Ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag2CrO4 nanocomposites as visible-light-driven photocatalysts with excellent activity

This work reports ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag₂CrO₄ nanocomposites as excellent visible-light-driven photocatalysts. The ZnO/AgI/Ag₂CrO₄ nanocomposite with 20% of Ag₂CrO₄ has the superior activity in degradation of rhodamine B. Activity of this nanocomposite is nearly 167, 6.5, and 45-fold higher than those of the ZnO, ZnO/AgI, and ZnO/Ag₂CrO₄ samples, respectively. The ternary nanocomposite also showed enhanced activity relative to its counterparts for degradation of methylene blue and methyl orange as two dye pollutants under visible-light irradiation. The UV–vis DRS and PL spectra confirmed that the excellent photocatalytic activities are due to more visible-light absorption ability and efficiently separation of the charge carriers. Based on the effects of different scavengers, it was found that superoxide ions are the primary reactive species to cause the degradation reaction. Furthermore, the highly enhanced activity of the ternary nanocomposite was described using a proposed mechanism.     

Effect of compositional dependence on physicochemical properties of Bi2Se3 doped system

Crystalline bulk compositions of Bi₂ (Se_1−xTe_x)₃ system with ( x=0.0–1.00) were prepared using the conventional melting method. The structural properties of bulk samples were studied with the aid of XRD and SEM analysis. Compositional element distribution and elemental ratios were estimated with EDX spectroscopy that attached with SEM. XRD patterns show that the prepared compounds are crystalline materials with single phases of Bi₂Se₃ and Bi₂Te₃ and/or a ternary phase. The grain size calculations were performed using the well-known Scherrer equation. The thermal studies analysis was carried out by using DSC. DSC studies revealed that the prepared samples are stable and none decomposable over the temperature range. Physicochemical properties such as compactness, molar volume and the free volume percentage were calculated for the concerned alloys based on the experimentally calculated densities of each compound. The measured parameters showed a strong dependence on the Te content.     

Photocatalytic degradation of methylene blue by Zn2SnO4-SnO2 system under UV visible radiation

Zn₂SnO₄-SnO₂ system was successfully synthesized by co-precipitation under ultrasonic radiation combined with high temperature calcination. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and UV–visible absorption spectroscopy revealed the presence of cubic particles mixed with nanoparticles of Zn₂SnO₄-SnO₂ composites which were synthesized from Zn:Sn molar ratios of 1:1 and 3:2. Upon using Zn:Sn molar ratios of 3:1 and 2:1, additional ZnO minor phase was detected. In addition, the calculated pseudo-first-order rate constant of the product synthesized from 3:2 molar ratio of Zn:Sn was the highest at 12.244×10^–3 min^–1.     

Fabrication of Bi2MoO6 nanoplates hybridized with g-C3N4 nanosheets as highly efficient visible light responsive heterojunction photocatalysts for Rhodamine B degradation

The Bi₂MoO₆/g-C₃N₄ heterojunction photocatalysts have been successfully fabricated using a simple liquid chemisorptions and thermal post-treatment. These nanostructured Bi₂MoO₆/g-C₃N₄ composites were extensively characterized by X-ray diffraction(XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR),UV–vis diffuse reflectance spectra (UV–vis DRS) and Photoluminescence (PL). The photocatalytic results show that 20 wt% Bi₂MoO₆/g-C₃N₄ sample exhibits efficient visible light activity and excellent photo-stability. The kinetic constant of RhB degradation over 20 wt% Bi₂MoO₆/g-C₃N₄ is about 5 and 2.5 times higher than that over pure Bi₂MoO₆ and g-C₃N₄ nanosheets, respectively. The enhanced photocatalytic performance is attributed to the construction of heterogeneous interface to promote photo-induced charge carrier pairs separation.     

Solvothermal synthesis and photocatalytic properties of CdS nanowires under UV and visible irradiation

CdS nanowires (NWs) were synthesized by the solvothermal method. The synthesis yields NWs with hexagonal phase structure. The phase, vibration modes, morphologies and optical properties of CdS NWs were investigated by X-ray powder diffraction (XRD), Raman spectrophotometry, scanning and transmission electron microscopy (SEM and TEM) and UV–visible spectroscopy, respectively. The results show that the as-synthesized product is hexagonal CdS NWs with the diameter of 20–30 nm and length of up to 5 μm. Photocatalytic degradation of methyl orange (MO) and rhodamine B (RhB) was investigated. It was found that CdS NWs possess excellent catalytic degradation activity owing to their effective absorption over the visible range. The highly photocatalytic activity suggested possible application in the treatment of organic pollutants under visible light irradiation.     

