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Mixed oxides combining d 0-and p -cations with stereoactive lone pair electrons exhibit excellent polarization abilities for potential photoelectric applications. This work reports the photochemical properties of V-doped Te–Nb mixed oxide Nb 2 Te 4 O 13 , which has the typical framework constructed by NbO 6 (d 0-) octahedra, TeO 4 , and TeO 3 (p -) polyhedra. The samples were prepared using the sol-gel method, which resulted in the final nanoparticles. The luminescence spectra, lifetimes of photoinduced electrons and holes, and conductivity properties of the samples were characterized. Nb 2 Te 4 O 13 has an indirect transition with a band energy of 2.98 eV V5+-doping shows a narrowing effect on the band gap, enhancing the harvest of the optical absorption in the visible light region. Photocatalysis tests were conducted via the photodegradation of RhB solutions under visible-light irradiation. V5+-doping depresses the intrinsic luminescence efficiency, while it significantly enhances photodegradation. It is suggested that the induced redox couples V5+/4+ and defects are responsible for the improvements of photocatalysis of Nb 2 Te 4 O 13. This work offers an effective method to modify photochemical properties via redox couples and defects induced by impurity ion doping. [ABSTRACT FROM AUTHOR]

Bismuth niobate semiconductors are of considerable interest in both contaminant degradation and H 2 -generation. However, the wide band gap strictly limits the optical absorption in visible-light wavelength. In this work, a new niobate semiconductor Bi 3 Nb 17 O 47 was prepared with co-precipitation synthesis. To modify the band structure, Te4+-, Ti4+-, and Te4+/Ti4+-doping were conducted in Bi 3 Nb 17 O 47 lattices. Rietveld refinements were used to investigate the crystal phase and structure. The UV–vis absorption measurements concluded that Te4+-, Ti4+- doping could greatly modify the band energy of Bi 3 Nb 17 O 47. The Te4+/Ti4+-doped sample could harvest more visible light in the longer-wavelength region being favorable for photocatalysis performances. This was verified by RhB photodegradation tests under the visible-light irradiation (λ > 420 nm). To discuss the photocatalytic mechanisms, XPS and impedance spectra were measured. The improved photocatalysis was related to the microstructure changes, charge carrier dynamics, oxygen vacancies, and redox couples of multivalent ions. The present work provides a valid route to modify the band structure and to improve the photocatalysis abilities via impurity ions Te4+/Ti4+-doping in bismuth niobate semiconductors. [ABSTRACT FROM AUTHOR]

The Bi3+-containing semiconductors have been widely reported as potential photocatalyst candidates for water-splitting and environmental pollution problems. This work reported a new kind Bi-heterojunction of LiBiO 2 /Bi 2 O 3 , which was synthesized by the facile hydrothermal reactions. The XRD (X-Ray powder diffraction) measurement was applied to investigate the phase formations. The composite crystals developed in the well-crystallized ultrathin nanosheets with the thickness about 320 nm. The UV–visible absorption indicated that LiBiO 2 /Bi 2 O 3 heterojunction has a similar optical absorption edge to that of LiBiO 2 (2.04 eV). This confirms the heterojunction has the actively optical abilities in visible wavelength region. The photocatalytic activities were tested by photo-degradation effects of rhodamine B (RhB) dye and colorless phenol solutions under the visible light irradiation. The experiments suggested that the photocatalysis activities could be greatly improved via coupling Bi 2 O 3 in LiBiO 2 /Bi 2 O 3 heterojunctions. The migration of light-induced charge-carriers adopts a typical direct Z -scheme in LiBiO 2 and LiBiO 2 /Bi 2 O 3 heterojunctions. Unlabelled Image • Well-crystallized LiBiO 2 /Bi 2 O 3 nanosheets were prepared via hydrothermal reactions. • LiBiO 2 /Bi 2 O 3 composite has efficient photocatalytic degradation on RhB dyes. • The composite adopts a typical direct Z -scheme in LiBiO 2 and LiBiO 2 /Bi 2 O 3. • The photocatalytic activity of LiBiO 2 indicates •OH is the main reactive species • The luminescence properties were applied to discuss the photocatalytic properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Cs-doped α-Bi 2 O 3 has been successfully synthesized by hydrothermal process. • Undoped and Cs-doped α-Bi 2 O 3 has a crystallographic phase of monoclinic form. • Cs-doped α-Bi 2 O 3 formed in microplates with high crystallization. • Cs-doped α-Bi 2 O 3 microplates are superior to that of undoped α-Bi 2 O 3. Abstract Cs-doped α-Bi 2 O 3 was synthesized via a facile hydrothermal reaction. The phase formations of the samples were investigated via X-ray powder diffraction (XRD) patterns and structural refinements. The samples present well-crystalized microplates with smooth surfaces and a thickness about 300 nm. The experiments revealed that the undoped and Cs-doped α-Bi 2 O 3 microplates could crystallized in a pure monoclinic phase. The band gap of α-Bi 2 O 3 could be reduced via the Cs-doping in the lattices. The photocatalytic activity on photo-degradation of methylene blue (MB) was significantly improved with the Cs-doping. The effective photocatalysis was discussed on the improved visible-light response, the enhanced dispersion in the valence band composed of hybrid orbitals of Bi6s, O2p and Cs3d, and the lowered electron–hole recombination. [ABSTRACT FROM AUTHOR]

