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排序方式: 共有155条查询结果,搜索用时 29 毫秒
1.
Hui Yang Mengjie Hao Yinghui Xie Xiaolu Liu Yanfang Liu Zhongshan Chen Xiangke Wang Geoffrey I. N. Waterhouse Shengqian Ma 《Angewandte Chemie (International ed. in English)》2023,62(30):e202303129
Optimizing the electronic structure of covalent organic framework (COF) photocatalysts is essential for maximizing photocatalytic activity. Herein, we report an isoreticular family of multivariate COFs containing chromenoquinoline rings in the COF structure and electron-donating or withdrawing groups in the pores. Intramolecular donor-acceptor (D-A) interactions in the COFs allowed tuning of local charge distributions and charge carrier separation under visible light irradiation, resulting in enhanced photocatalytic performance. By optimizing the optoelectronic properties of the COFs, a photocatalytic uranium extraction efficiency of 8.02 mg/g/day was achieved using a nitro-functionalized multicomponent COF in natural seawater, exceeding the performance of all COFs reported to date. Results demonstrate an effective design strategy towards high-activity COF photocatalysts with intramolecular D-A structures not easily accessible using traditional synthetic approaches. 相似文献
2.
Xiangxue Wang Shujun Yu Zhongshan Chen Wencheng Song Yuantao Chen Tasawar Hayat Ahmed Alsaedi Wei Guo Jun Hu Xiangke Wang 《中国科学:化学(英文版)》2017,60(1):107-114
To contribute to the understanding of Eu(III) interaction preperties on hydrous alumina particles in the absence and presence of fulvic acid (FA), the complexation properties of Eu(III) with hydrous alumina, FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy (TRLFS) techniques. The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(III). Eu(III) is adsorbed onto alumina particles as outer-sphere surface complexes of ≡(Al?O)?Eu· (OH)· 7H2O and ≡(Al?O)?Eu· 6H2O at low pH values, and as inner-sphere surface complexes as ≡(Al?O)2?Eu+· 4H2O at high pH. In FA solution, Eu(III) forms complexes with FA as (COO)2Eu+(H2O) x and the hydration water number in the first coordination sphere decreases with pH increasing. The formation of ≡COO?Eu?(O?Al≡)· 4H2O is observed on FA-alumina hybrids, suggesting the formation of strong inner-sphere surface complexes in the presence of FA. The surface complexes are also characterized by their emission spectra [the ratio of emission intensities of 5 D 0→7 F 1 (λ=594 nm) and 5 D 0→7 F 2 (λ=619 nm) transitions] and their fluorescence lifetime. The findings is important to understand the contribution of FA in the complexation properties of Eu(III) on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(III), or its analogue trivalent lanthanide and actinide ions in natural environment. 相似文献
3.
Characterization of sign patterns that allow diagonalizability has been a long-standing open problem. In this article, necessary and sufficient conditions for a sign pattern to allow diagonalizability are obtained, in terms of allowing related properties. Some properties of normal sign patterns are considered. In particular, it is shown that normal sign patterns of order up to 3 allow diagonalizability. Two combinatorial necessary conditions for a sign pattern to allow diagonalizability are also presented. 相似文献
4.
5.
Donggao Deng Zhongshan University China Yanchang Han South China Normal University China 《分析论及其应用》2005,21(3):280-293
Suppose μ is a Radon measure on Rd, which may be non doubling. The only condition assumed on μ is a growth condition, namely, there is a constant Co > 0 such that for all x ∈ supp(μ) and r > 0,μ(B(x,r)) ≤ Corn, where 0 < n ≤ d. We prove T1 theorem for non doubling measures with weak kernel conditions. Our approach yields new results for kernels satisfying weakened regularity conditions, while recovering previously known Tolsa's results. We also prove T1 theorem for Besov spaces on nonhomogeneous spaces with weak kernel conditions given in [7]. 相似文献
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7.
采用不同合成方法制备了4种组成为Ce0.5Zr0.5O2的铈锆固溶体.通过XRD,BET,H2-TPR,HREM以及SEAD等表征手段,研究了微观晶相结构对铈锆固溶体还原性能的影响规律,以及对固溶体储放氧能力的影响.分析结果表明,在同一组成下,不同制备方法得到截然不同的晶相组成,4种固溶体包含4种不同的晶相组合.通过对微观晶相结构的定量分析,发现立方相的形成对促进固溶体的还原性能起到重要作用.其中,反相微乳法制得的铈锆固溶体能够形成完整的立方相结构,在H2-TPR还原过程中耗氢量最大,表明其具有优良的可还原性及储放氧能力,适合作为TWC,POX等催化剂载体. 相似文献
8.
