Strain in layered transition‐metal dichalcogenides (TMDs) is a type of effective approach to enhance the catalytic performance by activating their inert basal plane. However, compared with ...traditional uniaxial strain, the influence of biaxial strain and the TMD layer number on the local electronic configuration remains unexplored. Herein, via a new in situ self‐vulcanization strategy, biaxially strained MoS2 nanoshells in the form of a single‐crystalline Ni3S2@MoS2 core–shell heterostructure are realized, where the MoS2 layer is precisely controlled between the 1 and 5 layers. In particular, an electrode with the bilayer MoS2 nanoshells shows a remarkable hydrogen evolution reaction activity with a small overpotential of 78.1 mV at 10 mA cm‐2, and negligible activity degradation after durability testing. Density functional theory calculations reveal the contribution of the optimized biaxial strain together with the induced sulfur vacancies and identify the origin of superior catalytic sites in these biaxially strained MoS2 nanoshells. This work highlights the importance of the atomic‐scale layer number and multiaxial strain in unlocking the potential of 2D TMD electrocatalysts.
The effect of biaxial strain and layer numbers of MoS2 nanoshells on the electrocatalytic activity is investigated in detail. Calculations reveal the superiority of biaxial strain over uniaxial strain and identify the ideal Mo coordination and S vacancies for maximal catalytic activity.
Unfilled natural rubber compounds composed of conventional (CV), semi-efficient (SEV), efficient (EV) and sulfur donor (SD) vulcanization systems were heat aged to promote sulfur reversion. ...Rheometry, hardness, strain-strain characteristics including Mooney-Rivlin analysis, equilibrium solvent swell and Double Quantum (DQ) Nuclear Magnetic Resonance (NMR) were used to monitor crosslink density changes. A loss of crosslink density was observed by rheometry, C1, equilibrium swelling and by DQ NMR as a function of cure extent. No chain scission reactions were operating in the time/temperature conditions used. All crosslink distributions were unimodal and the network homogeneity followed the order of EV > SD > SEV > CV. The crosslink distribution narrowed during the curing process for the CV and SEV systems. Non-oxidative maturation reactions were advantageous in promoting a more random distribution of crosslinks in the polymer matrix.
•Crosslink density loss observed by rheometry, Mooney-Rivlin C1, equilibrium swelling and DQ NMR.•Crosslink density loss followed CV > SEV > EV ≈ SD.•Chain scission reactions not observed during reversion.•Crosslink distributions were mono-distributed and narrowed during curing.•Network homogeneity followed EV > SD > SEV > CV.
Inverse vulcanization utilizes an organic compound as reagent for crosslinking elemental sulfur to result in corresponding polymeric material with a high sulfur content. This work, employing ...1,3,5‐triisopropylbenzene (TIPB) as the reagent, demonstrates the first attempt on extending the scope of crosslinking agents of inverse vulcanization to saturate compounds. Under nuclear magnetic spectroscopic analysis, the reactions between TIPB and elemental sulfur take places through ring‐opening reaction of S8 resulting in sulfur radicals at sulfur chain ends, radicals transferring to isopropyl groups of TIPB, and radical coupling reactions between carbon radicals and sulfur radicals. The obtained products are similar to the sulfur polymers from conventional inverse vulcanization processes and show self‐healing property.
This work demonstrates the first study on employing a saturate compound as the crosslinking agent for elemental sulfur through sequential radical transfer and coupling reactions in the “inverse vulcanization” processes. The sulfur‐rich polymers are similar to that from conventional inverse vulcanization agents. The scope of the reagents for inverse vulcanization has been successfully extended.
In order to study the influence of two‐stage vulcanization process on the hydrophobic characteristics of FKM, superhydrophobic surfaces were prepared based on template method (1000 mesh screen, 1600 ...mesh screen and 2000 mesh screen), and six kinds of FKM with micro‐rough surface were prepared by one‐stage vulcanization and two‐stage vulcanization process, respectively. At first, the influence of two‐stage vulcanization process on the physical and chemical properties of FKM was illustrated by characterizing the two‐dimensional convex structure, three‐dimensional roughness and chemical functional groups of FKM. Then, mechanical tests and wettability tests were carried out on different FKM prepared by primary vulcanization and secondary vulcanization. The results show that the hydrophobicity of FKM prepared by secondary vulcanization is improved compared with FKM prepared by primary vulcanization, and the contact angle of FKM prepared by secondary vulcanization can reach above 165°. The secondary vulcanization process enhances the hydrophobicity of FKM mainly by increasing the longitudinal size of the convex structure on the surface of FKM, homogenizing the sizes of the convex structure and pits on the surface of FKM, and increasing the roughness of FKM surface. In addition, in the process of secondary vulcanization, the chain reaction of FKM matrix occurred. In the matrix, the hydrophilic group OH disappears, and the polar hydrophilic group becomes nonpolar hydrophobic group.
