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71.
We fabricate F-doped and F-S-codoped diamond-like carbon (DLC) films using plasma-enhanced chemical vapor deposition system. The hardness, Raman spectra, and high-vacuum tribological behaviors indicate that the films are DLC films. The hardness is close related to the tribological properties of DLC films under high vacuum. The high hardness of DLC films would be helpful for obtaining the long lifetime under high vacuum. The lifetimes of F-S-codoped DLC films are about 120 and 140 seconds, which is attributed to the fast graphitization under high vacuum. The lifetime of F-doped DLC films is prolonged to the value of around 300 and 440 seconds, X-ray photoelectron spectroscopy analysis exhibits the existence of the “adsorption” F, and transmission electron microscopy analysis shows that the “adsorption” F could react with Fe to form layered FeF2 nanocrystal at the initial sliding, which could be helpful for prolonging the lifetime of F-doped DLC films under high vacuum. This investigation opens a new window to overcome the disadvantage of F, S-doped DLC films under high vacuum. 相似文献
72.
《Journal of separation science》2018,41(14):2924-2933
A magnetic solid‐phase extraction adsorbent that consisted of citrus peel‐derived nanoporous carbon and silica‐coated Fe3O4 microspheres (C/SiO2@Fe3O4) was successfully fabricated by co‐precipitation. As a modifier for magnetic microspheres, citrus peel‐derived nanoporous carbon was not only economical and renewable for its raw material, but exerted enormous nanosized pore structure, which could directly influence the type of adsorbed analytes. The C/SiO2@Fe3O4 also possessed the advantages of Fe3O4 microspheres like superparamagnetism, which could be easily separated magnetically after adsorption. Integrating the superior of biomass‐derived nanoporous carbon and Fe3O4 microspheres, the as‐prepared C/SiO2@Fe3O4 showed high extraction efficiency for target analytes. The obtained material was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and the Brunauer–Emmett–Teller method, which demonstrated that C/SiO2@Fe3O4 was successfully synthesized. Under the optimal conditions, the adsorbent was selected for the selective adsorption of seven insecticides before gas chromatography with mass spectrometry detection, and good linearity was obtained in the concentration range of 2–200 μg/kg with the correlation coefficient ranging from 0.9952 to 0.9997. The limits of detection were in the range of 0.03–0.39 μg/kg. The proposed method has been successfully applied to the enrichment and detection of seven insecticides in real vegetable samples. 相似文献
73.
Pu Duan Bo Zhi Luke Coburn Christy L. Haynes Klaus Schmidt-Rohr 《Magnetic resonance in chemistry : MRC》2020,58(11):1130-1138
The composition of fluorescent polymer nanoparticles, commonly referred to as carbon dots, synthesized by microwave-assisted reaction of citric acid and ethylenediamine was investigated by 13C, 13C{1H}, 1H─13C, 13C{14N}, and 15N solid-state nuclear magnetic resonance (NMR) experiments. 13C NMR with spectral editing provided no evidence for significant condensed aromatic or diamondoid carbon phases. 15N NMR showed that the nanoparticle matrix has been polymerized by amide and some imide formation. Five small, resolved 13C NMR peaks, including an unusual ═CH signal at 84 ppm (1H chemical shift of 5.8 ppm) and ═CN2 at 155 ppm, and two distinctive 15N NMR resonances near 80 and 160 ppm proved the presence of 5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA) or its derivatives. This molecular fluorophore with conjugated double bonds, formed by a double cyclization reaction of citric acid and ethylenediamine as first shown by Y. Song, B. Yang, and coworkers in 2015, accounts for the fluorescence of the carbon dots. Cross-peaks in a 1H─13C HETCOR spectrum with brief 1H spin diffusion proved that IPCA is finely dispersed in the polyamide matrix. From quantitative 13C and 15N NMR spectra, a high concentration (18 ± 2 wt%) of IPCA in the carbon dots was determined. A pronounced gradient in 13C chemical-shift perturbations and peak widths, with the broadest lines near the COO group of IPCA, indicated at least partial transformation of the carboxylic acid of IPCA by amide or ester formation. 相似文献
74.