Abstract In the present study, BiNb 5 O 14 and BiNb 5 O 14 /Nb 2 O 5 heterojunction were prepared with co-precipitation synthesis. The crystal structure was studied via XRD patterns and Rietveld refinements, which has a typical tetragonal tungsten bronze (TTB)-type structure. The samples crystallized in micorods with a length of 1–4 µm and a diameter about 1 µm. As an indirect transition semiconductor, BiNb 5 O 14 has a band energy of 2.81 eV with the valence-band formed by hybridized O-2p and Bi-6s, and the conduction band formed by Nb(6d) orbitals. The photocatalysis abilities of BiNb 5 O 14 and BiNb 5 O 14 /Nb 2 O 5 heterojunctions were evaluated via the photo-degradation of dye solutions. The photocatalytic activities were significantly improved via coupling BiNb 5 O 14 with Nb 2 O 5. In the photocatalysis reactions, •OH was the main reactive species, and the immigration rate of light-created charge-carriers was greatly improved via the heterojunction structure. The luminescence and decay lifetime were measured to discuss the photocatalysis mechanism. [ABSTRACT FROM AUTHOR]

Highlights • A novel Na-doped α-Bi 2 O 3 has been successfully synthesized by hydrothermal process. • Na-doped α-Bi 2 O 3 crystallized in flower-like profiles. • Na-doped α-Bi 2 O 3 crystallographic phase is monoclinic form with crystallization. • Na-doped α-Bi 2 O 3 microplates are superior to that of undoped α-Bi 2 O 3. Abstract Na-doped α-Bi 2 O 3 with a hierarchical flower-like shape was successfully prepared via a facile hydrothermal reaction. The samples consisted of well-crystalized nanoplates with smooth surfaces and a thickness of tens of nanometers. The phase formation was investigated via X-ray powder diffraction (XRD) patterns and structural refinements. The formations of oxygen vacancies were verified and its effects on the optical and photocatalysis were discussed. The band gap of α-Bi 2 O 3 was narrowed via forming the local energy levels by oxygen vacancy defect complexes in the lattices. The photocatalytic activities on photo-degradation of Rhodamine B (RhB) were significantly improved. The effective photocatalysis was discussed on the improved visible-light response, band structure, and dynamic luminescence decay. The photocatalysis of Na-doped α-Bi 2 O 3 was improved via the induced oxygen vacancies. The reported hydrothermal synthesis was advantageous approach to prepare α-Bi 2 O 3 by considering the simplicity, low reaction temperature, no post-sintering, without using any template or surfactant, large-scale production, low cost, etc. Graphical abstract Na-doped α-Bi 2 O 3 synthesized by hydrothermal process crystallized in flower-like profiles. The Na-doping induced oxygen vacancies gave a narrow band gap of α-Bi 2 O 3. Na-doped α-Bi 2 O 3 microplates are superior to that of undoped α-Bi 2 O 3. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Nano-sized V 2 O 5 has been widely investigated as photocatalysis due to good chemical stability and smaller band gap than TiO 2 . However, it suffers some disadvantages such as narrow optical absorption, easy recombination of photo-generated charges. In this work, CsV 3 O 8 was prepared by a facile hydrothermal synthesis without help of any additive inorganic chemicals. The samples developed into well-crystalized microplates with the length and width of about 1 and 3 µm, respectively. Phase formation and structure were investigated by XRD structure refinement. CsV 3 O 8 has an unusual V–O framework consisting of VO 6 octahedra, which constructs V 2 O 5 -like layer-structure. The samples were characterized with SEM, TEM, EDS and optical absorption. CsV 3 O 8 has an indirect allowed electronic transition with band energy 2.18 eV. Efficient photo-degradation of Rhodamine B (RhB) solutions in presence of CsV 3 O 8 was confirmed. The result suggests that vanadate semiconductor CsV 3 O 8 is a potential candidate for photocatalytic application under visible-light irradiation. [ABSTRACT FROM AUTHOR]