Preparation of point-line Bi2WO6@TiO2 nanowires composite photocatalysts with enhanced UV/visible-light-driven photocatalytic activity

Bi₂WO₆@TiO₂ nanowires composite photocatalysts (BWO-TNWS) with point-line structures have been successfully fabricated by hydrothermalsynthesis method, and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible diffuse reflectance spectra (UV–vis DRS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS). The effects of coupling narrow-band-gap semiconductor Bi₂WO₆ (BWO) to photocatalytic activity for degrading Rhodamine B (RhB) and Phenol under UV–vis light irradiation were investigated. The results demonstrate that the photocatalytic activities of the prepared photocatalysts are associated with the content of Bi₂WO₆ (BWO). 20% BWO-TNWS (containing 20 wt% BWO) composite exhibits the highest degradation rate for RhB and Phenol up to 78% and 33%, respectively. It can be concluded that the improved photocatalytic performance of the BWO-TNWS composite is mainly ascribed to its high photoinduced charge separation rate resulting from the effective heterojunction structure of BWO and TNWS, as well as the enlarged optical response range owing to coupling narrow-band-gap semiconductor BWO.     

Synthesis,characterization and solar photocatalytic performance of In2O3-decorated Bi2O3

In₂O₃/Bi₂O₃ composite photocatalysts with different In₂O₃ content were prepared using a pore impregnation method with Bi₂O₃ as the substrate. The composite photocatalysts exhibit enhanced photocatalytic activity compared to Bi₂O₃ for the degradation of aqueous methyl orange (MO) solution under solar irradiation. The samples were characterized in terms of BET surface area, X-ray diffraction (XRD), UV/Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and surface photovoltage (SPV). On the basis of the results, a mechanism is proposed to account for the enhanced photocatalytic activity of these In₂O₃/Bi₂O₃ composites.     

Self-Healing Cs3Bi2Br3I6 Perovskite Wafers for X-Ray Detection

Self-healing of defects imposed by external stimuli such as high energy radiation is a possibility to sustain the operational lifetime of electronic devices such as radiation detectors. Cs₃Bi₂Br₃I₆ polycrystalline wafers are introduced here as novel X-ray detector material, which not only guarantees a high X-ray stopping power due to its composition with elements with high atomic numbers, but also outperforms other Bi-based semiconductors in respect to detector parameters such as detection limit, transient behavior, or dark current. The polycrystalline wafers represent a size scalable technology suitable for future integration in imager devices for medical applications. Most astonishingly, aging of these wafer-based devices results in an overall improvement of the detector performance—dark currents are reduced, photocurrents are increased, and one of the most problematic properties of X-ray detectors, the base line drift is reduced by orders of magnitude. These aging induced improvements indicate self-healing effects which are shown to result from recrystallization. Optimized synthetic conditions also improve the as prepared X-ray detectors; however, the aged device outperforms all others. Thus, self-healing acts in Cs₃Bi₂Br₃I₆ as an optimization tool, which is certainly not restricted to this single compound, it is expected to be beneficial also for many further polycrystalline ionic semiconductors.     

(Bi0.88Ce0.12)2Ti2O7薄膜的结构及C-V特性

采用化学溶液分解法(CSD)在p型Si<100>衬底上制备了(Bi0.88Ce0.12)2Ti2O7薄膜,分别借助X线光电子能谱仪、紫外-可见分光光度计研究了薄膜的化学特性、紫外-可见吸收光谱等结构性能.结果表明,在烧绿石相Bi2Ti2O7薄膜中掺杂Ce3+取代部分Bi3+后,薄膜在高温退火下仍能保持原有的相结构.利用HP4192A型阻抗分析仪测试薄膜的电容-电压(C-V)特性,计算出600℃、650℃、700℃、750℃退火条件下薄膜的介电常数分别为144、190、214、176,固定电荷密度值分别为3.44×1011cm-2、5.82×1011cm-2、5.58×1011cm-2和2.49×1010cm-2.     

Formation of Bi2WO6 Bipyramids with Vacancy Pairs for Enhanced Solar‐Driven Photoactivity

In order to improve the photoactivity, many attempts have focused on increasing the exposure of highly reactive surfaces on crystals. However, the connection between the reactive surfaces and enhancement is still elusive. Herein, Bi₂WO₆ nanostructured bipyramids with a large fraction of {100} facets are fabricated by the solvothermal method. The formation of “Bi–O” dimer vacancy pairs on the {100} high‐energy facets is responsible for the reduction in band gap and the decrease in the recombination of photo‐excited charge carriers, which is unambiguously confirmed by the positron annihilation spectra (PAS), X‐ray photoelectron spectrum (XPS), and theoretical calculations. The effective separation of electron–hole pairs and the narrowing bandgap significantly improve the photoactivity of Bi₂WO₆ nanobipyramids, especially under solar light irradiation. These findings can be applied broadly to the design and fabrication of energy efficient and robust catalysts.     

