Search Results (20)

The photocatalytic activity of Bi₂WO₆ Aurivillius phase has been widely exploited for the degradation of a wide range of gaseous and aqueous molecules, as well as microorganisms, under the influence of visible irradiation. Strategies for the development of doped and co-doped bismuth tungstate materials require the thermodynamic data on this phase. The heat capacity of bismuth tungstate, Bi₂WO₆, was investigated using a DSC microcalorimeter on polycrystalline powder samples in the temperature range from 313 to 1103 K (40–830 °C) in two separate runs. The samples were synthesized by solid-state reaction from pure binary oxides at 1033 K (760 °C) in a platinum crucible with cover. The high temperature C_p(T) data were fitted by the Maier–Kelley equation and, from this relation, the standard molar heat capacity of γ-Bi₂WO₆ polymorph was estimated to be at 298.15 K 176.8 ± 3.9 J·K⁻¹·mol⁻¹. A reversible second-order transition of Bi₂WO₆ phase was observed in the experimental temperature range, with a peak close to 940 K (667 °C). Additionally, the extrapolation of C_p(T) to 0 K was proposed using a method based on the multiple Einstein model. Thermodynamic properties (heat capacity C_p(T), entropy S°(T), enthalpy H°(T), Gibbs energy G°(T)) of crystalline γ-Bi₂WO₆ were calculated in the temperature range of 298.15–1123 K (25–850 °C). Full article

This review analyzes TiO₂-based coatings formed by the plasma electrolytic oxidation (PEO) process of titanium for the photocatalytic degradation of methyl orange (MO) under simulated solar irradiation conditions. PEO is recognized as a useful technique for creating oxide coatings on various metals, particularly titanium, to assist in the degradation of organic pollutants. TiO₂-based photocatalysts in the form of coatings are more practical than TiO₂-based photocatalysts in the form of powder because the photocatalyst does not need to be recycled and reused after wastewater degradation treatment, which is an expensive and time-consuming process. In addition, the main advantage of PEO in the synthesis of TiO₂-based photocatalysts is its short processing time (a few minutes), as it excludes the annealing step needed to convert the amorphous TiO₂ into a crystalline phase, a prerequisite for a possible photocatalytic application. Pure TiO₂ coatings formed by PEO have a low photocatalytic efficiency in the degradation of MO, which is due to the rapid recombination of the photo-generated electron/hole pairs. In this review, recent advances in the sensitization of TiO₂ with narrow band gap semiconductors (WO₃, SnO₂, CdS, Sb₂O₃, Bi₂O₃, and Al₂TiO₅), doping with rare earth ions (example Eu³⁺) and transition metals (Mn, Ni, Co, Fe) are summarized as an effective strategy to reduce the recombination of photo-generated electron/hole pairs and to improve the photocatalytic efficiency of TiO₂ coatings. Full article

Phase change materials (PCMs) offer promising solutions for efficient thermal management in electronic devices, energy storage systems, and renewable energy applications due to their capacity to store and release significant thermal energy during phase transitions. This study investigates the thermal and physical properties of Bi-In-Sn/WO₃ composites, specifically for their use as phase change thermal interface materials (PCM-TIMs). The Bi-In-Sn/WO₃ composite was synthesized through mechanochemical grinding, which enabled the uniform dispersion of WO₃ particles within the Bi-In-Sn alloy matrix. The addition of WO₃ particles markedly improved the composite’s thermal conductivity and transformed its physical form into a putty-like consistency, addressing leakage issues typically associated with pure Bi-In-Sn alloys. Microstructural analyses demonstrated the existence of a continuous interface between the liquid metal and WO₃ phases, with no gaps, ensuring structural stability. Thermal performance tests demonstrated that the Bi-In-Sn/WO₃ composite achieved improved thermal conductivity, and reduced volumetric latent heat, and there was a slight increase in thermal contact resistance with higher WO₃ content. These findings highlight the potential of Bi-In-Sn/WO₃ composites for utilization as advanced PCM-TIMs, offering enhanced heat dissipation, stability, and physical integrity for high-performance electronic and energy systems. Full article