Ag-containing niobate AgNb 13 O 33 has been prepared by the sol–gel polymerized complex method. The structure was investigated via a good XRD Rietveld refinement in a typical perovskite-like framework. The morphological properties of the AgNb 13 O 33 nanoparticles were tested via transmission electron microscopy (TEM), scanning electron microscope (SEM), and energy dispersive spectra (EDS) measurements. AgNb 13 O 33 is a typical direct allowed semiconductor with band energy of 2.81 eV, which is much narrower than 3.4 eV of Nb 2 O 5 . This silver niobate can harvest both UV and near UV light, which is benefited from the (O-2p/Ag-4d) hybridization in the valence band. The photocatalytic abilities of AgNb 13 O 33 nanoparticles were reported. The sample presents more efficient photocatalytic effects on photo-degradation of methylene blue (MB) dye solutions than that of Nb 2 O 5 . The photocatalytic mechanism was discussed on band energy levels, trapping experiments, photoluminescence and the decay lifetime. [ABSTRACT FROM AUTHOR]

Mixed-metal oxides composed of Nb5+(d 0) and Te4+(p -) cations generally exhibit excellent optoelectronic properties due to the stereoactive lone pair of electrons in the structure. In this work, a mixed-metal niobate tellurite Nb 4 TeO 12 was prepared using solid state reaction method. The polycrystalline samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), optical absorption, photoluminescence (PL) and dynamic properties. This sample shows characteristic indirect electronic transitions with an interband energy of 3.01 eV. The bottom of conduction band and the top of valence band are +0.37 eV and +3.38 eV, respectively. Using a Nd:YAG pulsed laser as the excitation light source, the intrinsic luminescence of Nb 4 TeO 12 was investigated over a wide temperature range of T = 10–300 K. The broad band emission peaking at 513 nm corresponds to the self-activating luminescence of the niobate octahedral group [NbO 6 ]7−. The luminescence decay curve did not depend on the laser excitation energy, and it showed a non-exponential characteristic with two decay lifetime components. The experiments also preliminarily studied the performance of the luminescence application of Nb 4 TeO 12. • Mixed-metal niobate tellurite Nb 4 TeO 12 was prepared using solid state reaction. • Nb 4 TeO 12 is an n -type semiconductor (Eg = 3.01 eV) with indirectly allowed transitions. • Nb 4 TeO 12 shows the broad intrinsic luminescence band peaked at 480 nm. • Intrinsic luminescence originates from self-trapped exciton (STE) transitions. [ABSTRACT FROM AUTHOR]

A new silver-containing vanadate semiconductor Ag 2 ZnV 4 O 12 nanorod was prepared via the sol-gel synthesis. The detailed surface characteristics of the nanoparticles were reported. The band gap optical transition and the potential position of the conduction band (CB) and valence band (VB) were determined. Ag 2 ZnV 4 O 12 nanorods have small band energy of 1.61 eV characterized by the indirect allowed transitions. The narrowed band gap is due to the Ag3d–O2p hybridization in the valence band. The photocatalysis was investigated by photo-degradation of Rhodamine-B (RhB) excited by the light wavelength longer than 420 nm. Ag 2 ZnV 4 O 12 is more efficient to the photodegradation of organic dyes. The photocatalysis was discussed according to the band positions and the trapped experiments. [ABSTRACT FROM AUTHOR]

A silver vanadate semiconductor K 2/5 Ag 3/5 VO 3 with the stable α-AgVO 3 structure has been prepared via the hydrothermal method. The structural refinements were completed. Similar to the well-known β-AgVO 3 , K 2/5 Ag 3/5 VO 3 also keeps one-dimensional crystallization habit with a high ratio of length to diameter. The surface was characterized by the SEM, TEM, energy dispersive spectrometer (EDS) spectrum and nitrogen adsorption–desorption isotherms. The UV–vis absorption spectrum shows that K 2/5 Ag 3/5 VO 3 nanowire has narrow band energy (2.02 eV) characterized by indirect allowed electronic transition. K 2/5 Ag 3/5 VO 3 nanowires present a very good dispersion in water. Photocatalysis was tested by the photo-degradation of methylene blue (MB) solution. The textile structure of the nanowires makes recovery possible by filtering after photocatalytic reactions . K 2/5 Ag 3/5 VO 3 nanowires show effective photocatalytic ability under visible-light irradiation. [ABSTRACT FROM AUTHOR]

