Nb2O5 is a promising metal oxide electrode material for supercapacitors because of outstanding structural stability and wide electrochemical window, but low inherent conductivity hinders its many ...applications. This article reports one way for the synthesis of Nb2O5–graphene heterojunction composites using ethylene diamine tetraacetic acid and boron-functionalized graphene quantum dots (p-GQDs). p-GQDs were immobilized on graphene sheets by π–π stacking, followed by coordination with Nb(v), reduction into a hydrogel with ascorbic acid and annealing in nitrogen. The resulting Nb2O5-p-GQD-G offers a three-dimensional structure, ultrasmall size of Nb2O5 nanorods, PN junctions and Schottky heterojunctions. These dramatically improve the inherent conductivity, number of electrochemically active sites and a voltage window range. The n-Nb2O5-p-GQD-G electrode indicates a capacitance of 267.4 F g−1 at the current density of 1.0 A g−1, which is more than 1.5-fold that of the n-Nb2O5-n-GQD-G electrode, verifying that the formation of PN junctions can enhance the capacitance. The symmetrical supercapacitor with n-Nb2O5-p-GQD-G electrodes provides high specific capacitance (794 F g−1 at the current density of 0.2 A g−1 and 167.2 F g−1 at the current density of 2.0 A g−1), cycling stability (a capacity retention of 98.8% after 10 000 cycles at the current density of 1.5 A g−1) and energy density (110.3 W h Kg−1 at the power density of 200 W kg−1).
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.
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.
The paper firstly reports one strategy for scalable synthesis of Ta1.1O1.05/biomass carbon composite by boron-doped graphene quantum dots. The strategy breaks through the limitations of low intrinsic ...conductivity and insufficient electroactive sites of tantalum oxide, realizes the remarkable improvement of supercapacitor performance, and shows a bright prospect of application in high-performance supercapacitors.
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•We report one promising strategy for scalable synthesis of Ta1.1O1.05/biomass carbon composite.•The composite offers small size of Ta1.1O1.05, Abundant oxygen vacancies and PN heterojunction.•Unique structure achieves to ultrahigh electron conductivity and electrochemical active sites.•The composite electrode provides excellent electrochemical performances for supercapacitors.•The study proves oxygen vacancy and PN heterojunction improve supercapacitor performance.
Low intrinsic conductivity and insufficient electroactive sites hinder wide applications of tantalum oxide in supercapacitors. The study reports scalable synthesis of Ta1.1O1.05/biomass carbon (C) composite with multiple structure engineering by boron-doped graphene quantum dot (B-GQD). B-GQD was orderly coordinated with Ta(V) ion to produce Ta-B-GQD complex, sucked into cotton and dried. Followed by annealing at 900 °C in N2 to obtain B-GQD-Ta1.1O1.05/C. Experimental result and theoretical calculation demonstrate that the introduction of B-GQD results in formation of Ta1.1O1.05 nanorods with low valence, small size, highly exposed high-index crystal faces, oxygen vacancies and PN junction. The structure dramatically improves the intrinsic conductivity, electroactive sites and voltage window range. The B-GQD-Ta1.1O1.05/C electrode exhibits high capacitance of 528.3 F g−1 at 0.5 A/g, which is more than that of Ta1.1O1.05 electrode (130.9 F g−1). The flexible symmetrical supercapacitor provides ultrahigh capacitance of 374.1 F g−1 at 1 A/g, high-rate capacity of 207.8 F g−1 at 50 A/g, capacity retention of 98.7 % after 10,000 cycles at 10 A/g and energy density of 113.9 W h Kg−1 at 521.2 W kg−1. The supercapacitor has been successfully applied in the self-powered attitude sensor driven via friction nanogenerator to monitor human walking posture.
