High-entropy alloys have received considerable attention in the field of catalysis due to their exceptional properties. However, few studies hitherto focus on the origin of their outstanding ...performance and the accurate identification of active centers. Herein, we report a conceptual and experimental approach to overcome the limitations of single-element catalysts by designing a FeCoNiXRu (X: Cu, Cr, and Mn) High-entropy alloys system with various active sites that have different adsorption capacities for multiple intermediates. The electronegativity differences between mixed elements in HEA induce significant charge redistribution and create highly active Co and Ru sites with optimized energy barriers for simultaneously stabilizing OH
and H
intermediates, which greatly enhances the efficiency of water dissociation in alkaline conditions. This work provides an in-depth understanding of the interactions between specific active sites and intermediates, which opens up a fascinating direction for breaking scaling relation issues for multistep reactions.
Robust quality-of-service (QoS)-based and secrecy rate-based secure transmission designs are investigated for a multiple-input single-output system with multiple eavesdroppers and a cooperative ...jammer. Two scenarios are considered: (a) eavesdroppers' channel state information (ECSI) is available and (b) ECSI is unavailable. In scenario (a), a QoS-based design is considered to minimize the worst case signal-to-interference-and-noise ratio at the eavesdroppers and to guarantee the QoS of the legitimate receiver. A secrecy rate-based design is also studied where the worst case secrecy rate is maximized. In scenario (b), a QoS-based design is considered to maximize the power of jamming signals under the QoS constraint of the legitimate receiver, and the secrecy rate-based design is not applicable. In all these designs, we jointly optimize the transmit beamforming vector and the covariance matrix of jamming signals under individual power constraints. As the optimization problems are non-convex, we propose an algorithm for each problem through semidefinite relaxation. Our analysis and simulation results show that, even though the linear precoding scheme in our designs is transmit beamforming rather than the general rank transmit covariance, this does not cause any loss of optimality.
In this work, PVA nanocomposite films containing cellulose nanocrystals (CNC) and different amounts of lignin nanoparticles (LNP), prepared via a facile solvent cast method, were crosslinked by ...adding glutaraldehyde (GD). The primary objective was to investigate the effects of crosslinker and bio-based nanofillers loading on thermal, mechanical, antioxidant and water barrier behaviour of PVA nanocomposite films for active food packaging. Thermogravimetric analysis showed improved thermal stability, due to the strong interactions between LNP, CNC and PVA in the presence of GD, while Wide-angle X-ray diffraction results confirmed a negative effect on crystallinity, due to enhanced crosslinking interactions between the nanofillers and PVA matrix. Meanwhile, the tensile strength of PVA-2CNC-1LNP increased from 26 for neat PVA to 35.4 MPa, without sacrificing the ductility, which could be explained by a sacrificial hydrogen bond reinforcing mechanism induced by spherical-like LNP. UV irradiation shielding effect was detected for LNP containing PVA films, also migrating ingredients from PVA nanocomposite films induced radical scavenging activity (RSA) in the produced films in presence of LNP. Furthermore, PVA-CNC-LNP films crosslinked by GD showed marked barrier ability to water vapour.
In recent years, eco-friendly superhydrophobic materials have aroused much attention. Herein, biodegradable poly(lactic acid) (PLA) was selected as basic material to fabricate superhydrophobic foam ...with electrothermal effect by dip-coating graphene oxide (GO) on the surface of PLA foam constructed through freeze-drying process and the subsequent reduction with hydroiodic acid. Owing to the micro-nano rough structure of pristine PLA foam and the coverage of low-surface-energy reduced GO (rGO), the obtained rGO@PLA foam exhibited excellent water repellency with a high water contact angle of 150.6°. The foam was able to separate different oil–water mixtures, and the separation efficiencies were all above 96%. Importantly, the rGO layer also endowed the PLA foam with electrothermal conversion capability, and the surface temperature of the rGO@PLA foam rapidly increased to 129.5 °C from 30.8 °C at a low voltage of 15 V within only 120 s. By means of the generated Joule heat, the rGO@PLA foam was successfully applied for separating viscous crude oil from water, and the separation rate was about 14 times higher than that without voltage. Our findings conceivably stand out as a new tool to fabricate functional biodegradable materials for clean-up of viscous crude oil.
