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A nanoisland consists of center spin-5/2 and perimeter spin-3/2 atoms, which is described by transverse Ising model with single-ion anisotropy. Magnetic behaviors of the nanoisland are studied by the effective-field theory with correlations and the differential operator technique. The formulas of the magnetization and the phase transition of the system are given. The numerical results of the phase transition, the magnetization, the initial susceptibility and the internal energy have been discussed. Some interesting phenomena, such as a new reentrant, are found. Namely there are multitransition temperatures dependent on competition among the single-ion anisotropies, the transverse field and the interlayer coupling. These results can provide some guidance to structure design in the nanoislands. 相似文献
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催化裂化是石油化工的核心单元之一.从催化裂化尾气中分离出来的碳四馏分富含许多的不饱和烯烃,如1-丁烯、顺、反式-2-丁烯以及少量的1,3-丁二烯,这些不饱和烯烃可以通过后续聚合反应,生成合成橡胶和工程塑料的重要原料,具有重要的应用价值.上述工艺过程对原料中1,3-丁二烯的含量(<100~200 ppm)有严苛的要求.采用选择性加氢技术对碳四馏分中的1,3-丁二烯进行选择性加氢,将其转化为更高附加值的单烯烃是一个理想的解决方案.然而,1,3-丁二烯加氢反应得到的单烯烃可能发生深度加氢得到副产物丁烷.因此,开发高效选择性加氢催化剂对碳四资源的利用具有重要的现实意义.另一方面,1,3-丁二烯加氢反应可以作为模型反应,用来考察选择性加氢催化剂的性能.基于此,该反应无论在工业界还是学术界均受到广泛关注.尽管如此,有关1,3-丁二烯加氢催化剂研究进展方面的综述极少.仅有关于1,3-丁二烯加氢作为模型反应的综述报道.本文对过去半个世纪以来1,3-丁二烯加氢反应中不同催化剂的发展历程进行系统综述,特别是包括Pd,Pt和Au等的单一贵金属催化剂.重点介绍以下内容:(1)固体催化剂构效关系,包括活性金属尺寸效应、晶面和形貌效应以及载体效应(晶相、孔道和酸碱性);(2)高性能催化剂的设计新策略,如单原子催化剂、核壳结构催化剂、金属-离子液复合催化体系以及载体的形貌调控;(3)催化剂的反应机理和失活机理.提出了1,3-丁二烯选择性加氢高性能催化剂开发面临的挑战,并对潜在的发展方向进行了展望.本文认为随着纳米技术和金属纳米材料合成方法的快速发展,对贵金属活性组分进行原子层面上的调控(包括形貌、尺寸以及单原子配位环境等)已成为可能.这将有助于研制出一类新型高性能选择性加氢催化材料,从而实现高转化率条件下高附加值单烯烃的定向转化.此外,载体的酸碱性和孔道结构的调控有助于进一步调节催化剂的抗积炭性能,也是未来发展的一个重要方向. 相似文献
4.
Jing He Mohan Yu Maofu Pang Yanqing Fan Zhe Lian Dr. Ying Wang Prof. Wenguang Wang Prof. Yajun Liu Prof. Hua Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(13):e202103832
Structural designs combining cycloparaphenylenes (CPPs) backbone with planar chiral [2.2]paracyclophane ([2.2]PCP) lead to optical-active chiral macrocycles with intriguing properties. X-ray crystal analysis revealed aesthetic necklace-shaped structures and size-dependent packages with long-range channels. The macrocycles exhibit unique photophysical properties with high fluorescence quantum yield of up to 82 %, and the fluorescent color varies with ring size. In addition, size-dependent chiroptical properties with moderately large CPL dissymmetry factor of 10−3 and CPL brightness in the range of 30–40 M−1 cm−1 were observed. 相似文献
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《中国化学快报》2020,31(6):1654-1659
The carbon quantum dots(CQDs) and their functionalized materials are promising in biomedical field because of their unique properties;meanwhile,a growing concern has been raised about the potential toxicity of these modified materials in biosystem.In this study,we synthesized original CQDs and two common functionalized CQDs including N-doped CQDs(NCQDs) and folic acid-modified CQDs(FACQDs),and compared the toxicity and biocompatibility with each other in vitro and in vivo.L929,C6 and normal cell MDCK were selected to detect the adverse reaction of these materials in vitro.No acute toxicity or obvious changes were noted from in vitro cytotoxicity studies with the dose of these CQD materials increasing to a high concentration at 1 mg/mL.Among these materials,the FA-CQDs show a much lower toxicity.Moreover,in vivo toxicity studies were performed on the nude mice for 15 days.The experimental animals in 10 or 15 mg/kg groups were similar with animals treated by phosphate buffer solution(PBS) after 15 days.The results of the multifa rious biochemical parameters also suggest that the functionalized products of CQDs do not influence the biological indicators at feasible concentration.Our findings in vitro and in vivo through toxicity tests demonstrate that CQDs and their modified materials are safe for future biological applications. 相似文献
7.
