Co-precipitation synthesis,band modulation and improved visible-light-driven photocatalysis of Te4+/Ti4+-codoped Bi3Nb17O47

Bismuth niobate semiconductors are of considerable interest in both contaminant degradation and H₂-generation. However, the wide band gap strictly limits the optical absorption in visible-light wavelength. In this work, a new niobate semiconductor Bi₃Nb₁₇O₄₇ was prepared with co-precipitation synthesis. To modify the band structure, Te⁴⁺-, Ti⁴⁺-, and Te⁴⁺/Ti⁴⁺-doping were conducted in Bi₃Nb₁₇O₄₇ 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 Bi₃Nb₁₇O₄₇. 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.     

Tailoring structure and piezoelectric properties of CaBi2Nb2O9 ceramics by W6+-Doping

Calcium bismuth niobate (CaBi₂Nb₂O₉) is a typical bismuth-layer structured piezoelectrics (BLSPs) with a high Curie temperature (T_C) of ～943 °C, but it has low piezoelectric coefficient and high-temperature resistivity which severely limits signal acquisition in the high-temperature piezoelectric vibration sensors. Ion-doping modification is regarded as an effective way to enhance electrical properties. In this work, W⁶⁺ donor-doping at Nb⁵⁺ site in the CaBi₂Nb_2-xW_xO₉ (x = 0, 0.020, 0.025, 0.030, 0.035 and 0.040) piezoelectric ceramics with T_C of 931 ± 2 °C were fabricated by the conventional solid-state reaction method. The effects of W⁶⁺-doping on crystal structure of CaBi₂Nb_2-xW_xO₉ as well as microscopic morphology and electrical properties of ceramics were investigated systematically. The tetragonality, isotropy and electrical properties of the ceramics were enhanced with the introduction of W⁶⁺ dopant. It was found that x = 0.025 was the optimal W⁶⁺-doping ratio that yielded remnant polarization of 8.0 μC/cm², electrical resistivity of 3.0 × 10⁶ Ω cm at 600 °C, piezoelectric coefficient (d₃₃) of 14.4 pC/N, and good thermal depoling property. Our work has established a feasible approach to tune the structure of CaBi₂Nb₂O₉ to improve piezoelectric properties for potential applications in high-temperature piezoelectric vibration sensors.     

Multifunctionality of Active Centers in (Amm)oxidation Catalysts: From Bi–Mo–O x to Mo–V–Nb–(Te, Sb)–O x

Catalytic centers in selective (allylic) oxidation and ammoxidation catalysts are multimetallic and multifunctional. In the historically important bismuth molybdates, used for propylene (amm)oxidation, they are composed of (Bi³⁺)(Mo⁶⁺)₂ complexes in which the Bi³⁺ site is associated with the -H abstraction and the (Mo⁶⁺)₂ site with the propylene chemisorption and O or NH insertion. An updated reaction mechanism is presented. In the Mo–V–Nb–Te–O _x systems, three crystalline phases (orthorhombic Mo_7.5V_1.5NbTeO₂₉, pseudohexagonal Mo₆Te₂VO₂₀, and monoclinic TeMo₅O₁₆) were identified, with the orthorhombic phase being the most important one for propane (amm)oxidation. Its active centers contain all necessary key catalytic elements (2V⁵⁺/Mo⁶⁺, 1V⁴⁺/Mo⁵⁺, 2Mo⁶⁺/Mo⁵⁺, 2Te⁴⁺) for this reaction wherein a V⁵⁺ surface site (V⁵⁺ = O ⁴⁺V–O) is associated with paraffin activation, a Te⁴⁺ site with -H abstraction once the olefin has formed, and a (Mo⁶⁺)₂ site with the NH insertion. Four Nb⁵⁺ centers, each surrounded by five molybdenum octahedra, stabilize and structurally isolate the catalytically active centers from each other (site isolation), thereby leading to high selectivity of the desired acrylonitrile product. A detailed reaction mechanism of propane ammoxidation to acrylonitrile is proposed. Combinatorial methodology identified the nominal composition Mo_0.6V_0.187Te_0.14Nb_0.085O _x for maximum acrylonitrile yield from propane, 61.8% (86% conversion, 72% selectivity at 420 °C). We propose that this system, composed of 60% Mo_7.5V_1.5NbTeO₂₉, 40% Mo₆Te₂VO₂₀, and trace TeMo₅O₁₆, functions with a combination of compositional pinning of the optimum orthorhombic Mo_7.5V_1.5±x Nb_1±y Te_1±z O_29± phase and symbiotic mop-up of olefin intermediates through phase cooperation. Under mild reaction conditions, a single optimum orthorhombic composition might suffice as the catalyst; under demanding conditions this symbiosis is additionally required. Improvements in catalyst performance could be attained by further optimization of the elemental distributions at the active catalytic center of Mo_7.5V_1.5NbTeO₂₉, by promoter/modifier substitutions, and incorporation of compatible cocatalytic phases (preferably epitaxially matched). High-throughput methods will greatly accelerate the rational catalyst design processes.     