Christian Brackmann Odd Hole Bo Zhou Zhongshan S. Li Marcus Aldén 《Applied physics. B, Lasers and optics》2014,115(1):25-33
Two-photon laser-induced fluorescence (LIF) of ammonia (NH3) with excitation of the C′-X transition at 304.8 nm and fluorescence detection in the 565 nm C′-A band has been investigated, targeting combustion diagnostics. The impact of laser irradiance, temperature, and pressure has been studied, and simulation of NH3-spectra, fitted to experimental data, facilitated interpretation of the results. The LIF-signal showed quadratic dependence on laser irradiance up to 2 GW/cm2. Stimulated emission, resulting in loss of excited molecules, is induced above 10 GW/cm2, i.e., above irradiances attainable for LIF imaging. Maximum LIF-signal was obtained for excitation at the 304.8 nm bandhead; however, lower temperature sensitivity over the range 400–700 K can be obtained probing lines around 304.9 nm. A decrease in fluorescence signal was observed with pressure up to 5 bar absolute and attributed to collisional quenching. A detection limit of 800 ppm, at signal-to-noise ratio 1.5, was identified for single-shot LIF imaging over an area of centimeter scale, whereas for single-point measurements, the technique shows potential for sub-ppm detection. Moreover, high-quality NH3-imaging has been achieved in laminar and turbulent premixed flames. Altogether, two-photon fluorescence provides a useful tool for imaging NH3-detection in combustion diagnostics. 相似文献
9.
Stereoselective Total Synthesis of Hetisine‐type C20‐Diterpenoid Alkaloids: Spirasine IV and XI 下载免费PDF全文
Quanzheng Zhang Zhongshan Zhang Zhong Huang Changhui Zhang Song Xi Prof. Dr. Min Zhang 《Angewandte Chemie (International ed. in English)》2018,57(4):937-941
The first total synthesis of the architecturally complex hetisine‐type heptacyclic C20‐diterpenoid alkaloids (±)‐spirasine IV and XI is reported. The A/F/G/C tetracyclic skeleton with the challenging N?C6 and C14?C20 linkages was efficiently constructed by an intramolecular azomethine‐ylide‐based 1,3‐dipolar cycloaddition with unusual regioselectivity. SmI2‐mediated free‐radical addition to the arene moiety without prior dearomatization and a stereoselective intramolecular aldol reaction further enabled rapid access to the hetisine core, providing a bicyclo[2.2.2]octane ring with a new oxygen substitution pattern. 相似文献
10.
Chenlu Zhang Xing Li Zhongshan Chen Tao Wen Shuyi Huang Tasawar Hayat Ahmed Alsaedi Xiangke Wang 《中国科学:化学(英文版)》2018,61(3):281-293
An extremely effortless method was applied for successful synthesis of mesoporous carbonaceous materials(MCMs) using well-ordered mesoporous silica as template. Various characterizations(scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), Raman, X-ray photoelectron spectroscopy(XPS), Brunner-Emmet-Teller(BET) and Zeta potential) confirmed that MCMs had large surface area, uniform pore size distribution, and abundant oxygen-containing functional groups. The batch techniques were employed to study U(VI) adsorption on MCMs under a wide range of experiment conditions. The adsorption kinetics of U(VI) onto MCMs were well-fitted by pseudo-second-order kinetic model, indicating a chemisorption process. The excellent adsorption capacity of MCMs calculated from the Langmuir model was 293.95 mg g~(-1) at pH 4.0. The FT-IR and XPS analyses further evidenced that the binding of U(VI) onto MCMs was ascribed to the plentiful adsorption sites(–OH and –COOH groups) in the internal mesoporous structure, which could efficiently trap guest U(VI) ions. The results presented herein revealed that MCMs were ideal adsorbents in the efficient elimination of uranium or other lanthanides/actinides from aqueous solutions, which would play an important role in environmental pollution management application. 相似文献