Phase- and Crystal Structure-Controlled Synthesis of Bi₂O₃, Fe₂O₃, and BiFeO₃ Nanomaterials for Energy Storage Devices

Controlling the phase and crystal structure of nanomaterials is a challenging mission in a wet chemical method and has remarkable importance to the materials properties. Herein, we demonstrate a facile sol–gel method to synthesize Bi2O3, Fe2O3, BiFeO3, Bi36Fe2O57, secondary phase, and mixed phase of BiFeO3 (Bi25FeO40 and Bi2Fe4O9) by tailoring the parameters such as molar concentration, calcination temperature, and duration. Further, all the electrode materials were demonstrated for supercapacitor (SC) application. The pure-phase BiFeO3 nanoparticles show a highest specific capacitance of 253 F/g at a current density of 1 A/g compared to all other electrodes under a 3 M KOH electrolyte. The higher specific capacitance of BiFeO3 nanoparticles is ascribed to their higher surface area, pure ABO3 structure, and lower charge-transfer resistance. Moreover, the BiFeO3 nanoparticles were also tested under a neutral electrolyte (1 M Na2SO4) and found to have 3.7 times lower specific capacitance compared to the alkaline electrolyte (3 M KOH). The electrokinetic study of the as-synthesized active electrodes illustrates the maximum capacitive involvement to store the overall charge. The BiFeO3 nanoparticles display outstanding stability with a retention rate of 99.02% after 1100 consecutive galvanostatic charge–discharge cycles at various current densities. Moreover, a solid-state symmetric SC device (SSD) was fabricated using BiFeO3 nanoparticles. The device delivered a maximum energy density of 17.01 W h/kg at a current density of 1 A/g and a power density of 7.2 kW/kg at a current density of 10 A/g. The BiFeO3 SSD showed an excellent capacitive retention rate of 88% after 5000 cycles, suggesting that it could be a promising electrode material for practical application in energy storage devices

Microwave-Assisted Greener Synthesis of Defect-Rich Tungsten Oxide Nanowires with Enhanced Photocatalytic and Photoelectrochemical Performance

Exploring semiconductor materials with superior photocatalytic activity is desirable to mitigate the crisis associated with rapid depletion of fossil fuels and environmental pollutions. Herein we report the synthesis of orthorhombic stacked WO₃·H₂O square nanoplates by mixing WCl₆ (0.025 M) in ethanol at room temperature via a precipitation method. On the other hand, hierarchical urchin-like W₁₈O₄₉ nanostructures composed of nanowires were synthesized from the preceding solution within 10 min through a microwave-assisted route. The morphology evolution from nanoplates to nanowires proceeds through a dissolution and recrystallization mechanism, as demonstrated in detail by varying the reaction duration and temperature. The as-synthesized WO₃·H₂O nanoplates and W₁₈O₄₉ nanowires were employed for the photocatalytic degradation of rhodamine B and photoelectrocatalytic hydrogen generation through water splitting in a neutral medium. Furthermore, the as-synthesized W₁₈O₄₉ nanostructures are employed as electrocatalysts for hydrogen evolution reaction in both acidic and neutral electrolytes. The enhanced electrocatalytic and photocatalytic activity of W₁₈O₄₉ nanostructures are attributed to their larger surface area, oxygen vacancies, and faster charge transport properties. This work demonstrates a greener and simpler way to synthesize a promising defect-rich material (W₁₈O₄₉) in a short duration and its potential in electrocatalytic and photoelectrocatalytic hydrogen generation, and for degradation of pollutant

High Performance Solid-State Asymmetric Supercapacitor using Green Synthesized Graphene–WO₃ Nanowires Nanocomposite