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This work investigated, for the first time, the role of nanosized lignin (LNP), in comparison with microlignin (LMP), when introduced at two different weight amounts (5% and 10 wt%) in bulk ...phenol–formaldehyde resol as adhesive. Morphological analysis was performed to check out the dispersion and interfacial bonding of lignin in the phenolic resin. The curing process has been examined by differential scanning calorimetry (DSC), while the thermal stability of the composites has been evaluated by using thermogravimetric (TGA) and thermo-mechanical (TMA) analysis. Results exhibited that small amount of lignin could both favor the thermal cure reaction, due to its abundance of phenylpropane units, and the initial thermal resistance could be consequently improved, especially when the nano-sized lignin was used. Meanwhile, the effect of micro- and nano-modification on tensile shear strength of wood lap joints based on lignin-phenol–formaldehyde resol adhesives was also analyzed. Results showed that 5 wt% of LNP could positively increase the shear strength from 8.7 to 10.9 MPa, opening the possibility of using environmental friendly nanoscale lignin in cross linked traditional phenol wood adhesives with enhanced adhesion performance, strongly related to nanoparticles higher specific surface area and reactivity.
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•Nanosized (LNP) and microlignin (LMP) were added to phenol–formaldehyde resol adhesive.•Nanolignin could both favor the cure reaction, due to its abundance of phenylpropane units.•Nanosized lignin homogenously dispersed absorbed and inhibited dimensional changes.•Higher specific surface area and reactivity for LNP increase the shear strength of wood joints.
Poly(glycolic acid) as a promising substitution for traditional petroleum-based polymers suffers from its inherent brittleness and rapid hydrolysis. The improvement of toughness and hydrolysis ...resistance is usually accompanied with a sacrifice of strength and stiffness. In the present work, we propose a simple and effective strategy to address this obstacle by introducing poly (butylene adipate-co-terephthalate) (PBAT) and combining extensional stress and temperature field. The robust, ductile and durable PGA/PBAT films are fabricated via “high temperature melting-quenching-stretching-annealing” (QSA) process. Highly oriented crystallites constructed by stretching and annealing lead to the improvement of strength and stiffness. Stress-induced strengthened entanglement network contributes to stabilization of craze growth and slipping, thus leading to the ductile behavior. As the result, the QSA films exhibit 89 MPa and 131% in tensile strength and the elongation at break, which are increased by 195%, 126% respectively compared to the unstretched film. More impressively, stretching resulted in abundant rigid amorphous chains, which worked with oriented crystallites to impart enhanced heat and hydrolysis resistance for the films. This work paves an avenue toward a wider range of applications for PGA materials and might be guidance for other semi-crystalline polymer blends.
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•Strength, toughness and hydrolysis resistance of PGA-based films are simultaneously improved by stretching and annealing.•Highly oriented crystallites lead to the improvement of strength and stiffness.•Stress-induced strengthened entanglement network contributes to stabilization of craze growth and slipping.•Rigid Amorphous Fraction hinders the diffusion of water molecules.
Biodegradable poly(lactide)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends were prepared by reactive blending in the presence of chain-extenders. Two chain-extenders with multi-epoxy ...groups were studied. The effect of chain-extenders on the morphology, mechanical properties, thermal behavior, and hydrolytic degradation of the blends was investigated. The compatibility between the PLA and PBAT was significantly improved by in situ formation of PLA-co-PBAT copolymers in the presence of the chain-extenders, results in an enhanced ductility of the blends, e.g., the elongation at break was increased to 500% without any decrease in the tensile strength. The differential scanning calorimeter (DSC) results reveal that cold crystallization of PLA was enhanced due to heterogeneous nucleation effect of the in situ compatibilized PBAT domains. As known before, PLA is sensitive to hydrolysis and in the presence of PBAT and the chain-extenders, the hydrolytic degradation of the blend was evident. A three-stage hydrolysis mechanism for the system is proposed based on a study of weight loss and molecular weight reduction of the samples and the pH variation of the degradation medium.