Au nanoparticle modified flower-like ZnO structures with their enhanced properties for gas sensing

The flower-like ZnO (F-ZnO) synthesized by a solution approach was hydrothermally functionalized with Au nanoparticles (Au NPs). The Au coverage on the surface of F-ZnO was controllable by adjusting the Au concentration of the precursor. The gas sensing performance of the formed hybrid was systematically investigated. A Au-functionalized F-ZnO hybrid structure, combining excellent catalytic activity of Au NPs and efficient charge-transfer layer at the Au/ZnO interface, was demonstrated to possess the superior response to pristine ZnO. The optimal Au loading is 6 wt%, and its gas response is nearly 17 times higher than that of pristine ZnO and ~2.5 times higher than that of commercial ZnO functionalized with 6 wt% Au. Such a hybrid structure exhibits a great potential for gas sensing applications.     

Enhanced luminescence of CaSb2O6:Bi3+ blue phosphors by efficient charge compensation

This paper reported an enhanced photoluminescence of CaSb₂O₆:Bi³⁺ by efficient charge compensation. Charge compensated CaSb₂O₆:Bi³⁺,M⁺ (M=Li, Na and K) phosphors were prepared using a co-precipitation technique followed by heat-treatment. The structure and morphology of the as-prepared CaSb₂O₆:Bi³⁺,M⁺ samples were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that the obtained CaSb₂O₆:Bi³⁺,M⁺ samples are hexagonal crystal structure and this structure was retained regardless of co-doping by Li⁺, Na⁺ or K⁺. All samples showed sphere-like shape with particle size of 40–80 nm. The optical properties of products were studied by UV–vis diffuse reflectivity, photoluminescence spectra and luminescence decay measurements. Under the excitation of 336 nm light, all of the samples exhibited a strong blue emission peaking around 437 nm, which is attributed to the ³P₁–¹S₀ transition of the Bi³⁺ ion. It was found that the charge compensation has significant effect on the photoluminescence properties of CaSb₂O₆:Bi³⁺ and the best luminescence properties have been achieved for CaSb₂O₆:0.75Bi³⁺,0.75 Na⁺. The mechanism for the enhancement of the blue emission has also been studied in detail. Our results suggested that the optical properties of oxide nanostructures can be tailored through co-doping with aliovalent ions and the favorable luminescence properties of CaSb₂O₆:Bi³⁺,Na⁺ make it potential for lighting and display applications.     

All-pH Stable Sandwich-Structured MoO2/MoS2/C Hollow Nanoreactors for Enhanced Electrochemical Hydrogen Evolution

Molybdenum sulfide has great potential for the electrocatalytic hydrogen evolution, but its structural instability in acidic media and high barriers in alkaline/neutral media limits its practical applications. Herein, the design of monodispersed sandwich-structured MoO₂/MoS₂/C hollow nanoreactors is reported with a triple layer “conductor/catalyst/protector” configuration for efficient electrochemical hydrogen evolution over all pH values. Metallic MoO₂ substrates with ultrahigh pristine electroconductivity can promote the charge transfer while sulfur vacancies are introduced to activate the highly exposed (002) facets of MoS₂. The optimized MoO₂/MoS₂/C nanoreactor exhibits overpotentials of 77, 91, and 97 mV (10 mA cm⁻²) and Tafel slopes of 41, 49, and 53 mV dec⁻¹ in acidic, alkaline, and neutral media, respectively, which are much better than most of the MoS₂-based electrocatalysts. Moreover, defective carbon shells are in situ generated, preventing the electrocatalysts from corrosion in acidic and alkaline media; the structural stability is verified via in situ Raman and XRD characterizations. Based on the density functional theory calculations, vacancy engineering can regulate the band structures, electron density differences, total density of states, and the H* and H₂O adsorption-dissociation ability over the entire pH range. The findings may shed light on the rational development of practical pH-universal electrocatalysts for durable hydrogen evolution.     

Structural and optical properties of AlN/Si system

Aluminum nitride (AlN) is a wide band gap III–V semiconductor material which is often used for optical applications. Thin films of aluminum nitride were deposited by ion beam sputtering in an Ar–N₂ atmosphere on Si (1 0 0). For film preparation, the N₂ flow was kept at 5 sccm and the ratio of N₂ and Ar was 4:1. The films have been characterized by Grazing Incidence X-ray Diffraction (GIXRD), X-ray Reflectometry (XRR), Atomic Force Microscopy (AFM) and optical spectroscopy. GIXRD shows that the structure of the as-deposited sample of AlN is hexagonal. It is observed that neither the ion-beam-induced dissociation of the nitride film nor the enhanced nitrogen diffusion across the interface takes place after Au ion irradiation. XRR was used to determine the thickness of the films. The reflectance of the irradiated films increases in the range 200–280 nm. UV–vis spectra were taken in Kubelka Munk (KM) units for as-deposited and irradiated samples. The band gap was calculated for both types of samples, which shows that the band gap of irradiated films of aluminum nitride decreases due to the increase in metal content at the surface. AFM confirms that the roughness of aluminum nitride increases by irradiation.     