Development of active materials capable of delivering high specific capacitance is one of the present challenges in supercapacitor applications. Herein, we report a facile and green solvothermal approach to synthesize graphene supported tungsten oxide (WO₃) nanowires as an active electrode material. As an active electrode material, the graphene–WO₃ nanowire nanocomposite with an optimized weight ratio has shown excellent electrochemical performance with a specific capacitance of 465 F g^–1 at 1 A g^–1 and a good cycling stability of 97.7% specific capacitance retention after 2000 cycles in 0.1 M H₂SO₄ electrolyte. Furthermore, a solid-state asymmetric supercapacitor (ASC) was fabricated by pairing a graphene–WO₃ nanowire nanocomposite as a negative electrode and activated carbon as a positive electrode. The device has delivered an energy density of 26.7 W h kg^–1 at 6 kW kg^–1 power density, and it could retain 25 W h kg^–1 at 6 kW kg^–1 power density after 4000 cycles. The high energy density and excellent capacity retention obtained using a graphene–WO₃ nanowire nanocomposite demonstrate that it could be a promising material for the practical application in energy storage devices

High Performance Solid-State Asymmetric Supercapacitor using Green Synthesized Graphene–WO₃ Nanowires Nanocomposite

Development of active materials capable of delivering high specific capacitance is one of the present challenges in supercapacitor applications. Herein, we report a facile and green solvothermal approach to synthesize graphene supported tungsten oxide (WO₃) nanowires as an active electrode material. As an active electrode material, the graphene–WO₃ nanowire nanocomposite with an optimized weight ratio has shown excellent electrochemical performance with a specific capacitance of 465 F g^–1 at 1 A g^–1 and a good cycling stability of 97.7% specific capacitance retention after 2000 cycles in 0.1 M H₂SO₄ electrolyte. Furthermore, a solid-state asymmetric supercapacitor (ASC) was fabricated by pairing a graphene–WO₃ nanowire nanocomposite as a negative electrode and activated carbon as a positive electrode. The device has delivered an energy density of 26.7 W h kg^–1 at 6 kW kg^–1 power density, and it could retain 25 W h kg^–1 at 6 kW kg^–1 power density after 4000 cycles. The high energy density and excellent capacity retention obtained using a graphene–WO₃ nanowire nanocomposite demonstrate that it could be a promising material for the practical application in energy storage devices

Facile Synthesis of N-Doped WS2 Nanosheets as an Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction in Acidic Media

Transition metal chalcogenides have been widely studied as a promising electrocatalyst for the hydrogen evolution reaction (HER) in acidic conditions. Among various transition metal chalcogenides, tungsten disulfide (WS2) is a distinguishable candidate due to abundant active sites and good electrical properties. Herein, we report a facile and selective synthetic method to synthesize WS2 with an intriguing two-dimensional nanostructure by using cysteine (C3H7NO2S) as a chemical agent. In addition, nitrogen can be incorporated during chemical synthesis from cysteine, which may be helpful for enhancing the HER. The electrocatalytic activity of N-doped WS2 exhibits a promising HER in acidic conditions, which are not only higher than W18O49 nanowires and hex-WO3 nanowires, but also comparable to the benchmark Pt/C. Moreover, excellent electrocatalytic stability is also demonstrated for acidic HER during long-term tests, thus highlighting its potential use of practical applications as an electrolyzer

Facile Green Synthesis of WO₃·H₂O Nanoplates and WO₃ Nanowires with Enhanced Photoelectrochemical Performance

The synthesis of nanostructured materials with controlled shape without using a capping agent and/or a hazardous chemical is one of the major existing challenges. Herein, we report a facile precipitation method to synthesize stacked orthorhombic tungsten trioxide hydrate (WO₃·H₂O) nanoplates by simply mixing WCl₆ (0.025 M) in ethanol at room temperature for 1 h. On subsequent solvothermal treatment of WO₃·H₂O nanoplates at 200 °C in ethanol, formation of monoclinic tungsten trioxide (WO₃) nanowires of <20 nm diameter is demonstrated. The morphology evolution of WO₃ nanowires from WO₃·H₂O nanoplates and change in growth direction through dissolution and recrystallization process is further confirmed by varying the solvothermal duration and temperature. The as-synthesized WO₃·H₂O nanoplates and WO₃ nanowires are used as photoanodes for the hydrogen generation through photoelectrochemical (PEC) water splitting in a neutral pH. The photocurrent density of WO₃ nanowires is found ∼21 times higher than that of WO₃·H₂O nanoplates at 1.0 V vs saturated calomel electrode (SCE) and also higher than the reported WO₃ nanostructures. The superior PEC performance of WO₃ nanowires is justified on the basis of its (200) oriented one-dimensional morphology, large surface area, and small interfacial charge transfer resistance

