It is demonstrated that the luminescence efficiency of monolayers composed of MoS2, WS2, and WSe2 is significantly limited by the substrate and can be improved by orders of magnitude through ...substrate engineering. The substrate affects the efficiency mainly through doping the monolayers and facilitating defect‐assisted nonradiative exciton recombinations, while the other substrate effects including straining and dielectric screening play minor roles. The doping may come from the substrate and substrate‐borne water moisture, the latter of which is much stronger than the former for MoS2 and WS2 but negligible for WSe2. Using proper substrates such as mica or hexagonal boron nitride can substantially mitigate the doping effect. The defect‐assisted recombination depends on the interaction between the defect in the monolayer and the substrate. Suspended monolayers, in which the substrate effects are eliminated, may have efficiency up to 40% at room temperatures. The result provides useful guidance for the rational design of atomic‐scale light emission devices.
Luminescence efficiency in transition metal dichalcogenide monolayers can be improved by orders of magnitude through engineering the interaction with substrates. The luminescence efficiency of the monolayers is mainly affected through doping and facilitating nonradiative exciton recombination. Since the doping effect significantly depends on the kind of substrate, choosing the right type of substrates is a crucial step toward maximizing efficiency.
Four polysaccharide fractions (P‐1: 71.40%, P‐2: 1.95%, P‐3: 1.14%, P‐4: 1.64%) were isolated from crude Polygonatum sibiricum polysaccharide (PSP), processed by water extraction, ethanol ...precipitation, and further separated with diethylaminoethyl cellulose‐52 anion‐exchange chromatography. Their molecular weights and monosaccharide compositions were characterized by high performance gel chromatography with evaporative light scattering detector and ultraviolet–visible detector. The antioxidant activity of four polysaccharides fractions were assessed by the electron transfer menchanism (DPPH, ferric reducing power, and ABST assays) and chelation of transition metals (Fe2+ and Cu2+ chelation ability). The highest content fraction P‐1 exhibited the lowest antioxidant activity, and the ranking of antioxidant capacity was P‐4 > P‐3 > P‐2 > PSP > P‐1. After processed by microwave‐assisted degradation, the molecular weight of P‐1 was decreased from 2.99 × 105 to 2.33 × 103 Da, while the antioxidant activity of degraded P‐1 was about eightfold higher than natural P‐1. These results indicated that the proposed microwave‐assisted degradation approach was an efficacious methodology to improve their bioactivity by lower the molecular weight of polysaccharides.
Practical Application
This study provided an environmentally friendly, convenient and efficient microwave‐assisted degradation technology to process the neutral polysaccharides from Polygonatum sibiricum. The results could be used for the development and utilization of various plant polysaccharides as a kind of food supplement in our daily life.
The majority of commercial polyolefins are produced by coordination polymerization using early or late transition metal catalysts. Molecular catalysts containing these transition metals (Ti, Zr, Cr, ...Ni, and Fe, etc.) are loaded on supports for controlled polymerization behavior and polymer morphology in slurry or gas phase processes. Within the last few years, metal–organic frameworks (MOFs), a class of unique porous crystalline materials constructed from metal ions/clusters and organic ligands, have been designed and utilized as excellent supports for heterogeneous polymerization catalysis whose high density and uniform distribution of active sites would benefit the modulations of molecular weight distributions of high‐performance olefin oligomers and (co)polymers. Impressive efforts have been made to modulate the microenvironment surrounding the active centers at the atomic level for improved activities of MOFs‐based catalysts and controlled selectivity of olefin insertion. This review aims to draw a comprehensive picture of MOFs for coordination olefin oligomerization and (co)polymerization in the past decades with respect to different transition metal active centers, various incorporation sites, and finally microenvironment modulation. In consideration of more efforts are needed to overcome challenges for further industrial and commercial application, a brief outlook is provided.
Metal–organic frameworks (MOFs) are designed as excellent supports for heterogeneous polymerization catalysis, and impressive efforts are made to modulate the microenvironment for improving activities and selectivity of MOFs. This review aims to draw a comprehensive picture of MOFs for coordination olefin oligomerization and (co)polymerization with respect to different transition metal active centers, various incorporation sites, and finally microenvironment modulation.
