Fabricating BiOCl/BiVO4 nanosheets wrapped in a graphene oxide heterojunction composite for detection of an antihistamine in biological samples.

Antibiotics are essential medications for human and animal health, as they are used to battle urinary infections and bacterial diseases. Therefore, the rapid determination of antibiotic drugs in biological samples is necessary to address the current clinical challenge. Here, we developed a heterojunction ternary composite of BiOCl/BiVO4 nanosheets enriched with graphene oxide (BiOCl/BiVO4@GO) for accurate and minimal-level detection of an antihistamine (promethazine hydrochloride, PMZ) in urine samples. The BiOCl/BiVO4 nanosheets were prepared by a wet chemical approach using a deep eutectic green solvent. The spectroscopic and analytical methods verified the formation and interaction of the BiOCl/BiVO4@GO composite. Our results showed that the thoroughly exfoliated BiOCl/BiVO4@GO composite retained good electrical conductivity and fast charge transfer toward the electrode-electrolyte interface in neutral aqueous media. In addition, the experimental conditions were accurately optimized, and the BiOCl/BiVO4@GO composite showed excellent electrocatalytic activity toward the oxidation of PMZ. Indeed, the BiOCl/BiVO4@GO composite demonstrated a good linear response range (0.01-124.7 µM) and a detection level of 3.3 nM with a sensitivity of 1.586 µA µM-1 cm-2. In addition, the BiOCl/BiVO4@GO composite had excellent storage stability, good reproducibility, and reliable selectivity. Finally, the BiOCl/BiVO4@GO displayed a desirable recovery level of PMZ in urine samples for real-time monitoring.

Effect of Heat Treatment on the Microstructure and Performance of Cu Nanofoams Processed by Dealloying.

Cu nanofoams are promising materials for a variety of applications, including anodes in high-performance lithium-ion batteries. The high specific surface area of these materials supports a high capacity and porous structure that helps accommodate volume expansion which occurs as batteries are charged. One of the most efficient methods to produce Cu nanofoams is the dealloying of Cu alloy precursors. This process often yields nanofoams that have low strength, thus requiring additional heat treatment to improve the mechanical properties of Cu foams. This paper provides the effects of heat treatment on the microstructures, mechanical properties, and electrochemical performance of Cu nanofoams. Annealing was conducted under both inert and oxidizing atmospheres. These studies ultimately reveal the underlying mechanisms of ligament coarsening during heat treatment.

Mechanical and biocorrosive properties of magnesium-aluminum alloy scaffold for biomedical applications.

This study investigates the morphology, microstructure, compressive behavior, biocorrosion properties, and cytocompatibility of magnesium (Mg)-aluminum (Al) alloy (AE42) scaffolds for their potential use in biodegradable biomedical applications. Mg alloy scaffolds were successfully synthesized via a camphene-based freeze-casting process with precisely controlled heat treatment. The average porosity was approximately 52% and the median pore diameter was ∼13 µm. Salient deformation mechanisms were identified using acoustic emission (AE) signals and adaptive sequential k-means (ASK) analysis. Twinning, dislocation slip, strut bending, and collapse were dominant during compressive deformation. Nonetheless, the overall compressive behavior and deformation mechanisms were similar to those of bulk Mg based on ASK analysis. The corrosion potential of the Mg alloy scaffold (-1.44 V) was slightly higher than that of bulk AE42 (-1.60 V), but the corrosion rate of the Mg alloy scaffold was faster than that of bulk AE42 due to the enhanced surface area of the Mg alloy scaffold. As a result of cytocompatibility evaluation following ISO10993-5, the concentration of the Mg alloy scaffold extract reducing cell growth rate to 50% (IC50) was 10.7%, which is higher (less toxic) than 5%, suggesting no severe inflammation by implantation into muscle.

Acoustic emission analysis of the compressive deformation of iron foams and their biocompatibility study.

We synthesized Fe foams using water suspensions of micrometric Fe2O3 powder by reducing and sintering the sublimated Fe oxide green body to Fe under 5% H2/Ar gas. The resultant Fe foam showed aligned lamellar macropores replicating the ice dendrites. The compressive behavior and deformation mechanism of the synthesized Fe foam were studied using an acoustic emission (AE) method, with which we detected sudden localized structural changes in the Fe foam material. The evolution of the deformation mechanism was elucidated using the adaptive sequential k-means (ASK) algorithm; specifically, the plastic deformation of the cell struts was followed by localized cell collapse, which eventually led to fracturing of the cell walls. For potential biomedical applications, the corrosion and biocompatibility characteristics of the two synthesized Fe foams with different porosities (50% vs. 44%) were examined and compared. Despite its larger porosity, the superior corrosion behavior of the Fe foam with 50% porosity can be attributed to its larger pore size and smaller microscopic surface area. Based on the cytotoxicity tests for the extracts of the foams, the Fe foam with 44% porosity showed better cytocompatibility than that with 50% porosity.