Selectivity issues in (amm)oxidation catalysis

Selectivity is currently taking center stage in heterogeneous oxidation catalysis as the cost of feed materials escalates. Particularly important and imperative for commercial processes is selectivity at acceptably high conversions. Dealing with this demanding quest we proposed, some 40 years ago, the concept of site isolation, defining one of the key requirements needed to achieve selectivity in oxidation catalysis. This principle continues to be useful in the conceptual design of new selective oxidation catalysts and has successfully described the selectivity behavior of many commercial (amm)oxidation catalysts, including now the MoVNbTeO system for propane ammoxidation to acrylonitrile (or oxidation to acrylic acid). In its catalytically optimum form, this system is comprised of at least two crystalline phases, orthorhombic Mo_7.8V_1.2NbTe_0.94O_28.9 (M1) and pseudo-hexagonal Mo_4.67V_1.33Te_1.82O_19.82 (M2). The M1 phase is the key paraffin activating and ammoxidation catalyst, its active centers containing all of the key elements V⁵⁺, Te⁴⁺, Mo⁶⁺, properly arranged to catalytically transform propane to acrylonitrile, and four Nb⁵⁺ centers, each surrounded by five molybdenum-oxygen octahedra, isolating the active centers from each other, thereby preventing overoxidation and leading to the observed high selectivity of the desired acrylonitrile product. Symbiosis between the M1 and M2 phases occurs when the two phases are synthesized concurrently in one vessel; or between physical mixtures of the two separately prepared phases provided they are finally divided (≤5 μm), thoroughly mixed and in micro-/nano-scale contact with each other. This phenomenon is particularly pronounced at high propane conversion when the M2 phase begins to serve as a co-catalyst to the M1 paraffin activating phase, converting extraneous, desorbed propylene intermediate, emanating from the M1 phase, effectively to acrylonitrile in a phase cooperation mode. The M2 phase is incapable of propane activation, lacking V⁵⁺ sites, but is a better propylene to acrylonitrile catalyst than the M1 phase since it possesses a higher concentration of Te⁴⁺ sites (i.e., propylene activating sites). Reaction networks for propane (amm)oxidation are proposed for these catalysts.     

Tuning the permittivity of tellurium dioxide by Ti substitution

Structure with the asymmetric environment of cation has a large effect on the polarization mechanism and dielectric response. In this study d⁰ cation, Ti⁴⁺ is introduced into asymmetric α-TeO₂ to prepare Ti_xTe_(1-x)O₂ (x = 0 to 0.25) by conventional solid-state method. In all the samples, it is found that the dielectric response increases relative to the parent α-TeO₂. Sample with x = 0.25 forms cubic TiTe₃O₈ phase and shows maximum dielectric permittivity of 77. The remaining samples show biphasic nature comprising cubic (TiTe₃O₈) and tetragonal (α-TeO₂) phase and their dielectric behaviour follows the Lichtenecker logarithmic mixing rule of composites. Structural analysis reveals that the cubic TiTe₃O₈ phase consists of TeO₄ and TeO₆ framework structure with locally strained TeO₄ units compared to α-TeO₂ and the Raman study complements this observation. The local strain enhances the dipolar polarizability of TeO₄ unit; additionally, ionic polarizability of TiO₆ unit also contributes to high dielectric permittivity in TiTe₃O_8.     

