In situ etching WO3 nanoplates: Hydrothermal synthesis, photoluminescence and gas sensor properties

A novel hydrothermal process using p-nitrobenzoic acid as structure-directing agent has been employed to synthesize plate-shaped WO₃ nanostructures containing holes. The p-nitrobenzoic acid plays a critical role in the synthesis of such novel WO₃ nanoplates. The morphology, structure and optical property of the WO₃ nanoplates have been characterized by transmission electron microcopy (TEM), scanning electron microcopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL). The lateral size of the nanoplates is 500-1000 nm, and the thickness is about 80 nm. The formation mechanism of WO₃ nanoplates is discussed briefly. The gas sensitivity of WO₃ nanoplates was studied to ethanol and acetone at different operation temperatures and concentrations. Furthermore, the WO₃ nanoplate-based gas sensor exhibits high sensitivity for ethanol and acetone as well as quick response and recovery time at low temperature.     

Solvothermal preparation of Bi2WO6 nanocrystals with improved visible light photocatalytic activity

Bismuth tungstate (Bi₂WO₆) nanocrystals with the average size of ca. 12 nm had been successfully synthesized by a simple solvothermal method at 180 °C for 2 h. The as-synthesized Bi₂WO₆ nanocrystals were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectra, and N₂ adsorption–desorption measurements. The visible-light-driven photocatalytic activity of the sample was evaluated by photo-degradation of rhodamine-B (RhB) at room temperature, which is much higher than that of the hydrothermal synthesized Bi₂WO₆ square plates and the commercially available TiO₂ (P-25). We believed that the high photocatalytic activity could be ascribed to the intrinsically small grain size and high surface-to-volume ratio associated with the Bi₂WO₆ nanocrystals.     

Synthesis, characterization and photocatalytic properties of nanosized Bi2WO6, PbWO4 and ZnWO4 catalysts

Nanosized Bi₂WO₆, PbWO₄ and ZnWO₄ photocatalysts were synthesized by a mild hydrothermal crystallization process. The physical and photophysical properties of the catalysts were characterized by X-ray diffractometry, Brunauer-Emmet-Teller surface area and porosity measurements, transmission electron microscopy, Raman spectra, and diffused reflectance spectroscopy. The rhodamine-B photodegradation in aqueous medium was employed as a probe reaction to test the photoactivities of the as-prepared samples under four irradiation wavelengths. Bi₂WO₆ not only presented the photocatalytic activity in the wide spectral scope, including UV and visible light but also exhibited the strong photosensitized capability to transform RhB under visible light irradiation (λ > 490 nm). ZnWO₄ only displayed relatively high photoactivity under UV irradiation. However, PbWO₄ showed poor photoactivity under any light irradiation. On the basis of the calculated density functional theory (DFT), the photocatalytic mechanisms were discussed.     

Urchin-like Co2P nanocrystals: Synthesis, characterization, influencing factors and photocatalytic degradation property

In this paper, cobalt phosphides (Co₂P) nanocrystals with urchin-like structures have been successfully synthesized via a water-ethanol mixed-solvothermal route, employing white phosphorus (WP) and cobalt dichloride as starting reactants, sodium acetate as the pH adjustor, and sodium dodecyl benzene sulfonate (SDBS) as the surfactant. The as-obtained product was characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS), (high resolution) transmission electron microscopy (TEM/HRTEM), selected area electron diffraction (SAED) and field emission scanning electron microscopy (FESEM). It was found that sodium acetate played an important role in the formation of Co₂P nanocrystals with urchin-like structures. Some factors influencing the morphology of the product, including the reaction temperature, time, amounts of WP and SDBS and so on, were investigated. The photocatalytic property of the product for the degradation of organic dyes was studied. A possible formation mechanism of urchin-like Co₂P nanocrystals was suggested based on the experiment results.     

Solvent directed fabrication of Bi2WO6 nanostructures with different morphologies: Synthesis and their shape-dependent photocatalytic properties

In this work, Bi₂WO₆ with complex morphologies, namely, flower-like, pancake-like, and tubular shapes have been controllably synthesized by a facile solvothermal process. The as-obtained samples are systematically investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). The effects of solvents on the morphologies of Bi₂WO₆ nanostructures are systematically investigated. According to the time-dependent experiments, a two-step growth mode basing on Ostwald ripening process and self-assembly has been proposed for the formation of the flower-like and pancake-like Bi₂WO₆ nanostructures. The photocatalytic properties of Bi₂WO₆ nanostructures are strongly dependent on their shapes, sizes, and structures for the degradation of rhodamine B (RhB) under visible-light irradiation. The deduced reasons for the differences in the photocatalytic activities of these Bi₂WO₆ nanostructures are further discussed.     