Lignin nanoparticles (LNP) were obtained by an acidolysis process from corn pristine lignin. X-ray photoelectron spectroscopy (XPS) and radical scavenging activity (RSA) of the free radical ...2,2-diphenyl-1-picrylhydrazyl (DPPH) confirmed a significant enhancement in reactivity of LNP in comparison with pristine lignin. Polyurethane (PU) nanocomposites were prepared by pre-polymerization of polyethylene glycol and diisocyanates in the presence of different contents (1, 3, 5 and 7 wt%) of LNP. The effects of LNP, serving as both biobased polyol and crosslinker, on the mechanical, hydrophobicity and dielectric behavior of the resulted PU nanocomposites were investigated. Tensile test results showed an overall enhancement for mechanical performance, and the elongation at break exceeded 1000% for all studied PU nanocomposites. Meanwhile, dynamic mechanical analysis (DMA) revealed that the crosslinking densities gradually increased with LNP addition. Furthermore, LNP based PU nanocomposites showed inherent resistance towards ultraviolet radiation and frequency dependent behavior for electrical conductivity. On the other hand, LNP based PU nanocomposites revealed good thermal reprocessability due to the transcarbamoylation reaction in the presence of DBTDL catalyst.
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•Lignin nanoparticles were obtained by a facile acidolysis process from corn lignin.•LNP served as both biobased polyol and crosslinker in polyurethane nanocomposites.•The thermal decomposition temperature of the PU nanocomposites was enhanced.•PU-LNP nanocomposites have inherent resistance towards ultraviolet radiation.•PU-LNP nanocomposites show a frequency dependent behavior for electrical conductivity.
Regime transitions and the morphology changes and kinetic analysis of biosynthesized polyhydroxyalkanoate (PHA) crystals from the melt were investigated by differential scanning calorimetry (DSC) and ...microscopic techniques. The PHA ultra-thin films with an average thickness of 60–70 nm were isothermally crystallized at different temperatures. Surprisingly, as the temperature increased, the crystal morphology of the PHA ultra-thin films changed from banded spherulites to non-banded spherulites to lath-like single crystals. At temperatures above 120 °C, lath-like single crystals were formed from the melt. Kinetic analysis of crystal growth in the PHA ultra-thin films demonstrated that the regime transitions of PHA crystal growth, from regime
II
to regime
I
and from regime
III
to regime
II
, occurred at around 100 and 70 °C, respectively. The transition at 100 °C induced morphology changes whereby non-banded spherulites transformed into lath-like single crystals, which was reported for the first time. As for the transition between regimes
III
and
II
, banded spherulites transformed into non-banded spherulites.
The poor mechanical properties induced by unsatisfactory crystallization ability limit the widespread use of biosynthesized poly (3-hydroxybutyrate-co-3-hydroxyhexanate) (PHBH). In this work, poly ...(3-hydroxybutyrate) (PHB) with a high melting point was first used as a homogeneous nucleating agent to increase the crystallization rate of PHBH by a self-nucleation method with a wider processing temperature window and crystallization kinetics and storage stability of mechanical properties of the PHBH/PHB mixtures were systematically investigated. By controlling the processing temperature and PHB content, the crystal nucleus density and crystallization rate of PHBH could be greatly increased while secondary crystallization was inhibited. When the processing temperature is 185 °C and PHB content is 20 wt%, the half crystallization time is shortened by 96% and the crystallinity was increased to 37.2%. Meanwhile, the mechanical performance of PHBH and its storage stability are greatly improved. Therefore, this work provides a simple and efficient way to improve the crystallization and mechanical performance of PHBH, which is expected to be applied to industrial production on a large scale.
•PHB with a high melting point was first used as a homogeneous nucleating agent.•Crystallization rate of PHBH was greatly increased by self-nucleation.•Mechanical performance of PHBH and storage stability is improved vastly.•A simple and efficient way to improve crystallization of PHBH was provided.
Partially biobased thermoplastic vulcanizates (TPV) with novel morphology, superior properties and partial degradability were prepared by dynamic cross-link of saturated poly(lactide) and ...ethylene-co-vinyl acetate (PLA/EVA) blends using 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (AD) as a free radical initiator. EVA showed higher reactivity with free radicals in comparison with PLA, leading to much higher gel content of the EVA phase (G f‑EVA) than that of the PLA phase (G f‑PLA). However, the G f‑PLA increased more steeply at AD content larger than 1 wt % where the reaction of EVA approached to a saturation point. The competing reaction changed the viscosity ratio of the two components (ηPLA/ηEVA) that resulted in a novel morphology evolution of the TPV, i.e., from sea–island-type morphology to phase inversion via a dual-continuous network-like transition and finally cocontinuity again with increasing the AD content. The cross-link and phase inversion considerably enhanced the melt viscosity (η*), elasticity (G′) and the solid-like behavior of the PLA/EVA-based TPV. Meanwhile, superior tensile strength (σt = 21 MPa), low tensile set (T s = 30%), moderate elongation (εb = 200%) and suitable stiffness (E′ = 350 MPa, 25 °C) were successfully achieved by tailoring the cross-link structure and phase morphology. In addition, the TPV are partially degradable in aqueous alkali. A degradation rate of approximately 5 wt % was achieved within 10 weeks at 25 °C and the degradation mechanism was investigated from both molecular and macroscopic levels. Therefore, this work provides a new type of partially biobased and degradable materials for substitution of traditional TPV.
