Construction of a novel S-type γ-Bi2O3/CeO2 heterojunction for highly efficient photocatalytic degradation of antibiotics.

Cubic nanoparticles of CeO2 were partly covered on the tetrahedron surface of γ-Bi2O3 through a hydrothermal reaction and then a calcination process to construct a novel S-type γ-Bi2O3/CeO2 heterojunction. The optimized sample removed 96% of lomefloxacin and 81% of tetracycline. During the cycling test, the photocatalytic efficiency of lomefloxacin and tetracycline was maintained above 87% and 80%, respectively, for five consecutive cycles. According to XRD and Raman spectra characterization, the sample after cycling held a stable crystal structure. Holes, OH-˙, O2˙, and electrons participated in the degradation of lomefloxacin, while tetracycline was removed via the effect of the former three active substances. Based on theoretical calculation and experimental tests, the excellent photocatalytic activity of γ-Bi2O3/CeO2 came from the fast transfer of charge carriers along the S-type path. Moreover, the CB electrons of γ-Bi2O3 and VB holes of CeO2 were preserved to generate free radicals for antibiotic degradation. The colony numbers of Escherichia coli were 1.50 × 10-6 CFU mL-1 and 1.39 × 10-6 CFU mL-1 in solutions after the degradation of the two pollutants, which represents the non-toxicity of the final products. The γ-Bi2O3/CeO2 sample has a potential application for antibiotic removal from modern sewage.

UV-excited single-component white phosphor of Lu2WO6 with broad-band emission for pc-WLED.

Obtaining white light from a single-component phosphor is still a significant challenge due to the complex energy transfer between multiple luminescent centers. Herein, white light emission is obtained in a single-component lutetium tungstate without any doping elements. By tuning the pH values during the hydrothermal synthesis, the orthorhombic Lu2W3O12 transformed into monocline Lu6WO12 and rhombohedra Lu6WO12. Only the monoclinic Lu2WO6 phase emitted light, whereas the other two phases did not. The main reason was that the exciton binding energy of Lu2WO6 was larger than that of Lu2W3O12 and Lu6WO12. Except for the 480 nm intrinsic emission of Lu2WO6, new long-wavelength excitation and emission bands were observed with the center at 340 nm and 520 nm. Based on the first-principle calculation, this new photoluminescence band comes from the electron transition between the local states of oxygen vacancies and valence band. Owing to this new broad-band emission, the white light LED lamp is fabricated by combining Lu2WO6 phosphor synthesized at pH values of 4.5 and 6 and 365 nm LED chips. The CIE coordinates of the pc-WLEDs are (0.346, 0.359) and (0.380, 0.380), respectively, and both are located in the white light region. Our research demonstrated a facile way to obtain a single-component white light emission phosphor without any doping components for pc-WLED applications.

Nanosheets loaded on tetrahedral surfaces form a Z-type Bi2MoO6/γ-Bi2O3 heterojunction to enhance the photocatalytic degradation activity of lomefloxacin and Rhodamine B.

The Bi2MoO6 nanosheets are loaded on to γ-Bi2O3 tetrahedron surfaces to form Bi2MoO6/γ-Bi2O3 heterojunctions using a simple calcination method. The photocatalytic degradation efficiencies of the lomefloxacin and the Rhodamine B using the optimum sample are 96% and 99%, respectively, much higher than that of pure phase samples. When the waters from different regions in China were used as solvents, the removal efficiencies of the lomefloxacin and the Rhodamine B are still higher than 88% and 90%, respectively, which shows excellent prospects for practical applications. The photocatalytic degradation efficiencies of these two pollutants are higher than 91% and 95% in the five cycling tests, and the crystal structure of the sample is not changed after cycling. Based on the first-principles calculation, Bi2MoO6 and γ-Bi2O3 form a Z-type energy band structure which accelerates the separation of the photogenerated charge carriers. The Bi2MoO6 valence band potential of 3.25 V and the γ-Bi2O3 conduction band potential of -0.21 V are reserved to generate ˙OH- and O2-, respectively, for the photocatalytic reaction. The degradation of the lomefloxacin is ascribed to the shedding of functional groups and bond breaking with the final products being CO2, F-, H2O, and NO3-. This research shows that Bi2MoO6/γ-Bi2O3 heterojunctions can be employed to purify domestic and textile industrial sewage.

Sunlight driven isotropic ß-Bi2O3 with high charge-carrier mobility for the efficient degradation of bisphenol A and phenol.

