Papers by Keyword: Hierarchical Structure

Abstract: Transition metal phosphides (TMPs) are potential candidates for supercapacitors. To improve their performance by adjusting their morphology and composition, hierarchical CoP@NiMn-P nanocomposites were successfully prepared by the hydrothermal method, electrodeposition, and low-temperature phosphorization. NiMn-P nanosheets were coated on CoP nanowires to form a hierarchical structure. Electrochemical analysis results indicated that the specific capacitance reached 2162.2 F g^-1 at 1 A g^-1 with a high capacitance retention ratio of 83.3% after 5000 cycles at a current density of 10 A g^-1. This excellent electrochemical performance was attributed to the large specific surface area and enhanced conductivity. Furthermore, an asymmetric supercapacitor, CoP@NiMn-P//AC, was prepared using CoP@NiMn-P as the positive electrode and AC as the negative electrode. A large voltage window of 1.6 V and high energy density of 21.1 Wh kg^-1 at 804.3 W kg^-1 with a good capacity retention rate were achieved. The results confirm that CoP@NiMn-P has good potential for application in high-performance energy storage devices and provide a reference for the design of phosphide with morphology/composition optimization.

Abstract: A new synthetic procedure to Metal/metal sulfide hierarchical pore array composites was described. That is, a layer of Ni-Co-S nanoflakes was in situ constructed on the Ni ordered bowl-like micro/nanoarrays through a two-step electrodeposition method with the assistance of a colloidal sphere template. Such as-grown hierarchical composites could increase the specific surface areas and provide more active sites for electrocatalytic reactions. It exhibited a high catalytic activity to glucose, with a high sensitivity of 1210.1 μM‧mM^-1cm^-2 and a wide linear range from 0.5 μM to 2.0 mM. This work provides another candidate material for the development of planar non-enzymatic glucose sensors.

Abstract: This research is aimed at testing the ability of high-end 3D printers to reproduce complex structures having some acoustic performances in terms of sound absorption and sound transmission loss. Specifically, some experiments were made on four different types of geometries to compare their acoustic behaviour. The sound absorption and sound insulation of the samples have been evaluated by means of a four-microphone impedance tube. The adopted technique allows to retrieve the transfer matrix of each specimen and then, through a composition of the matrices, to virtually determine the acoustic performances of any arrangement of the different samples. The experiments revealed promising results in terms of quality, finishing and precision of the jetting process, highlighting benefits and critical issues related to the acoustic performances.

Abstract: The aim of the present study was to characterize two kinds of TiN/TiO₂ coatings in terms of topography, composition, and electrochemical stability after immersion in simulated body fluid (SBF). Micropatterning of the substrate (Ti-5Al-4V alloy) was done by using electron beam modification (EBM) by scanning electron beam while nanostructured TiN/TiO₂ films were deposited over EBM Ti5Al4V substrates using two physical vapor deposition techniques: 1) magnetron sputtering, and 2) cathodic arc and glow-discharge methods. When immersed for 7 and 14 days in SBF at static conditions (37±0.05 °C, pH 7.4), Ca/P ratio of the apatite deposits increased from approximately 1.5 up to near stoichiometric (1.67), respectively. After the initial decrease, the pH of the solution during soaking increased gradually reaching values close to 7.7 for both coatings. However, the weight gain of the samples with Arc coatings after the immersion period in SBF was nearly three times more than those with magnetron deposited coating. The electrochemical potentiodynamic tests performed in SBF indicated a shift in the corrosion potentials towards nobler direction after 7 and 14 days of immersion compared to non-immersed samples, whereas the corrosion current density was slightly increased.

