α-Bi2O3 nanosheets: An efficient material for sunlight-driven photocatalytic degradation of Rhodamine B

Herein, we report the sunlight driven photocatalytic degradation of toxic organic dye, Rhodamine B using α-Bi₂O₃ nanosheets as an effective photocatalyst. The α-Bi₂O₃ nanosheets were prepared by simple annealing assisted thermal decomposition method and characterized by several techniques in order to understand its morphological, compositional, structural and optical properties. Morphological, structural and compositional investigations confirmed the formation of sheet-like morphologies, high-crystalline monoclinic crystal structure, and pure α-Bi₂O₃, respectively. The synthesized α-Bi₂O₃ nanosheets exhibited a high photocatalytic degradation of a toxic organic dye, i.e. Rhodamine B (RhB). Under optimal reaction conditions, ～95% photocatalytic degradation of RhB (10 mg/L, pH 10) was observed in 180 min using 0.75 g/L catalyst dosage under sunlight irradiation. According to the findings, the synthesized catalyst had outstanding photocatalytic properties and can be used to cleanse textile wastewater under direct sunlight.     

Preparation and pore-forming mechanism of MgO–Al2O3–CaO-based porous ceramics using phosphorus tailings

A simple strategy for preparing MgO–Al₂O₃–CaO-based porous ceramics (MACPC) with high strength and ultralow thermal conductivity has been proposed in this work based on the raw material of phosphorus tailings. The effects of phosphorus tailings content, carbon black addition and heat treatment temperature on the properties of MACPC were studied, and their pore-forming mechanism during sintering was revealed. The results showed that the main phase composition of MACPC was magnesia alumina spinel and calcium aluminate after sintering at 1225 °C. Furthermore, the MACPC exhibited excellent comprehensive properties when 60 wt% phosphorus tailings and 40 wt% alumina were added, whose apparent porosity was 62.8%, cold compressive strength was 14.8 MPa, and the thermal conductivity was 0.106 W/(m·K) at 800 °C. The synchronously enhanced strength and thermal insulation properties of MACPC were related to the formation of uniformly distributed micropores (<2 μm) and passages in the matrix, which originated from the decomposition of phosphorus tailings and the burnt out of carbon black during the sintering process. The preparation of MACPC with high temperature resistance and excellent mechanical and thermal insulation properties with the raw material of phosphorus tailings provided an effective method for the high-value utilization of phosphorus tailings.     

Preparation of AlN–Al2O3 composites exhibiting antibacterial and water purification properties

This study aimed to develop new antibacterial and water purification materials without heavy metal contamination. Herein, AlN–Al₂O₃ composites were prepared by changing the content of AlN in raw material. The results showed that AlN, Al₂O₃, aluminum oxynitride, and yttrium aluminum garnet phases were generated by adjusting the AlN: Al₂O₃ ratio. The difference in the ability of AlN and aluminum oxynitride to release substances such as ammonium ions and aluminum hydroxide when reacting with water resulted in remarkably different pH values of the sample immersion solution, which led to an increase in the material antibacterial efficiency with the addition of AlN. Similar results were also obtained with zinc ion absorption. Therefore, AlN–Al₂O₃ composite ceramics can potentially be used as novel antibacterial and water purification materials without heavy metal contamination through the release of ammonium ions for conferring antibacterial effects and of aluminum hydroxide for absorbing heavy metals and suspended impurities.     