We have demonstrated that multiple functionalities of transition-metal dichalcogenide (TMDC) monolayers may be substantially improved by the intercalation of small cations (H+ or Li+) between the ...monolayers and underlying substrates. The functionalities include photoluminescence (PL) efficiency and catalytic activity. The improvement in PL efficiency may be up to orders of magnitude and can be mainly ascribed to two effects of the intercalated cations: p-doping to the monolayers and reducing the influence of substrates, but more studies are necessary to better understand the mechanism for the improvement in the catalytic functionality. The cation intercalation may be achieved by simply immersing substrate-supported monolayers into the solution of certain acids or salts. It is more difficult to intercalate under the monolayers interacting with substrates stronger, such as as-grown monolayers or the monolayers on 2D material substrates. This result presents a versatile strategy to simultaneously optimize multiple functionalities of TMDC monolayers.
Water-in-salt (WIS) electrolytes are successfully introduced into carbon-based supercapacitors to effectively promote energy density. However, temperature-dependent performance of carbon-based ...supercapacitors with these electrolytes is rarely discussed, and the key factors, determined electrochemical performance at a wide temperature range, are not revealed completely. Herein, three rose petal-derived porous carbons (RPC) with different pore properties are prepared by a KOH activation strategy. The electrochemical performance of RPC-based supercapacitors with different concentration LiTFSI WIS electrolytes is investigated from −20 to 100 °C. The working voltage of these supercapacitors can reach 2.4 V, and thus the energy density of RPC supercapacitors with 20 m LiTFSI electrolyte can highly attain 44 W h kg−1 at 564 W kg−1 and 60 °C. Even though the power density is 3.5 kW kg−1 at 25 °C, it can be maintained to 12 W h kg−1. More importantly, the electrochemical performance intimately depends on the temperature. Both electrolyte concentration and pore properties of RPC significantly influence the electrochemical performance of these supercapacitors at different temperature. Therefore, to achieve superior performance for carbon-based supercapacitors with the LiTFSI WIS electrolyte at a wide temperature range, the optimization of electrolyte concentration and rational design for pore properties of carbon materials are essential strategies.
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•Electrochemical performance of RPC supercapacitors is explored from −20 to 100 °C.•Working voltage of RPC supercapacitors can reach 2.4 V.•Energy density of RPC supercapacitors can attain 44 W h kg−1 at 564 W kg−1 and 60 °C.•The electrochemical performance intimately depends on the temperature.•Electrolyte concentration and pore properties influence electrochemical performance.
Two-dimensional materials provide extraordinary opportunities for exploring phenomena arising in atomically thin crystals. Beginning with the first isolation of graphene, mechanical exfoliation has ...been a key to provide high-quality two-dimensional materials, but despite improvements it is still limited in yield, lateral size and contamination. Here we introduce a contamination-free, one-step and universal Au-assisted mechanical exfoliation method and demonstrate its effectiveness by isolating 40 types of single-crystalline monolayers, including elemental two-dimensional crystals, metal-dichalcogenides, magnets and superconductors. Most of them are of millimeter-size and high-quality, as shown by transfer-free measurements of electron microscopy, photo spectroscopies and electrical transport. Large suspended two-dimensional crystals and heterojunctions were also prepared with high-yield. Enhanced adhesion between the crystals and the substrates enables such efficient exfoliation, for which we identify a gold-assisted exfoliation method that underpins a universal route for producing large-area monolayers and thus supports studies of fundamental properties and potential application of two-dimensional materials.
Although polyvinyl siloxane (PVS) materials and polyether (PE) materials have been the recommended materials for making impressions for implant-supported fixed complete dentures (IFCDs), a consensus ...regarding the optimal impression materials has yet to be established.
The purpose of this systematic review and meta-analysis was to evaluate the effect of impression materials on the accuracy of conventional impressions for IFCDs and to provide guidance for selecting the optimal impression material.
The PubMed, Web of Science, and Embase databases were searched and supplemented via hand searches. Studies comparing the accuracy of conventional impressions for IFCDs using PVS and PE materials with either direct (open-tray) or indirect (closed-tray) techniques were included. Linear distance deviations and angular deviations between adjacent implants were evaluated. The mean difference (MD) with a 95% confidence interval (CI) was calculated for continuous data. A subgroup analysis was conducted to evaluate the impact of implant angulation (α=.05).