A new visible-light-driven and nano-sized photocatalyst was developed in the well-known cathode material of inverse spinel-type lithium nickel vanadate LiNiVO 4 . The nanoparticles were prepared by a modified Pechini method and characterized with the measurements such as X-ray diffraction (XRD), scanning electron microscope (SEM), Transmission electron microscopy (TEM), and UV–vis absorption spectrum. The photocatalytic activities of LiNiVO 4 nanoparticles were evaluated by photodegradation of methylene blue (MB) under visible-light irradiation in air. LiNiVO 4 nanoparticles showed an excellent photocatalytic activity duo to an efficient absorption in the UV–visible light wavelength region with a narrowed band gap energy of 2.10 eV and an indirect allowed electronic transition. These results indicate that this pyrovanadate could be a potential photocatalyst driven by visible-light. The effective photocatalytic activity was discussed on the base of the crystal structure. [ABSTRACT FROM AUTHOR]

• Te 2 V 2 O 9 combining d 0 and p cations with stereo-active lone pair electrons was synthesized. • Nb5+, Ta5+-doping can modify luminescence and photocatalysis of Te 2 V 2 O 9 nanobelts. • Both Nb5+ and Ta5+-doping reduce luminescence of the host. • Nb5+ doping shows more efficient photodegradation than Ta5+ ions. • Redox couples V5+/4+ induced by Nb5+ doping attribute photocatalytic improvement. [Display omitted] Materials combining d 0 and p cations with stereo-active lone pair electrons have excellent polarization for photoelectric applications. This work reports the modifications of photochemical properties via Nb5+-, Ta5+-doping in Te-V mixed oxide Te 2 V 2 O 9 with d 0 -(V5+) and p -(Te4+) cations. Nb5+-, Ta5+-doped Te 2 V 2 O 9 nanobelts were prepared using the sol-gel method. The structure, morphologies, and optical absorption properties were reported. The calculation and experimental results indicate that the Te-V mixed oxide Te 2 V 2 O 9 has an indirect transition with band energy of 2.19 eV. The photodegradation of RhB dye solutions was conducted under the irradiation of visible-light irradiation (λ ≥ 420 nm). The conductivity properties, lifetime of charge carriers were characterized via impedance spectra and decay curves, respectively. The multivalent cations were confirmed via XPS measurements. The experiments concluded that both Nb5+ and Ta5+ ions can depressed the luminescence, and enhanced photocatalysis to some extent. While, compared with Ta5+, the Nb5+ doping shows much more significant improvement of photodegradation. It was concluded that the redox couples V5+/4+ induced by Nb5+ doping attribute to the photocatalysis. This work offers an effective method to modify the photochemical properties via the redox couples and defects induced by heterovalent substitution on the cations. [ABSTRACT FROM AUTHOR]

• A new semiconductor of Nb 2 WO 8 with its nature was reported. • Nb 2 WO 8 presents self-activated luminescence at room temperature. • The luminescence and photocatalysis were enhanced with Li-doping. • Li+ stands in the interstitial position in the hexagonal tunnels in the lattices of Nb 2 WO 8. Transition metal oxide semiconductors have been reported to be potential for light-energy conversion and storage-related applications because of the unique structures and properties. This work reports a transition metal oxide Nb 2 WO 8 synthesized by the sol-gel synthesis. The crystal structure, optical band nature, intrinsic luminescence, and photocatalytic properties were investigated. Nb 2 WO 8 is a typical indirect allowed semiconductor and the band transition energy is 3.58 eV. The top of the valence band (E VB) and the minimum of the conduction band (E CB) are +2.88 eV and −0.7 eV, respectively. Nb 2 WO 8 presents an intrinsic emission at 300 K with the maximum wavelength at 510 nm and the lifetime was 1.96 μs. The introduction of the impurity ions Li+ into the lattices of Nb 2 WO 8 resulted in the improved luminescence efficiency. Meanwhile, compared with the undoped sample, the luminescence thermal stability of Nb 2 WO 8 :Li was also enhanced. The decay lifetime of Nb 2 WO 8 :Li was prolonged to 2.41 μs. The slow decay time could delay the recombination of the photo-produced holes and electrons after light excitation. This improves photocatalytic performances by delaying the charge-separation. Therefore, the photodegradation of RhB by Nb 2 WO 8 :Li is much more efficient than that by the reference sample of Nb 2 WO 8 under visible light irradiation. Li+ doping is an effective way to modify the optical properties of Nb 2 WO 8 semiconductor. [ABSTRACT FROM AUTHOR]

