. The photochemical activities of the ZnWO₄ rods for the decomposition of Rhodamine 6G were examined. The photocatalytic activity was found to depend on the aspect ratio of the ZnWO₄ rods.     

Surfactant-free synthesis of Bi2WO6 multilayered disks with visible-light-induced photocatalytic activity

The synthesis of bismuth tungstate (Bi₂WO₆) multilayered disk which was constructed by oriented square nanoplates was easily realized via a simple surfactant-free hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to investigate the as-obtained product. The results indicated that the three-dimensional (3D) Bi₂WO₆ multilayered disk was constructed by self-assembly of square nanoplates via a perfect oriented manner. The formation mechanism of the product was carefully investigated on the basis of the results of time-dependent experiments. In addition, studies of the photocatalytic property demonstrated that the as-obtained Bi₂WO₆ could exhibit excellent visible-light-driven photocatalytic activity for the degradation of Rhodamine B (RhB).     

Fabrication and photocatalytic activity of porous TiO2 nanowire microspheres by surfactant-mediated spray drying process

A novel, porous TiO₂ nanowire microsphere with a diameter of 3-8 μm was successfully fabricated via spray drying of TiO₂ nanowire suspension with the assistance of surfactant (F127). The products were characterized by FESEM, XRD and N₂ adsorption-desorption analysis and results revealed that the resulting TiO₂ nanowire microspheres possessed a hierarchically macro/mesoporous structure, as well as a high BET surface area of 38.2 m²/g. Systematic studies showed that the presence of surfactant in the suspension feed for spray drying was critical in the formation of porous microspheres. The structure of the fabricated microspheres depends on the nanowire concentration in the feed. The TiO₂ nanowire microspheres exhibited significant photocatalytic degradation of Methylene blue (MB) as compared to commercial TiO₂ nanoparticles (P25). It was also revealed that the microspheres have excellent stability on photocatalytic activity and mechanical strength, which are both crucial factors when considering reuse of these photocatalysts.     

Electronic structure and photocatalytic water splitting of lanthanum-doped Bi2AlNbO7

Bi_2−xLa_xAlNbO₇ (0 ≤ x ≤ 0.5) photocatalysts were synthesized by the solid-state reaction method and characterized by powder X-ray diffraction (XRD), infrared (IR) spectra and ultraviolet-visible (UV-vis) spectrophotometer. The band gaps of the photocatalysts were estimated from absorption edge of diffuse reflectance spectra, which were increased by the doping of lanthanum. It was found from the electronic band structure study that orbitals of La 5d, Bi 6p and Nb 4d formed a conduction band at a more positive level than Bi 6p and Nb 4d orbitals, which results in increasing the band gap. Photocatalytic activity for water splitting of Bi_1.8La_0.2AlNbO₇ was about 2 times higher than that of nondoped Bi₂AlNbO₇. The increased photocatalytic activity of La-doped Bi₂AlNbO₇ was discussed in relation to the band structure and the strong absorption of OH groups at the surface of the catalyst.     

New compounds Cu2MnTi3S8 and Cu2NiTi3S8 with thiospinel structure

Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈ compounds were prepared by high-temperature synthesis. The crystal structure of these quaternary phases was investigated by X-ray powder diffraction. The compounds are described in the thiospinel structure (space group ) with the lattice constants a = 1.00353(1) nm (Cu₂MnTi₃S₈) and a = 0.99716(1) nm (Cu₂NiTi₃S₈). The atomic parameters were calculated in anisotropic approximation (R_I = 0.0456 and R_I = 0.0520 for Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈, respectively).     

Structural characterization and photocatalytic properties of novel Bi2YVO8

Bi₂YVO₈ was prepared by solid-state reaction for the first time. The structural and photocatalytic properties of Bi₂YVO₈ were studied. The results showed that this compound has the tetragonal crystal system with space group I4/mmm. The band gap of Bi₂YVO₈ was estimated to be about 2.09 eV by plotting (αhν)² versus hν and obtaining the hν axis intercept value according to Tauc's equation. For the photocatalytic water splitting reaction, H₂ or O₂ evolution was observed from pure water with Bi₂YVO₈ as the photocatalyst under ultraviolet light irradiation (wavelength = 390 nm). Degradation of aqueous methylene blue photocatalyzed by this compound was investigated under visible light irradiation. Bi₂YVO₈ showed higher photocatalytic activity compared to Bi₂YTaO₇, Bi₂InTaO₇ or TiO₂ (P-25). Complete removal of aqueous methylene blue was achieved after visible light irradiation for 170 min. The decrease of the total organic carbon and the formation of inorganic products such as SO₄²⁻ and NO₃⁻ revealed the continuous mineralization of aqueous methylene blue during photocatalytic reaction.     