Silver nanoparticles (AgNPs) with a diameter of 3–6 nm were uniformly reacted onto the surface of nanocrystal cellulose (NCC) via complexation leading to NCC–Ag nanohybrids with an AgNP content of 8 ...wt %. Subsequently, antibacterial green nanocomposites containing renewable and biodegradable poly(lactide) (PLA), poly(butylene adipate-co-terephthalate) (PBAT) and NCC–Ag nanohybrids were synthesized and investigated. The PBAT as flexibilizer improved the toughness of the PLA matrix while the uniformly dispersed NCC–Ag nanohybrids enhanced the compatibility, thermal stability, crystallization, and antibacterial properties of the PLA/PBAT blends. The crystallization rate and the storage modulus (E′) of the green nanocomposites were increased obviously with increasing content of CNC–Ag nanohybrids. Meanwhile, notably the antibacterial activity of the PLA/PBAT/NCC–Ag nanocomposites was achieved against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus cells. The antibacterial performance was mainly related to the antibacterial nature of the finely dispersed NCC–Ag nanohybrids. The study demonstrates great potential of the green nanocomposites in functional packaging and antibacterial textile applications.
Melanin is a kind of ubiquitous natural pigment, which serves a variety of protective functions in many organisms. In the present study, natural melanin and synthetic melanin nanoparticles (NPs) were ...systematically investigated for its potential application in polymeric optical materials. A significant short-wavelength shielding and high visible light transparency polymer nanocomposite was easily obtained via tuning the melanin particle size. In particular, the nanocomposite film with melanin NPs (diameter ≈ 15 nm) loading even as low as 1 wt % blocks most ultraviolet light below 340 nm and still keeps high visible light transparency (83%) in the visible spectrum. More importantly, because of the excellent photoprotection and radical scavenging capabilities of melanin, the resulting polymer nanocomposite exhibits outstanding photostability. In effect, such fantastic melanin NPs is promising for applications in various optical materials.
The development of a bio-based plasticizer with good plasticizing performance, migration resistance, and thermal stability for polyvinyl chloride (PVC) is still a notable challenge due to the ...trade-off between molecular weight and compatibility. Herein, epoxidized isosorbide-based esters featuring multiple epoxy groups were prepared via the esterification of isosorbide with various aliphatic acids with C-18 alkyl chains (oleic acid, linoleic acid, and linolenic acid) followed by epoxidation. The resulting epoxidized isosorbide-based esters were utilized as PVC resin plasticizers, and the overall performance of these plasticized PVC specimens was investigated in detail. Moreover, the esterification reaction was optimized and 1-propylsulfonic-3-methylimidazolium hydrogensulfate ionic liquid was selected as the catalyst. After the reaction was complete, the ionic liquid and product were in separate phases, enabling facile catalyst recycling in a simple, convenient, and environmentally friendly process. The most superior plasticizing effect was achieved by epoxidized isosorbide linolenate (EGLA-ISB). In comparison to the PVC samples plasticized with dioctyl terephthalate (DOTP), those plasticized with EGLA-ISB demonstrated a 15-fold increase in thermal stability during isothermal testing (a PVC/50EGLA-ISB film had a low weight loss of approximately 1.5% after heating at 200 °C for 120 min). Furthermore, the initial thermal decomposition temperature of the PVC plasticized by EGLA-ISB increased by almost 40 °C (up to 306.9 °C) compared to pure PVC, and a higher elongation at break (387%) was also observed. The excellent performance of the PVC plasticized by EGLA-ISB was attributed to the C-18 alkyl chains and multiple epoxy groups of EGLA-ISB, which improved its PVC compatibility, enhanced the thermal stability of the PVC.
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•EGLA-ISB was prepared via the esterification of isosorbide with linolenic acid and followed by epoxidation.•1-Propylsulfo-3-methylimidazolium hydrogen sulfate ionic liquid was chosen as the catalyst for the esterification reaction.•After the reaction was complete, the ionic liquid and product were in separate phases, enabling facile catalyst recycling.•PVC/50EGLA-ISB film has a low weight loss of approximately 1.5% after heating at 200 °C for 120 min.•EGLA-ISB avoids the trade-off between molecular weight and compatibility.
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