Nonlinear Optical Properties of TeO2-Based Glasses: MOx-TeO2 (M = Sc, Ti, V, Nb, Mo, Ta, and W) Binary Glasses

The third-order nonlinear optical susceptibilities, X⁽³⁾, of TeO₂-based glasses containing transition metal oxides (M = Sc₂O₃, TiO₂, V₂O₅, Nb₂O₅, MoO₃, Ta₂O₅, and WO₃) glasses have been measured by the third harmonic generation (THG) method in order to investigate the effect of the empty d-orbital contributions to the third-order nonlinear optical susceptibilities. It is found that the addition of TiO₂, Nb₂O₅, and WO₃ to TeO₂ glass increases the X⁽³⁾ value as well as the refractive index, while others decrease both of them. The positive effect of the TiO₂, Nb₂O₅, or WO₃, on the X⁽³⁾ of TeO₂ glass was interpreted in terms of the cationic empty d-orbital contribution. There is an almost linear relation between the X⁽³⁾ and the term (n²_ω+ 2)³.(n²_ω -1).E_d/E²₀ containing three measurable parameters only, irrespective of the kinds of MO, which was derived based on the bond orbital theory developed by M. E. Lines. The largest X⁽³⁾ value obtained is 1.69 × 10⁻¹² esu for 30NbO_2.5.70TeO₂ glass, about 60 times larger than that of pure fused silica glass.     

Doping effect on sinterability of polycrystalline yttria: From the viewpoint of cation diffusivity

The sintering behavior of Y₂O₃ doped with 1 mol% of a trivalent or tetravalent cation was investigated by pressureless sintering in air. Ga³⁺ or Ge⁴⁺-doped Y₂O₃ bodies exhibited higher relative densities than the undoped Y₂O₃, while the La³⁺ or Zr⁴⁺-doping suppressed the densification of Y₂O₃. An interdiffusion experiment was performed on the diffusion couples of polycrystalline Er₂O₃ and Y₂O₃ doped with Ni²⁺ or Zr⁴⁺, which are some of the most effective and least effective dopants for the improvement of the sinterability, respectively. The lattice and grain boundary diffusion coefficients of the Er³⁺ cation in Y₂O₃ were increased by the Ni²⁺-doping, but were decreased by the Zr⁴⁺-doping. High-resolution transmission electron microscopy observations and nano-probe X-ray energy dispersive spectroscopy analyses confirmed that the dopant cations segregate along the grain boundaries without forming an amorphous phase. The doping effect on the sinterability of Y₂O₃ must result from the change in the diffusivity in Y₂O₃.     

Enhanced dielectric and piezoelectric properties in Na0.5Bi4.5Ti4O15 ceramics with Pr-doping

The bismuth layer-structured Na_0.5Bi_4.5-xPr_xTi₄O₁₅ (x?=?0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr³⁺) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr³⁺ contents on dielectric, ferroelectric and piezoelectric properties of Na_0.5Bi_4.5Ti₄O₁₅ ceramics were investigated. The grain size of Pr³⁺-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature T_c gradually decreased with increasing Pr³⁺ contents, and the dielectric loss decreased at high temperature by Pr³⁺-doping. Moreover, the activation energy (E_a), resistivity (Z’), remanent polarization (2P_r) and piezoelectric constant (d₃₃) increased by Pr³⁺-doping. The NBT-xPr³⁺ ceramics with x?=?0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250?kHz), E_a of 1.122?eV, Z’ of 7.9?kΩ?cm (725 ºC), d₃₃ of 18 pC/N, 2P_r of 12.04 μC/cm². The enhancement was due to the addition of Pr³⁺ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr³⁺ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na_0.5Bi_4.5Ti₄O₁₅ ceramics in electrical properties.     