Among the 597 publications identified, 27 in vitro studies were included for qualitative analysis, and 12 were included for quantitative analysis. The general analysis revealed no significant differences in linear distance and angular deviations between the 2 impression materials with the direct or indirect technique. The subgroup analysis demonstrated that a statistically significant difference in linear distance deviations was found when implants were placed at an angle greater than 15 degrees, favoring PE materials when using the direct technique (P=.010, MD: 32.54 μm; 95% CI: 6.83 to 58.24) and indirect technique (P=.020, MD: 138.15 μm, 95% CI: 19.17 to 257.13). However, only 2 relevant studies assessed the indirect technique.
When providing IFCDs, conventional impressions obtained using PVS and PE materials were found to have similar accuracy in most scenarios. PE materials yielded better outcomes when implants were placed at an angle greater than 15 degrees.
It is essential to enhance the in vitro maturation (IVM) condition for immature oocytes after cryopreservation, particularly if limited numbers of oocytes collected from specific donors. The ...objective of this study was to determine if quality of vitrified porcine immature oocytes was enhanced by coculturing with fresh oocytes during IVM. To distinguish fresh versus vitrified oocytes, we used two types of coculture systems: (a) transwell two‐chamber coculture; (b) labeling and tracing fresh oocytes with CellTracker™ Green CMFDA during conventional culture. Coculture systems significantly accelerated meiotic progression of vitrified oocytes and significantly increased blastocyst formation rates following parthenogenetic activation and somatic cell nuclear transfer. Reactive oxygen species generation in vitrified oocytes was ameliorated by the coculture conditions, with no significant difference between fresh and vitrified oocytes for intracellular glutathione level. Both coculture systems significantly increased rate of normal mitochondrial distribution in vitrified oocytes, but did not affect fluorescence intensity of mitochondria. The percentage of oocytes with normal endoplasmic reticulum (ER) distribution and ER fluorescence intensity were significantly higher in vitrified oocytes cocultured with fresh oocytes. After 20 hr of IVM, mRNA expression of COX2, HAS2, PTX3, and TNFAIP6 remained significantly higher in cumulus cells derived from vitrified oocytes and coculture systems significantly decreased the expression of these genes. Additionally, coculture methods prevented the reduction of mRNA expression for BMP15, ZAR1, POU5F1, and DNMT3A in vitrified oocytes. In conclusion, oocyte quality and subsequent embryo development of vitrified porcine immature oocytes were significantly improved by fresh oocyte coculture during IVM.
Coculture with fresh oocytes during in vitro maturation (IVM) meliorated meiotic progression, reactive oxygen species generation, mitochondrial and endoplasmic reticula features, and gene expression patterns in cumulus cells and oocytes, with enhanced developmental competence of vitrified porcine immature oocytes. This coculture approach for IVM would be especially valuable for limited numbers of vitrified oocytes collected from specific donors, providing benefits for biomedical research and preservation of genetic resources.
Developing high-performance biomass-derived carbons and understanding the relationship between their structures and performance are highly desired for carbon-based supercapacitors. Herein, a wheat ...gluten-derived carbon with porous sheet-like structure, high specific surface area, and oxygen- and nitrogen-based heteroatom groups is fabricated. Their pore properties and heteroatom doping amount are adjusted through controlling the activation temperature. In aqueous electrolyte there is a significant synergistic effect between pore properties and heteroatom amount on the electrochemical performance of the gluten-derived carbon; while their performance is mainly determined by their pore properties in ionic liquid electrolytes. Besides, whatever in the aqueous and ionic liquid electrolytes ion sieving effect also affects their capacitive performance. The gluten-derived carbon prepared at 700 °C with reasonable pore properties and heteroatom amount shows the highest specific capacitance of 350 F g−1 at 0.5 A g−1 in 6 mol L−1 KOH. But the gluten-derived carbon prepared at 800 °C with the highest specific surface area of 2724 m2 g−1 possesses a high specific capacitance of 197 F g−1 at 0.25 A g−1 in the ionic liquid electrolyte. This work can provide a guideline for optimizing the performance of biomass-derived carbons through matching their pore properties and heteroatom with different electrolytes.
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•GC possesses high SSA, porous sheet-like structure, and abundant O and N groups.•GC exhibits high capacitance, excellent rate performance, and long-term stability.•In aqueous and ionic liquid electrolytes ion sieving effect affects performance.•Pore properties determine the performance of GC in ionic liquid electrolytes.•Synergistic effect of pore properties and heteroatom exists in aqueous electrolyte.
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