Capital Normal University

About: Capital Normal University is a education organization based out in Beijing, China. It is known for research contribution in the topics: Terahertz radiation & Quantum entanglement. The organization has 11441 authors who have published 11988 publications receiving 159071 citations. The organization is also known as: Shǒudū Shīfàn Dàxué.

Tuning transport performance in two-dimensional metal-organic framework semiconductors: Role of the metal d band

Abstract: Hybrid metal-organic frameworks have some exotic electronic properties, such as extremely high electron and hole mobilities and nontrivial topological properties. Here, we systematically study the electronic properties of the two-dimensional metal-organic framework semiconductors (MOFSs) (M3S6C6, M = Mg, Ca, Zn, Cd, Ge, and Sn) using the first principles calculations. We find that the metal d band is important in determining the hole transport properties of M3S6C6. The p-d hybridization between the metal d and S-C p bands will delocalize the wavefunction of the band edge states and reduce the effective mass. From group IIA (Mg, Ca) to IVA (Ge, Sn) to IIB (Zn, Cd), as the p-d coupling increases, the hole effective masses dramatically decrease. Additionally, due to the fact that the conduction band minimum of group IIB (Zn, Cd) MOFSs is mainly dominated by the delocalized M s state, they also have the very small electron effective mass. Therefore, the 2D group IIB (Zn, Cd) MOFSs have excellent hole and electron effective masses, which are comparable with the conventional semiconductors and even better than the popular 2D materials WS2 and MoS2. This result suggests that Zn3S6C6 and Cd3S6C6 MOFSs could be the promising 2D semiconductors for the electronic applications.

Application of terahertz time-domain spectroscopy combined with chemometrics to quantitative analysis of imidacloprid in rice samples

Abstract: Terahertz time-domain spectroscopy (THz-TDS) has been utilized as an effective tool for quantitative analysis of imidacloprid in rice powder samples. Unlike previous studies, our method for sample preparation was mixing imidacloprid with rice powder instead of polyethylene. Then, terahertz time domain transmission spectra of these mixed samples were measured and the absorption coefficient spectra of the samples with frequency range extending from 0.3 to 1.7 THz were obtained. Asymmetric least square (AsLS) method was utilized to correct the slope baselines that are presented in THz absorption coefficient spectra and improve signal-to-noise ratio of THz spectra. Chemometrics methods, including partial least squares (PLS), support vector regression (SVR), interval partial least squares (iPLS), and backward interval partial least squares (biPLS), were used for quantitative model building and prediction. To achieve a reliable and unbiased estimation, bootstrapped Latin partition was chosen as an approach for statistical cross-validation. Results showed that the mean value of root mean square error of prediction (RMSEP) for PLS (0.5%) is smaller than SVR (0.7%), these two methods were based on the whole absorption coefficient spectra. In addition, PLS performed a better performance with a lower RMSEP (0.3%) based on the THz absorption coefficient spectra after AsLS baseline correction. Alternatively, two methods for variable selection, namely iPLS and biPLS, yielded models with improved predictions. Comparing with conventional PLS and SVR, the mean values of RMSEP were 0.4% (iPLS) and 0.3% (biPLS) by selecting the informative frequency ranges. The results demonstrated that an accurate quantitative analysis of imidacloprid in rice powder samples could be achieved by terahertz time-domain transmission spectroscopy combined with chemometrics. Furthermore, these results demonstrate that THz time-domain spectroscopy can be used for quantitative determinations of other pesticides in other agricultural products.

Synthesis, Structure and Luminescence Properties of Four Novel Terbium2-Fluorobenzoate Complexes

Abstract: Four new complexes [Tb(2-FBA) 3 .(2-HFBA).H 2 O] 2 (1), ([Tb(2-FBA)3.(4,4'-bpy).H 2 O] 3 } n (2), [Tb(2-FBA)3.(2,2'-bpy}] 2 (3), and [Tb(2-FBA} 3 .phen.CH 3 CH 2 OH] 2 .[Tb(2-FBA) 3 .phen] 2 (4) (2-HFBA: 2-fluorobenzoic acid; 4,4'-bpy: 4,4'-bipyridine; 2,2'-bpy: 2,2'-bipyridine; phen: 1,10-phenanthroline) have been synthesized and characterized by X-ray diffraction analysis. Complex 1 is a dimeric molecule with a one-dimensional supramolecular structure formed by hydrogen bonds. Complex 2 is an infinite one-dimensional polymer chain formed by bridging carboxylato groups; its 2D framework structure is formed by hydrogen bonds. The structure of complex 3 contains three independent binuclear molecules in the asymmetric unit. In two of them, two Tb 3 + ions are held together by four 2-FBA groups, with two of them in a bidentate-bridging mode and the other two in a chelating-bridging mode. In the third, two Tb 3 + ions are held together by four 2-FBA groups, all of which are in the bidentate-bridging mode. One 2-FBA group and one 2,2'-bpy chelate to one Tb 3 + ion, resulting in coordination numbers of the central terbium ion of nine and eight, respectively. The structure of complex 4 contains two nonequivalent binuclear molecules in the asymmetric unit - [Tb(2-FBA) 3 .phen-CH 3 CH 2 OH] 2 and [Tb(2-FBA) 3 .phen] 2 . In the former, the Tb 3 + ion is surrounded by eight atoms, five O atoms from five 2-FBA groups, one O atom from one ethanol molecule and two N atoms from phen, and the 2-FBA groups act in monodentate and bridging coordination modes. In the latter, the Tb 3 + ion is coordinated by nine atoms, seven O atoms from five 2-FBA groups and two N atoms of phen, and the 2-FBA groups link the Tb 3 + ion in chelating, bridging, and chelating-bridging coordination modes. Complexes 1, 3, and 4 emit a bright green light under UV light in the solid state. There are four emission peaks in the luminescence spectra at 488, 543, 584, and 618 nm, corresponding to the 5 D 4 → 7 F 6 , 5 D 4 → 7 F 5 , 5 D 4 → 7 F 4 , and 5 D 4 → 7 F 3 transitions, respectively, of the Tb 3 + ion.