High-temperature thermoelectric properties of polycrystalline CaMn1-xNbxO3-δ

The structural and thermoelectric (TE) properties of polycrystalline CaMn_1-xNb_xO_3-δ (0.025?≤?x?≤?0.25) were studied with X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and electrical transport measurements, with an emphasis placed on the Nb⁵⁺ content. The CaMn_1-xNb_xO_3-δ crystallized in an orthorhombic perovskite structure of the Pnma space group. The density and grain size of the CaMn_1-xNb_xO_3-δ samples gradually decreased when Nb⁵⁺ ions substituted Mn⁴⁺ ions. The CaMn_0.95Nb_0.05O_3-δ sample contained charge-ordered domains, stacking faults, and micro-twins. The substitution of Nb⁵⁺ for Mn⁴⁺ up to x?=?0.15 led to an increase in electrical conductivity, mainly due to an increased electron concentration. The CaMn_1-xNb_xO_3-δ samples with low Nb⁵⁺ contents (0.025?≤?x?≤?0.15) showed metallic behavior, whereas those with high Nb⁵⁺ contents (0.2?≤?x?≤?0.25) showed semiconducting behavior. The Nb⁵⁺ substitution lowered the absolute value of the Seebeck coefficient for the CaMn_1-xNb_xO_3-δ samples due to an increased electron concentration. The largest power factor (1.19?×?10^?4 W?m^?1 K^?2) was obtained for CaMn_0.95Nb_0.05O_3-δ at 800?°C. The partial substitution of Nb⁵⁺ for Mn⁴⁺ in CaMnO_3-δ proved to be highly effective for improving high-temperature TE properties.     

Sb-doping effects on twin-shift option and microwave dielectric properties of Ba8CoNb6O24 eight-layer hexagonal perovskite ceramics

B-site deficient eight-layer hexagonal perovskites possess in general high quality factors and large positive temperature coefficients of resonant frequency (τ_f). Recently we successfully lowered τ_f of shifted perovskite Ba₈CoNb₆O₂₄ down to near zero through one-third Ta⁵⁺ substitution but raised the cost of the materials. In this work, Ba₈CoNb₆O₂₄ was doped with cheaper elements Sb⁵⁺ on Nb⁵⁺ sites using conventional solid-state reactions, and near-zero τ_f of 0.66(2) ppm/°C, modest ε_r of 27.99(3), Q × f of 1.016(6) × 10⁴ GHz, and significantly reduced cost of the ceramics were achieved on the composition Ba₈CoNb_5.4Sb_0.6O₂₄. The lower polarizability of Sb⁵⁺ than Nb⁵⁺ results in smaller ε_r and therefore τ_f values. About 15 % Sb⁵⁺ substitution for Nb⁵⁺ in Ba₈CoNb_6-xSb_xO₂₄ dramatically transforms the shifted structure to twinned structure, in contrast with 50 % Ta⁵⁺ substitution in the Ta⁵⁺ case. This is ascribed to reduced SOJT effects and ionic size of d¹⁰ Sb⁵⁺ compared with d° Nb⁵⁺ and Ta⁵⁺.     