Photocatalysis can reduce CO₂ to available energy by means of light energy, which is considered to be an effective solution to alleviate energy and environmental problems. In this paper, an MPS@Bi₂WO₆ composite photocatalyst was prepared by in situ hydrothermal method. BWO grew on the surface of MPS, which increased the CO₂ absorption capacity of the photocatalyst and improved the microstructure. Under the synergistic effect of the two aspects, BWS achieves the enhancement of light energy absorption capacity and can effectively excite electron-hole pairs. The transition electrons with high reduction ability migrate to the surface and contact with high concentrations of CO₂, achieving efficient CO₂ reduction under visible light. Among the photocatalysts in this paper, BWS-1 (BWO: MPS = 1:1) has efficient CO₂ gas phase reduction ability under visible light, and the CO yield reaches 29.51 μmol/g. The MPS@BWO photocatalyst is a low-cost and efficient CO₂ photoreduction catalyst with broad application prospects. Full article

Bismuth-based photocatalytic materials have been widely used in the field of photocatalysis in recent years due to their unique layered structure. However, single bismuth-based photocatalytic materials are greatly limited in their photocatalytic performance due to their poor response to visible light and easy recombination of photogenerated charges. At present, constructing semiconductor heterojunctions is an effective modification method that improves quantum efficiency by promoting the separation of photogenerated electrons and holes. In this study, the successful preparation of an In₂O₃/Bi₂WO₆ (In₂O₃/BWO) II-type semiconductor heterojunction composite material was achieved. XRD characterization was performed to conduct a phase analysis of the samples, SEM and TEM characterization for a morphology analysis of the samples, and DRS and XPS testing for optical property and elemental valence state analyses of the samples. In the II-type semiconductor junction system, photogenerated electrons (e⁻) on the In₂O₃ conduction band (CB) migrate to the BWO CB, while holes (h⁺) on the BWO valence band (VB) transfer to the In₂O₃ VB, promoting the separation of photoinduced charges, raising the quantum efficiency. When the molar ratio of In₂O₃/BWO is 2:6, the photocatalytic degradation degree of rhodamine B (RhB) is 59.4% (44.0% for BWO) after 60 min illumination, showing the best photocatalytic activity. After four cycles, the degradation degree of the sample was 54.3%, which is 91.4% of that of the first photocatalytic degradation experiment, indicating that the sample has good reusability. The XRD results of 2:6 In₂O₃/BWO before and after the cyclic experiments show that the positions and intensities of its diffraction peaks did not change significantly, indicating excellent structural stability. The active species experiment results imply that h⁺ is the primary species. Additionally, this study proposes a mechanism for the separation, migration, and photocatalysis of photoinduced charges in II-type semiconductor junctions. Full article

In this study, a chemical precipitation approach was adopted to produce a photocatalyst based on bismuth tungstate Bi₂WO₆ for enhanced and environmentally friendly organic pollutant degradation. Various tools such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), optical spectroscopy and X-ray photoelectron spectroscopy, were employed to assess the structural and morphological properties. Hence, the XRD profiles showed a well crystallized Bi₂WO₆ orthorhombic phase. The photocatalytic performance of the resulting photocatalyst was assessed by the decomposition of Rhodamine B (RhB) and methyl orange (MO) with a decomposition efficiency of 97 and 92%, along with the highest chemical oxygen demand of 82 and 79% during 120 min of illumination, respectively. The principal novelty of the present work is to focus on the changes in the crystalline structure, the morphology, and the optical and the photoelectrochemical characteristics of the Bi₂WO₆, by tuning the annealing temperature of the designed photocatalyst. Such physicochemical property changes in the as-prepared photocatalyst will affect in turn its photocatalytic activity toward the organic pollutant decomposition. The photocatalytic mechanism was elaborated based on electrochemical impedance spectroscopy, photocurrent analysis, photoluminescence spectroscopy, and radical trapping measurements. The overall data indicate that the superoxide O₂^•− and holes h⁺ are the principal species responsible for the pollutant photodegradation. Full article

