Morphology-controlled fabrication of nanostructured WO3 thin films by magnetron sputtering with glancing angle deposition for enhanced efficiency photo-electrochemical water splitting

Herein, the tungsten trioxide (WO₃) nanostructure thin films with different morphologies are firstly fabricated by magnetron sputtering with glancing angle deposition technique (MS-GLAD), followed by the post annealed treatment process in air ambient for 2 h. It is demonstrated that the geometry of MS-GLAD setup, mainly substrate position, played a crucial role in determining the morphology, crystallinity, optical transmittance, and photo-electrochemical (PEC) performance of the WO₃ nanostructured thin film. With the different substrate positions in the MS-GLAD system, the WO₃ nanorod film layer could be precisely changed to combine an underlying dense layer with a nanorod layer and then nanocolumnar film. Moreover, the prepared samples' chemical composition and work function are studied by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), respectively. The combining WO₃ nanostructure produced high PEC efficiency compared to the single layer of the WO₃ nanorods sample and the dense WO₃ thin film sample. Thus, morphology-controlled nanostructure film based on the MS-GLAD technique in our study provides a simple approach to enhance the photo-anode for PEC water splitting application.     

CuxNi1-xO nanostructures and their nanocomposites with reduced graphene oxide: Synthesis,characterization, and photocatalytic applications

NiO nanostructure was synthesized using a simple co-precipitation method and was embedded on reduced graphene oxide surface via ultrasonication. Structural investigations were made through X-ray diffraction (XRD) and functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR). XRD analysis revealed the grain size reduction with doping. Fourier transform infrared spectroscopy confirmed the presence of metal-oxygen bond in pristine and doped NiO nanostructure as well as the presence of carbon containing groups. Scanning electron microscopy (SEM) indicated that the particle size decreased when NiO nanostructure was doped with copper. BET surface area was found to increase almost up to 43 m²/g for Cu doped NiO nanostructure/rGO composite. Current-voltage measurements were performed using two probe method. UV–Visible spectroscopic profiles showed the blue and red shift for Cu doped NiO nanostructure and Cu doped NiO Nanostructure/rGO composite respectively. Rate constant for Cu doped NiO nanostructure/rGO composite found to increase 4.4 times than pristine NiO nanostructure.     

Zinc ferrite based gas sensors: A review

Flammable, explosive and toxic gases, such as hydrogen, hydrogen sulfide and volatile organic compounds vapor, are major threats to the ecological environment safety and human health. Among the available technologies, gas sensing is a vital component, and has been widely studied in literature for early detection and warning. As a metal oxide semiconductor, zinc ferrite (ZnFe₂O₄) represents a kind of promising gas sensing material with a spinel structure, which also shows a fine gas sensing performance to reducing gases. Due to its great potentials and widespread applications, this article is intended to provide a review on the latest development in zinc ferrite based gas sensors. We first discuss the general gas sensing mechanism of ZnFe₂O₄ sensor. This is followed by a review of the recent progress about zinc ferrite based gas sensors from several aspects: different micro-morphology, element doping and heterostructure materials. In the end, we propose that combining ZnFe₂O₄ which provides unique microstructure (such as the multi-layer porous shells hollow structure), with the semiconductors such as graphene, which provide excellent physical properties. It is expected that the mentioned composites contribute to improving selectivity, long-term stability, and other sensing performance of sensors at room or low temperature.     

An integrated method based on energy concentration for evaluating normally distributed spectra in the visible region

This work proposes a method to scientifically quantify the quality of normally distributed visible spectra from the viewpoint of energy concentration: high transmittance, narrow spectral width, and small deviation from the target wavelength in the target region. In the proposed method, the spectral width of the spectrum is compared with that of a reference spectrum before its deviation from the target wavelength is examined. After extracting the maximum transmittance, a performance index of the spectrum is obtained in a percentile value. The effectiveness of the proposed method was analytically proven by surface plasmon resonance-generated spectra with five design features and five variations in each feature. The results indicated that the proposed method not only substantially reflected the predictions made by intuitive visual inspections, but also avoided misleading and ambiguous results evaluated by existing full-width-at-half-maximum (FWHM) method, figure-of-merit (FOM) method, and coordinates on the chromaticity diagram. In addition to the numerical analysis, the experimentally obtained spectra of phosphors in white light emitting diodes were also evaluated. The results proved that the proposed method can successfully highlight the scaled performance difference among the spectra, which is not supported by existing FWHM and FOM methods by simultaneously considering the aforementioned three characteristics of a spectrum.     

Effect of copper on improving the electrochemical storage of hydrogen in CeO2 nanostructure fabricated by a simple and surfactant-free sonochemical pathway

Introducing high-performance compounds for hydrogen sorption is of interest because of their advantages for substantial applications such as energy storage. Here, the role of copper addition on hydrogen storage capability and Coulombic efficiency of CeO₂ nanostructure (fabricated by an easy and surfactant-free sonochemical pathway) was examined, for the first time. Nanostructured oxides were fabricated with loading various percentages of copper (4 wt% and 40 wt%) inside CeO₂. Nanostructured copper-ceria binary oxides were checked by diverse analyses. The hydrogen storage performance as well as Coulombic efficiency of the nanostructured copper-ceria binary oxides and the net CeO₂ were checked through chronopotentiometry charge−discharge pathway in the alkaline medium. The outcomes exhibited that the hydrogen storage capacity of CeO₂ nanostructure could be enhanced with adding the proper dosage of copper as a beneficial low-cost solution. Self-assembled copper-doped CeO₂ hierarchical nanostructures could display the most appropriate performance than the net CeO₂ and nanostructured Cu₂O–CeO₂. The discharge capacity for the self-assembled copper-doped CeO₂ hierarchical nanostructures (fabricated by adding 4 wt% copper) could rise to 5070 mAh/g at 22nd cycle. Appropriate porosity, special architecture and unique morphology as well as convenient surface area of the self-assembled copper-doped CeO₂ hierarchical nanostructures render they can be very beneficial compounds in the energy storage.     