Preparation and properties of porous SiC–Al2O3 ceramics using coal ash

In this paper, we first reported that porous SiC–Al₂O₃ ceramics were prepared from solid waste coal ash, activated carbon, and commercial SiC powder by a carbothermal reduction reaction (CRR) method under Ar atmosphere. The effects of addition amounts of SiC (0, 10, 15, and 20 wt%) on the postsintering properties of as-prepared porous SiC–Al₂O₃ ceramics, such as phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal shock resistance, and thermal diffusivity have been investigated. It was found that the final products are β-SiC and α-Al₂O₃. Meanwhile, the SEM shows the pores distribute uniformly and the body gradually contacts closely in the porous SiC–Al₂O₃ ceramics. The properties of as-prepared porous SiC–Al₂O₃ ceramics were found to be remarkably improved by adding proper amounts of SiC (10, 15, and 20 wt%). However, further increasing the amount of SiC leads to a decrease in thermal shock resistance and mechanical properties. Porous SiC–Al₂O₃ ceramics doped with 10 wt% SiC and sintered at 1600°C for 5 hours with the median pore diameter of 4.24 μm, room-temperature compressive strength of 21.70 MPa, apparent porosity of 48%, and thermal diffusivity of 0.0194 cm²/s were successfully obtained.     

Composite soft template-assisted construction of a flower-like β-Bi2O3/Bi2O2CO3 heterojunction photocatalyst for the enhanced simulated sunlight photocatalytic degradation of tetracycline

A three-dimensional (3D) flower-like β-Bi₂O₃/Bi₂O₂CO₃ heterojunction photocatalyst was synthesized via decomposition of the precursor fabricated using a composite soft template, which was constructed from dl-aspartic acid and nonionic amphiphilic triblock copolymer (Pluronic F127). The morphology, phase structure, composition, effect of reactant concentration, and possible formation mechanism were systematically studied. The results showed that dl-aspartic acid was chosen as the coordination- and structure-directing agent, while F127 was used as the capping agent during preparation of the precursor. The as-prepared flower-like β-Bi₂O₃/Bi₂O₂CO₃ heterojunction obtained after calcination of the self-sacrificing precursor at 290 °C showed excellent photocatalytic performance in the degradation of the refractory colorless antibiotic agent tetracycline (TC) under simulated sunlight irradiation, with 98.79% TC degradation being achieved within 60 min of irradiation. This excellent photocatalytic performance was attributed to the narrow band gap, heterojunction structure, and 3D hierarchical structure. The results further revealed that photogenerated holes (h⁺) and hydroxyl radicals (^•OH) dominated the photocatalytic process. Furthermore, the β-Bi₂O₃/Bi₂O₂CO₃ heterojunction catalyst was not photocorroded after six consecutive cycles, suggesting an excellent photostability.     

Synthesis and characterization of α/β-Bi2O3 with enhanced photocatalytic activity for 17α-ethynylestradiol

The α/β-Bi₂O₃ photocatalyst was successfully synthesized by a novel solvothermal-calcination method. The physical and chemical properties of as-prepared samples were characterized based on XRD, XPS, SEM, TEM, EDS, BET, UV–vis DRS and PL techniques. The synthesized α/β-Bi₂O₃ photocatalyst exhibited enhanced photocatalytic activity for 17α-ethinylestradiol (EE2), and 96.9% of EE2 was degraded after only 24 min of visible-light irradiation using α/β-Bi₂O₃ as photocatalyst. The reaction rate constant over α/β-Bi₂O₃ photocatalyst was 1.42, 2.23, 9.22 and 54.1 times higher than pure β-Bi₂O₃, α-Bi₂O₃+β-Bi₂O₃, α-Bi₂O₃ and P25 respectively. Effect of catalyst dosage and pH value was investigated. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. α/β-Bi₂O₃ was a fairly stable and efficient photocatalyst under the studied experimental conditions, proving that the α/β-Bi₂O₃ photocatalyst was a promising photocatalyst for the practical application.     