Investigation of the Microstructure Evolution and Deformation Mechanisms of a Mg-Zn-Zr-RE Twin-Roll-Cast Magnesium Sheet by In-Situ Experimental Techniques.

Twin roll casting (TRC), with a relatively fast solidification rate, is an excellent production method with promising potential for producing wrought semi or final Mg alloy products that can often suffer from poor formability. We investigate in this study the effect of the TRC method and the subsequent heat treatment on the microstructure and deformation mechanisms in Mg-Zn-Zr-Nd alloy deformed at room temperature using the in-situ neutron diffraction and acoustic emission techniques and ex-situ texture measurement and microscopy, respectively. Although a higher work hardening is observed in the rolling direction due to the more intensive -type dislocation activity, the difference in the mechanical properties of the specimens deformed in the RD and TD directions is small in the as-rolled condition. An additional heat treatment results in recrystallization and significant anisotropy in the deformation. Due to the easier activation of the extension twinning in the TD given by texture, the yield stress in the TD is approximately 40% lower than that in the RD.

Electrochemically Synthesized Nanoporous Molybdenum Carbide as a Durable Electrocatalyst for Hydrogen Evolution Reaction.

Demands for sustainable production of hydrogen are rapidly increasing because of environmental considerations for fossil fuel consumption and development of fuel cell technologies. Thus, the development of high-performance and economical catalysts has been extensively investigated. In this study, a nanoporous Mo carbide electrode is prepared using a top-down electrochemical process and it is applied as an electrocatalyst for the hydrogen evolution reaction (HER). Anodic oxidation of Mo foil followed by heat treatment in a carbon monoxide (CO) atmosphere forms a nanostructured Mo carbide with excellent interconnections, and these structural characteristics lead to high activity and durability when applied to the HER. Additionally, characteristic behavior of Mo is observed; metallic Mo nanosheets form during electrochemical anodization by exfoliation along the (110) planes. These nanosheets are viable for chemical modification, indicating their feasibility in various applications. Moreover, the role of carbon shells is investigated on the surface of the electrocatalysts, whereby it is suggested that carbon shells serve as a mechanical barrier against the oxidative degradation of catalysts that accompanies unavoidable volume expansion.

Multidimensional Anodized Titanium Foam Photoelectrode for Efficient Utilization of Photons in Mesoscopic Solar Cells.

Mesoscopic solar cells based on nanostructured oxide semiconductors are considered as a promising candidates to replace conventional photovoltaics employing costly materials. However, their overall performances are below the sufficient level required for practical usages. Herein, this study proposes an anodized Ti foam (ATF) with multidimensional and hierarchical architecture as a highly efficient photoelectrode for the generation of a large photocurrent. ATF photoelectrodes prepared by electrochemical anodization of freeze-cast Ti foams have three favorable characteristics: (i) large surface area for enhanced light harvesting, (ii) 1D semiconductor structure for facilitated charge collection, and (iii) 3D highly conductive metallic current collector that enables exclusion of transparent conducting oxide substrate. Based on these advantages, when ATF is utilized in dye-sensitized solar cells, short-circuit photocurrent density up to 22.0 mA cm-2 is achieved in the conventional N719 dye-I3- /I- redox electrolyte system even with an intrinsically inferior quasi-solid electrolyte.

Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting.

Nanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro-architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze-casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm-2 before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm-2 and an accordingly high incident photon-to-current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance.

Study of the compression and wear-resistance properties of freeze-cast Ti and Ti‒5W alloy foams for biomedical applications.

Ti and Ti‒5wt% W alloy foams were produced by freeze-casting process and their mechanical behaviors were compared. The Ti‒5W alloy foam showed a typical acicular Widmanstätten α/ß structure with most of the W dissolved in the ß phase. An electron-probe microanalysis revealed that approximately 2wt% W was uniformly dissolved in the Ti matrix of Ti‒5W alloy foam with few partially dissolved W particles. The compressive-yield strength of Ti‒5W alloy foam (~323MPa) was approximately 20% higher than that of the Ti foam (~256MPa) owing to the solid-solution-strengthening effect of W in the Ti matrix, which also resulted in a dramatic improvement in the wear resistance of Ti‒5W alloy foam. The compressive behaviors of the Ti and Ti‒5W alloy foams were predicted by analytical models and compared with the experimental values. Compared with the Gibson-Ashby and cellular-lattice-structure-in-square-orientation models of porous materials, the orientation-averaging method provided prediction results that are much more accurate in terms of both the Young's modulus and the yield strength of the Ti and Ti‒5W alloy foams.