This work developed a new method to modify the phase formation, morphological characteristics and photoenergy conversion of Eu3+-doped bismuth oxides via solvothermal preparation and post-annealing treatments. As-prepared products are the tetragonal-structured Bi/ t -Bi 2 O 2.75 :Eu3+ nanocomposites via introducing metallic Bi0 by in-situ reduction, which showed a ball-like profile (100 nm). After the post-annealing treatments, as-prepared Bi/ t -Bi 2 O 2.75 :Eu3+ developed into cubic phase crystals of Eu3+-stabilized δ-Bi 2 O 3 (δ-Bi 2 O 3 :Eu3+), which had a plate-like shape with the length and width of 1–2 μm. The dark colored Bi/ t -Bi 2 O 2.75 :Eu3+ shows a very broad absorption band from UV to 735 nm. The post-annealed δ-Bi 2 O 3 :Eu3+ shows a yellow nature color and an abrupt cut-off of absorption edge around 570 nm. The investigations focused on different photo-energy conversion modes of two samples, i.e., photoluminescence and photocatalysis. The photo-degradation abilities on RhB solutions were evaluated with the excitation of visible light. As-prepared Bi/ t -Bi 2 O 2.75 :Eu3+ showed much more excellent photocatalytic behaviors than the post-annealed δ-Bi 2 O 3 :Eu3+. Compared with pure δ-Bi 2 O 3 , δ-Bi 2 O 3 :Eu3+ has comparable photocatalytic ability. The post-annealed δ-Bi 2 O 3 :Eu3+ shows very efficient red-luminescence with preferable excitation of near UV-light. The photo-energy conversion mechanisms were proposed to discuss the luminescence properties, decay lifetimes and multivalent ions. Eu3+-doped Bi 2 O 3 could be a good candidate with multimodal photo-energy conversion applications, i.e., photocatalyst and phosphor, depending on the reductant in the synthesis and post-annealing treatment. • Sb 3 Nb 3 O 13 nanoparticles were synthesized in situ co-precipitation. • Stoichiometric deviation is effective to prepare Zr 6 Nb 2 O 17 -based heterojunctions. • Photocatalysis greatly promoted in Sb 3 Nb 3 O 13 /Nb 2 O 5 and Sb 3 Nb 3 O 13 /Sb 2 O heterojunctions. • Energy states at heterojunction interface altered the semiconducting properties. [ABSTRACT FROM AUTHOR]

Bi 13 Mo 4 VO 34 has a peculiar structure with an infinite (Bi 12 O 14) n columns surrounded by (Mo,V)O 4 tetrahedra. The substitutions of Te4+ for Bi3+ and V5+ for Mo6+ could result in higher electrostatic effects between the columns and tetrahedra networks reducing the impedance in the lattices. On this motivation, Bi 13-x Te x Mo 4-x V 1+x O 34 (0 ≤ x < 2.5) solid-solutions were synthesized to investigate the changes of band energies and its activities on photo-degradation. The precursor films could be coated by the colloidal sols, which were dried and then sintered to get the final loosely aggregated particles. Rietveld refinements were applied to investigate the structure. UV–vis absorption concluded that Te4+/V5+ cation substitutions could greatly modify the band gap of Bi 13-x Te x Mo 4-x V 1+x O 34 , i.e., the band energies processed a monotonic decrease with the increase of the substitution concentration. Consequently, the cation substituted samples could harvest more visible light in longer-wavelength region being favorable for photocatalysis performances. This was verified by RhB photodegradation in presence of Bi 13-x Te x Mo 4-x V 1+x O 34 under visible-light irradiation (>420 nm). To elucidate photocatalysis mechanisms, XPS, luminescence and lifetime were measured. The improved photocatalysis was related with the microstructure changes and the characteristics such as the multivalent V and Mo ions, longer lifetimes of light-induced charges. Unlabelled Image • Nanoparticles Bi 13-x Te x Mo 4-x V 1+x O 34 (0 ≤ x < 2.5) were prepared via modified sol-gel synthesis. • Band gap was greatly narrowed with the increase of Te4+/V5+ substitutions. • Band structures were modified via introduction of electronic components and band dispersion. • Substituted nanoparticles present improved photodegradation on RhB dye solutions. • Microstructure, multivalent ions and longer lifetimes of induced charges were focused. [ABSTRACT FROM AUTHOR]