In this work, a surface dispersed heterojunction of BiVO₄-nanoparticle@WO₃-nanoflake was successfully prepared by hydrothermal combined with solvothermal method. We optimized the morphology of the WO₃ nanoflakes and BiVO₄ nanoparticles by controlling the synthesis conditions to get the uniform BiVO₄ loaded on the surface of WO₃ arrays. The phase composition and morphology evolution with different reaction precursors were investigated in detail. When used as photoanodes, the WO₃/BiVO₄ composite exhibits superior activity with photocurrent at 3.53 mA cm⁻² for photoelectrochemical (PEC) water oxidation, which is twice that of pure WO₃ photoanode. The superior surface dispersion structure of the BiVO₄-nanoparticle@WO₃-nanoflake heterojunction ensures a large effective heterojunction area and relieves the interfacial hole accumulation at the same time, which contributes to the improved photocurrents together with the stability of the WO₃/BiVO₄ photoanodes. Full article

Multicomponent flux systems based on both Li₂WO₄-B₂O₃-Li₂O-CuO-Cr₂O₃ and Bi₂O₃-MoO₃-B₂O₃-Na₂O-CuO-Cr₂O₃ were studied in order to grow Cu₂CrBO₅ crystals. The conditions for Cu₂CrBO₅ crystallization were investigated by varyingthe component ratios, and the peculiarities of their interaction were characterized by studying the formation sequence of high-temperature crystallizing phases. Special attention was paid to the problem of Cr₂O₃ solubility. Phase boundaries between CuCrO₂, Cu₂CrO₄, and Cu₂CrBO₅ were considered. The crystal structure of the obtained samples was studied viasingle crystal and powder X-ray diffraction. The chemical composition of the grown crystals was examined using the EDX technique. Anactual ratio of Cu:Cr = 1.89:1.11 was found for Cu₂CrBO₅ grown from the lithium-tungstate system, which showed a small deviation from 2:1, implying the presence of a part of bivalent Cr²⁺ in the samples. Anomalies in the thermal dependence of magnetization were analyzed and compared with the previously obtained data for Cu₂CrBO₅. The anomaly at T_C ≈ 42 K and the antiferromagnetic phase transition at T_N ≈ 119 K were considered. Polarized Raman spectra of Cu₂CrBO₅ were obtained for the first time, and a comparative analysis of the obtained data with other monoclinic and orthorhombic ludwigites is presented. Along with the polarized room temperature spectra, the thermal evolution of Raman modes near the antiferromagnetic phase transition temperature T_N ≈ 119 K is provided. The influence of the magnetic phase transition on the Raman spectra of Cu₂CrBO₅ is discussed. Full article

The phase formation processes in 0.25ZnO–0.25Al₂O₃–0.25WO₃–0.25Bi₂O₃ ceramics with variation in the thermal annealing temperature were evaluated in this study. According to the obtained data on the phase composition dependent on the annealing temperature, the phase transformation dynamics, which can be written in the form of ZnO/Bi₂O₃/WO₃/Al₂O₃ → ZnBi₃₈O₆₀/ZnO/Bi₂WO₆/WO₃ → Bi₂Al₄O₉/ZnBi₃₈O₆₀/Bi₂WO₆/ZnO/WO₃ → ZnWO₄/Bi₂WO₆/ZnAl₂O₄/ZnO → ZnWO₄/Bi₂WO₆/ZnAl₂O₄ → Bi₂WO₆/ZnWO₄/ZnAl₂O₄ → ZnAl₂O₄/Bi₂WO₆/Bi₂W₂O₉, were established. It has been found that the formation of phases of complex oxides of the ZnWO₄, Bi₂WO₆ and Bi₂W₂O₉ types in the composition of ceramics leads to an increase in the density of ceramics up to 8.05–8.10 g/cm³, which positively affects the shielding efficiency and strength characteristics. According to the data on the change in strength characteristics, it was found that a change in the density of ceramics from 6.3 to 8.05–8.10 g/cm³ leads to strengthening and an increase in the crack resistance of ceramics by 75–80%, which indicates a high strength of ceramics and their increased resistance to external influences. As shown by the evaluation of the shielding characteristics, an increase in the density of ceramics due to a phase composition change leads to an increase in the shielding efficiency and a decrease in gamma intensity by a factor of 3–3.5. At the same time, on the base of the data presented, it can be concluded that ceramics obtained in the range of 900–1100 °C have both high shielding characteristics and high strength and resistance to external influences. Full article