Structure and photocatalytic activity studies of TiO2-supported over Ce-modified Al-MCM-41

Ce-Al-MCM-41, TiO₂/Al-MCM-41 and TiO₂/Ce-Al-MCM-41 materials with varying contents of Ce (by impregnation) and TiO₂ loaded (by solid-state dispersion) on Al-MCM-41 support are prepared. The Ce modified and TiO₂ loaded composite systems are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS) techniques. The DRS and XPS of low Ce content (0.2-0.5 wt.%) modified Al-MCM-41 samples are showing more characteristic of Ce³⁺ species wherein cerium in interaction with Al-MCM-41 and that of high Ce (0.8, 3.0 wt.%) content modified samples are showing the characteristic of both Ce⁴⁺and Ce³⁺species. A series of Ce-modified Al-MCM-41 and TiO₂ loaded composite catalysts are evaluated for photocatalytic degradation of phenol under UV irradiation. Low Ce content in Ce³⁺ state on Al-MCM-41 is showing good photoactivity in comparison with high Ce content samples and pure ceria. The composite TiO₂/Ce-Al-MCM-41 is showing enhanced degradation activity due decreased rate of electron-hole recombination on TiO₂ surface by the redox properties of cerium. The photocatalyst TiO₂/Ce-Al-MCM-41 with an optimum of 10 wt.% TiO₂ and 0.3 wt.% Ce is showing maximum phenol degradation activity. The possible mechanism of phenol degradation on the composite photocatalyst is proposed.     

One-dimensional lone electron pair micelles in the crystal structure of Pb5(SiO4)(VO4)2

The structure of Pb₅(SiO₄)(VO₄)₂ (hexagonal, P6₃/m, a = 9.9865(11), c = 7.3599(12) Å, V = 635.67(14) Å³, Z = 2) has been solved by direct methods and refined to R₁ = 0.051 on the basis of 440 unique observed reflections with |F_o|≥4σ_F. The compound belongs to the apatite structure type. The Pb coordination polyhedra are distorted due to the presence of stereoactive lone electron pairs Ψ. The structure contains channels running along the c axis and centered at (00z). The channels are most probably occupied by the lone electron pairs of the Pb²⁺ cations and thus represent lone electron pair micelles. The existence of such micelles in the structure may well be the reason for the electrogyratory effect and protonic conductivity observed in crystals of the title compound.     

Preparation and ethanol sensing properties of the superstructure SnO2/ZnO composite via alcohol-assisted hydrothermal route

Self-assembled superstructure of SnO₂/ZnO composite was synthesized by using alcohol-assisted hydrothermal method gas sensing properties of the material were investigated by using a static test system. The structure and morphology of the products were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM). The diameter of the SnO₂ nanorods was about 40 nm with a length of about 300 nm, SnO₂ nanorods and ZnO nanosheets interconnect each other to form a superstructure. The gas sensing properties of superstructure SnO₂/ZnO composite with different content of ZnO were investigated. Furthermore, the superstructure SnO₂/ZnO composite sensor is characterized at different operating temperatures and its long-term stability in response to ethanol vapor is tested over a period of 3 months.     

Cu5Sb2O8SiO4, an open framework structure with copper uncommon coordination modes: CuO6 and CuO8

Cu₅Sb₂O₈SiO₄ is orthorhombic, space group Pcca, with a = 19.031 (2), b = 9.3944 (6), c = 9.602 (2) Å, and z = 8. Its crystal structure was determined using single crystal X-ray diffraction (R₁ = 0.0432 and wR₂ = 0.1146). The compound presents a parwelite-like structure. Its anionic three-dimensional framework is built up of corner-sharing SbO₆ octahedra and SiO₄ tetrahedra, delimiting interconnected channels wherein Cu²⁺ with different coordination modes, are located. The χ_M and χ_MT product versus T plots, showed the Cu₅Sb₂O₈SiO₄ material to exhibit an anti-ferromagnetic character with a Neel temperature of about 27 K.