基于明胶制备碳量子点及其光学性能的研究

通过水热法采用热解明胶制备出有蓝色荧光的碳量子点,并通过单因素优化实验对制备碳量子点的温度、时间进行优化以选择出制备碳量子点的最佳条件,结果表明在水热反应温度为200 ℃,反应时间为6 h时制备的碳量子点的荧光性能最强。同时,利用透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、Ｘ射线衍射(XRD)、紫外-可见吸收光谱(UV)及荧光光谱(PL)等手段对最佳条件下制备的碳量子点进行测试与表征,结果表明,该方法制备的碳量子点量子产率为39.4%,与不掺杂的碳量子点相比其量子产率相对较高,这可能是因为有N元素的存在使得量子产率有所提高;所制备的碳量子点不仅具有丰富的含氧官能团而且抗光漂白性能良好,形态主要是均匀分散的球形,没有明显的晶格条纹,这与相关文献报道的碳量子点的形态相一致,其在250～300 nm有较弱的吸收,但无明显的特征吸收峰,这可能是由于C=O基团的n-π*跃迁引起的;此外,还讨论了氙灯照射时间、pH、碳量子点浓度、不同类型溶剂及离子强度等因素对碳量子点荧光性能的影响,研究结果表明,氙灯照射时间及离子强度对碳量子点荧光性能几乎无影响,在过酸或过碱的条件下其荧光强度相对较弱,原因可能是在过酸或过碱的条件下发生质子化或非质子化的作用导致其荧光强度减弱;且碳量子点溶液随着其浓度的增加,荧光强度先增加后减小;而对于溶剂类型而言,其在极性溶剂中的荧光强度大于其在非极性溶剂中的荧光强度,说明该方法制备的碳量子点具有良好的水溶性。     

Physicochemical properties of ionic liquids based on imidazolium/pyrrolidinium cations and maleate/phthalate anions

Ionic liquids (ILs) based on imidazolium/pyrrolidinium cations and maleate/phthalate anions can be used as excellent electrolyte materials for electrolytic capacitors. In this study, we synthesized four ILs of this family and investigated their thermal behaviors, ionic conductivities and sparking voltages. The four ILs have high thermal stability for capacitor requirements. The conductivities of imidazolium ILs are slightly higher than those of pyrrolidinium analogs and the conductivities of maleate anion-based ILs are higher than those of corresponding phthalate anion-based ILs. Besides, the long-term thermal stability of imidazolium ILs in conductivity is superior to that of pyrrolidinium analogs. Whereas the long-term thermal stability of phthalate anion-based ILs is better than that of corresponding maleate anion-based ILs. The influence of cationic structure of the ILs on conductivity was analyzed. The temperature dependence of conductivity was also discussed in this work. The Vogel–Tammann–Fulcher (VTF) equation accurately describes the temperature dependence of conductivity for the ILs. In addition, the result of sparking voltage measurement shows that neither Ikonopisov nor Albella model is valid for the ILs.     

Effects of coating parameters on the morphology of SiO2-coated TiO2 and the pigmentary properties

SiO₂-coated TiO₂ powders were prepared by the chemical deposition method starting from rutile TiO₂ and Na₂SiO₃. The SiO₂-coated TiO₂ powders were characterized by X-ray photoelectron spectroscopy, Zeta-potential analysis, Fourier transform infrared spectroscopy, and transmission electron microscopy. The evolution of island-like and uniform coating layers was found to depend upon the ratio of Na₂SiO₃ to TiO₂, reaction temperature, and pH. The whiteness and brightness of the SiO₂-coated TiO₂ powders increased in response to an increase in the SiO₂ loading, but there was a maximum value among the light scattering indexes. The SiO₂-coated TiO₂ powders possessed more negative Zeta potentials than the naked TiO₂. The dispersibility of the SiO₂-coated TiO₂ powders with the continuous and uniform SiO₂ coating layers was higher than that of the naked TiO₂ and the SiO₂-coated TiO₂ powders with the island-like SiO₂ coating layers.     

