Design of Multilayers of Urchin-like ZnO Nanowires Coated with TiO₂ Nanostructures for Dye-Sensitized Solar Cells

In dye-sensitized solar cells, the photovoltaic efficiency of nanowires (NW) is still limited by their surface area and loss of light absorption compared with nanoparticle (NP) architectures. To overcome this limitation, the light harvesting efficiencies must be improved by increasing the total NW array surface area, without increasing too much the traveled distance of electrons. Here, we describe the design of a 3D architecture based on polystyrene spheres (PS) coated with ordered multilayers of urchin-like ZnO NWs (U-ZnO NWs) to be used as a high surface area nanostructure photoanode for dye-sensitized solar cells. Two to four layers of U-ZnO NWs were synthesized by using PS of 1 and 5 μm in diameter. The ordered layers of U-ZnO NWs were then coated with a thin layer of TiO₂ by atomic layer deposition, and topped with a ∼9–14 μm thick layer of anatase TiO₂ NPs. We found that assembling organized layers of U-ZnO NWs significantly increased the surface area and provided better photon absorption. Moreover, coating the U-ZnO NWs with a thin TiO₂ layer decreased the charge recombination and consequently enhanced the photovoltaic efficiency

Facile Synthesis and High Rate Capability of Silicon Carbonitride/Boron Nitride Composite with a Sheet-Like Morphology

We report synthesis of a sheet-like composite composed of hexagonal boron nitride (or BN) chemically integrated with silicon carbonitride (SiCN) matrix via a simple pyrolysis route. The composite offers several unique features such as improved electrical conductivity, high-temperature oxidation resistance (at 1000 °C), and high electrochemical activity toward Li-ions generally not observed in SiCN or boron-doped SiCN. Tested as electrode in Li-ion half-cell, SiCN/BN show charge capacity of ∼517 mAh g^–1 at 100 mA g^–1 and 283 mAh g^–1 at 2400 mA g^–1 with respect to total weight of electrode. Additionally, a stable charge capacity of ∼401 mAh g^–1 at 100 mA g^–1 is retained even after continuous operation for 1000 cycles at 1600 mA g^–1. Chemical characterization of the composite suggests that addition of BN to polysilazane in moderate amounts (∼10 wt %) and subsequent pyrolysis resulted in an increased free-carbon content in the amorphous SiCN phase, which exceeded the percolation limit, leading to the improved electrical conductivity and Li-reversible capacity

Mesoporous ZnFe₂O₄@TiO₂ Nanofibers Prepared by Electrospinning Coupled to PECVD as Highly Performing Photocatalytic Materials

Zinc ferrite @ titanium dioxide (ZnFe₂O₄@TiO₂) composite nanofibers were elaborated by combining the two different techniques: electrospinning and plasma-enhanced chemical vapor deposition (PECVD). The nanofiber compositions were controlled using different ratios of zinc to iron. Their structural, morphological, and optical properties were analyzed by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, BET surface area, Raman spectroscopy, and UV–visible spectrophotometry. The photocatalytic activity has been investigated by the degradation of methylene blue under visible light. The results indicate that the combination of spinel structure with titanium dioxide improves the photodegradation up to 98%. The deposition of TiO₂ via PECVD on zinc ferrite enhances the absorption of TiO₂ into the visible region and increases the electron–hole separation. In addition, the improved surface area can promote adsorption, desorption, and diffusion of reactants and products, which is favorable to obtain a high photocatalytic activity

Mesoporous ZnFe₂O₄@TiO₂ Nanofibers Prepared by Electrospinning Coupled to PECVD as Highly Performing Photocatalytic Materials

Zinc ferrite @ titanium dioxide (ZnFe₂O₄@TiO₂) composite nanofibers were elaborated by combining the two different techniques: electrospinning and plasma-enhanced chemical vapor deposition (PECVD). The nanofiber compositions were controlled using different ratios of zinc to iron. Their structural, morphological, and optical properties were analyzed by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, BET surface area, Raman spectroscopy, and UV–visible spectrophotometry. The photocatalytic activity has been investigated by the degradation of methylene blue under visible light. The results indicate that the combination of spinel structure with titanium dioxide improves the photodegradation up to 98%. The deposition of TiO₂ via PECVD on zinc ferrite enhances the absorption of TiO₂ into the visible region and increases the electron–hole separation. In addition, the improved surface area can promote adsorption, desorption, and diffusion of reactants and products, which is favorable to obtain a high photocatalytic activity