Nickel titanate microtubes constructed by nearly spherical nanoparticles: Preparation, characterization and properties

In this paper, we report the successful synthesis of NiTiO₃ microtubes constructed by nearly spherical nanoparticles via a simple solution-combusting method employing a mixture of ethanol and ethyleneglycol (V/V = 60/40) as the solvent, nickel acetate as the nickel source, tetra-n-butyl titanate as the titanium source and oxygen gas in the atmosphere as the oxygen source. The as-obtained product was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDS). The UV-vis absorption spectrum of the product showed two absorption peaks centered at 258.6 and 350.1 nm, respectively. The Brunauer-Emmett-Teller (BET) surface area of the product was 14.06 m²/g and the pore size distribution mainly located from 20 to 30 nm. The photocatalytic degradation property of the product for organic dyes showed that the as-obtained porous NiTiO₃ microtubes could strongly promote the degradation of organic dyes including Pyronine B, Safranine T and Fluorescein.     

Nest-like structures of Sr doped Bi2WO6: Synthesis and enhanced photocatalytic properties

A series of Sr-doped Bi₂WO₆ with three-dimensional (3D) nest-like structures were synthesized through simple hydrothermal route and characterized by XRD, FESEM, TEM, XPS, UV-vis DRS, etc. Morphology observation revealed that the as-synthesized Bi₂WO₆ were self-assembled three-dimensional (3D) nest-like structures, which were constructed from nanoplates. UV-vis diffuse reflectance spectra indicated that the samples had absorption in both UV and visible light areas. Their photocatalytic activities were evaluated by photodegradation of rhodamine B (RhB) under UV and visible light irradiation (λ > 420 nm). The photocatalytic properties were enhanced after Sr doping. Samples subsequently thermal treated at 500 °C showed higher photocatalytic activities. The reasons for the differences in the photocatalytic activities of these nest-like Bi₂WO₆ microstructures were further investigated.     

Synthesis and photocatalytic performance of novel CdS quantum dots sensitized Bi2WO6 photocatalysts

Novel quantum dots sensitized CdS-Bi₂WO₆ composite photocatalysts were synthesized to improve the visible-light-driven photocatalytic performance. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) UV-vis diffuse reflectance spectra (DRS). The photocatalytic activities of QDs sensitized CdS-Bi₂WO₆ samples were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 420 nm). The DRS results revealed that CdS-Bi₂WO₆ samples have a red shift and stronger absorption in the visible light region. After being sensitized by quantum dots CdS, the Bi₂WO₆ samples showed the high efficiency for the degradation of methyl orange. This study may provide an approach to treatment of organic pollutants by using visible light.     

Photocatalytic activities of Mo-doped Bi2WO6 three-dimensional hierarchical microspheres

The Mo-doped Bi₂WO₆ three-dimensional (3D) hierarchical microspheres from nanoplates have been synthesized by a hydrothermal route. The products were characterized in detail by multiform techniques: X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The results of the photocatalytic degradation of Rhodamine-B (RhB) in aqueous solution showed that molybdenum ions doping greatly improved the photocatalytic efficiency of Bi₂WO₆ 3D hierarchical microspheres. The Mo-doped Bi₂WO₆ microspheres with atomic ratio of Mo-W of 0.05 had the best activity in photodegradation of RhB in aqueous solution under 500 W Xe lamp light irradiation.     

Hierarchical BiOI and hollow Bi2WO6 microspheres: Topochemical conversion and photocatalytic activities

We present here a facile one-pot surfactant-free solvothermal route to synthesize hierarchical BiOI microspheres assembled from nanosheets at 120 °C for 16 h. The as-synthesized BiOI microspheres could be topochemically converted into hollow hierarchical Bi₂WO₆ ones built by nanoplates for the first time under hydrothermal condition because of the analogies of crystal structures. The transformation process of hierarchical BiOI microspheres to hollow Bi₂WO₆ ones was surveyed through XRD analyses and FE-SEM observations of the intermediates at different reaction stages. Rhodamine B (RhB) was selected as pollutant model and visible-light-driven photocatalytic activities of hierarchical BiOI and Bi₂WO₆ microspheres under the same measurement conditions were comparatively studied. As a result, the photocatalytic activities of BiOI obviously outshone Bi₂WO₆. The present study not only develops a new method for fabricating hierarchical architectures but also provides some useful information on relative visible-light-responding photocatalytic activity of hierarchical BiOI and Bi₂WO₆ microspheres.     