Te4+ and V5+-codoped Bi 2 O 3 nanoparticles were synthesized via the sol-gel method. The sample showed a loose aggregation with the ball-like nanoparticles (of 200–400 nm). X-ray powder diffraction (XRD) refinements were used to investigate the crystallinity formations. As-prepared Bi 2− x Te x V x O 3 (x = 0.1, 0.2) samples present δ-Bi 2 O 3 phase with space group of Fm-3m at room temperature. The results indicate that the cubic structure could be stabilized via Te4+ and V5+-codoping in Bi 2 O 3 lattices. UV–vis absorption measurements concluded that Te4+/V5+-codoping could modify the band gap of δ-Bi 2 O 3. Te/V-doped samples could harvest more visible light in longer-wavelength region. The improved photocatalysis of Bi 2− x Te x V x O 3 (x = 0.1, 0.2) on RhB photodegradation was in presence with the irradiation of visible-light (λ > 420 nm). To elucidate the photocatalytic mechanisms, XPS measurements, luminescence and lifetimes and impedance spectra were measured and analyzed. The improved photocatalysis was related with the microstructure changes and the multivalent V ions. Unlabelled Image • Te4+/V5+-codoping in Bi 2 O 3 stabilizes its cubic δ-phase at room temperature. • Band gap of Te4+/V5+-codoped δ-Bi 2 O 3 was narrowed in comparison with α-phase. • Bi 2− x Te x V x O 3 (x = 0.1, 0.2) showed the improved photocatalysis performances. • Existence of multivalent V ions plays an important role on photocatalysis. [ABSTRACT FROM AUTHOR]

LiBiO 2 was synthesized via the facile hydrothermal growth. The sample showed the ultrathin nanosheets with the thickness of 80–100 nm. The structural refinements were conducted on the base of XRD measurement. LiBiO 2 presents a typical indirect transition with band gap energy of 2.04 eV. The density functional theory (DFT) calculations indicate that conduction band (CB) potential is −0.86 eV, and valence-band (VB) potential is 1.18eV. The conduction band is formed by Bi-6p electronic orbitals; and the hybridization between O-2p and Bi-6s forms the valence-band (VB). The luminescence and lifetimes of the electronic transitions were reported. The photocatalytic activities were verified through photodegradation of rhodamine B (RhB). •O 2 − was regarded to be the active species responsible for the photocatalysis. The results suggested that the reported synthesis routine could be a superior method to prepare LiBiO 2 by taking into account of its advantages such as low temperature, no template or surfactant, etc. Image 1 • LiBiO 2 ultrathin nano-sheets were prepared through hydrothermal synthesis. • Detailed crystal structure of LiBiO 2 was investigated. • The detailed band gap energy and electronic structure of LiBiO 2 were reported. • LiBiO 2 nanosheets present the improved photochemical activities. • The detailed luminescence and lifetime of the electronic transitions were reported. [ABSTRACT FROM AUTHOR]

Pure and V 5+ -doped Bi 6 Mo 2 O 15 (3Bi 2 O 3 ·2MoO 3 ) photocatalysts were synthesized through electrospinning, followed by low-temperature heat treatment. The samples developed into nanoparticles with an average size of approximately 50 nm. The crystalline phases were verified via X-ray powder diffraction measurements (XRD). The surface properties of the photocatalysts were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. The UV–vis spectra showed that V doping in Bi 6 Mo 2 O 15 shifted the optical absorption from the UV region to the visible-light wavelength region. The energy of the band gap of Bi 6 Mo 2 O 15 was reduced by V doping in the lattices. The photocatalytic activities of the pure and V-doped Bi 6 Mo 2 O 15 were tested through photodegradation of rhodamine B (RhB) dye solutions under visible light irradiation. Results showed that 20 mol% V-doped Bi 6 Mo 2 O 15 achieved efficient photocatalytic ability. RhB could be degraded by V-doped Bi 6 Mo 2 O 15 in 2 h. The photocatalytic activities and mechanisms were discussed according to the characteristics of the crystal structure and the results of EIS and XPS measurements. [ABSTRACT FROM AUTHOR]