Abstract: The focus of this review is to outline the remarkable ability of the gecko to climb surfaces vertically, at tremendous speed (over 1 m/s) using van der Waals forces (one of nature’s amazing “sticking and unsticking” directional dry adhesion design) as well as contact splitting mechanism. Further, the elasticity of the hairs conforming to the topology of the surface and hence contributing to an increased adhesion force is discussed, apart from the applications of gecko feet bio-inspired solutions. Such applications are in areas as diverse as, and not restricted to, climbing vertically and horizontally on glass surfaces; fitting televisions and computers on the walls; in robots for the inspection and maintenance of installations in space stations and self-cleaning surfaces. By this review, we hope to inspire and motivate the current generation of engineers to study, mimic and abstract the fundamental hierarchical structures as well as the incredible dry adhesion principles (as closely as is possible) objects of nature. This approach will help in improving upon the existing methods to produce gecko feet-like materials with dry adhesion as well as self-cleaning properties. Such refinement strategies can also include the development of hybrid structures utilizing a combination of designs found in other organisms in Mother Nature (for e.g., the mushroom-shaped structure found in the beetle). This requires improvements in the fundamental hierarchical arrangement of the gecko feet-like hairs and their inter-facial interactions with model substrata. Also, the mechanical deformations of the different gecko feet-like materials as well as how sliding velocity impacted adhesional and frictional phenomena should be studied and better understood. This will enable the engineer to develop better gecko feet-like adhesives.

Abstract: The addition of certain co-solvents to the hydrothermal synthesis starting solution can greatly alter morphology and enhance different morphology dependent properties of the synthesized material. While ethanol is the most common co-solvent used for the synthesis of various SnO₂ nano/microstructures by hydro/solvothermal process, it is not clear how the use of some other alcoholic co-solvents (for example, methanol or isopropanol) affect morphology and properties of SnO₂, especially if synthesis is done under similar conditions as in the case of ethanol co-solvent. In the present study, we investigated how the use of various alcoholic co-solvents (methanol, ethanol, 2-propanol, ethylene glycol and glycerol) affects crystal structure, morphology and specific surface area of the hydrothermally synthesized SnO₂. Additionally, sensitivity towards 100 ppm ethanol of the synthesized materials was tested. The formation of nanoparticles, rod-cluster structures and spherical SnO₂ structures were observed depending on the alcoholic co-solvent used. The highest sensitivity (~22 at 250 °C) showed the material that was synthesized in the presence of ethanol co-solvent.

Abstract: Nature is a perfect designer in fabricating biomaterials with well-defined and hierarchical nanostructures. Here we report a biomineralization-inspired approach for preparing hierarchical ZnO structure with high UV-light efficiency. The results show that biomacromolecules play an important role on controlling growth and assembly of ZnO nanostructures. It is found that the biomacromolecules favoring the isotropic growth of ZnO at the high concentration.

Abstract: This paper provides a novel route to prepare silica monoliths with hierarchical porous structure via freeze drying. In this method, macroporous silica monoliths were first produced by freeze-drying and calcination. By adjusting the concentration of cetyltrimethylammonium bromide in ethylsilicate, a layer of mesoporous thin film was attached on the macroporous silica monolith. The structural characterization of the hierarchical porous monoliths were studied by field emission scanning electron microscopy, mercury porosimeter and nitrogen adsorption-desorption techniques (BET). It turned out that the pore distribution of the obtained monoliths was ranged from 3.72 nm to 23.21nm and the maximum specific surface area calculated from BET was about 288 m^2/g, which indicated the existence of hierarchical structure in the obtained material.

Abstract: A fuzzy clustering analysis model based on the quotient space is proposed. Firstly, the conversion from coarse to fine granularity and the hierarchical structure are used to reduce the multidimensional samples. Secondly, the fuzzy compatibility relation matrix of the model is converted into fuzzy equivalence relation matrix. Finally, the diagram of clustering genealogy is generated according to the fuzzy equivalence relation matrix, which enables the dynamic selection of different thresholds to effectively solve the problem of cluster analysis of the samples with multi-dimensional attributes.

Abstract: Hierarchically structured LDHs are being actively investigated due to their potential applications in bioseparation and catalysis which result from their special surface structures and positively charged nanosheets. This work presents an effective method of fabricating hierarchical LDHs based materials with high surface-to-volume ratios. To do this, the microscaled Al₂O₃ fibers are fabricated via a simple biotemplate method employing paper fibers as templates and in the second step the nanoscaled Ni-Al LDH platelets are fabricated into hierarchical architectures based on crystal growth on surface of Al₂O₃ fibers. In order to obtain the multi-component and multi-scale structure LDHs based materials, the ZnO/LDHs composites are obtained by controlling crystal growth process. The developed facile route is highly valuable and feasible for hierarchical porous LDHs based materials for applications in research and industrial fields.