Microfluidization of juice extracted from partially granulated citrus fruits: Effect on physical attributes, functional quality and enzymatic activity

Citrus juice sac granulation reduces the yield of extractable juice and impairs its nutritional and functional quality. Therefore, present study was carried out to improve the physico-functional quality of juice extracted from partially granulated ‘Dancy’ tangerine. Juice was passed through microfluidizer under varying pressure (41, 62, 83, 103, 124 MPa) for different number of passes (1, 2, 3). The microfluidized juice was evaluated for different quality attributes, viz. cloud value, fractal dimension, lacunarity, colour attributes and pectin methyl esterase (PME) activity. Naringin and hesperidin were quantified through HPLC. Control juice exhibited the highest fractal dimension (18.89), indicating irregular cell structure, while 103MPa/3 passes (1.04) displayed the lowest indicating uniformity in juice. Microfluidized juice showed improved opalescence stability, greater hue, low PME activity and augmented hesperidin and naringin contents. Juice treated at 103 MPa for a single pass exhibited the best organoleptic quality. The high pressure applied during microfluidization can drastically improve the quality of otherwise low quality juice extracted from granulated citrus fruits. Application of appropriate processing pressure and number of passes through the microfluidizer yields citrus juice possessing enhanced bioactive constituents, reduced enzymatic activity with good organoleptic acceptability

Microwave-Assisted Solvothermal Synthesis of Cupric Oxide Nanostructures for High-Performance Supercapacitor

Enhancing the performance and stability of the low-cost materials for electrochemical energy storage device is an important aspect. Herein, we report microwave-assisted solvothermal synthesis of three-dimensional (3D) spherical CuO structures composed of either one-dimensional (rod-like) or two-dimensional (2D) flake-like building blocks by varying the reaction medium, i.e., water and ethylene glycol (EG). A higher EG in the reaction medium facilitates formation of the flake-like structures. A specific surface area of 168.47 m² g^–1 is achieved with the 3D flower-like CuO, synthesized using copper acetate precursor in 1:3 water/EG solvent ratio. The same sample delivers a specific capacitance of 612 F g^–1 at an applied current density of 1 A g^–1 and shows high stability with capacity retention of 98% after 4000 galvanostatic charge–discharge cycles. The high specific capacitance of flower-shaped CuO architecture is attributed to large surface area and availability of sufficient pores for ions diffusion. Furthermore, two-electrode asymmetric supercapacitor device is fabricated using the 3D flower-shaped CuO as positive electrode and activated carbon as negative electrode, which shows an energy density of 27.27 Wh kg^–1 at a power density of 800 W kg^–1. This underlines the potential of inexpensive CuO architecture as an active material for energy storage devices

Enhanced catalytic activity without the use of an external light source using microwave-synthesized CuO nanopetals

We report enhanced catalytic activity of CuO nanopetals synthesized by microwave-assisted wet chemical synthesis. The catalytic reaction of CuO nanopetals and H2O2 was studied with the application of external light source and also under dark conditions for the degradation of the hazardous dye methylene blue. The CuO nanopetals showed significant catalytic activity for the fast degradation of methylene blue and rhodamine B (RhB) under dark conditions, without the application of an external light source. This increased catalytic activity was attributed to the co-operative role of H2O2 and the large specific surface area (≈40 m2·g−1) of the nanopetals. We propose a detail mechanism for this fast degradation. A separate study of the effect of different H2O2 concentrations for the degradation of methylene blue under dark conditions is also illustrated