基于菲涅耳透镜阵列的红外气体传感器

菲涅耳透镜同时具有分光与会聚特性, 且体积小、重量轻和易复制, 使其在光谱检测中得到逐步应用, 但典型光谱成像仪采用菲涅耳透镜沿光轴扫描的方法来获得连续谱线, 不利于光谱仪的稳定性。考虑到气体探测需求, 选用多通道方式来获得多光谱, 提出了一种基于菲涅耳透镜阵列的新型红外气体传感器, 可实现吸收波长在3～5 μm的CO2,CO,CH4,SO2气体的实时检测。利用球面波的传输理论和瑞利判据, 推导了菲涅耳透镜光谱分辨率与透镜结构参数之间的函数关系, 并以光谱分辨率小于50nm为性能指标, 对1μm工艺的8台阶菲涅耳透镜阵列的结构参数进行了计算和误差分析。结果表明, 透镜阵列所需焦距为47.84 mm, 平均数值孔径大于0.4。     

New Conserved Quantities of Noether-Mei Symmetry for Nonholonomic Mechanical System

Two new types of conserved quantities deduced by Noether-Mei symmetry of nonholonomic mechanical system are studied. The definition and criterion of Noether-Mei symmetry for the system are given. A coordination function is introduced, and the conditions under which the Noether-Mei symmetry leads to the two types of conserved quantities and the forms of the two types of conserved quantities are obtained. An illustrative example is given. The coordination function can be selected according to the demand for finding the gauge function, and the choice of the coordination function has multiformity, so more conserved quantities deduced from Noether-Mei symmetry of mechanical system can be obtained.     

Convolution Theorem of Fractional Fourier Transformation Derived by Representation Transformation in Quantum Mechancis

Based on our previous paper （Commun. Theor. Phys. 39 （2003） 417） we derive the convolution theorem of fractional Fourier transformation in the context of quantum mechanics, which seems a convenient and neat way. Generalization of this method to the complex fractional Fourier transformation case is also possible.     

Improvement of the magnetic properties of low-neodymium magnets by minor addition of titanium

Rapidly solidified nanocomposite Nd₉Fe_77−xB₁₄Ti_x alloys, consisting of magnetic Nd₂Fe₁₄B phase and soft magnetic phases, were investigated. The effect of titanium addition on the structure and magnetic properties was studied. It was found that 2–4 at% Ti addition leads to substantial increase of the coercivity and maximum energy product, maintaining the remanence unchanged. The highest properties: J_r=0.81 T, _JH_c=907 kA/m, (BH)_max=99 kJ/m³, were achieved for the Nd₉Fe₇₃B₁₄Ti₄ alloy. This effect we attribute to the formation of fine and homogeneous grain structure and a change of the phase morphology in the Ti-containing alloys. The initial magnetization curve indicates a change of the coercivity mechanisms giving rise to pinning of domain walls, which is caused by reduction of the crystallite size.     

Magnetic properties and electron spin resonance of Ecuadorian obsidians. Application to provenance research of archeological samples

Obsidians from major Ecuadorian sources were analyzed by SQUID magnetometry and electron spin resonance (ESR). The association of these two techniques permits to differentiate obsidians from the sources of Cotopaxi volcano and from the Quiscatola and Mullumica–Callejones sources of the Chacana caldera, taking into account various parameters arising from the M vs. H cycles and the X-band ESR spectra. The analysis of 27 archeological samples coming from the prehispanic site of La Maná allowed us to infer that most of them come from the Mullumica–Callejones source.     

Hard magnetic properties in Pr2Fe14B/α-Fe nanocomposite magnets with a combined addition of V and C

Nanostructured Pr₈Fe_86−xV_xB_6−yC_y (x=0, 1; y=0, 1) ribbons composed of Pr₂Fe₁₄B and α-Fe phases with a high coercivity are fabricated by direct melt spinning. The effects of a single addition of V and a combined addition of V and C on the structures and magnetic properties of melt-spun Pr₈Fe₈₆VB_6−xC_x (x=0 and 1) ribbons have been investigated. Compared with addition-free ribbons, 1 at% V addition is found to reduce the grain sizes of the samples and improve their magnetic properties due to a strong exchange coupling between the hard and the soft phase. A remanence ratio of 0.82, a coercive field of 6.2 kOe and a maximum energy product of 23.4 MGOe in melt-spun Pr₈Fe₈₅VB₆ ribbons are obtained at room temperature. The combined addition of V and C is found to lead to the formation of an intermediate phase of VC at grain boundaries, which appears as a pinning barrier during magnetization and results in an increase of the coercivity value to 6.9 kOe for melt-spun Pr₈Fe₈₅VB₅C ribbons.     

Engineering Polymer Informatics: Towards the Computer‐Aided Design of Polymers

The computer‐aided design of polymers is one of the holy grails of modern chemical informatics and of significant interest for a number of communities in polymer science. This paper outlines a vision for the in silico design of polymers and presents an information model based on modern semantic web technologies, thus laying the foundations for achieving the vision.