Lithium Hydrazinidoborane: A Polymorphic Material with Potential for Chemical Hydrogen Storage

Herein, we describe the synthesis and characterization (chemical, structural, and thermal) of a new crystal phase of lithium hydrazinidoborane (LiN₂H₄­BH₃, LiHB), which is a new material for solid-state chemical hydrogen storage. We put in evidence that lithium hydrazinidoborane is a polymorphic material, with a stable low-temperature phase and a metastable high-temperature phase. The former is called β-LiHB and the latter α-LiHB. Results from DSC and XRD showed that the transition phase occurs at around 90 °C. On this basis, the crystal structure of the novel β-LiHB phase was solved. The potential of this material for solid-state chemical hydrogen storage was verified by TGA, DSC, and isothermal dehydrogenations. Upon the formation of the α-LiHB phase, the borane dehydrogenates. At 150 °C, it is able to generate 10 wt % of pure H₂ while a solid residue consisting of polymers with linear and cyclic units forms. Reaction mechanisms and formation of bis­(lithium hydrazide) of diborane [(LiN₂H₃)₂­BH₂]⁺­[BH₄]⁻ as a reaction intermediate are tentatively proposed to highlight the decomposition of β-LiHB in our conditions

Porous Gelatin Membrane Obtained from Pickering Emulsions Stabilized by Graphene Oxide

This article presents a novel procedure for preparing porous membranes from water-soluble polymers involving the formation of a Pickering emulsion. Gelatin is a biodegradable biopolymer obtained by the partial hydrolysis of collagen. A biopolymer such as gelatin is capable of adsorbing at an oil/water interface, resulting in decreased interfacial energy. Hence, gelatin is widely employed as an alternate for synthetic surfactants to stabilize emulsions in the food industry. However, high-molecular-weight gelatin leads to large emulsion droplets and poor emulsion stability. The amphoteric nature of graphene oxide (GO) nanosheets was helpful in stabilizing the oil/water interface and allows for the preparation of a stable gelatin/GO emulsion. Membranes fabricated using gelatin/GO have a uniformly distributed porous structure. However, prepared membranes are highly hydrosoluble, so the membranes were cross-linked without affecting their morphology. XRD results evidenced that gelatin effectively exfoliated the graphite oxide which is essential to stabilizing the emulsion. Fabricated gelatin/GO membranes possess uniformly distributed pores and are highly stable in aqueous solution. Pure water filtration tests were conducted on the membranes. The permeability results proved that the membranes fabricated by a Pickering emulsion are promising materials for filtration

Tuning Optical Properties of Al₂O₃/ZnO Nanolaminates Synthesized by Atomic Layer Deposition

Nanolaminates are of great interest for their unique properties such as high dielectric constants and advanced mechanical, electrical, and optical properties. Here we report on the tuning of optical and structural properties of Al₂O₃/ZnO nanolaminates designed by atomic layer deposition (ALD). Structural properties of nanolaminates were studied by SEM, GIXRD, and AFM. Optical characterization was performed by transmittance and photoluminescence (PL) spectroscopy. Complex study of monolayer properties was performed by ellipsometry. Optical constants for Al₂O₃ and ZnO monolayer were calculated. The band gap of ZnO single layers and the excitonic PL peak position were shifted to the UV region related to quantum confinement effects. No peaks in the UV region were observed in nanolaminates with 2 nm ZnO single layer thickness due to fully depleted region in small crystalline grains (<2 nm). The improved room temperature photoluminescence of nanolaminates makes them prominent materials for optical biosensors applications

Enhanced Ionic Transport Mechanism by Gramicidin A Confined Inside Nanopores Tuned by Atomic Layer Deposition

The confinement and the understanding of ion transport through ionic channels when they are confined inside solid-state nanopores smaller than 10 nm remains a challenge. Here we report on the fabrication of biomimetic nanopores with high length (5 μm)/diameter (smaller than 10 nm) ratio obtained using both a track-etched technique and atomic layer deposition on flexible membranes. These membranes present uniform hydrophobic nanopores with a low roughness inside the pores. Gramicidin A is then confined inside nanopores (diameter 10.6, 5.7, and ∼2 nm) leading to the NaCl ionic transport mechanism through a hybrid nanopore similar to the biological ones especially for small diameter (5.7 and ∼2 nm)