用艾奇逊炉在不同温度提纯碳纳米管

利用艾奇逊炉分别在3 000 ℃和2 800 ℃下进行碳纳米管的提纯实验。利用ICP、EDS、TGA检测了提纯碳纳米管的主要催化金属含量、灼烧残余物含量;用四探针薄膜电阻仪检测其电阻率;利用SEM、XRD、FT-IR研究了不同温度提纯碳纳米管的组织结构变化和表面特点。研究结果表明,艾奇逊炉在不同温度下提纯的碳纳米管都可以有效降低碳纳米管粉体中的催化金属含量和灼烧残余物含量,满足动力电池导电剂要求。与原生碳纳米管比较,3 000 ℃提纯的碳纳米管的电阻率显著下降,石墨晶化程度提高;而2 800 ℃提纯的碳纳米管的电阻率略有提高,石墨晶化程度变化不大,表面官能团数量减少。     

Mg掺杂调制铜铁矿结构CuAlO2多晶的微结构和电热传导

采用固相反应法制备铜铁矿结构的CuAl_1-xMg_xO₂ (x=0、0.005、0.01、0.02、0.03、0.04)多晶,研究了Mg掺杂对CuAlO₂多晶结构和性能的影响。Mg掺杂量x从0增加到0.02,样品均为菱方R3m单相,密度依次提高;所有样品呈半导体的热激活电输运行为,x=0.02样品在室温下的电阻率是未掺杂样品的1/19,热激活能显著下降(x=0时,ρ_{300 K}~5.54 Ω·m,E_a~0.328 eV;x=0.02时,ρ_{300 K}~0.29 Ω·m,E_a~0.218 eV),载流子浓度增加1个量级,主要因为Mg²⁺取代Al³⁺,引入新的受主能级。x>0.02时,MgAl₂O₄尖晶石杂相出现,使其电导率和热导率降低。CuAl_1-xMg_xO₂多晶的晶格热导率在总热导率中占绝对优势,且随温度升高(300~500 K)而下降,晶格热导Callaway模型模拟表明,所有样品的热阻主要源于点缺陷-声子散射。与x=0相比,x=0.02样品的室温热导率增大1倍(κ~13.065 0 W/(m·K)),声速增大,点缺陷-声子散射减弱,分析认为掺Mg形成强的Mg—O键,提高了晶体的弹性模量和声子频率,减弱了本征点缺陷、Mg掺杂引起的质量波动和应变场波动对声子的散射,同时Mg掺杂样品的密度提高也有利于增加热导率。     

Unsymmetrical photochromic bithienylethene-bridge tetraphenylethene molecular switches: Synthesis,aggregation-induced emission and information storage

Aggregation-induced emission(AIE) active photochromic molecules have attracted growing attention for their versatile applications.Here we designed and synthesized five newly unsymmetrical photochromic diarylethene(DAE) dyads(BTE1-5) by connecting tetraphenylethene(TPE) and aromatic substituent via bithienylethene(BTE) bridge.The chemical structures of those compounds were identified by ^1H NMR,¹³C NMR and HRMS.The absorption and emission of these dyads were investigated by UV-vis and fluore scence spectroscopy,respectively.The results showed that all those compounds exhibited typically AIE or aggregation-induced emission enhancement(AIEE) characteristic.Particularly,when an aggregationcaused quenching(ACQ) fluorophore(triphenylamine) was grafted to the molecule,connecting with TPE via BTE-bridge,the ACQ phenomenon was dissipated and converted to an AIE luminophore,and those compounds exhibited photochromism upon irradiation with alternative UV and visible light.The solution or solid of those compounds showed distinctly fluorescence switching "ON" or "OFF" observation upon irradiation with alternative UV and visible light.It is interesting that BTE1 could be applied in recording and rewritable information storage,and the cyclization quantum yields could be affected by substituent significantly.     

Surface defect kink solitons

We reveal the existence of dynamically stable nonlinear defect kink modes at an interface separating a defocusing Kerr medium and an imprinted semi-infinite lattice with a positive or negative defect covering single or several lattice sites. Increasing the number of defect sites equivalently results in a band-gap shift of lattice which in return alters the existence domains and stability properties of defect solitons. Comparing with the uniform semi-infinite lattice, the instability of kink soliton in lattice with a negative defect is significantly suppressed, especially for in-phase soliton. Our results provide an effective way for the realization of stable in-phase kink solitons.     

Emergence of a Lanthanide Chalcogenide as an Ideal Scintillator for a Flexible X-ray Detector

The development of high-performance X-ray detectors requires scintillators with fast decay time, high light yield, stability, and X-ray absorption capacity, which are difficult to achieve in a single material. Here, we present the first example of a lanthanide chalcogenide of LaCsSiS₄ : 1 % Ce³⁺ that simultaneously integrates multiple desirable properties for an ideal scintillator. LaCsSiS₄ : 1 % Ce³⁺ demonstrates a remarkably low detection limit of 43.13 nGy_air s⁻¹ and a high photoluminescence quantum yield of 98.24 %, resulting in a high light yield of 50480±1441 photons/MeV. Notably, LaCsSiS₄ : 1 % Ce³⁺ exhibits a fast decay time of only 29.35±0.16 ns, making it one of the fastest scintillators among all lanthanide-based inorganic scintillators. Furthermore, this material shows robust radiation and moisture resistance, endowing it with suitability for chemical processing under solution conditions. To demonstrate the X-ray imaging capacity of LaCsSiS₄ : 1 % Ce³⁺, we fabricated a flexible X-ray detector that achieved a high spatial resolution of 8.2 lp mm⁻¹. This work highlights the potential of lanthanide chalcogenide as a promising candidate for high-performance scintillators.     

NMR detection of single-walled carbon nanotubes in solution

The detection of nanotube carbons in solution by (13)C NMR is reported. The highly soluble sample was from the functionalization of (13)C-enriched single-walled carbon nanotubes (SWNTs) with diamine-terminated oligomeric poly(ethylene glycol) (PEG(1500N)). The ferromagnetic impurities due to the residual metal catalysts were removed from the sample via repeated magnetic separation. The nanotube carbon signals are broad but partially resolved into two overlapping peaks, which are tentatively assigned to nanotube carbons on semiconducting (upfield) and metallic (downfield) SWNTs. The solid-state NMR signals of the same sample are similarly resolved. Mechanistic and practical implications of the results are discussed.     

Single-walled carbon nanotubes displaying multivalent ligands for capturing pathogens

A single-walled carbon nanotube was exploited for its semi-flexible pseudo-one-dimensional nanostructure as a unique scaffold to display multivalent carbohydrate ligands, with a specific demonstration showing that galactosylated carbon nanotubes were effective in the capturing of pathogenic Escherichia coli in solution.     

时变参数动力系统的两种跟踪性质

在时变参数动力系统中引入链传递,伪轨跟踪以及渐进伪轨跟踪的概念,并通过这些概念讨论时变参数动力系统的伪轨跟踪和渐进伪轨跟踪的性质.证明了扩张的时变参数动力系统满足伪轨跟踪性质蕴含其满足渐近伪轨跟踪性质;论证了时变参数动力系统的积系统满足伪轨跟踪和渐进伪轨跟踪性质的充要条件是其每一个分系统也满足相应的性质.最后构造出了一个时变参数动力系统的例子:(∑∞X,F),证明了(∑∞X,F)是拓扑传递的,并且满足渐近伪轨跟踪性质.