In this study, composite materials based on nanocrystalline anatase TiO₂ doped with nitrogen and bismuth tungstate are synthesized using a hydrothermal method. All samples are tested in the oxidation of volatile organic compounds under visible light to find the correlations between their physicochemical characteristics and photocatalytic activity. The kinetic aspects are studied both in batch and continuous-flow reactors, using ethanol and benzene as test compounds. The Bi₂WO₆/TiO₂-N heterostructure enhanced with Fe species efficiently utilizes visible light in the blue region and exhibits much higher activity in the degradation of ethanol vapor than pristine TiO₂-N. However, an increased activity of Fe/Bi₂WO₆/TiO₂-N can have an adverse effect in the degradation of benzene vapor. A temporary deactivation of the photocatalyst can occur at a high concentration of benzene due to the fast accumulation of non-volatile intermediates on its surface. The formed intermediates suppress the adsorption of the initial benzene and substantially increase the time required for its complete removal from the gas phase. An increase in temperature up to 140 °C makes it possible to increase the rate of the overall oxidation process, and the use of the Fe/Bi₂WO₆/TiO₂-N composite improves the selectivity of oxidation compared to pristine TiO₂-N. Full article

The purpose of this paper is to study the effect of PbO doping of multicomponent composite glass-like ceramics based on TeO₂, WO₃, Bi₂O₃, MoO₃, and SiO₂, which are one of the promising materials for gamma radiation shielding. According to X-ray diffraction data, it was found that the PbO dopant concentration increase from 0.10 to 0.20–0.25 mol results in the initialization of the phase transformation and structural ordering processes, which are expressed in the formation of SiO₂ and PbWO₄ phases, and the crystallinity degree growth. An analysis of the optical properties showed that a change in the ratio of the contributions of the amorphous and ordered fractions leads to the optical density increase and the band gap alteration, as well as a variation in the optical characteristics. During the study of the strength and mechanical properties of the synthesized ceramics, depending on the dopant concentration, it was found that when inclusions in the form of PbWO₄ are formed in the structure, the strength characteristics increase by 70–80% compared to the initial data, which indicates the doping efficiency and a rise in the mechanical strength of ceramics to external influences. During evaluation of the shielding protective characteristics of the synthesized ceramics, it was revealed that the formation of PbWO₄ in the structure results in a rise in the high-energy gamma ray absorption efficiency. Full article