Eu 2+ -doped Mg 3 (BO 3 )F 3 phosphors were synthesized by solid-state reaction. The structural refinement, the luminescence and decay curves were investigated. The phosphor presents a broad emission band assigned to 4f 6 5d→4f 7 ( 8 S 7/2 ) transitions in blue range, which was overlapped with the peculiar 4f 7 ( 6 P 7/2 )→4f 7 ( 8 S 7/2 ) transitions even at room temperature. In addition, the 4f 7 ( 6 P 7/2 )→4f 7 ( 8 S 7/2 ) transition presents extremely strong intensity compared with the peculiar 4f 7 ( 6 P 7/2 )→4f 7 ( 8 S 7/2 ) transitions. The decay properties and the thermal activation energy (Δ E ) were reported. It shows high activation energy of 0.71 eV on temperature quenching. The maximum absolute quantum efficiency (QE) was measured to be 83% under UV light. The phosphor could deserve further investigations because of its peculiar spectral characteristics for basic studies and excellent application performances. [ABSTRACT FROM AUTHOR]

The δ-Bi 2 O 3 -structural Bi 11 VO 19 nanoparticles with the average size of ∼70 nm were fabricated through the Pechini method for a possible photocatalytic application. The crystal structure was investigated by X-ray powder diffraction (XRD) and the structural refinement. The as-synthesized sample was also characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), UV–vis spectroscopy and photoluminescence measurements. The experimental results demonstrate that Bi 11 VO 19 nanoparticles have an efficient visible light absorption with band-gap energy of 2.23 eV. The photocatalytic activity was evaluated by the photodegradation of the methylene blue (MB) under visible light irradiation ( λ > 420 nm) as a function of time. All the results indicate that Bi 11 VO 19 could be a potential photocatalyst driven by visible-light. The effective photocatalytic activity was discussed on the base of the crystal structure characteristic. [ABSTRACT FROM AUTHOR]

A new visible-light-driven photocatalyst of Na 2 Ni(MoO 4 ) 2 particle was prepared by the modified Pechini method. The crystal structure was measured by X-ray diffraction (XRD) and the structural refinement. The sample was investigated by scanning electron microscope (SEM), transmission electron microscopy (TEM), and UV–vis absorption spectrum measurements. The average size of Na 2 Ni(MoO 4 ) 2 particle is about 180 nm. Na 2 Ni(MoO 4 ) 2 particle have an efficient optical absorption in the UV–visible light wavelength region with a direct allowed electronic transition of 2.06 eV. The effective photodegradation of methylene blue (MB) dye was demonstrated, which benefits from the special crystal structure of Na 2 Ni(MoO 4 ) 2 particle. This crystal lattice has two infinite chains formed by (Ni,Na)O 6 and MoO 4 polyhedra standing in lines alone with the inner wall of the hexagonal tunnels. This results in the efficient optical absorption and provides more chances for electron–hole separations, which can further react with dye molecules to oxidize the dye pollutant into non-toxic products. [ABSTRACT FROM AUTHOR]

Abstract: A new visible-light-driven photocatalyst of pyrovanadate CaZnV2O7 was synthesized by the conventional solid-state reaction method. The polycrystalline samples were investigated by the X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and UV–vis diffuse absorption spectra measurements. CaZnV2O7 shows intense absorption bands in the visible light region due to band gap transitions. Ni2+-doping in CaZnV2O7 can narrow the band gap energy from 2.362eV to 2.275eV. Photocatalytic activities by photo-degradation reaction of methylene blue (MB) were investigated under visible-light irradiation. The results indicate that this pyrovanadate could be a potential photocatalyst driven by visible-light. [Copyright &y& Elsevier]

