Probing the electronic structure of ZnO nanowires by valence electron energy loss spectroscopy

Valence electron energy loss spectroscopy in a transmission electron microscope is employed to investigate the electronic structure of ZnO nanowires with diameter ranging from 20 to 100 nm. Its excellent spatial resolution enables this technique to explore the electronic states of a single nanowire. We found that all of the basic electronic structure characteristics of the ZnO nanowires, including the 3.3 eV band gap, the single electron interband transitions at approximately = 9.5, approximately = 13.5,and approximately = 21.8 eV, and the bulk plasmon oscillation at approximately 18.8 eV, resemble those of the bulk ZnO. Momentum transfer resolved energy loss spectra suggest that the 13.5 eV excitation is actually consisted of two weak excitations at approximately = 12.8 and approximately = 14.8 eV, which originate from transitions of two groups of the Zn 3d electrons to the empty density of states in the conduction band, with a dipole-forbidden nature. The energy loss spectra taken from single nanowires of different diameters show several size-dependent features, including an increase in the oscillator strength of the surface plasmon resonance at approximately = 11.5 eV, a broadening of the bulk plasmon peak, and splitting of the O 2s transition at approximately = 21.8 eV into two peaks, which coincides with a redshift of the bulk plasmon peak, when the nanowire diameter decreases. All these observations can be well explained by the increased surface/volume ratio in nanowires of small diameter.     

核磁共振任意波形发生器的研制

任意波形发生器（又叫函数发生器）作为一种通用的信号源,在物理、电子、计算机等领域有着广泛的应用. 本文提出了一种不依赖PC机总线的、完全独立的、 可用于低场磁共振成像的多用途任意波形发生器（Arbitrary Waveform Generator, AWG）设计方案,围绕着这种方案,研制了80 MHz通用磁共振任意波形发生器. 并提供了实际测试数据和成像实验结果,对研制情况和实验结果进行了总结和讨论.     

高可见光催化降解污染物和产氢活性的Z型N-掺杂K4Nb6O17/g-C3N4异质结

随着人口增长和全球工业化进程加快,人们饱受环境污染和能源短缺问题的困扰.半导体光催化技术作为一种高效、可持续、环境友好、有潜力的新技术,在环境净化和能源开发方面有着广阔的应用前景.到目前为止,人们已开发出多种半导体光催化剂,并广泛应用于污染物降解、氢气制备和二氧化碳还原等领域.其中,化合物K4Nb6O17具有典型的层状结构、合适的电子能带结构、结构易改性以及良好的电荷传输性能等特点,在光催化领域得到了广泛研究.然而,单纯K4Nb6O17仍存在光响应范围窄、光生载流子复合率高等问题,限制了K4Nb6O17的进一步应用.因此,需要对K4Nb6O17进行改性,拓宽其光吸收范围,提高其光生载流子分离效率,从而提高其光催化活性.本研究通过简单焙烧法制备Z型N-掺杂K4Nb6O17/g-C3N4(KCN)异质结光催化剂,其中石墨相氮化碳(g-C3N4)在复合材料中质量比约为50%.层状K4Nb6O17层板的电子结构通过N掺杂进行调控,拓宽其光响应范围,使其具有可见光响应;同时,形成的g-C3N4位于N-掺杂K4Nb6O17的外层以及内层空间,在这两种组分之间形成异质结,有利于提高光生载流子的分离效率.荧光光谱、时间分辨荧光光谱和光电化学测试表明,N掺杂和异质结的形成有利于增强光生电子-空穴对的传输和分离效率.通过在可见光照射下降解罗丹明B(RhB)和产氢来评估材料的光催化性能.相比g-C3N4(8.24μmol/h)和Me-K4Nb6O17(~1.30μmol/h),KCN复合材料光催化产氢效率(~16.91μmol/h)得到了极大提高,并显示出极好的光催化产氢稳定性能.对于光催化降解RhB体系,KCN复合材料也显示出较好的光催化活性和稳定性,并能很好地将RhB矿化.鉴于KCN复合材料具有较小的比表面积(9.9 m^2/g)且无孔结构,认为比表面积对光催化活性影响较小.因此,与单组分相比,KCN复合材料光催化产氢和RhB降解活性都得到了极大提高,活性的增强主要归功于N掺杂和异质结形成的协同效应,其中N掺杂可以拓宽光捕获能力,异质结形成可提高电荷载流子的分离效率.电子自旋共振(ESR)谱表明,在KCN降解RhB体系中,超氧自由基(·O2^?)、羟基自由基(·OH)和空穴(h^+)作为主要活性物质都参与了反应.结合实验结果可以推测KCN复合材料满足了Z型光催化体系,该体系具有高效的光生载流子分离效率和较高的氧化还原能力.     