Xiao-Shu Yu Hong-Juan Cui Qi-Zhi Wang Jian-Sheng Li Fang Su Lan-Cui Zhang Xiao-Jing Sang Zai-Ming Zhu 《应用有机金属化学》2020,34(8):e5720
The wheel-like tungstophosphate ([P8W48O184]40−, abbreviated as P8W48) reacted with estertin trichloride (Cl3SnRCH3, R = CH2CH2COO) in aqueous solution, resulting in a new wheel-like polyoxometalate (POM) containing six SnR fragments, formulated as K6Na24[{(SnR(H2O))2(μ-OH)(μ-SnR(H2O))}2(P8W48O184)]·59H2O (abbreviated as Sn 6 - P 8 W 48 ). Based on this, the transition metal (TM) was further introduced into the Sn 6 - P 8 W 48 system, self-assembling three other wheel-like POMs with the general formula KxNayH26 − x − y[{TM(H2O)3(SnR(H2O))2(μ-OH)(μ-SnR(H2O))}2(P8W48O184)]·nH2O (abbreviated as TM 2 - Sn 6 - P 8 W 48 , TM = Mn, Co, Ni; x = 0, 1, 2; y = 19, 22, 15; n = 72, 85, 75, respectively). The structures of these new organometal and TM co-modified compounds were characterized using infrared, UV–Vis. spectroscopy, 119Sn NMR, and powder- and single-crystal X-ray diffraction analysis. The estertin precursor hydrolyzed into carboxyethyltin (SnR) fragment in these crystalline POM materials, which can improve their adhesion to titanium dioxide (TiO2). The photocatalytic performance of Sn 6 - P 8 W 48 , TM 2 - Sn 6 - P 8 W 48 , and their TiO2 composites was examined by studying the degradation of a model dye pollutant Rhodamine B (RhB) under visible-light irradiation without adding hydrogen peroxide (H2O2), and the photocatalytic mechanism was also discussed. The experimental results show that the title compounds exhibit a quicker and better photocatalytic degradation effect on RhB compared with their parent compound, indicating that the introduced organotin groups play a significant role. Moreover, it was found that H2O2 was produced after illumination pretreatment for POM solution, promoting the photocatalytic reaction. 相似文献
8.
Photoluminescence of green nanophosphors Sr2MgSi2O7 doped with Tb3+ under 374-nm excitation 下载免费PDF全文
A series of Sr2MgSi2O7:Tb3+ nanophosphors is prepared using a high-temperature solid-state reaction. The x-ray diffraction patterns show that the crystal structure of the sample is not significantly affected by Tb3+ ions. However, the images of the scanning electron microscope illustrate that the average size of nanoparticles becomes larger with the increase of Tb3+ concentration. Unlike earlier investigations on down-conversion emission of Tb3+ ion excited by deep ultraviolet light, in this work, the photoluminescence characteristics of Sr2MgSi2O7 nanophosphors doped with different Tb3+ concentrations are analyzed under 374-nm excitations. The intense green emission at 545 nm is observed at an optimal doping concentration of 1.6 mol%. The main reason for the concentration quenching is due to the electric dipole-electric dipole interaction among Tb3+ ions. 相似文献
9.
《中国化学快报》2023,34(6):107939
The water promotion effects, where water can provide a solution-mediated reaction pathway in various heterogeneous chemical catalysis, have been presented and attracted wide attention recently, yet, the rational design of catalysts with a certain ability of enhancing water-induced reaction process is full of challenges and difficulties. Here, we show that by incorporating alkali (Na, K) cations as an electronic and/or structural promoter into Pd/rGO-ZnCr2O4 (rGO, reduced graphene oxide), the obtained Pd(Na)/rGO-ZnCr2O4 as a representative example demonstrates an outstanding benzyl alcohol oxidation activity in the Pickering emulsion system in comparison to the alkali-free counterpart. The response experiments of water injection confirm the enhanced activity, and the Na-modified catalyst can further enhance the promotion effects of water on the reaction. The effects of alkali cations for Pd nanoparticles are identified and deciphered by a series of experimental characterizations (XPS, in situ CO-DRIFTS, and CO-TPR coupled with MS), showing that there is abundant −OH on the surface of the catalyst, which is stabilized by the formation of Pd−OHx. The alkali-stabilized Pd−OHx is helpful to enhance the water-induced reaction process. According to the results of in situ Raman as well as UV-vis absorption spectra, the Na-modulated Pd(Na)/rGO-ZnCr2O4 enables the beneficial characteristics for distorting the benzyl alcohol structure and enhancing the adsorption of benzyl alcohol. Further, the mechanism for enhanced water promotion effects is rationally proposed. The strategy of alkali cations-modified catalysts can provide a new direction to effectively enhance the chemical reaction involving small molecule water. 相似文献
10.
《中国化学快报》2023,34(8):108099
Rosmarinic acid (RA) is promising as a natural and nontoxic food additive. However, many analysis methods for RA generally depend on large instruments and single signals for quantitative detection. A new up-conversion fluorescence, colorimetric and photothermal multi-modal sensing strategy is developed for the quantification of RA. β-cyclodextrin (CD) modified citric acid (Cit) wrapped NaYF4:Yb/Er-Cit-CD (Y:Yb/Er-Cit-CD) up-conversion nanocomposite has been synthesized, which emits green fluorescence at 550 nm under 980 nm near-infrared (NIR) excitation. In the presence of oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB), the green fluorescence is significantly quenched attributed to the fluorescence inner filter effect (IFE) between oxTMB and Y:Yb/Er-Cit-CD. When RA is intervened, blue oxTMB is reduced to colorless 3,3′,5,5′-tetramethylbenzidine (TMB) inducing the recovery of up-conversion fluorescence. At the same time, colorimetric and photothermal signals readout can be easily achieved thanks to the color indication and photothermal effect of the oxTMB. The constructed Y:Yb/Er-Cit-CD/oxTMB sensor displays high sensitivity, visibility and simplicity for RA, and the limits of detection (LOD) for fluorescence, colorimetric and photothermal were 0.004 µmol/L, 0.036 µmol/L and 0.043 µmol/L, respectively. This sensing system is successfully performed for the detection of RA in food samples. 相似文献