Preparation and photocatalytic properties of a novel kind of loaded photocatalyst of TiO2/SiO2/γ‐Fe2O3

A novel kind of loaded photocatalyst of TiO₂/SiO₂/γ‐Fe₂O₃ (TSF) that can photodegrade effectively organic pollutants in the dispersion system and can be recycled easily by a magnetic field is reported in this paper. The γ‐Fe₂O₃ cores in TiO₂/γ‐Fe₂O₃ are found to reduce the activity of the TiO₂ photocatalyst in the photodegradation of dyes under either UV or visible light irradiation. Addition of a SiO₂ membrane between the γ‐Fe₂O₃ core and the TiO₂ shell weakens efficiently the influence of the γ‐Fe₂O₃ cores on the TiO₂ photocatalytic activity and leads to a highly active and magnetically separable photocatalyst on TSF. Comparison of the photodegradation processes of dyes under UV and visible irradiation is also carried out. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transparent CaF2 surface crystallized CaO–2B2O3 glass possessing efficient photocatalytic and antibacterial properties

This study aims to fabricate surface crystallized transparent calcium borate glass (CaO–2B₂O₃) for photocatalytic and antibacterial applications. The CaO–2B₂O₃ glass was fabricated by using the conventional melt-quenching technique. Instead of using traditional high temperature and longer soaking time heat-treatment, the acid etching method was adopted to get surface crystallization. Surface etching of as-quenched glass was performed at room temperature by using three different concentrations of hydrogen fluoride in order to attain the different amount of calcium fluoride crystals at the surface. The characterization of surface crystallized glass was performed with an X-ray diffraction pattern and scanning electron microscope-EDS mapping system. Sufficient transparency (65%) was retained even at highest crystallization of glass surface. Surface crystallization with CaF₂ induces hydrophilicity and photocatalytic character in glasses which was evaluated with contact angle measurements and smart resazurin (Rz) ink test. Around 68% of methylene blue (MB) dye degradation was also displayed by the crystallized glass. Crystallized glasses portrayed good antibacterial property against Escherichia coli (gram-negative bacteria). Ninety-nine per cent of bacterial depletion was recorded in 3 hours exposure time with surface crystallized glass without any external intervention. Interesting morphological changes were observed in bacterial shape and physical appearance under field emission scanning electron microscope after exposure to crystallized glasses.     

Synthesis of β-Bi2O3 nanoparticles via the oxidation of Bi nanoparticles: Size,shape and polymorph control,anisotropic thermal expansion,and visible-light photocatalytic activity

Bismuth trioxide (Bi₂O₃) is known for its simple composition but rich polymorphism that allows a number of phase-dependent physicochemical properties and technical applications. We here report our controllable synthesis of highly discrete β-Bi₂O₃ (tetragonal) nanoparticles (NPs) via the thermal oxidation of nearly-monodisperse Bi NPs. The size and shape (spherical and tear- or rod-like) of β-Bi₂O₃ NPs are tunable by the size of parent Bi NPs whereas β and α (monoclinic) polymorphs can be selectively achieved by tailoring the oxidation temperature. The phase stability of β polymorph from room temperature to 450 °C enables us to perform an in situ high-temperature XRD study on the temperature dependence of its lattice parameters, which reveals a marked thermal expansion anisotropy in β-Bi₂O₃ with a linear thermal expansion coefficient of +35.1 × 10^?6 °C^?1 in the c axis, fifteen times higher than that in the a axis. Meanwhile, the narrow band gap (2.27 eV for β vs. 2.77 eV for α) and strong visible-light absorption endow β-Bi₂O₃ NPs with a good photocatalytic activity for the visible-light Rhodamine B dye degradation. We expect that our work could be a valuable reference for the studies on the size, shape and polymorph control, thermal property, and photocatalytic application of Bi₂O₃.     

Preparation of magnetic α-Fe2O3/ZnFe2O4@Ti3C2 MXene with excellent photocatalytic performance

The high conductivity Ti₃C₂ MXene with the unique lamellar nanostructure can effectively improve photoelectrocatalytic ability of composite as cocatalyst. In this paper, the magnetic α-Fe₂O₃/ZnFe₂O₄ heterojunctions were obtained using one-step hydrothermal synthesis. And α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene photocatalyst can be easily obtained by ultrasonic assisted self-assembly approach for dispersing magnetic α-Fe₂O₃/ZnFe₂O₄ heterojunctions on Ti₃C₂ MXene surface. Due to the improving photoelectron ability, the α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene was found to exhibit the higher photocatalytic ability than the α-Fe₂O₃/ZnFe₂O₄ heterojunctions in eliminating Rhodamine B (RhB) pollutant and toxic Cr(Ⅵ) in water. Even more important, as a magnetic composite, the 10 wt% α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene photocatalyst exhibited the excellent reusability. The terrific photocatalytic ability is due to the numerous heterostructure interfaces, the increase of visible light harvesting and high conductivity.     