A Triple Crosslinking Design toward Epoxy Vitrimers and Carbon Fiber Composites of High Performance and Multi-shape Memory

It remains a challenge to use a simple approach to fabricate a multi-shape memory material with high mechanical performances. Here,we report a triple crosslinking design to construct a multi-shape memory epoxy vitrimer(MSMEV), which exhibits high mechanical properties,multi-shape memory property and malleability. The triple crosslinking network is formed by reacting diglycidyl ether of bisphenol F(DGEBF) with4-aminophenyl disulfide, γ-aminopropyltriethoxysilane(APTS) and poly(propylene glycol) bis(2-aminopropyl ether)(D2000). The triple crosslinking manifests triple functions: the disulfide bonds and the silyl ether linkages enable malleability of the epoxy network; the silyl ether linkages impart the network with high heterogeneity and broaden the glass transition region, leading to multi-shape memory property; a small amount of D2000 increases the modulus difference between the glassy and rubbery states, thereby improving the shape fixity ratio. Meanwhile,the high crosslinking density and rigid structure provide the MSMEV with high tensile strength and Young's modulus. Moreover, integrating carbon fibers and MSMEV results in shape memory composites. The superior mechanical properties of the composites and the recyclability of carbon fiber derived from the dissolvability of MSMEV make the composites hold great promise as structural materials in varied applications.     

How Aromatic Fluorination Exchanges the Interaction Role of Pyridine with Carbonyl Compounds: The Formaldehyde Adduct

The rotational spectrum of the weakly bound complex pentafluoropyridine⋅⋅⋅formaldehyde has been investigated using Fourier transform microwave spectroscopy. From the analysis of the rotational parameters of the parent species and of the ¹³C and ¹⁵N isotopologues, the structural arrangement of the adduct has been unambiguously established. The full ring fluorination of pyridine has a dramatic effect on its binding properties: It alters the electron density distribution at the π-cloud of pyridine creating a π-hole and changing its electron donor-acceptor capabilities. In the complex, formaldehyde lies above the aromatic ring with one of the oxygen lone pairs, as conventionally envisaged, pointing toward its centre. This lone pair⋅⋅⋅π-hole interaction, reinforced by a weak C−H⋅⋅⋅N interaction, indicates an exchange of the electron-acceptor roles of both molecules when compared to the pyridine⋅⋅⋅formaldehyde adduct. Tunnelling doublets due to the internal rotation of formaldehyde have also been observed and analysed leading to a discussion on the competition between lone pair⋅⋅⋅π-hole and π⋅⋅⋅π stacking interactions.     

1，1'-二羟基-5，5'-联四唑的镧系金属配合物的合成、表征及热行为

以1,1′-二羟基-5,5′-联四唑(H_2BTO)为配体,镧系金属离子作为金属中心,采用溶剂热法制备了5种金属配合物:[La_2(BTO)_3(H_2O)_8]·2H_2O (1)、[Ce_2(BTO)_3(H_2O)_8]·2H_2O (2)、[Pr_2(BTO)_3(H_2O)_8]·2H_2O (3)、[Sm_2(BTO)_3(H_2O)_8]·2H_2O (4)和[Nd_2(BTO)_3(DMF)_4]·6H_2O (5)。通过单晶X射线衍射和元素分析对5种配合物的结构进行了表征。结果表明,5种配合物均属于单斜晶系,P2_1/n空间群。利用差示扫描量热法研究了配合物1～4的热稳定性,采用Kissinger法和Ozawa法分别计算了其热分解动力学参数。     