Tunable luminescence properties and efficient energy transfer in Eu,Mn co-doped Ba2MgP4O13

A series of Ba₂Mg_1−xMn_xP₄O₁₃ (x = 0-1.0) and Ba_1.94Eu_0.06Mg_1−xMn_xP₄O₁₃ (x = 0-0.15) phosphors were prepared by conventional solid-state reaction. X-ray powder diffraction (XRD), the photoluminescence spectra, and the decay curves are investigated. XRD analysis shows that the maximum tolerable substitution of Mn²⁺ for Mg is about 50 mol% in Ba₂MgP₄O₁₃. Mn²⁺-singly doped Ba₂MgP₄O₁₃ shows weak red-luminescence peaked at about 615 nm. The Eu²⁺/Mn²⁺ co-doped phosphor emits two distinctive luminescence bands: a blue one centered at 430 nm originating from Eu²⁺ and a broad red-emitting one peaked at 615 nm from Mn²⁺ ions. The luminescence of Mn²⁺ ions can be greatly enhanced with the co-doping of Eu²⁺ in Ba₂MgP₄O₁₃. The efficient energy transfer from Eu²⁺ to Mn²⁺ is verified by the excitation and emission spectra together with the luminescence decay curves. The emission colors could be tuned from the blue to the red-purple and eventually to the deep red. The resonance-type energy transfer via a dipole-quadrupole interaction mechanism is supported by the decay lifetime data. The energy transfer efficiency and the critical distance are calculated and discussed. The temperature dependent luminescence spectra of the Eu²⁺/Mn²⁺ co-doped phosphor show a good thermal stability on quenching effect.     

Copper polytellurite-chlorides with A2 + cations (ACd,Pb) obtained by CVT reactions

Two novel polytellurite-chlorides Pb₅Cu₂(Te₄O₁₁)Cl₈ (1) and CdCu₂(Te₃O₈)Cl₂ (2) were obtained by a chemical vapor transport (CVT-reactions) reactions. The structure of 1 is based on [Pb₅Cu₂(Te₄O₁₁)]^8 + one-dimensional blocks with full and partially occupied Cl sites around. The structure of 2 can be described as being formed by two types of one-dimensional units formed by Cd,Cu-centered polyhedra and TeO₃, TeO₄ pyramids sharing via common O atoms into electroneutral [CdCu₂(Te₃O₈)Cl₂]⁰ sheets. Obtaining of novel polytellurite-chlorides demonstrates effectiveness of CVT techniques for preparation of different tellurite-based complex layered materials.     

Redox transformations of vanadium species at the rutile surface

Redox transformations of vanadium species, deposited on the surface of a rutile monocrystal by annealing rutile with V₂O₅ were investigated by cyclic voltammetry. Two different vanadium species were observed at the surface: first, present in the crystal lattice of rutile, which undergoes the redox transformation V⁴⁺/V³⁺ only, and the second, present at the surface, which undergoes both the V⁵⁺/V⁴⁺ and V⁴⁺/V³⁺ redox transformations. The latter appears only when the subsurface layer becomes saturated with the former.     

Structural dependence of microwave dielectric properties in ilmenite-type Mg(Ti1-xNbx)O3 solid solutions by Rietveld refinement and Raman spectra

Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were prepared by the conventional solid-state reaction method. The phase composition, sintering characteristics, microstructure and dielectric properties of Ti⁴⁺ replacement by Nb⁵⁺ in the formed solid solution Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were systematically studied. The structural variations and influence of Nb⁵⁺ doping in Mg(Ti_1-xNb_x)O₃ were also systematically investigated by X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction and its Rietveld refinement results confirmed that Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics crystallised into an ilmenite-type with R-3 (148) space group. The replacement of the low valence Ti⁴⁺ by the high valence Nb⁵⁺ can improve the dielectric properties of Mg(Ti_1-xNb_x)O₃ (x = 0–0.09). This paper also studied the different sintering temperatures for Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics. The obtained results proved that 1350 °C is the best sintering temperature. The permittivity and Q × f initially increased and then decreased mainly due to the effects of porosity caused by the sintering temperature and the doping amount of Nb₂O₅, respectively. Furthermore, the increased Q × f is correlated to the increase in Ti–O bond strength as confirmed by Raman spectroscopy, and the electrons generated by the oxygen vacancies will be compensated by Nb⁵⁺ to a certain extent to suppress Ti⁴⁺ to Ti³⁺, which was confirmed by XPS. The increase in τ_f from ?47 ppm/°C to ?40.1 ppm/°C is due to the increment in cell polarisability. Another reason for the increased τ_f is the reduction in the distortion degree of the [TiO₆] octahedral, which was also confirmed by Raman spectroscopy. Mg(Ti_0.95Nb_0.05)O₃ ceramics sintered at 1350 °C for 2 h possessed excellent microwave dielectric properties of ε_r = 18.12, Q × f = 163618 GHz and τ_f = ?40.1 ppm/°C.     