Self‐Templated Fabrication of CoO–MoO2 Nanocages for Enhanced Oxygen Evolution

Oxygen evolution reaction (OER) plays a key role in energy conversion and storage processes such as water splitting and carbon dioxide reduction. However, the sluggish kinetics caused by insufficient active surface and limited charge transfer hinder OER's wide applications. In this work, a novel self‐templating strategy for the fabrication of composite CoO–MoO₂ nanocages with enhanced OER performance is proposed. By designing a nanocage structure and incorporating conductive MoO₂ to promote both mass and charge transfer, high OER activity (η = 312 mV at 10 mA cm^?2) as well as good stability in the resulting CoO–MoO₂ composite nanostructure can be achieved. This versatile synthetic strategy can also be extended to other metals (such as W) to provide greater opportunities for the controlled fabrication of mixed metal oxide nanostructures for electrochemical applications.     

BiFeO_3改性Bi_(1/2)Na_(1/2)TiO_3-BaTiO_3基陶瓷电性能

采用固相反应法制备了新型(0.95–x)Bi1/2Na1/2TiO3-0.05BaTiO3-xBiFeO3(x=0~0.09)系无铅压电陶瓷,研究了BiFeO3掺杂量对其晶体结构、介电及压电性能的影响。结果表明:在所研究的组成范围内陶瓷均能形成纯钙钛矿型固溶体。介温曲线(10kHz)显示该陶瓷体系具有明显的弥散相变特征。该陶瓷体系的压电性能较Bi1/2Na1/2TiO3-BaTiO3陶瓷(d33=125pC/N)有较大提高,当x=0.05时,具有最佳的压电性能:d33=142pC/N,kp=0.29;此时εr=891,tanδ=0.046,Qm=110。     

On the role of Bi2Sr2Ca1Cu2O8 and Bi2Sr2Cu1O6 on the weak links and critical currents in (Bi,Pb)2Sr2Ca2Cu2O10/Ag superconducting tapes

Silver-sheated (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ (Bi2223) superconducting tapes with different Bi₂Sr₂CaCu₂O₈ (Bi2212) and Bi₂Sr₂Cu₁O₆ (Bi2201) concentrations, were prepared by using a two-step sintering processing and by varying cooling rates in the fabrication of the superconductors. The effect of residual Bi2212 and Bi2201 phases on weak links and critical currents of the Bi2223/Ag tapes was investigated. It was found that residual Bi2201 caused weak links at grain boundaries and limited the current-carrying capacity of the tapes. Comparatively, the residual Bi2212 phase had much less influence on both weak links and critical currents. Elimination of Bi2201 by sintering tapes at a low temperature in the final thermal cycle, or by cooling the tapes slowly, increased critical current by a factor of two. Flux pinning property was also improved by removing the residual Bi2201 phase.     

测定离子注入单晶损伤与应变的双晶(n~v,-n~v)排列方法

依据双晶摇摆曲线的形成原理,提出了一种高分辨率,高灵敏度的测定离子注入单晶损伤与应变的双晶(n~v,—n~v)排列方法。考虑到掠入射情形的色散效应,对掠射角的选择进行了讨论。对Ga注入Si单晶样品的测定证实了(n~v—n~v)排列的优越性,摇摆曲线上得到了未曾见过的细微振荡。     

Effects of Sb,Zn doping on structural,electrical and optical properties of SnO2 thin films

Highly transparent, low resistive pure and Sb, Zn doped nanostructured SnO₂ thin films have been successfully prepared on glass substrates at 400° C by spray pyrolysis method. Structural, electrical and optical properties of pure and Sb, Zn doped SnO₂ thin films are studied in detail. Powder X-ray diffraction confirms the phase purity, increase in crystallinity, size of the grains (90–45 nm), polycrystalline nature and tetragonal rutile structure of thin films. The scanning electron microscopy reveals the continuous change in surface morphology of thin films and size of the grains decrease due to Sb, Zn doping in to SnO₂. The optical transmission spectra of SnO₂ films as a function of wavelength confirm that the optical transmission increases with Sb, Zn doping remarkably. The optical band gap of undoped film is found to be 4.27 eV and decreases with Sb, Zn doping to 4.19 eV, 4.07 eV respectively. The results of electrical measurements indicate that the sheet resistance of the deposited films improves with Sb, Zn doping. The Hall measurements confirm that the films are degenerate n-type semiconductors.