Recent advances in the applications of [1.1.1]propellane in organic synthesis

As a highly strained small molecule, [1.1.1]propellane has been widely used in various synthetic transformations owing to the exceptional reactivity of the central bond between the two bridgehead carbons. Utilizing strain-release approaches, the rapid development of strategies for the construction of bicyclo[1.1.1]pentane (BCP) and cyclobutane derivatives using [1.1.1]propellane as the starting material has been witnessed in the past few years. In this review, we highlight the most recent advances in this field. Accordingly, the reactivity of [1.1.1]propellane can be divided into three pathways, including radical, anionic and transition metal-catalyzed pathways under appropriate conditions.     

CO2 and photo-controlled reversible conversion of supramolecular assemblies based on water soluble pillar[5]arene and coumarin-containing guest

In this communication,a new supramolecualr amphiphile was successfully constructed based on water soluble pillar[5]arene and a unique guest which contain a CO₂ responsive tertiary amine unit and a UV responsive coumarin group.When guest molecule 1 dispersed in water,it self-assembled into sheet-like structures.Upon bubbling CO₂,1 transformed into 1 H due to the tertiary amine unit was protonated,accompany the nano-sheets transformed into vesicles.Further irradiation of 1 H with 365 nm light for 3 h,the coumarin group reacted with each other to form bola-type amphiphie 2 H.In this case,vesicles collapsed and re-assembled into nano-tubes.However,when addition of WPS into the solution of 1 H,the vesicles transformed into micelles,this is due to the formation of supramolecular amphiphile WP5&1 H.Upon irradiation of WP5&1 H with 365 nm light for 3 h,nano-ribbons observed instead of micelles in the solution.Notably,nanotubes from 2 H could also transform into nano-ribbons after adding WPS.The selfassembly process and the resultant assemblies were characterized by TEM,SEM,DLS,SAXS and NMR technologies.Due to both CO₂ and light are "green" for living organisms,we anticipated our system can offer the possibilities in "on demand" drug absorption and release.     

水溶液法原位构建ZnO亲锂层稳定锂-石榴石电解质界面

固态电池以其高安全性和高能量密度而备受关注。石榴石型固体电解质(LLZO)由于具有较高的离子导电性和对锂金属的稳定性,在固态电池中具有应用前景,但陶瓷与锂金属较差的界面接触会导致高的界面阻抗和可能形成的枝晶穿透。我们利用LLZO表层独特的H⁺/Li⁺交换反应,提出了一种简便有效的金属盐类水溶液诱发策略,在电解质表面原位构建ZnO亲锂层,界面处LiZn合金化实现紧密连续的接触。引入改性层后,界面阻抗可显著降低至约10Ω·cm²,对称电池能够在0.1mA·cm^-2的电流密度下实现长达1000h的长循环稳定性。匹配正极LiFePO₄(LFP)或LiNi_0.5Co_0.2Mn_0.3O₂(NCM523)的准固态电池在室温下能够稳定循环100次以上。     

Catalytic transfer hydrogenation of biomass-derived furfural to furfuryl alcohol with formic acid as hydrogen donor over CuCs-MCM catalyst

Catalytic transfer hydroge nation(CTH) of furfural(FF) to furfu ryl alcohol(FFA) has received great intere st in recent years.He rein,Cu-Cs bimetallic supported catalyst,CuCs(2)-MCM,was developed for the CTH of FF to FFA using formic as hydrogen donor.CuCs(2)-MCM achieved a 99.6% FFA yield at an optimized reaction conditions of 170℃,1 h.Cu species in CuCs(2)-MCM had dual functions in catalytically decomposing formic acid to generate hydrogen and hydrogenating FF to FFA.The doping of Cs made the size of Cu particles smaller and improved the dispersion of the Cu active sites.Impo rtantly,the Cs species played a favorable role in enhancing the hydrogenation activity as a promoter by adjusting the surface acidity of Cu species to an appropriate level.Correlation analysis showed that surface acidity is the primary factor to affect the catalytic activity of CuCs(2)-MCM.