Scintillation characteristics of transparent Eu2O3–BaO–TeO2 glass-ceramics

Tellurite glass (TeG) and its glass-ceramics (TeGC435 and TeGC455), with a composition of 10Eu₂O₃–10BaO–80TeO₂, were prepared and their luminescence properties were evaluated. TeG was prepared via the melt quenching technique, while TeGC435 and TeGC455 were fabricated by heat treating TeG at 435 and 455 °C, respectively, for 5 h each. The Eu₂Te₆O₁₅ crystal phase was formed in TeGC435 and TeGC455. Both the glass and glass-ceramics showed sharp photoluminescence and scintillation peaks, attributed to the 4f→4f transitions of Eu³⁺. The highest quantum yield was obtained for TeG, whereas the highest integrated scintillation intensity was obtained for TeGC455. The scintillation intensity of TeGC455 was approximately 10% of that of the Bi₄Ge₃O₁₂ single crystal. Furthermore, typical decay times derived from the 4f→4f transitions were obtained for TeG, TeGC435, and TeGC455 during photoluminescence and scintillation.     

Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics

Nb₂O₅ doped Ba(Zr_0.2Ti_0.8)O₃ (short as BZT20) ceramics were prepared by a mixed-oxide method using a high-energy planetary ball mill and the influence of Nb₂O₅ addition on microstructure, dielectric properties and diffuse phase transition behavior of BZT20 ceramics were investigated. It was demonstrated that Nb⁵⁺entered the B-site of BZT20 ceramic and substituted for Ti⁴⁺, which caused the expansion and distortion of crystal lattice. BZT20 ceramics doped with 0.2 mol% Nb₂O₅ showed excellent dielectric property and lower diffusivity with ε_m=37,823 and γ=1.49. We supposed that the increase of dielectric constant and decrease of diffuseness parameter with increasing Nb₂O₅ content were caused by lattice disorder and unbalancing of cations induced by the substitution of Ti⁴⁺ by Nb⁵⁺ in the B sites of BZT20 ceramics. The Curie temperature decreased with the increase of Nb₂O₅ content, which can be attributed to enlarged distortion energy of the Nb doped BZT20 structure. Besides, grain size effect on the dielectric property and diffuse phase transition behavior of Nb₂O₅ doped BZT20 ceramics was also investigated.     

One-pot in situ fabrication of Cu-coupled rugby-shaped BiVO4 sosoloid for enhancing photocatalytic activity with SPR effect via ultrasonic hydrothermal strategy

