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Insights into Different Reaction Behaviors of Propane and CO Oxidation over Pt/CeO2 and Pt/Nb2O5: The Crucial Roles of Support Properties
No full textPt/CeO2 and Pt/Nb2O5 catalysts were employed to catalyze CO and propane oxidation. It was found that the Pt/CeO2 catalyst was more active than the Pt/Nb2O5 catalyst for CO oxidation, while it was less active in propane oxidation. The different behaviors were closely related to the nature of the support, which affected the properties of the active Pt species as well as the reaction pathways. For CO oxidation, the reaction took place at the Pt-CeO2 interface of the Pt/CeO2 catalyst. The facile activation of oxygen species on the CeO2 with abundant oxygen vacancies accounted for its high activity, while the competitive adsorption of CO and O-2 on the surface Pt atoms led to a strong inhibiting role of oxygen on the reactivity, which was indicated by a negative reaction order of oxygen on the Pt/Nb2O5 catalyst. For the propane oxidation, as metallic Pt species were beneficial for the activation of C-H bond in propane, the high concentration of metallic Pt species in the Pt/Nb2O5 induced by the stabilizing effect of surface acidity of the Nb2O5 support was responsible for its higher activity compared to the Pt/CeO2 with oxidized Pt species
Preparation of cellulose-based fluorescent materials as coating pigment by use of DMSO/DBU/CO2 system
No full textA series of cellulose-based fluorescent materials are prepared under relative mild conditions by use of the DMSO/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/CO2 system to utilize as coating pigments. Through the observation under 365 nm UV light, the cellulose-based fluorescent materials exhibit good fluorescence response and bright color. Furthermore, due to the limitation of the molecular skeleton of cellulose, the intrinsic aggregation caused quenching phenomenon commonly existed in conventional organic fluorescent pigments can be effectively inhibited, which is very helpful to retain good fluorescence response in epoxy-based coating material and its coating films. Moreover, the addition of cellulose-based fluorescent materials also increases the mechanical properties of the coating film. The increase of tensile strength and tensile modulus respectively reaches similar to 39% and similar to 66%. Solvent resistance and thermal property of the coating films generally remain unchanged. The fabrication of cellulose-based fluorescent materials in DMSO/DBU/CO2 system provides a feasible way to develop the functional application of cellulose
Self-regulated parallel process 3-D array microfabrication with metal direct-write
No full textParallel process direct-write manufacturing of ultrahigh aspect ratio 3-D metal microstructures remains one of the ultimate challenges in 3-D manufacturing. Its development promises novel solutions for high density chip scale packaging and sorting that require precision microscale mechanical and electrical interfaces to microelectronics. Herein, we exploited a self-regulated growth mechanism revealed in the meniscus-confined direct-write electro-deposition to realize the parallel process fabrication of high-density area arrays of ultrahigh aspect-ratio metal microwire structures. We demonstrated the direct-write fabrication of an array of curvilinear metal spirals over 800 mu m in height and 50 mu m in array spacing, structurally and mechanically appropriate for high density wafer probe testing applications that cannot otherwise be fabricated with any other existing methods. (C) 2021 Elsevier Ltd. All rights reserved
Boosting charge-transfer kinetics and cyclic stability of complementary WO3-NiO electrochromic devices via SnOx interfacial layer
No full textThe effect of interfacial layer (SnOx) on the performance of the complementary electrochromic devices (ECDs) was examined, revealing that the SnOx/WO3 bilayer cathodes could enhance the electrochromic performance, such as a superior long-term cycling stability over 10,000 cycles, a high coloration efficiency of 101.61 cm(2) C-1 and a maximum transmittance modulation of 49.27%@633 nm. Moreover, compared with the single layer WO3, the SnOx/WO3 bilayer exhibited improved electrochemical activities and reaction kinetics. The probable explanation is that the introduced interfacial layer can boost the double injection of ions and electrons, balance the transport of ions and electrons, and protect the electrode from degradation by serving as a buffer layer during coloration/bleaching cycles. These results further provide a valuable insight for improving the electrochromic properties of the films instead of relying on conventional methods such as nanostructural or compositional control. (C) 2021 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi
The origin of the 500 nm luminescence band related to oxygen vacancies in ZrO2
No full textIn this paper, ion-beam-induced luminescence (IBIL) spectra of raw ZrO2 irradiated with 2 MeV H+ ions and photoluminescence (PL) spectra of annealed (200, 500 and 800 degrees C in air, nitrogen or oxygen) ZrO2 were investigated. The luminescence intensity decreased with increasing fluence, which indicated that the concentration of luminescence centers decreased during irradiation. The PL spectral results show that, with increasing partial pressure of oxygen during annealing, the intensity of luminescence decreases due to the decrease in oxygen vacancies. First-principles calculations were used to study the formation energy and transition level for oxygen vacancies (Vo), Ti-substituted Zr (Ti) and Ti adjacent to the nearest Vo (Ti-Vo) complex. The binding energies of Ti3+ and Vo(+) are 2.10 eV, which indicates that oxygen vacancies benefit the formation of Ti3+. The calculated configuration coordinate diagram and IBIL results indicated that Vo is not the luminescence origin. A new light-emitting structure of the Ti-Vo complex (F-A center) structure was proposed based on our calculations and previous studies. The calculated results of the luminescence model match the PL and IBIL spectra remarkably. The emission band of ZrO2 at approximately 500 nm was assigned to the F-A center or Ti3+ (the e(g) to t(2g) transition) adjacent to Vo(+)
Super-anticorrosive inverse nacre-like graphene-epoxy composite coating