High-resolution FIB-TEM-STEM structural characterization of grain boundaries in the high dielectric constant perovskite CaCu3Ti4O12

In this work, the grain boundaries composition of the polycrystalline CaCu₃Ti₄O₁₂ (CCTO) was investigated. A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samples of the grain boundaries interface of CCTO ceramics. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS) and Electron Energy Loss Spectroscopy (EELS) systems were used to characterize the composition and nanostructure of the grain and grain boundaries region. It is known that during conventional sintering, discontinuous grain growth occurs and a Cu-rich phase appears at grain boundaries. This Cu-rich phase may affect the final dielectric properties of CCTO but its structure and chemical composition remained unknown. For the first time, this high-resolution FIB-TEM-STEM study of CCTO interfacial region highlights the composition of the phases segregated at grain boundaries namely CuO, Cu₂O and the metastable phase Cu₃TiO_4.     

Synthesis of manganese titanate and its precursors from xerogel

An overview of research on the synthesis of manganese titanates is presented. The xerogel of Mn–Ti–O–C–H composition was synthesized from manganese acetate and titanium tetrabutylate via liquid-phase method using organic solvents. The calcination of xerogel in air at 450 °C and 700 °C yielded manganese titanate precursors in the form of a nanostructured mixture of Mn₂O₃ and TiO₂. Annealing at 1000 °C, manganese metatitanate MnTiO₃ was obtained. Reference experiments with initial reagents included, separately, thermal decomposition of Mn(CH₃COO)₂×4H₂O and the product of Ti(OC₄H₉)₄ hydrolysis. The composition, structure, and properties of the products were studied using X-ray diffraction, scanning electron microscopy, elemental analysis, diffuse reflectance IR Fourier spectroscopy, thermogravimetry, and by measuring specific surface area. The data presented by these different techniques are basically consistent with each other (with an increase in the annealing temperature, an increase in globule size and decrease in specific surface area are observed; structuring occurs within the long- and short-range order; the size of the crystallites does not exceed that of the globules; elemental composition correlates with phase composition; the endothermic character of the reaction of MnTiO₃ formation at 900 °C is confirmed by a thermodynamic calculation). Nevertheless, some unexpected effects were revealed (based on the FTIR diffuse reflection spectra, mixed oxide Mn–Ti–O is formed in the surface layer of particles already at 450 °C and 700 °C; etc.). Application of the proposed technique for modifying Al₂O₃ powders, with the aim of implementing low-temperature sintering of corundum ceramics, is discussed.     

High sensitivity nanostructure incorporated interdigital silicon based capacitive accelerometer

Interdigital structures are realized on silicon substrates with high sensitivity to acceleration. The process employs a combination of anisotropic back-side micromachining with front-side vertical deep reactive ion etching of silicon. The incorporation of silicon-based nano-structures on the vertical planes of fingers leads to a significant increase in the capacitance of the device from 0.45 for simple planes to 40 pF for the nano-structured planes. Such structures show high sensitivity to inclination and accelerations, which could be due to field emission of electrons from nano-metric features. Around 8% change in the capacitance is observed upon a tilting sensor from 0° to 90° angle, which makes it proper for possible use as an earthquake sensor. A preliminary model for the capacitance and its dependence on the measurement voltage is presented.     

Functional nanostructured materials: Aerosol,aerogel, and de novo synthesis to emerging energy and environmental applications

In this review, we introduce advanced synthetic methods for functional nanostructured materials (in powder form) bridging to the development in emerging energy and environmental applications. Three types of synthetic methods (aerosol-based, aerogel-based, and de novo methods) are introduced, all of which have shown to be extensively investigated as novel routes to create nanostructured materials with designed material properties (i.e., controlled size, shape, porosity, and chemical composition are to be achievable). The typical experimental setup and the general experimental procedure for material preparation via the above three synthesis routes are discussed. Complementary characterization approaches are employed to study material properties of the synthesized nanostructured materials via the three synthesis routes. Here we investigate: (1) Cu_xO-CeO₂, Ni-CeO₂, and Cu_xO nanoparticle-encapsulating metal–organic framework (MOF) hybrid nanoparticles synthesized via the aerosol-based method; (2) Cr-encapsulating MOF (Cr-MOF-199), Au-encapsulating MOF (Au@ZIF-8), and MOF-derived nanocomposites (CuO/CuCr₂O₄) produced via the de novo route; (3) a variety of aerogels (carbon, metal oxide, polymer) with high porosity created by the aerogel-based approach. Finally, several examples of emerging energy and environmental applications are introduced using these functional nanostructured materials, including (1) catalytic transformation to chemicals by using precious metal nanoparticles-embedded MOFs and the MOF-derived nanocomposites as the catalysts; (2) methane combustion using Cu_xO-CeO₂ hybrid nanoparticles as catalyst, (3) methane dry reforming with CO₂ using Ni-CeO₂ hybrid nanoparticles as catalyst; (4) CO₂ capture by fluoroalkyl silane-modified mesoporous silica and polymethylsilsesquioxane (PMSQ) aerogel membranes; (5) adsorption of organic solvent, dye, and oil by cetyltrimethylammonium bromide-modified PMSQ aerogel.