The enhanced visible light photocatalytic activity of nanosheet-like Bi2WO6 obtained by acid treatment for the degradation of rhodamine B

Bi₂WO₆ samples were fabricated by chemical solution decomposition (CSD) method and nanosheet-like Bi₂WO₆ samples could be obtained by concentrated nitric acid treatment at 70 °C for 20 min. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and UV-vis diffuse reflectance spectra. Photocatalytic activities of the samples were evaluated by the degradation of rhodamine B (RhB) under visible light irradiation. The temperature of acid treatment obviously influenced morphology and the visible light photocatalytic activity of the Bi₂WO₆ samples. The nanosheet-like Bi₂WO₆ photocatalysts obtained by acid treatment exhibited the highest photocatalytic activity under visible light irradiation.     

Facile fabrication of flower-shaped Bi2WO6 superstructures and visible-light-driven photocatalytic performance

Flower-shaped porous Bi₂WO₆ superstructures assembled from squared nanoplates have been successfully fabricated by a facile hydrothermal method without any surfactants or additives. Parameter-dependent experiments show that the initial strong acidic condition of the hydrothermal precursor is essential for the construction of tiny nanoplates into hierarchical Bi₂WO₆ flowers. The sample exhibits improved visible-light-driven photocatalytic activity in the degradation of Rhodamine-B, compared with Bi₂WO₆ multilayered disks, isolated platelets prepared at elevated pH values and bulk Bi₂WO₆ obtained by solid state method, respectively. It is believed that the higher BET surface area and nano/mesopore structure can afford more reactive sites and abundant transport paths for the degradation reaction. Moreover, the sample shows excellent circulation stability, suggesting its potential application in dealing with enviromental pollutions.     

Bi2WO6 with significantly enhanced photocatalytic activities by nitrogen doping

The nitrogen-doped Bi₂WO₆ were synthesized via a facile hydrothermal process. Systematic analysis of the photocatalytic activities of N-doped Bi₂WO₆ photocatalysts with a wide range of doping levels was carried out. The effects of nitrogen doping on the crystal structure, optical properties, and photocatalytic activities of the Bi₂WO₆ catalyst were investigated. The results showed that the doped samples exhibit 2–3 times higher photocatalytic activities than the undoped one, which was strongly dependent on the N-doping level. Close investigation revealed that doping Bi₂WO₆ with N could not only broaden the range of light adsorption in the visible region, but also inhibit the photogenerated electron–hole recombination losses and increased the transfer rate, which might be ascribed to the significantly enhanced photocatalytic activities.     

Preparation of grape-like Bi2O3/Ti photoanode and its visible light activity

Compact and grape-like bismuth oxide (Bi₂O₃) coated titania (Ti) anode was prepared by oxalic acid (H₂C₂O₄) etching, electrodeposition and calcination in order to explore its photoelectrocatalytic activities. The Bi₂O₃ coating was demonstrated to be full of pores, and a good combination between Bi₂O₃ layer and honeycomb-like Ti substrate was observed by scanning electron microscopy. The characteristic morphology of Bi₂O₃ coating indicated that the electrode is stable during degradation. The Bi₂O₃/Ti electrode was used in oxidative degradation of Acid Orange 7 by electrolysis, photocatalytic oxidation and photoelectrocatalytic oxidation processes. The pseudo-first order kinetics parameter (K_app) of photoelectrocatalytic process was 1.15 times of the sum of electrolysis and photocatalytic oxidation under visible light irradiation at 420 nm. The results indicated that the synergy of electrolysis and photocatalysis lead to an excellent photoelectrocatalytic property of the Bi₂O₃/Ti electrode.     

Synthesis of uniform WO3 square nanoplates via an organic acid-assisted hydrothermal process

Two kinds of tungsten oxide (WO₃) square nanoplates have been prepared by a simple hydrothermal method using l(+)-tartaric acid or citric acid as assistant agents. The products are characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). XRD, SEM and TEM images of the products illustrate that WO₃ square nanostructures prepared in the presence of l(+)-tartaric acid have a hexagonal phase, length of ∼ 200 nm and thickness of ∼ 100 nm, while WO₃ nanostructures synthesized in the presence of citric acid have an orthorhombic phase, length of ∼ 500 nm and thickness of ∼ 100 nm. Selected area electron diffraction (SAED) suggests that both of the as-prepared WO₃ square nanoplates are single crystalline. The plausible growth mechanism for the formation of WO₃ square nanostructures is also proposed.     

