Bi2O3 induced tremella-like Bi2WO6 with visible light catalytic performance

The development of single phase photocatalyst is expected to realize clean energy and pollution treatment. Herein, we reported a novel Tremella-like Bi₂WO₆ catalyst which was obtained by facile hydrothermal technique. The formation of Tremella-like Bi₂WO₆ strongly depended on introduction of Bi₂O₃. Based on the Kirkendall effect, Bi₂O₃ induced Bi(NO₃)₃·5H₂O to form biscuit-like Bi₆O₆(OH)₃(NO₃)₃·3H₂O particles which provided templates and reacted simultaneously with WO₄^2? to synthesize Tremella-like Bi₂WO₆. The Tremella-like Bi₂WO₆ exhibited remarkable visible-light catalytic performance. The degradation rate of RhB dye reached 100% with 10 min, the reduction rate of CO₂ was 5.5 times higher than pure Bi₂WO₆. Moreover, the Tremella-like Bi₂WO₆ catalyst displayed excellent stability during the recycle experiments. The high catalytic activity makes single phase Bi₂WO₆ catalyst great potential in environmental protection field.     

Mesoporous yolk-shell structure Bi2MoO6 microspheres with enhanced visible light photocatalytic activity

Mesoporous yolk-shell structure Bi₂MoO₆ (BMO-YS) microspheres were successfully synthesized via a facile solvothermal route in Bi₂MoO₆ precursor solution. The morphology, structure and photocatalytic performance of the BMO-YS in the degradation of Rhodamine B (RhB) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption–desorption, UV–vis absorption spectroscopy and electrochemical impedance spectra, respectively. The as-prepared BMO-YS mainly consists of microspheres with diameters of about 1.5 μm. The photocatalytic studies reveal that the BMO-YS not only exhibits optimum photocatalytic performance, which may be attributed to the excellent charge separation characteristics and the enhanced light absorption offered by its unique yolk-shell structure, but also possesses excellent recyclability for photocatalysis.     

Bi2MoO6 hierarchical hollow microspheres with remarkable electrochemical performance

Hierarchical hollow architectures have demonstrated a remarkable electrochemical performance. In this contribution, Bi₂MoO₆ hierarchical hollow microspheres constructed by nanosheets are prepared by a facile hydrothermal method without any post-treatment, and investigated firstly as anode of lithium-ion batteries. The time-dependent experiments show the morphology evolution from solid microspheres to hierarchical hollow microspheres. Compared with the previous reports, the results manifest expectedly a superior lithium storage performance in terms of specific capacity, cycling stability, rate capability, active energy and Li⁺ diffusion kinetics.     

Hierarchically ordered foams derived from polysiloxanes with catalytically active coatings

Pt free and Pt containing hierarchically ordered macro/micro porous foams were generated by using polysiloxanes and platinic acid as precursors and expanded polystyrene beads as templates to generate macro pores. By pyrolysis at 500 °C micro porosity and thus high specific surface areas were generated. The foams were analyzed in terms of macro- and microstructures (SEM, micro-computer tomography, TEM, BET) and catalytic properties (CO oxidation). For the crack free foams a method was additionally developed that allows the application of a thin Pt-containing layer only on the cell walls. The well known problems arising from mass transport limitation in micro porous materials can be diminished due to the generation of thin struts and this minimized Pt coating on the cell walls as demonstrated by catalytic experiments.     

Facile fabrication of ordered assembled TiO2/g-C3N4 nanosheets with enhanced photocatalytic activity

A series of assembled porous TiO₂/g-C₃N₄ (TC) powders composed of spherical nanoparticles were synthesized by controlling the molar ratio of urea to tetrabutyl titanate (TBOT) in a facile hydrothermal process. A nanosheets-constructed hierarchical structure was obtained at the molar ratio of urea to TBOT of 10:1, which possessed uniform mesopores with bimodal distribution (0.5–1.5 nm and 2–20 nm) and interconnected macropores between TC nanosheets. The specific surface area achieved 98.4 m² g^?1. X-ray diffraction (XRD) patterns and high resolution transmission electron microscope (HRTEM) analysis proved that the nanosheets are made of overlapping TC nanocomposite. Photoluminescence (PL) spectra results illustrated that a well-defined hierarchical porous structure is particularly desired for the low recombination rate of carriers. Further, the TC-decorated carbon fiber (CF) cloth was obtained based on the nanosheets assembled hierarchical structure, which showed more outstanding photocatalytic behavior with high degradation capability for Rhodamine B (RhB) (99.9%) and tetracycline hydrochloride (89.8%) at 60 min by 500 W Xe lamp irradiation. After five consecutive cycles, the degradation efficiencies of TC/CF cloth for both RhB and tetracycline hydrochloride all remained above 90% of the initial value.     