Nanostructured ß-Bi2O3 was synthesized and used for the photocatalytic degradation of bisphenol A and phenol. After 90 minutes of sunlight irradiation, the degradation efficiencies toward bisphenol A and phenol were 96% and 97%, respectively. Changes in sunlight due to the season and the calcination temperature and duration displayed weak influence on the degradation efficiencies for these two pollutants. Although the use of tap water, river water, lake water, and seawater exhibited a certain impact on the photocatalytic efficiency, the final removal efficiencies for bisphenol A and phenol in seawater still reached 89% and 90%, respectively. Moreover, the photocatalytic efficiencies toward bisphenol A and phenol remained above 91% and 86% during testing over five cycles. Superoxide groups (O2-) and holes were the main active substances, while hydroxyl radicals (˙OH-) also played a certain role in photocatalysis. The charge-carrier concentration and mobility of ß-Bi2O3 were 4.82 × 1021 cm-3 and 4.0017 cm2 V-1 s-1, respectively, based on the Hall test. ß-Bi2O3 was an isotropic semiconductor based on first-principles calculations, and its excellent photocatalytic activity originated from the high electron mobility and moderate hole mobility. The bisphenol A and phenol degradation mechanisms on the ß-Bi2O3 surface were revealed based on adsorption model calculations. Finally, the reduction in total organic carbon content further verified the degradation of these two contaminants.

Photogenerated charge separation and recombination path modification in monocline Lu2WO6via lattice transition and Bi-O antibonding states.

Monoclinic Lu2WO6 undergoes diphase-to-perovskite BiLuWO6 transition via selective occupancy of Bi in three Lu sites. The transformation mechanism, process, and structure stabilities are revealed by variable cell nudged elastic band method, video, and phonon spectrum. Lattice transition brings about photogenerated charge separation in BiLuWO6. This is verified by indirect band gap transition, high electron migration rate, weak exciton binding energy, large photocurrent response, and small impedance. The electron-hole life time is elongated to produce abundant superoxide and hydroxyl radicals for the degradation of rhodamine B and phenol molecules. Bi-O antibonding states serve as immediate energy levels to change the recombination path, inducing 340 nm excitation band and 510 nm green light emission of Lu2WO6. Furthermore, multicolor emission of 1 at% Bi3+ + RE3+ (RE = Sm/Eu/Dy)-codoped Lu2WO6 is acquired via synergistic modification of the Bi-O antibonding state and RE3+ 4f states. Thus, the photogenerated charge motion in Lu2WO6 is tuned to expand application fields.

Monoclinic Lu2-xSmxWO6-Based White Light-Emitting Phosphors: From Ground-Excited-States Calculation Prediction to Experiment Realization.

Through ground state and constrained density function calculations, Sm3+ ions luminescence in self-activated monoclinic Lu2WO6 was originated from intra 4f → 4f transitions, not inter 5d → 4f transitions. Theoretically the white luminescence was obtained by combining red and blue-green emissions of 4f energy levels and W-O charge transfer transitions. Experimentally, pure and Sm3+ doping Lu2WO6 powders were synthesized using solid phase reaction calcined in air atmosphere. By the analysis of X-ray photoelectron spectroscopy and Rietveld refinement, element Sm charge state was trivalent, and Sm3+ doping was concentration-dependent selectively doping in three Lu sites. With the increase of Sm3+ concentrations, the color coordinates changed gradually from blue (0.17, 0.17) through white light (0.33, 0.25) toward orange (0.44, 0.32) in the visible spectral under 325 nm excitation. On the basis of the theoretical prediction and experimental preparation, a white emission LED lamp was produced using a 365 nm ultraviolet chip and Lu1.99Sm0.01WO6 phosphor. The present design method can be applied to select excellent activators from a large number of rare-earth (Re) ions like Sm3+ and Eu3+/2+ or non-Re ions like Bi3+ and Mn4+ in various matrixes.

Tuning oxygen vacancy photoluminescence in monoclinic Y2WO6 by selectively occupying yttrium sites using lanthanum.

The effect of isovalent lanthanum (La) doping on the monoclinic Y2WO6 photoluminescence was studied. Introducing the non-activated La(3+) into Y2WO6 brings new excitation bands from violet to visible regions and strong near-infrared emission, while the bands position and intensity depend on the doping concentration. It is interesting to find that doping La(3+) into Y2WO6 promotes the oxygen vacancy formation according to the first-principle calculation, Raman spectrum, and synchrotron radiation analysis. Through the Rietveld refinement and X-ray photoelectron spectroscopy results, La(3+) is found to mainly occupy the Y2 (2f) site in low-concentration doped samples. With increasing doping concentration, the La(3+) occupation number at the Y3 (4g) site increases faster than those at the Y1 (2e) and Y2 (2f) sites. When La(3+) occupies different Y sites, the localized energy states caused by the oxygen vacancy pair change their position in the forbidden band, inducing the variation of the excitation and emission bands. This research proposes a feasible method to tune the oxygen vacancy emission, eliminating the challenge of precisely controlling the calcination atmosphere.