The poor enantioselectivity and catalytic activity of chiral metal nanocrystals limit their wide applications in chiral synthesis. In this study, we report a strategy for the synthesis of chiral gold ...nanocrystals
via
the reduction of HAuCl
4
with ascorbic acid in the presence of CTAC, KBr and KI to form trioctahedral gold nanocrystals and their asymmetric structural evolution induced by
d
/
l
-cysteine. The resulting gold nanocrystals offer unique structures with a chiral morphology, chiral ligand and more exposed high-index facets. The formed
d
-Cys-Au and
l
-Cys-Au under optimized conditions exhibited high enantioselectivity and catalytic activity for the catalytic oxidation of glucose enantiomers. The catalytic activity of
d
-Cys-Au for
l
-glucose was 3.1-fold higher than that for
d
-glucose. The catalytic activity of
l
-Cys-Au for
d
-glucose was 3.4-fold higher than that for
l
-glucose. The DPV current of
d
-Cys-Au linearly increased and the DPV current of
l
-Cys-Au linearly decreased with an increase in the
l
-glucose/
d
-glucose ratio. The catalytic behavior of gold nanocrystals highly depend on the chiral morphology and chiral ligand.
l
-Cys-Au prepared with an evolution time of 20 min exhibited the best enantioselectivity. The increase in the coverage of
l
-cystine on
l
-Cys-Au resulted in reduced catalytic activity but improved enantioselectivity. The introduction of
l
-ascorbic acid hardly affected the catalytic activity of
l
-Cys-Au for
d
-glucose but obviously decreased the catalytic activity for
l
-glucose.
In recent decades, the continuous depletion of fossil fuels and the increasingly serious environmental issue have aroused wide attention on the development of biopolymers based on renewable biomass. ...Lignin is the second most abundant organic bio‐based macromolecule second to cellulose, and it can be widely found in plants. Furthermore, various phenol derivatives can be obtained by their depolymerization processes. The development of bio‐renewable polymeric materials originating from lignin‐derivative phenol monomers, such as vanillin, syringaldehyde, eugenol, vanillyl alcohol, vanillic acid, and ferulic acid, will not only valorize the bio‐sourced materials but also effectively reduce petroleum resource consumption and mitigate the environmental pollution. Therefore, an updated overview of the synthesis processes of these bio‐based polymers developed in the past decade, which includes both thermosets and thermoplastics such as epoxy, phenolic, polyimine, polybenzoxazine, polyurethane, and polyesters, are elucidated. In addition, the applications of these bio‐based polymers and their composites in flame‐retarded materials, degradable and reprocessable materials, dielectric materials, optoelectronic materials, as well as smart responsive materials are also intensively discussed. In line with the gradual development of synthesis technologies, we believe that derivatives of lignin will turn into one of the most promising materials to be considered for the preparation of high‐performance and functional bio‐based polymer materials.
Lignin, as an ideal “carbon” resource, is the second most abundant bio‐based macromolecule next to cellulose that can be widely found in plants, and various phenol derivatives such as vanillin, vanillyl alcohol, vanillic acid, eugenol, syringaldehyde and ferulic acid can be extracted by depolymerization processes from lignin. The synthesis processes of the bio‐renewable polymers based on lignin‐derived phenol monomers including both thermosets and thermoplastics such as epoxy, phenolic, polyimine, polybenzoxazine, polyurethane, and polyesters were well‐elucidated. In addition, the applications of these bio‐based polymers and their composites used for flame retarding materials, degradable and reprocessable materials, dielectric materials, optoelectronic materials, as well as smart responsive materials have been also intensively discussed.
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