Design and fabrication of photocatalytic coatings with α/β-Bi2O3 and recycled-fly ash for environmental remediation and solar fuel generation

To promote a circular economy, alkali-activated recycled fly ash (AAFA) can be used as an alternative binder for fabricating mortar coatings. The AAFA binder can also be functionalized with photocatalysts for application in environmental remediation. Here, α/β-Bi₂O₃ homojunction photocatalysts were incorporated into AAFA mortar coatings to confer photocatalytic properties for two applications, namely, self-cleaning and solar fuel generation from CO₂ photoconversion. The α/β-Bi₂O₃ homojunctions were prepared using three methods. The homojunctions had a higher proportion of the β-Bi₂O₃ phase compared to α-Bi₂O₃; additionally, they exhibited with a 2D morphology and a bandgap suitable for visible-light activation. X-ray diffraction and energy dispersive spectroscopy analysis of the mortar coatings showed that the inorganic matrix comprised two frameworks based on calcium silicate hydrate and aluminosilicate hydrate, with high porosity. The photocatalytic mortar coatings exhibited self-cleaning activity, with the highest efficiency of 31%. This result was corroborated by total organic carbon analysis, which showed ~15% mineralization. The specimens also showed high activity for CO₂ photoconversion to solar fuels such as formic acid (1932 μmol/g) and methanol (6 μmol/g) under visible light. These results were related to the synergistic effect of the mesoporous framework developed after alkaline activation, more efficient charge transfer in the homojunctions, enhanced CO₂ affinity, and the presence of CaO, MgO, Na₂O, and SiO₂ in the binder. The efficiencies for both applications are comparable to those reported previously. The present approach is potentially applicable not only for minimizing the environmental impact of waste materials by reducing the disposal of fly ash in landfills, but also for producing value-added compounds and reducing the maintenance cost of buildings.     

Construction of a novel Ca2Bi2O5/α-Bi2O3 semiconductor heterojunction for enhanced visible photocatalytic application

Bi³⁺-containing compounds have been intensively investigated for their potential application as photocatalysts for degrading pollutants and splitting water. In this work, a Ca₂Bi₂O₅/α-Bi₂O₃ heterojunction photocatalyst was successfully prepared via the facile sol–gel method. The excess of the initial Bi raw material can result in the Ca₂Bi₂O₅/α-Bi₂O₃ heterojunction of the final products. The as-synthesized nanoparticles were investigated via X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy-dispersive spectrometry, UV–Vis optical absorption, and X-ray photoelectron spectroscopy. The band energy of the Ca₂Bi₂O₅ substrate semiconductor was 2.49 eV and characterized with a direct transition nature. The photocatalytic effect on the photodegradation of Rhodamine B solutions was evaluated. Ca₂Bi₂O₅/α-Bi₂O₃ heterojunctions showed improved photocatalytic abilities compared with single Ca₂Bi₂O₅ and α-Bi₂O₃ under viable light irradiation. The mechanism was discussed in terms of the microstructure, luminescence intensities, and decay curves (lifetimes). The photo-produced electrons and holes can be adequately separated in Ca₂Bi₂O₅/α-Bi₂O₃ heterojunctions ensuring its photocatalytic activities. The present results can serve as reference for investigating the optical properties of Bi semiconductors.     