Electrochemical synthesis of nanoporous tungsten carbide and its application as electrocatalysts for photoelectrochemical cells.

Photoelectrochemical (PEC) cells are promising tools for renewable and sustainable solar energy conversion. Currently, their inadequate performance and high cost of the noble metals used in the electrocatalytic counter electrode have postponed the practical use of PEC cells. In this study, we report the electrochemical synthesis of nanoporous tungsten carbide and its application as a reduction catalyst in PEC cells, namely, dye-sensitized solar cells (DSCs) and PEC water splitting cells, for the first time. The method employed in this study involves the anodization of tungsten foil followed by post heat treatment in a CO atmosphere to produce highly crystalline tungsten carbide film with an interconnected nanostructure. This exhibited high catalytic activity for the reduction of cobalt bipyridine species, which represent state-of-the-art redox couples for DSCs. The performance of tungsten carbide even surpassed that of Pt, and a substantial increase (∼25%) in energy conversion efficiency was achieved when Pt was substituted by tungsten carbide film as the counter electrode. In addition, tungsten carbide displayed decent activity as a catalyst for the hydrogen evolution reaction, suggesting the high feasibility for its utilization as a cathode material for PEC water splitting cells, which was also verified in a two-electrode water photoelectrolyzer.

Mechanical behavior and microstructure of compressed Ti foams synthesized via freeze casting.

Pure Ti and Ti-5%W foams were prepared via freeze casting. The porosity and grain size of both the materials were 32-33% and 15-17µm, respectively. The mechanical behavior of the foams was investigated by uniaxial compression up to a plastic strain of ~0.26. The Young׳s moduli of both foams were ~23GPa, which was in good agreement with the value expected from their porosity. The Young׳s moduli of the foams were similar to the elastic modulus of cortical bones, thereby eliminating the osteoporosis-causing stress-shielding effect. The addition of W increased the yield strength from ~196MPa to ~235MPa. The microstructure evolution in the grains during compression was studied using electron backscatter diffraction (EBSD) and X-ray line profile analysis (XLPA). After compression up to a plastic strain of ~0.26, the average dislocation densities increased to ~3.4×10(14)m(-2) and ~5.9×10(14)m(-2) in the Ti and Ti-W foams, respectively. The higher dislocation density in the Ti-W foam can be attributed to the pinning effect of the solute tungsten atoms on dislocations. The experimentally measured yield strength was in good agreement with the strength calculated from the dislocation density and porosity. This study demonstrated that the addition of W to Ti foam is beneficial for biomedical applications, because the compressive yield strength increased while its Young׳s modulus remained similar to that of cortical bones.

3D macroporous electrode and high-performance in lithium-ion batteries using SnO2 coated on Cu foam.

A three-dimensional porous architecture makes an attractive electrode structure, as it has an intrinsic structural integrity and an ability to buffer stress in lithium-ion batteries caused by the large volume changes in high-capacity anode materials during cycling. Here we report the first demonstration of a SnO2-coated macroporous Cu foam anode by employing a facile and scalable combination of directional freeze-casting and sol-gel coating processes. The three-dimensional interconnected anode is composed of aligned microscale channels separated by SnO2-coated Cu walls and much finer micrometer pores, adding to surface area and providing space for volume expansion of SnO2 coating layer. With this anode, we achieve a high reversible capacity of 750 mAh g(-1) at current rate of 0.5 C after 50 cycles and an excellent rate capability of 590 mAh g(-1) at 2 C, which is close to the best performance of Sn-based nanoscale material so far.

Facile and gram-scale synthesis of metal-free catalysts: toward realistic applications for fuel cells.

Although numerous reports on nonprecious metal catalysts for replacing expensive Pt-based catalysts have been published, few of these studies have demonstrated their practical application in fuel cells. In this work, we report graphitic carbon nitride and carbon nanofiber hybrid materials synthesized by a facile and gram-scale method via liquid-based reactions, without the use of toxic materials or a high pressure-high temperature reactor, for use as fuel cell cathodes. The resulting materials exhibited remarkable methanol tolerance, selectivity, and stability even without a metal dopant. Furthermore, these completely metal-free catalysts exhibited outstanding performance as cathode materials in an actual fuel cell device: a membrane electrode assembly with both acidic and alkaline polymer electrolytes. The fabrication method and remarkable performance of the single cell produced in this study represent progressive steps toward the realistic application of metal-free cathode electrocatalysts in fuel cells.

Next-generation polymer-electrolyte-membrane fuel cells using titanium foam as gas diffusion layer.