The main purpose of this work is to study the effect of substitution of zinc oxide for bismuth oxide in the composition of (1−x)ZnO–0.25Al₂O₃–0.25WO₃–xBi₂O₃ ceramics, as well as the accompanying processes of phase transformations and their influence on the optical and strength properties of ceramics. The use of these oxide compounds as materials for creating shielding coatings or ceramics is due to the combination of their structural, optical, and strength properties, which make it possible to compete with traditional protective glasses based on rare earth oxide compounds. Interest in these types of ceramics is due to their potential for use as basic materials for shielding ionizing radiation as well as for use as radiation-resistant coatings. The main research methods were X-ray diffractometry to determine the phase composition of ceramics; scanning electron microscopy and energy dispersive analysis to determine the morphological features and isotropy of the distribution of elements in the structure; and UV-V is spectroscopy to determine the optical properties of ceramics. During the studies, it was found that an increase in the Bi₂O₃ concentration leads to the formation of new phase inclusions in the form of orthorhombic Bi₂WO₆ and Bi₂W₂O₉ phases, the appearance of which leads to an increase in the density of ceramics and a change in the dislocation density. An analysis of the strength properties, in particular, hardness and crack resistance, showed that a change in the phase composition of ceramics with an increase in the Bi₂O₃ concentration leads to a significant strengthening of the ceramics, which is due to the effect of the presence of interfacial boundaries as well as an increase in the dislocation density. Full article

We report a new photohydrothermal method to prepare a Bi₂WO₆/WO₃ catalytic material for CO₂ photoreduction by solar concentrators. The photohydrothermal treatment improves the physico-chemical properties of the Bi₂WO₆/WO₃ material and forms well contact Bi₂WO₆/WO₃ heterojunctions, which increase the maximum reaction rate of CO₂ photoreduction to 8.2 times under the simulated light, and the hydrocarbon yield under the real concentrating solar light achieves thousands of μmol·g_cata⁻¹. The reason for the high activity is attributed to the direct Z-scheme effect of Bi₂WO₆/WO₃ heterojunctions and the photothermal effect during the course. These findings highlight the utilization of solar energy in CO₂ photoreduction and open avenues for the rational design of highly efficient photocatalysts. Full article

Using sunlight to convert CO₂ into solar fuel is an ideal solution to both global warming and the energy crisis. The construction of direct Z-scheme heterojunctions is an effective method to overcome the shortcomings of single-component or conventional heterogeneous photocatalysts for photocatalytic CO₂ (carbon dioxide) reduction. In this work, a composite photocatalyst of narrow-gap SnS₂ and stable oxide Bi₂WO₆ were prepared by a simple hydrothermal method. The combination of Bi₂WO₆ and SnS₂ narrows the bandgap, thereby broadening the absorption edge and increasing the absorption intensity of visible light. Photoluminescence, transient photocurrent, and electrochemical impedance showed that the coupling of SnS₂ and Bi₂WO₆ enhanced the efficiency of photogenerated charge separation. The experimental results show that the electron transfer in the Z-scheme heterojunction of SnS₂/Bi₂WO₆ enables the CO₂ reduction reactions to take place. The photocatalytic reduction of CO₂ is carried out in pure water phase without electron donor, and the products are only methanol and ethanol. By constructing a Z-scheme heterojunction, the photocatalytic activity of the SnS₂/Bi₂WO₆ composite was improved to 3.3 times that of pure SnS₂. Full article

The exploration of cost-effective and highly efficient photocatalysts is still a great challenge. In this work, a cost-effective and highly active Bi₂WO₆/calcined mussel shell (CMS/BWO) composite photocatalyst was prepared by a facile solvothermal route, in which Bi₂WO₆ nanosheets were tightly, evenly, and vertically grown on waste calcined mussel shells (CMS). Multiple techniques are adopted to characterize the phases, morphology, and chemical properties of the as-fabricated catalysts. In contrast to the stacked Bi₂WO₆, CMS/BWO has numerous exposed edges and open transfer pathways, which can create more open space and reactive sites for photocatalytic reactions. Such favorable characteristics enable CMS/BWO to efficiently degrade organic pollutants (e.g., rhodamine B (RhB), methylene blue (MB), tetracycline hydrochloride (TC)) under visible light. Moreover, the generation of reactive species during the photocatalytic process is also examined by trapping experiments, disclosing the pivotal role of photo-generated holes (h⁺) and hydroxyl radicals (•OH) in the photo-degradation of pollutants. Above all, this study not only provides an efficient photocatalyst for environmental remediation, but it also opens up new possibilities for waste mussel shell reutilization. Full article