Preparation and characterization of mesoporous γ-Al2O3 membranes

以粒径为0.3～0.4 μm的α-Al₂O₃为原料,通过悬浮液真空抽吸法,制备出平均孔径约为70 nm的完整无缺陷的片状α-Al₂O₃支撑体;以仲丁醇铝为前驱体,采用颗粒溶胶路线制备出稳定的Boehmite溶胶,以此溶胶采用浸浆法,在制备的α-Al₂O₃支撑体上制备出完整无缺陷的γ-Al₂O₃中孔膜,并考察了烧成温度对γ-Al₂O₃中孔膜性能的影响。结果表明,本文制备出的γ-Al₂ O₃膜的孔径约为3 nm,对PEG的截留分子量为2800～5300,纯水渗透通量为11.5～25.9 L.m^-2.h^-1［7.6×10⁵ Pa,（14±1）℃］。说明在孔径为70 nm左右的载体上直接制备孔径为3 nm的完整的中孔膜是可行的。     

Preparation and characterization of MnOOH and β-MnO2 whiskers

MnOOH and β-MnO₂ whiskers are obtained for the first time in our work. MnOOH whiskers are chemically synthesized in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The product is obtained under extremely low surfactant concentrations under basic conditions, using MnSO₄·H₂O as the manganese source and ethylamine as the alkali source. After the subsequent heat treatment of MnOOH at 300 °C for 1 h, β-MnO₂ whiskers retaining the similar morphologies are obtained. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry analysis (TGA) are used to characterize the products.     

Understanding δ-Bi2O3 fluorite degradation mechanism and related solutions for promising applications in distributed multigeneration

Oxygen selective membrane on the base of cermet δ-Bi₂O₃/Ag with an interpenetrating structure has the maximum potential efficiency of air separation. However, the degradation processes, including the phase degradation of fluorite δ-Bi₂O₃, do not make it possible to create a membrane with the required perfection and durability. In this work, the ordering of oxygen vacancies with the transformation of fluorite into the rhombohedral phase (S.G. R-3) was studied by powder HT XRD in situ at 600 °C on dense Bi_0.78Er_0.2Hf_0.02O_1.51 ceramics. Fast regeneration of disordered fluorite occurs at T = 640–700 °C. The phase degradation of fluorite due to the segregation of dopants at the second stage leads into stable phases - sillenite, tetragonal or rhombohedral phase (S.G. R-3m), depending on the composition of δ-Bi₂O₃. Fast regeneration of fluorite occurs when heated to 820 °C, which is unacceptable for membranes. Analysis of all available data allows us to propose approaches to optimize the composition of δ-Bi₂O₃ and technical solutions for creating durable oxygen selective membranes with promising use in distributed multigeneration. As a result of the analysis, a new solid electrolyte with better parameters was obtained.     

Y2O3-Bi2O3可见光催化降解甲基橙

采用固相合成法制备了Y<,2>O<,3>-Bi<,2>O<,3>复合可见光催化剂,用XRD、DRS对复合催化剂进行了表征.以甲基橙为模拟废水,在日光色镝灯光照下,研究了废水浓度、催化剂投加量、温度、pH等对Y<,2>O<,3>-Bi<,2>O<,3>光催化活性的影响.实验结果表明:在甲基橙质量浓度为20 mg/L、Y<...     

Characteristics of porous mullite developed from clay and AlF3·3H2O

Porous mullite with interlocked needle shape microstructure was developed from China clay and aluminium fluoride trihydrate (AlF₃·3H₂O). The effects of various parameters like sintering temperature, sintering time and the amount of AlF₃·3H₂O on the phase evolution, microstructure and porosity have been studied. Quantitative analysis of mullite was carried out using X-ray diffraction combined with Rietveld-RIR method (Internal standard method). Porous mullite ceramics with 62% open porosity have been prepared at a relatively lower temperature of 1400?°C. The results show that the nucleation of mullite can be achieved from 700?°C onwards using hydrated aluminium fluoride without the formation of intermediate topaz crystals. The high amount of water vapour produced within the system during the in-situ reaction has a crucial role in deciding the reaction mechanism.     