Hierarchical polypyrrole encapsulating Bi2O4 to enhance charge separation and light absorption with boosted visible light photocatalytic activity

Bi₂O₄, as a typical visible-light responsive photocatalyst (band gap～ 2.0 eV), has aroused enormous attention in recent years. However, single Bi₂O₄ has the problem of high recombination probability of photogenerated electron-hole pairs, which inevitably hampers its photocatalytic performance. Herein, hierarchical polypyrrole encapsulated Bi₂O₄(Bi₂O₄@PPy) has been constructed via an in-situ vapor-phase polymerization method, producing PPy tightly coated Bi₂O₄ core-shell structure photocatalyst. Thanks to this full coating and hierarchical structure, the charges separation efficiency, and the light absorption capacity of Bi₂O₄@PPy hybrid are promoted, leading to obviously enhanced visible light photocatalytic activity. The optimal Bi₂O₄@PPy composite could be obtained through controlling the polymerization time for 9 h, whose catalytic activity is as 2.43 times as that of Bi₂O₄ alone. The active species trapping experiments suggest that holes play a vital role in the photocatalytic degradation process. A plausible reaction mechanism over the Bi₂O₄@PPy hybrid photocatalyst is also proposed based on the characterization and experimental results.     

Design of hierarchical core-shell ZnFe2O4@MnO2@RGO composite with heterogeneous interfaces for enhanced microwave absorption

In order to overcome the problems caused by electromagnetic pollution, the design and development of high-performance microwave absorbers is urgently required. In this work, a hierarchical ZnFe₂O₄@MnO₂@RGO composite was successfully fabricated via a facile and rapid hydrothermal method. Its unique core-shell structure and synergistic effect between multiple components are beneficial for electromagnetic wave absorption. The morphology, elemental composition, microstructure and microwave absorption characteristics were systematically studied. With a filler loading of 20 wt%, the composite presents a minimum reflection loss (R_Lmin) of ?46.7 dB and an effective absorption bandwidth (EAB) as wide as 5.2 GHz at a thickness of 2.5 mm. The superior absorption ability profits from a special microstructure, good impedance matching, multiple attenuation features, interfacial polarization, and the synergistic effect of dielectric and magnetic loss. Consequently, this work lays a foundation for the design of high-performance electromagnetic wave absorbers with multicomponent heterogeneous structures.     

Synthesis of parallel squared nanosheet-assembled Bi2WO6 microstructures under alkalescent hydrothermal treatment

The hierarchical Bi₂WO₆ microstructures, which were two-dimensionally assembled by parallel squared nanosheets, were synthesized under alkalescent hydrothermal treatment. The crystalline phase, morphology, size, lattice plane and crystalline structure of the products were characterized by X-ray diffraction, scanning/transmission electron microscopy and selected area electron diffraction. The formation of parallel squared nanosheet-assembled hierarchical Bi₂WO₆ microstructures was elucidated by the oriented attachment growth mechanism based on our experimental results. The aqueous ammonia, which was employed as the alkalescent environment, had a critical effect on the formation of such hierarchical Bi₂WO₆ microstructures with a large proportion of {001} facets. The parallel squared nanosheet-assembled hierarchical Bi₂WO₆ microstructures obtained at the hydrothermal temperature of 120 °C showed high photocatalytic activity under visible-light irradiation.     

Synthesis of hierarchical core-shell NiFe2O4@MnO2 composite microspheres decorated graphene nanosheet for enhanced microwave absorption performance

A ternary functional composite NiFe₂O₄@MnO₂@graphene was synthesized successfully via a facile method. The phase constitution, microstructures, morphologies and chemical compositions of the samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) and X-ray photoelectron spectroscopy (XPS). It was observed that the NiFe₂O₄ nanoparticles were coated by hierarchically MnO₂ shells and distributed on the surface of graphene. Investigations of EM wave absorption indicated that NiFe₂O₄@MnO₂@ graphene composite has the strongest reflection loss of −47.4 dB at 7.4 GHz at the matching thickness of 3 mm, compared to NiFe₂O₄ and NiFe₂O₄@MnO₂, and its maximum absorption bandwidth (<−10 dB) is 4.3 GHz (from 5.1 to 9.4 GHz). The enhanced microwave absorption performance can be attributed to the hierarchical structure of MnO₂, void space between MnO₂ and graphene, and better impedance matching of ternary composite. The above results indicate that the novel hierarchical NiFe₂O₄@MnO₂@graphene composite, with intense absorption and wide absorption bandwidth, would be a promising absorber with less EM wave interference.     