No full textGraphene-based coatings (GCs) have emerged as attractive candidates for engineering applications. Despite recent progresses, efforts to achieve high-performance and durable GCs through conventional blending have been frustrated due to the uncontrolled distribution and orientation of graphene nanosheets, which degrades anticorrosion properties. By mimicking the nacre's microstructure, here we successfully fabricated a bioinspired GC, in which graphene nanosheets self-assembly in smectic can order in the epoxy matrix. As the bioinspired coating (similar to 98 wt% of epoxy polymer) shows an inverse composition to nacre (similar to 96 wt% of aragonite nanoplatelets), thus which is called an ``inverse nacre-like'' coating. The resultant bioinspired coating has high compactness and alignment degree, resulting in greatly enhanced physical barrier property and anticorrosion performance. Electrochemical tests reveal that the impedance modulus is 3 orders of magnitude much higher than that of blank coating. More importantly, the bioinspired coating shows a highly anisotropic conductivity due to the anisotropic graphene layers, preventing local galvanic corrosion through eliminating the current leakage in the outof-plane direction. (C) 2021 Elsevier Ltd. All rights reserved
Nano dual-phase CuNiTiNbCr high entropy alloy films produced by high-power pulsed magnetron sputtering
No full textDual-phase high entropy alloys have been proved to have the ability to overcome the strength-ductility trade-off. However, high-entropy alloy films are difficult to obtain a dual-phase structure due to the extremely high cooling rate during the preparation process and the high-entropy effect of the film itself. In this paper, the dual-phase CuNiTiNbCr high-entropy alloy films were prepared by high-power pulsed magnetron sputtering at different working pressures. The composition, microstructures, mechanical properties and electrochemical corrosion performance were tested by energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), nano-indentation, Vickers indentation and electrochemical polarization. The CuNiTiNbCr films exhibited a dual-phase structure composed of FCC matrix phase and Cu-rich BCC precipitated phase. The film presented a two-layer structure, the single FCC phase structure near the substrate and the FCC + BCC structure above. Comparing with FCC phase, the dual-phase structure exhibited higher hardness. With the increase of deposition pressure, the structure of the film became looser, and the hardness, toughness and corrosion resistance were all decreased due to the influence of the structure. It is proved that high-power pulsed magnetron sputtering is a feasible way for the phase structure regulation and performance improvement of high-entropy alloy films
Tailoring Highly Ordered Graphene Framework in Epoxy for High-Performance Polymer-Based Heat Dissipation Plates
No full textAs the power density and integration level of electronic devices increase, there are growing demands to improve the thermal conductivity of polymers for addressing the thermal management issues. On the basis of the ultrahigh intrinsic thermal conductivity, graphene has exhibited great potential as reinforcing fillers to develop polymer composites, but the resultant thermal conductivity of reported graphenebased composites is still limited. Here, an interconnected and highly ordered graphene framework (HOGF) composed of high-quality and horizontally aligned graphene sheets was developed by a porous film-templated assembly strategy, followed by a stress-induced orientation process and graphitization post-treatment. After embedding into the epoxy (EP), the HOGF/EP composite (24.7 vol %) exhibits a record-high in-plane thermal conductivity of 117 W m(-1) K-1, equivalent to similar to 616 times higher than that of neat epoxy. This thermal conductivity enhancement is mainly because the HOGF as a filler concurrently has high intrinsic thermal conductivity, relatively high density, and a highly ordered structure, constructing superefficient phonon transport paths in the epoxy matrix. Additionally, the use of our HOGF/EP as a heat dissipation plate was demonstrated, and it achieved 75% enhancement in practical thermal management performance compared to that of conventional alumina for cooling the high-power LED
To Clarify the Resilience of PEBA/MWCNT Foams via Revealing the Effect of the Nanoparticle and the Cellular Structure
No full textThe objective of this study is to clarify the resilience of the poly(ether-mb-amide)/multiwalled carbon nanotube (PEBA/MWCNT) composite foams from the perspectives of the nanoparticle and the cellular structure. The PEBA/MWCNT composites were prepared via a solution blending process with different contents of MWCNTs (0, 0.1, 1, and 5 wt %), and then the PEBA/MWCNT foams were prepared via a subsequent two-step batch foaming technique. The cyclic tensile test was performed with a universal testing machine, and the inelastic behavior of the composites and the foams was estimated based on the cyclic strain-stress curves. It was found that the incorporation of the MWCNT not only enhances the inelastic behavior of the composites via increasing the modulus but also brings in improved resilience of the foams compared to the composites via decreasing the cell size and increasing the cell density. The foam with 0.1 wt % content of MWCNT exhibits the best resilience. It is considered that the competition between the two effects of the nanoparticles of restricting chain mobility and altering the cellular structure might be the reason to bring the best resilience at a suitable content of the nanoparticles. The resilience of the foams with different contents of MWCNT showed no significant dependence on the expansion ratio and the modulus, which allows for their potential applications in the fields of high-end sport shoes and sports apparatus
Recent Progress in Superhydrophilic Carbon-Based Composite Membranes for Oil/Water Emulsion Separation
No full textThe purification of stabilized oil/water emulsions is essential to meet the ever increasing demand for monitoring water in the environment, which has been addressed with superwetting carbon-based separation membranes. These include superhydrophilic carbon-based membranes whose progress in recent years and perspectives are reviewed in this paper. The membrane construction strategy is organized into four parts, vacuum-assisted selfassembly, sol-gel process, electrospinning, and vacuum-assisted filtration. In each section, the design strategies and their responding disadvantages have been comprehensively discussed. The challenges and prospects concerning the superhydrophilic carbon-based separation membranes for oily wastewater purification are also summarized to arouse researchers to carry out more studies