One-pot wet chemistry strategy via an ultrasonic hydrothermal in situ procedure has been applied to construct a serial of monoclinic Cu-coupled rugby-shaped hierarchical BiVO₄ sosoloids with diverse Cu coupling amount. The SEM and TEM images indicate that the coupled copper content had no effect on the crystalline phase of bismuth vanadate, but it had an important effect on its morphology, which changed from seed shape to rugby shape. As demonstrated by XRD and XPS analysis, it was found parts of Cu²⁺ doped into the BiVO₄ monoclinic lattice to make it self-assemble into a rugby-shaped solid solution and another part of Cu loaded on the surface of BiVO₄ sosoloids. Under visible light illumination (>420 nm), as-obtained 1.5% Cu-BiVO₄ sosoloid had a degradation rate reached 99% for RhB within 50 min, and its photodegradation activity was 5.6 times higher than that of pure BiVO₄. and remained above 96% after 5 cycles. The enhanced photocatalytic efficiency of xCu-BiVO₄ sosoloids may be mainly attributed to the superior Cu-coupled rugby-shaped BiVO₄ sosoloid microstructures with large specific surface area. During the ultrasonic hydrothermal process, the doping Cu²⁺ can effectively replace V⁵⁺ ions to form a virtual energy level accompanied by V⁴⁺, which can become a trapping center and capture the excitation electrons on the conduction band. The surface plasmon resonance (SPR) effect of copper can effectively expand the range of visible light response. On the other hand, d orbital electrons of Cu can quickly transfer to the BiVO₄ conduction band according to Fermi energy level, so as to promote the interfacial charge transfer process, thus inhibiting the recombination of photo-generated carriers and improving the photocatalytic activity. Based on the synergetic effects of components in degradation of organic contaminants, this study provides a promising photocatalytic material driven by visible light for environmental remediation and protection.     

Structure of NaF–TeO2 glasses and glass-ceramics

The structure of NaF–TeO₂ glasses and glass-ceramics has been studied by XRD, TEM, SEM, Raman and FTIR techniques. The results suggest that, for NaF ≤10 mol%, the entire NaF content enters the structure to convert TeO₄ units into TeO_3/2F and Na⁺[TeO₃₊₁]^– units. It has also been shown that NaF partially forms amorphous and/or crystalline phases for higher NaF content, where the relative concentration of each phase depends on the NaF content. SEM images show agglomerates of different sizes, which are discrete and spread within the structure. XRD revealed formation of crystalline Te₂O₃F₂ for NaF ≤50 mol%, and a dominant phase of crystalline NaF for NaF >50 mol%. Raman and FTIR spectra have been analyzed to calculate the concentrations of the various structural units in glasses and glass-ceramics.     

Acceleration of the redox kinetics of VO2+/VO2 + and V3+/V2+ couples on carbon paper

The redox kinetics of VO²⁺/VO₂ ⁺ and V³⁺/V²⁺ couples on a carbon paper (CP, HCP030 N, Shanghai Hesen, Ltd., China) electrode were investigated in terms of their standard rate constant (k ₀) and reaction mechanism. The values determined for k ₀ for VO²⁺ ?? VO₂ ⁺ and V³⁺ ?? V²⁺ using the CP electrode are 1.0 × 10^?3 and 1.1 × 10^?3 cm s^?1, respectively. The value of k ₀ increases by one or two order(s) of magnitude compared with values obtained using electrodes composed of pyrolytic graphite and glassy carbon. The acceleration of the redox kinetics of vanadium ions is a result of the large surface area of the CP electrode. An inner-sphere mechanism for the reaction on the surface of the electrode is proposed. The kinetic features of vanadium redox reactions on the CP electrode reveal that CP is suitable for use as the electrodes in vanadium redox-flow batteries.     

Phase formation and crystal structure determination in the Y2O3–TeO2 system prepared in an oxygen atmosphere

The solid state synthesis of phases in the Y₂O₃–TeO₂ system under oxygen atmosphere is presented here as a method of obtaining pure material starting from simple oxides such as Y₂O₃ and α-TeO₂. In the composition range of 0–100% of TeO₂, the compounds Y₆TeO₁₂, Y₂TeO₆, Y₂Te₄O₁₁, Y₂Te₅O₁₃ and Y₂Te₆O₁₅ were synthesized after annealing at 770–1100 °C. The reactions of decomposition of the phases at higher temperatures are also reported.The crystal structure of Y₆TeO₁₂ has been refined by the Rietveld method from X-ray powder diffraction data. It crystallizes with the rhombohedral space group R-3 (S.G. no. 148) as the homologous compound In₆TeO₁₂. It is based on a three dimensional arrangement of isolated TeO₆ octahedra (TeO = 1.94 Å) and edge-shared YO₇ polyhedra (YO bond lengths ranging from 2.18 to 2.65 Å).