Synthesis of hierarchical Ni11(HPO3)8(OH)6 superstructures based on nanorods through a soft hydrothermal route

In this paper, we reported the successful synthesis of hierarchical Ni₁₁(HPO₃)₈(OH)₆ superstructures based on nanorods via a facile hydrothermal route, employing NiCl₂·6H₂O and NaH₂PO₂·H₂O as the reactants in the presences of polyvinylpyrrolidone (PVP) and CH₃COONa·3H₂O. The reaction was carried out at 170 °C for 10 h. HPO₃²⁻ ions were provided via the dismutation reaction of H₂PO₂⁻ ions in a weak basic solution. The as-obtained products were characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS), field emission scanning electron microscopy (SEM), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). Some factors influencing the morphology of the hierarchical Ni₁₁(HPO₃)₈(OH)₆ nanorods, such as the reaction temperature, time, the amounts of PVP and CH₃COONa, and the initial concentration of Ni²⁺ ions, were systematically investigated. A possible growth mechanism was proposed based on experimental results.     

Characterization and photocatalytic activity of Bi3TiNbO9 nanocrystallines synthesized by sol-gel process

Nanocrystalline Bi₃TiNbO₉ powders were synthesized by a sol-gel process, based on a colloid solution of bismuth acetate, titanium butoxide and niobium ethoxide. X-ray diffraction analysis revealed that pure Aurivillius phase of Bi₃TiNbO₉ could be prepared at a calcination temperature of 500 °C. By using scanning electron microscopy and gas adsorption method, the morphology and the specific surface area of the powders were examined. The photophysical properties of Bi₃TiNbO₉ were investigated by means of the UV-visible diffuse reflectance spectrum, from which a band gap ∼3.2 eV was empirically calculated. The as-prepared Bi₃TiNbO₉ powders were applied in the photodegradation of organic contaminant for the first time, and they showed effective photocatalytic activity for the complete decomposition of methyl orange under UV light irradiation.     

La-doped ZnO nanoparticles: Simple solution-combusting preparation and applications in the wastewater treatment

La-doped ZnO nanoparticles have been successfully synthesized by a simple solution combustion method via employing a mixture of ethanol and ethyleneglycol (v/v = 60/40) as the solvent. Zinc acetate and oxygen gas in the atmosphere were used as zinc and oxygen sources, and La(NO₃)₃ as the doping reagent. The as-obtained product was characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. Experiments showed that La-doped ZnO nanoparticles exhibited the higher capacities for the removal of Pb²⁺ and Cu²⁺ ions in water resource than undoped ZnO nanoparticles.     

Synthesis of stable spherical platinum diphosphide, PtP2/carbon nanocomposite by reacting Pt(PPh3)4 at elevated temperature under autogenic pressure

The synthesis of microsized carbon spheres supporting the semiconductor platinum diphosphide, PtP₂, was conducted by the thermal decomposition of an organometallic precursor. This novel reaction was carried out using the reaction under autogenic pressure at elevated temperature (RAPET) method by dissociating Pt(PPh₃)₄ at 1000 °C. The product was characterized using methods of electron microscopy (scanning electron microscope (SEM), transmission electron microscope (TEM), selected area energy dispersive spectroscopy (SAEDS), elemental analyzer (EA) and energy dispersive X-ray analysis (EDX)) and powder-XRD. Transmission electron microscope images indicate that the particle size of the nanoparticles of PtP₂ coated on the carbon spheres is 50 nm.     

Electrochemical lithium insertion in the solid solution Bi2WO6-Sb2WO6 with Aurivillius framework

Following the structural evolution of the Aurivillius crystalline framework in the solid solution Bi₂WO₆-Sb₂WO₆ we have carried out an electrochemical lithium insertion study in this system. A slight loss of the specific capacity of the electrochemical cell was observed as amount of Sb was increased. In general, the different compositions within solid solution Bi_2−xSb_xWO₆ (0.25 ≤ x ≤ 0.75) exhibited a similar behaviour featured mainly by two semiconstant potential regions located at 1.7 and 0.8 V versus Li⁺/Li^o. The oxide Sb₂WO₆ with Autivillius structure but without Bi was tested as cathode too. The maximum amount of lithium inserted, 13.5 lithium atoms per formula, is the same amount inserted in its homologous bismuth oxide Bi₂WO₆.