多层纳米结构蓝色TiO2的电化学氧化性能和稳定性

蓝色TiO₂具有出色的电催化活性,被认为是降解有机污染物的最有潜力的阳极材料之一。然而蓝色TiO₂的电催化活性受表面形貌和界面性质的影响较大。本文采用冰水浴阳极氧化和阴极还原制备了由纳米颗粒、多孔层、纳米管阵列依次堆叠的多层纳米结构蓝色TiO₂,并探究了其电化学氧化性能。与无冰水浴辅助制备的相比,该方法制备的蓝色TiO₂具有更多的Ti³⁺含量、更大的活性面积和良好的电子传输能力,可有效降解亚甲基蓝（97.7%,120min,20mA/cm²）和实际废水（COD在180min内被完全去除）。自由基淬灭实验结果表明,添加Na₂SO₄能促进蓝色TiO₂产生羟基自由基和硫酸根自由基,而污染物的降解主要依赖于羟基自由基的氧化作用,硫酸根自由基仅在高Na₂SO₄浓度、低电流密度和高初始pH条件下有较大贡献。通过冰水浴阳极氧化制备的蓝色TiO₂的使用寿命是无冰水浴制备的2.4倍,表明这种多层纳米结构有利于提高蓝色TiO₂的稳定性。     

色氨酸辅助合成光催化活性增强的球形纳米TiO2

以L-色氨酸（L-Trp）为生物模板,采用简单水解及煅烧后制备了球形结构TiO₂纳米光催化剂。通过X射线衍射、扫描电子显微镜、红外光谱、紫外-可见漫反射光谱、光致发光光谱和N₂吸附-解吸等方法对制得的TiO₂纳米材料进行表征。在催化剂合成过程中,L-Trp作为生物模板发挥至关重要的作用,能够指导球形结构纳米TiO₂的形成。考察了不同煅烧温度下制备的TiO₂样品光催化活性,结果表明550℃时制备的TiO₂样品具有优异的光催化活性,紫外光照射30min对甲基橙溶液的降解率达到95%左右,主要是由于较大比表面积和球形结构的协同效应。光催化剂稳定性实验表明,所制备的TiO₂纳米材料可作为一种实用有效的光催化剂用于紫外光照射下降解有机染料。同时,对L-Trp辅助下球形结构TiO₂纳米颗粒的可能生长机理进行讨论。     

Fabrication of TiO2 nanofibers assembled by Bi2WO6 nanosheets with enhanced visible light photocatalytic activity

A series of Bi₂WO₆/TiO₂ nanofibers (BT NF) hierarchical photocatalysts were synthesized by a facile two-step strategy consisting of electrospinning technique and subsequent solvothermal method. The results showed that the secondary two-dimensional Bi₂WO₆ nanosheets were uniformly assembled onto the surface of the TiO₂ NF. It was also verified that the density of Bi₂WO₆ nanosheets could be tailed by controlling the precursor concentration during the solvothermal process. Photocatalytic tests demonstrated that BT NF with a low concentration of precursor (S1) possessed a much higher visible light degradation rate for Rhodamine B than TiO₂ NF, Bi₂WO₆ and their mixture. The enhanced photocatalytic activity of S1 was ascribed to the extension of the light absorption region induced by the introduction of narrow band gap Bi₂WO_6, and the formation of heterojunction accelerating the interfacial charge separation. Moreover, BT NF with a high concentration of precursor (S2) manifested a higher photocatalytic activity than S1 due to the higher loading of Bi₂WO₆ nanosheets. S2 could be reused by sedimentation, and the photocatalytic activities of S2 were retained with a slight decline after four cycles, which confirmed its stability. Therefore, BT NF composites will be ideal candidates for highly efficient and recyclable photocatalysts for the treatment of organic pollutants under visible light.     

Low-temperature sintering of BF-PT-BZ ternary solid solutions with enhanced piezoelectric properties

The 0.34BiFeO₃-0.46PbTiO₃-0.2BaZrO₃ (BF-PT-0.2BZ) ternary solid solutions were prepared by the solid-state reaction methods. Different amounts of Li₂CO₃-Bi₂O₃ (LB) additives were introduced into the based materials after the calcination process. Upon using LB additives, the sintering temperature of BF-PT-0.2BZ ceramics was lowered to 950°C, while the relative density was enhanced to the highest of about 97% for LB of 1 wt%. XRD results indicate that BF-PT-0.2BZ ceramics exhibit the perovskite structure without detectable second phases. SEM images reveal that BF-PT-0.2BZ ceramics are well densified and the grain size is enhanced with the addition of LB. Moreover, the piezoelectric properties are enhanced significantly, achieving the highest d₃₃ and bipolar strain of 350 pC/N and 0.53%, respectively, for BF-PT-0.2BZ ceramics with LB of 1 wt%. Our results indicate that low-temperature sintered BF-PT-0.2BZ ceramics with excellent piezoelectric properties have promising applications in multilayer piezoelectric actuators.     