In spite of their high conversion efficiency and no emission of greenhouse gases, polymer electrolyte membrane fuel cells (PEMFCs) suffer from prohibitively high cost and insufficient life-span of their core component system, the membrane electrode assembly (MEA). In this paper, we are proposing Ti foam as a promising alternative electrode material in the MEA. Indeed, it showed a current density of 462 mA cm(-2), being ca. 166% higher than that with the baseline Toray 060 gas diffusion layer (GDL) (278 mA cm(-2)) with 200 ccm oxygen supply at 0.7 V, when used as the anode GDL, because of its unique three-dimensional strut structure promoting highly efficient catalytic reactions. Furthermore, it exhibits superior corrosion resistance with almost no thickness and weight changes in the accelerated corrosion test, as opposed to considerable reductions in the weight and thickness of the conventional GDL. We believe that this paper suggests profound implications in the commercialization of PEMFCs, because the metallic Ti foam provides a longer-term reliability and chemical stability, which can reduce the loss of Pt catalyst and, hence, the cost of PEMFCs.

Tribological properties of biocompatible Ti-10W and Ti-7.5TiC-7.5W.

This study investigates and compares the microstructure, biocompatibility, and tribological properties of two different Ti-based composites, Ti-10W and Ti-7.5TiC-7.5W, with those of pure Ti for their potential use in biomedical applications. In particular, cold and hot isostatic-pressing and arc-melting methods were utilized and compared for the microstructure of the composites. Nano-scratch measurements and pin-on-disk wear tests were employed to understand their tribological behavior. As compared to pure Ti, Ti-10W and Ti-7.5TiC-7.5W showed significantly improved nano-scratch resistance (by 85 and 77%, respectively) and wear resistance (by 64 and 66%, respectively), in good agreement with hardness measurements. For biocompatibility examination, both microculture tetrazolium test (MTT) and water soluble tetrazolium (WST-1) test were used to quantify the cell viability of human osteoblasts and mouse fibroblasts on the materials. Both of the Ti-based composites showed acceptable biocompatibility in comparison with the pure Ti control.

Ordered macroporous platinum electrode and enhanced mass transfer in fuel cells using inverse opal structure.

Three-dimensional, ordered macroporous materials such as inverse opal structures are attractive materials for various applications in electrochemical devices because of the benefits derived from their periodic structures: relatively large surface areas, large voidage, low tortuosity and interconnected macropores. However, a direct application of an inverse opal structure in membrane electrode assemblies has been considered impractical because of the limitations in fabrication routes including an unsuitable substrate. Here we report the demonstration of a single cell that maintains an inverse opal structure entirely within a membrane electrode assembly. Compared with the conventional catalyst slurry, an ink-based assembly, this modified assembly has a robust and integrated configuration of catalyst layers; therefore, the loss of catalyst particles can be minimized. Furthermore, the inverse-opal-structure electrode maintains an effective porosity, an enhanced performance, as well as an improved mass transfer and more effective water management, owing to its morphological advantages.

Self-assembled Fe3O4 nanoparticle clusters as high-performance anodes for lithium ion batteries via geometric confinement.

Although different kinds of metal oxide nanoparticles continue to be proposed as anode materials for lithium ion batteries (LIBs), their cycle life and power density are still not suitable for commercial applications. Metal oxide nanoparticles have a large storage capacity, but they suffer from the excessive generation of solid-electrolyte interphase (SEI) on the surface, low electrical conductivity, and mechanical degradation and pulverization resulted from severe volume expansion during cycling. Herein we present the preparation of mesoporous iron oxide nanoparticle clusters (MIONCs) by a bottom-up self-assembly approach and demonstrate that they exhibit excellent cyclic stability and rate capability derived from their three-dimensional mesoporous nanostructure. By controlling the geometric configuration, we can achieve stable interfaces between the electrolyte and active materials, resulting in SEI formation confined on the outer surface of the MIONCs.

Yttrium-doped cobalt nanoferrites prepared by sol-gel combustion method and its characterization.

Ferrites are extremely important magnetic ceramics in the production of electronic components because they reduce the energy losses by the induced currents acting as electrical insulators. Similarly, the spinel-structured cobalt-based ferrites are promising materials for stress, torsion sensors and energy storage applications (anode materials in lithium batteries, fuel cells and solar cells). Therefore, many studies have focused on cobalt ferrites obtained using conventional techniques. Different sintering conditions, types and levels of substitution result in different microstructures and magnetostriction coefficients under a wide range of preparation conditions. Despite many attempts, there are no specific reports on the trivalent substitution of yttrium in cobalt ferrite to the best of our knowledge. In the present study, yttrium-doped cobalt ferrite was prepared with different concentrations to identify the crystallite size with respect to the yttrium concentration, temperature and changes in the structural and electrical properties. In addition, the resistance of the nanostructured yttrium-doped cobalt ferrites nanopowders was analyzed. The resistance was increased by the addition of yttrium to cobalt ferrites.