Leiqing Hu Sankhajit Pal Hien Nguyen Vinh Bui Haiqing Lin 《Journal of polymer science. Part A, Polymer chemistry》2020,58(18):2467-2481
Over the last two decades, polymers with superior H2/CO2 separation properties at 100–300 °C have gathered significant interest for H2 purification and CO2 capture. This timely review presents various strategies adopted to molecularly engineer polymers for this application. We first elucidate the Robeson's upper bound at elevated temperatures for H2/CO2 separation and the advantages of high-temperature operation (such as improved solubility selectivity and absence of CO2 plasticization), compared with conventional membrane gas separations at ~35 °C. Second, we describe commercially relevant membranes for the separation and highlight materials with free volumes tuned to discriminate H2 and CO2, including functional polymers (such as polybenzimidazole) and engineered polymers by cross-linking, blending, thermal treatment, thermal rearrangement, and carbonization. Third, we succinctly discuss mixed matrix materials containing size-sieving or H2-sorptive nanofillers with attractive H2/CO2 separation properties. 相似文献
75.
Ding Tian Taliehsadat Alebrahim Gregory K. Kline Liwen Chen Haiqing Lin Chulsung Bae 《Journal of polymer science. Part A, Polymer chemistry》2020,58(18):2654-2663
Polymeric membrane-based gas separation technology has significant advantages compared with traditional amine-based CO2 separation method. In this work, SEBS block copolymer is used as a polymer matrix to incorporate triethylene oxide (TEO) functionality. The short ethylene oxide segment is chosen to avoid crystallization, which is confirmed by differential scanning calorimetry and wide-angle X-ray scattering characterizations. The gas permeability results reveal that CO2/N2 selectivity increased with increasing content of TEO functional group. The highest CO2 permeability (281 Barrer) and CO2/N2 selectivity (31) were obtained for the membrane with the highest TEO incorporation (57 mol%). Increasing the TEO content in these copolymers results in an increase in CO2 solubility and a decrease in C2H6 solubility. For example, as the grafted TEO content increased from 0 to 57 mol%, the CO2 solubility and CO2/C2H6 solubility selectivity increased from 0.72 to 1.3 cm3(STP)/cm3 atm and 0.47 to 1.3 at 35°C, respectively. The polar ether linkage in TEO-grafted SEBS copolymers exhibits favorable interaction with CO2 and unfavorable interaction with nonpolar C2H6, thus enhancing CO2/C2H6 solubility selectivity. 相似文献
76.
Guanjia Zhu Prof. Wan Jiang Prof. Jianping Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(7):1488-1496
The successful commercialization of promising silicon-based anode materials has been hampered by their poor cycling stability caused by the huge volume change. Integration of the carbon matrix with silicon-based (C/Si-based) anode materials has been demonstrated to be a powerful solution to achieve satisfactory electrochemical performance. This minireview aims to outline recent developments on C/Si-based composites, with the emphasis on the importance of carbon distribution at multiple scales. In addition, the forms of the carbon framework (carbon sources and doping of heteroatoms) have been summarized. Particularly, a novel C/Si-based hybrid with carbon distributed at the atomic scale has been highlighted. 相似文献
77.
Dan Xie Huan-Huan Li Yan-Hong Shi Wan-Yue Diao Ru Jiang Prof. Hai-Zhu Sun Prof. Xing-Long Wu Dr. Wenliang Li Dr. Chao-Ying Fan Prof. Jing-Ping Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(4):853-862
The Fe-based transition metal oxides are promising anode candidates for lithium storage considering their high specific capacity, low cost, and environmental compatibility. However, the poor electron/ion conductivity and significant volume stress limit their cycle and rate performances. Furthermore, the phenomena of capacity rise and sudden decay for α-Fe2O3 have appeared in most reports. Here, a uniform micro/nano α-Fe2O3 nanoaggregate conformably enclosed in an ultrathin N-doped carbon network (denoted as M/N-α-Fe2O3@NC) is designed. The M/N porous balls combine the merits of secondary nanoparticles to shorten the Li+ transportation pathways as well as alleviating volume expansion, and primary microballs to stabilize the electrode/electrolyte interface. Furthermore, the ultrathin carbon shell favors fast electron transfer and protects the electrode from electrolyte corrosion. Therefore, the M/N-α-Fe2O3@NC electrode delivers an excellent reversible capacity of 901 mA h g−1 with capacity retention up to 94.0 % after 200 cycles at 0.2 A g−1. Notably, the capacity rise does not happen during cycling. Moreover, the lithium storage mechanism is elucidated by ex situ XRD and HRTEM experiments. It is verified that the reversible phase transformation of α↔γ occurs during the first cycle, whereas only the α-Fe2O3 phase is reversibly transformed during subsequent cycles. This study offers a simple and scalable strategy for the practical application of high-performance Fe2O3 electrodes. 相似文献
78.