The invention of inverse vulcanization provides great opportunities for generating functional polymers directly from elemental sulfur, an industrial by‐product. However, unsatisfactory mechanical ...properties have limited the scope for wider applications of these exciting materials. Here, we report an effective synthesis method that significantly improves mechanical properties of sulfur‐polymers and allows control of performance. A linear pre‐polymer containing hydroxyl functional group was produced, which could be stored at room temperature for long periods of time. This pre‐polymer was then further crosslinked by difunctional isocyanate secondary crosslinker. By adjusting the molar ratio of crosslinking functional groups, the tensile strength was controlled, ranging from 0.14±0.01 MPa to 20.17±2.18 MPa, and strain was varied from 11.85±0.88 % to 51.20±5.75 %. Control of hardness, flexibility, solubility and function of the material were also demonstrated. We were able to produce materials with suitable combination of flexibility and strength, with excellent shape memory function. Combined with the unique dynamic property of S−S bonds, these polymer networks have an attractive, vitrimer‐like ability for being reshaped and recycled, despite their crosslinked structures. This new synthesis method could open the door for wider applications of sustainable sulfur‐polymers.
Functional sulfur: The synthesis of sulfur‐polymers with significantly improved mechanical properties and controlled performance is reported. In the process a linear pre‐polymer containing hydroxyl functional group is crosslinked by difunctional isocyanate secondary crosslinkers. Control of hardness, flexibility, solubility and function of the material is demonstrated.
Layered double hydroxides (LDHs) are promising cathode materials for supercapacitors because of the enhanced flow efficiency of ions in the interlayers. However, the limited active sites and ...monotonous metal species further hinder the improvement of the capacity performance. Herein, cobalt sulfide quantum dots (Co9S8‐QDs) are effectively created and embedded within the interlayer of metal‐organic‐frameworks‐derived ternary metal LDH nanosheets based on in situ selective vulcanization of Co on carbon fibers. The hybrid CF@NiCoZn‐LDH/Co9S8‐QD retains the lamellar structure of the ternary metal LDH very well, inheriting low transfer impedance of interlayer ions. Significantly, the selectively generated Co9S8‐QDs expose more abundant active sites, effectively improving the electrochemical properties, such as capacitive performance, electronic conductivity, and cycling stability. Due to the synergistic relationship, the hybrid material delivers an ultrahigh electrochemical capacity of 350.6 mAh g−1 (2504 F g−1) at 1 A g−1. Furthermore, hybrid supercapacitors fabricated with CF@NiCoZn‐LDH/Co9S8‐QD and carbon nanosheets modified by single‐walled carbon nanotubes display an outstanding energy density of 56.4 Wh kg−1 at a power density of 875 W kg−1, with an excellent capacity retention of 95.3% after 8000 charge–discharge cycles. Therefore, constructing hybrid electrode materials by in situ‐created QDs in multimetallic LDHs is promising.
Cobalt sulfide quantum dots (Co9S8‐QDs) are anchored in situ within NiCoZn‐LDHs (layered double hydroxides) based on an approach of selective vulcanization of Co, and the lamellar structure of the LDHs is retained very well. Due to inheriting the characteristics of LDHs and QDs, the hybrid CF@NiCoZn‐LDH/Co9S8‐QD delivers an outstanding electrochemical performance.
Sulfur deficiency in soils has become an increasing concern over the past decades. Despite elemental sulfur (S8) vast utilization as a commercial fertilizer, S8 has to be biologically oxidized for ...plant assimilation, drastically limiting its efficiency. Therefore, we propose a new fertilizer in which S8 structure is more accessible to oxidizing microorganisms by chemical modification via inverse vulcanization technique, a solvent-free copolymerization method, with soybean oil as comonomer. Sulfur oxidation experiments were performed by A. niger submerged cultivation, confirming that the homogeneous rubbery-like material provides enhanced oxidation, with great potential as multifunctional sulfur-fertilizer.
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•Polysulfide fertilizers were synthesized via inverse vulcanization.•The polysulfides achieved superior S-oxidation than elemental sulfur.•The alkene content of the polymer contributed as substrate for biological activity.
Sulfur is an underused by‐product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed into functional polymers, by ...stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control of their physical properties is needed. Here we report four new terpolymers prepared from sulfur and two distinct alkene monomers that can be predictively tuned in glass transition, molecular weight, solubility, mechanical properties, and color.
Strengthening, altering and controlling the properties of inverse vulcanized sulfur polymers is of great importance. Over 60 million tons of sulfur are produced in excess by the petrochemical industry, and the potential applications of sulfur polymers are widespread. We investigate the mechanical properties and create a library of sulfur terpolymers.
The purpose of this work is to study the interaction of the croton fraction with amides – urea and thiourea and to develop technologies for obtaining accelerators for vulcanization of rubbers for the ...rubber industry.
The sulfur curing system, peroxide curing system and their combinations were applied for the cross-linking of unfilled and carbon black-filled rubber formulations based on ...ethylene-propylenediene-monomer rubber. The results demonstrated that the type of curing system influenced the course and shape of curing isotherms. This resulted in the change of curing kinetics of rubber compounds. The cross-link density of materials cured with combined vulcanization systems was lower than that for vulcanizates cured with the peroxide or sulfur system. Good correlation between the cross-link density as well as the structure of the formed cross-links and physical–mechanical characteristics of the cured materials was established. Both filled and unfilled vulcanizates cured with combined vulcanization systems exhibited a higher tensile strength and elongation at break when compared to their equivalents vulcanized in the presence of the peroxide or sulfur curing system. It can be stated that by proper combination of vulcanization systems, it is possible to modify the tensile behavior of vulcanizates in a targeted manner. On the other side, dynamical–mechanical properties were found not be significantly influenced by the curing system composition.
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