Attenuation properties of epoxy-Ta2O5 and epoxy-Ta2O5-Bi2O3 composites at γ-ray energies 59.54 and 662 keV

Epoxy resin filled with suitable high Z elements can be a potential shield for X-rays and γ-rays. In this work, we present the γ-ray attenuation properties of epoxy composites filled with (0–30 wt%) Tantalum pentoxide (Ta₂O₅) and Ta₂O₅-Bi₂O_3, which were prepared by open mold cast technique. X-ray diffraction patterns showed crystalline peaks of Ta₂O₅ and bismuth oxide (Bi₂O₃) in the prepared epoxy-Ta₂O₅ and epoxy-Ta₂O₅-Bi₂O₃ composites. Homogeneity of the samples at higher filler wt% was revealed by SEM images. Mechanical characterization showed the enhanced mechanical strength of epoxy-Ta₂O₅-Bi₂O₃ composites compared to epoxy-Ta₂O₅. Higher storage modulus and glass transition temperature of the epoxy-Ta₂O₅-Bi₂O₃ composites showed enhanced stiffness and thermal stability when compared to neat and epoxy-Ta₂O₅. Decrease in the value of tan(δ) at higher content of filler loadings indicated the good adhesion between filler and matrix. Mass attenuation coefficients of epoxy-Ta₂O₅ (30 wt%) composites at γ-ray energies 59.54 and 662 keV were found to be 0.876 cm² g^–1 and 0.084 cm² g^–1, while that of epoxy-Ta₂O₅-Bi₂O₃ (30 wt% Bi₂O₃) composite were 1.271 cm² g^–1 and 0.088 cm² g^–1, respectively. The epoxy-5% Ta₂O₅-30% Bi₂O₃ composites with higher μ/ρ value and tensile strength may be a potential γ-ray shield in various radiation environments.     

Free growth of one-dimensional β-Ga2O3 nanostructures including nanowires,nanobelts and nanosheets using a thermal evaporation method

Large-scale β-Ga₂O₃ nanostructures (nanowires-NWs, nanobelts-NBs and nanosheets-NSs) were synthesized via thermal evaporation of GaN powder in an ambient argon atmosphere. The effect of the substrate type (Si, AlN-thin film/Si and ZnO-thin film/Si) on the growth of β-Ga₂O₃ nanostructures was investigated. The morphology changes from NWs to NBs or NSs when the substrate changes from Si to AlN-thin film/Si or ZnO-thin film/Si, respectively. The size and dimensionality were the most influential parameters on the structure of the as-grown β-Ga₂O₃. The as-grown nanostructures crystallize within the monoclinic crystal structure of the β-Ga₂O₃ phase. The obtained nanostructures show intense blue-red emission characterized by a broadband photoluminescence spectrum with peaks located at 430, 500–525 and 688–700 nm. These emissions originate from the defect-related donor-acceptor pair recombination mechanism and depend on the nanostructure dimensionality and morphology. A vapor-solid growth mechanism for the growth of various β-Ga₂O₃ nanostructures was also proposed.     

Preparation of Ag-Al₂O₃ nano structures by combustion method and investigation of photocatalytic activity

In this research, Ag-Al₂O₃ nanostructures have been prepared via combustion synthesis and ammonium acetate and urea have been applied as fuels. The prepared Ag-Al₂O₃ nanostructures were characterized by DTA, XRD, SEM, TEM, and BET spectroscopy. The effect of different ratios of silver to alumina and fuel percentage on morphology and particle size of prepared products were investigated. The results showed that using ammonium acetate fuel led to the production of Ag-γ-Al₂O₃ nanocompounds, while using urea produced Ag-α-Al₂O₃. Also, the photocatalytic activity of Ag-Al₂O₃ nanostructures for Congo red degradation was evaluated by UV-Vis diffuse reflectance spectroscopy. The photocatalytic activity of Ag-Al₂O₃ was examined under UV-Vis irradiation and showed significant photocatalytic efficiency.