Lishuang Fan Yu Zhang Zhikun Guo Bing Sun Da Tian Yujie Feng Naiqing Zhang Kening Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(42):9314-9318
Flexible asymmetric supercapacitors are more appealing in flexible electronics because of high power density, wide cell voltage, and higher energy density than symmetric supercapacitors in aqueous electrolyte. In virtues of excellent conductivity, rich porous structure and interconnected honeycomb structure, three dimensional graphene aerogels show great potential as electrode in asymmetric supercapacitors. However, graphene aerogels are rarely used in flexible asymmetric supercapacitors because of easily re-stacking of graphene sheets, resulting in low electrochemical activity. Herein, flower-like hierarchical Mn3O4 and carbon nanohorns are incorporated into three dimensional graphene aerogels to restrain the stack of graphene sheets, and are applied as the positive and negative electrode for asymmetric supercapacitors devices, respectively. Besides, a strong chemical coupling between Mn3O4 and graphene via the C-O-Mn linkage is constructed and can provide a good electron-transport pathway during cycles. Consequently, the asymmetric supercapacitor device shows high rate cycle stability (87.8 % after 5000 cycles) and achieves a high energy density of 17.4 μWh cm−2 with power density of 14.1 mW cm−2 (156.7 mW cm−3) at 1.4 V. 相似文献
79.
Forrest Nichols Dr. Jia En Lu Rene Mercado Ryan Dudschus Prof. Frank Bridges Prof. Shaowei Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(18):4136-4142
Electrochemical hydrogen generation is a rising prospect for future renewable energy storage and conversion. Platinum remains a leading choice of catalyst, but because of its high cost and low natural abundance, it is critical to optimize its use. In the present study, platinum oxide nanoparticles of approximately 2 nm in diameter are deposited on carbon nitride (C3N4) nanosheets by thermal refluxing of C3N4 and PtCl2 or PtCl4 in water. These nanoparticles exhibit apparent electrocatalytic activity toward the hydrogen evolution reaction (HER) in acid. Interestingly, the HER activity increases with increasing Pt4+ concentration in the nanoparticles, and the optimized catalyst even outperforms commercial Pt/C, exhibiting an overpotential of only −7.7 mV to reach the current density of 10 mA cm−2 and a Tafel slope of −26.3 mV dec−1. The results from this study suggest that the future design of platinum oxide catalysts should strive to maximize the Pt4+ sites and minimize the formation of the less active Pt2+ species. 相似文献
80.
Ayumi Suzuki Dr. Yuichiro Mutoh Dr. Noriko Tsuchida Chi-Wai Fung Dr. Shoko Kikkawa Prof. Isao Azumaya Prof. Shinichi Saito 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3795-3802
Although the chemistry of transition-metal complexes with carbonyl (CO) and thiocarbonyl (CS) ligands has been well developed, their heavier analogues, namely selenocarbonyl (CSe) and tellurocarbonyl (CTe) complexes remain scarce. The limited availability of such CSe and CTe complexes has so far hampered our understanding of the differences between such chalcogenocarbonyl (CE: E=O, S, Se, Te) ligands. Herein, we report the synthesis and properties of a series of cationic half-sandwich ruthenium CE complexes of the type [CpRu(CE)(H2IMes)(CNCH2Ts)][BArF4] (Cp=η5-C5H5−; H2IMes=1,3-dimesitylimidazolin-2-ylidene; ArF=3,5-(CF3)2C6H3). A combination of X-ray diffraction analyses, NMR spectroscopic analyses, and DFT calculations revealed an increasing π-accepting ability of the CE ligands in the order O<S<Se<Te. A variable-temperature NMR analysis of the thus obtained chiral-at-metal CE complexes indicated high stereochemical stability. 相似文献