• Te 3 Nb 2 O 11 is a narrow band semiconductor with heavy dispersion between Nb-3d and Te-5s CB. • Intrinsic luminescence and decay time of Te 3 Nb 2 O 11 were reported. • Surface oxygen vacancies can be induced on Te 3 Nb 2 O 11 :Eu3+ on via low-temperature annealing. • Both luminescence and photocatalysis were all enhanced by the surface defects. • Active paths of light-created charges were demonstrated. Luminescence and photocatalysis are two important properties of optical materials for photoenergy conversion. In this work, pure- (TNO) and Eu3+-doped-Te 3 Nb 2 O 11 (TNO:Eu) were prepared by sol–gel method combined with solid-state reaction routine. Te 3 Nb 2 O 11 shows an intrinsic luminescence band peaked at 485 nm, which was quenched after Eu3+ doping. TNO:Eu presents red-emitting color from radiative transitions 5D 0 → 7F J (J = 0–4) of Eu3+ ions. Surface oxygen vacancies could be successfully induced on Eu3+-doped-Te 3 Nb 2 O 11 nanoparticles via low-temperature annealing in the CO atmosphere. The annealed TNO:Eu sample with surface oxygen vacancies can narrow the bandgap via broadening the valence band. Both red-luminescence and photocatalysis were greatly enhanced after the annealing treatments. The surface oxygen vacancies were verified by the measurements such as X-ray photoelectron spectroscopy (XPS), Raman spectra, induced optical absorption, and electron paramagnetic resonance (EPR), etc. It could be suggested that fast decay time (6.14 μs) of Te 3 Nb 2 O 11 causes an efficient recombination of the light-induced charges. The introduction of different Eu3+ midgap states in TNO:Eu provides longer decay time (1.25 ms) for the excited states improving charge-separation upon photo-excitation during photocatalysis. [ABSTRACT FROM AUTHOR]

Silver-containing lanthanum metaniobate Ag 0.5 La 0.5 Nb 2 O 6 nanoparticles were synthesized by sol-gel polymerized complex method. A typical defect-perovskite structure was confirmed by XRD Rietveld refinements. The surface characteristics of the sample were tested by SEM, TEM and EDS measurements. SEM and TEM show that the sample presents ball-like particles with the diameters of 100 nm to 400 nm. The sample shows both self-activated luminescence and photocatalytic activities. Ag 0.5 La 0.5 Nb 2 O 6 has a direct transition with band energy of 2.85 eV. The Ag4d-O2p hybridization in the valence band contributes to the narrowed band gap. The luminescence properties of Ag 0.5 La 0.5 Nb 2 O 6 have been investigated for the first time. The luminescence is characterized by two emission centers with maximum wavelength near 460 and 530 nm. The emission and excitation spectra, decay curves and the thermal quenching mechanism were discussed. Ag 0.5 La 0.5 Nb 2 O 6 shows the efficient photocatalytic activities and the photodegradation rate for methylene blue dye (MB) can reach about 95% under visible light (> 420 nm) irradiation in 5 h. The trapped experiments for the active species were tested and discussed, which verified that OH radicals could be the major active species in photocatalysis. [ABSTRACT FROM AUTHOR]

Silver-containing niobate AgNb 7 O 18 nanoparticles were prepared via sol-gel polymerized complex synthesis. The sample was given a good XRD Rietveld refinement in a typical perovskite-like structure. The detailed surface properties of AgNb 7 O 18 nanoparticles were tested by SEM, EDS, TEM, nitrogen adsorption-desorption isotherms and XPS measurements. AgNb 7 O 18 is characterized via a direct transition and the band energy is 2.76 eV. The hybridization between O 2p and Ag 3d states in valence band contributes to the narrowed band gap. The first principles electronic structure elucidation supports the narrow band gap of AgNb 7 O 18 . The sample shows an efficient degradation of methylene blue dye (MB) solutions. The trapping tests were performed to elucidate the real active species in the photocatalytic reactions. The results indicate that the superoxide radical is the main active species in the photocatalytic system, and the photocatalyst also shows a good stability and durability. [ABSTRACT FROM AUTHOR]

The vanadate-sillenite Bi 25 VO 40 nanoparticles were prepared through the facile Pechini method. The average size is about 70 nm. The sample was investigated by X-ray powder diffraction (XRD) and the structural refinement. The surface properties of the nanoparticles were investigated by the measurements such as the transmission electron microscopy (TEM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopic (XPS) and Brunauer–Emmett–Teller (BET) measurements. The nanoparticles have indirect allowed electronic transition and a narrow band gap of 2.31 eV. The photocatalysis was detected by the photodegradation of methylene blue (MB) solutions under the irradiation of visible-light. Hybridization of the 6s and 6p orbitals of Bi 3 + and the resulting lone electron pair yield interesting properties. The photocatalytic activity was discussed on the base of the structural characteristics such as the strong polarizing fields, rich oxygen ion vacancies, and high structure openness degree of the lattice. Bi 25 VO 40 nanoparticles could be potential in the application as a photocatalyst under visible light. [ABSTRACT FROM AUTHOR]