Hierarchical manganese sillenite Bi12MnO20 microparticles assembled by nanocubes with microwave absorption enhancement

Pure manganese sillenite (Bi₁₂MnO₂₀) microparticles with average sizes of 11.5–16.8 μm were prepared via an oxidation-precipitation method assisted by microwave-heating. Their microstructures are characterized by the shapes of single or multiple intersecting tetrahedrons and the massive nanocubes in ordered arrays on each tetrahedron surface. Such hierarchical Bi₁₂MnO₂₀ microparticles have not been reported so far, while their growth mechanisms may include the formation of active centers, the selective nucleation on active center surfaces and the growth of nanocubes along certain orientations. In electromagnetic determination, noticeable resonances both in permittivity and permeability were revealed beyond relaxations. A cone-like reflection loss peak was obtained with the minimum value of −39.1 dB and a broad effective microwave absorption bandwidth covering 12.7–14.6 GHz. Moreover, the reflection loss peak stagnates at the same frequency regardless of the absorbent thickness variations, suggesting a high performance in microwave attenuation.     

The enhanced visible light driven photocatalytic inactivation of Escherichia coli with Z-Scheme Bi2O3/Bi2MoO6 heterojunction and mechanism insight

Recently, photocatalytic technology has been deemed as a prospective strategy for pathogenic microorganism removal. In this article, a nontoxcity Z-scheme Bi₂O₃/Bi₂MoO₆ (BO/BMO) heterojunction was rationally fabricated for photocatalytic inactivation against E. coli cells under visible light stimulation (λ > 420 nm). The 30% BO/BMO heterojunction presented the strongest bactericidal ability and the 7-log 10 cfu/mL of E. coli cells were absolutely inactivated within 5 h treated, which was much superior to the pure Bi₂MoO₆. The elevated photocatalytic performance of the BO/BMO heterojunctions could be ascribed to the higher spatially separation efficiency of the photoexcited electron-hole pairs and improved visible light absorption ability. The trapping experiments of reactive oxygen species (ROS) disclosed that the ·OH, e^? and h⁺ played the predominant role in the E.coli inactivation. Moreover, the transfer of the photoexcited hole-electron pairs over the BO/BMO heterojunctions was verified to follow the Z-scheme model. The mechanism of photocatalytic inactivation of E.coli could be interpreted by the disruption of the cell membrane, leakage and destroy of the cellular biomoleculars (e.g. DNA and protein) as tested by the SEM and electrophoresis technology. This work may provide a promising avenue to explore a novel Bi₂MoO₆-based photocatalysts for pathogenic microorganisms removal.     

Aluminum-doped ceria-zirconia solid solutions with enhanced thermal stability and high oxygen storage capacity

A facile solvothermal method to synthesize aluminum-doped ceria-zirconia (Ce_0.5Zr_0.5-xAl_xO_2-x/2, x = 0.1 to 0.4) solid solutions was carried out using Ce(NH₄)₂(NO₃)₆, Zr(NO₃)₃·2H₂O Al(NO₃)₃·9H₂O, and NH₄OH as the starting materials at 200°C for 24 h. The obtained solid solutions from the solvothermal reaction were calcined at 1,000°C for 20 h in air atmosphere to evaluate the thermal stability. The synthesized Ce_0.5Zr_0.3Al_0.2O_1.9 particle was characterized for the oxygen storage capacity (OSC) in automotive catalysis. For the characterization, X-ray diffraction, transmission electron microscopy, and the Brunauer-Emmet-Teller (BET) technique were employed. The OSC values of all samples were measured at 600°C using thermogravimetric-differential thermal analysis. Ce_0.5Zr_0.3Al_0.2O_1.9 solid solutions calcined at 1,000°C for 20 h with a BET surface area of 18 m² g⁻¹ exhibited a considerably high OSC of 427 μmol-O g⁻¹ and good OSC performance stability. The same synthesis route was employed for the preparation of the CeO₂ and Ce_0.5Zr_0.5O₂. The incorporation of aluminum ion in the lattice of ceria-based catalyst greatly enhanced the thermal stability and OSC.     

Triple-doping of (Ga1/2Nb1/2)xTi1-xO2 ceramics with Al3+ for enhanced giant dielectric response with simultaneous decrease in dielectric loss

An acceptor-donor co-doped (Ga_1/2Nb_1/2)_0.1Ti_0.9O₂ ceramic is triple-doped with Al³⁺, followed by sintering at 1450 °C for 5 h to obtain (Al_xGa_1/2-xNb_1/2)_0.1Ti_0.9O₂ ceramics with improved giant dielectric properties. Homogeneous dispersion of all dopants inside the grains, along with the partially segregated dispersion of the Ga³⁺ dopant along the grain boundaries, is observed. The (Al_xGa_1/2-xNb_1/2)_0.1Ti_0.9O₂ ceramics exhibit high dielectric permittivities (ε′～4.2–5.1 × 10⁴) and low loss tangents (tanδ～0.007–0.010), as well as a low-temperature coefficients (<±15%) between ? 60 and 200 °C. At 1 kHz, tanδ is significantly reduced by ～4.4 times, while ε′ is increased by ～3.5 times, which is attributed to the higher Al³⁺/Ga³⁺ ratio. The value of tanδ at 200 °C is as low as 0.04. The significantly improved dielectric properties are explained based on internal and surface barrier-layer capacitor effects, which are primarily produced by the Ga³⁺ and Al³⁺ dopants, respectively, whereas the semiconducting grains are attributed to Nb⁵⁺ doping ions.     

Preparation and optimization of ZrO2 modified P2-type Na2/3Ni1/6Co1/6Mn2/3O2 with enhanced electrochemical performance as cathode for sodium ion batteries

Surface stabilization is necessary for cathode materials to gain a long-term cycling stability because of unfavorable side reactions and exfoliation caused by corrosive environment. To improve the cyclic stability of P2-type ternary cathode Na_2/3Ni_1/6Co_1/6Mn_2/3O₂ for sodium ion batteries, we prepare a ZrO₂-coated Na_2/3Ni_1/6Co_1/6Mn_2/3O₂ through a simple wet chemical method. The coating layer is distributed homogeneously on the surface, and the fraction of ZrO₂ (1 wt-%, 2 wt-%, 3 wt-%, 4 wt-%, 5 wt-%) helps control the thickness of the coating layer. It turns out that all the materials exhibit pure P2 structure without any impurities. The material with a 2 wt-% ZrO₂ coating exhibits the best electrochemical performance in rate capability and long-term cyclic stability. It delivers a superior initial discharge capacity of 140 mA h·g⁻¹ between 2 and 4.5 V at 20 mA g⁻¹. Even cycles at high current density (100 mA g⁻¹), it shows 106 mA h·g⁻¹ reversible discharge capacity with 88% capacity retention after 300 cycles. The improvement in electrochemical performance is attributed to the segregation of cathode materials from the corrosive electrolyte by the nano-sized ZrO₂ layer. The EIS results confirm that a thin ZrO₂ coating layer can effectively protect the electrode from dissolution and stabilize the SEI film. This study can be used to develop the electrochemical performance of cathode materials for sodium ion batteries by surface modification via ZrO₂.     

Structural dependence of microwave dielectric properties of spinel structured Mg2(Ti1-xSnx)O4 solid solutions: Crystal structure refinement,Raman spectra study and complex chemical bond theory

Mg₂(Ti_1-xSn_x)O₄ (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg₂(Ti_1-xSn_x)O₄ average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg₂(Ti_1-xSn_x)O₄ compounds were obtained (${\epsilon }_r$= 12.18, $Q\times f$?=?170,130?GHz, ${\tau }_f$?=??53.1?ppm/°C, x?=?0.2).     

Anomalous photovoltaic effect in Bi(Ni2/3Ta1/3)O3-PbTiO3 ferroelectric solid solutions

Dense Bi(Ni_2/3Ta_1/3)O₃-PbTiO₃ (BNT-PT) ceramics were prepared by solid-state reaction method. Morphotropic phase boundary between tetragonal and rhombohedral phase was observed around the composition 0.38BNT-0.62PT, at which large photovoltages of 13.2V were obtained under 405 nm laser illumination with power density of 200 mW/cm². By B-site Ni²⁺ ions doping, the bandgap values of BNT-PT solid solutions were reduced to 2.25~1.85 eV, and the anomalous photovoltaic response was extended from the ultraviolet region to a wavelength of 550 nm at the visible light region.