NaY分子筛Lewis酸促进甲醇经亚硝酸甲酯分解制二甲氧基甲烷※

二甲氧基甲烷(Dimethoxymethane, DMM)作为一种基础有机化学品, 在树脂、溶剂、燃料等领域具有广泛用途. 传统合成方法采用甲醇甲醛缩合, 反应效率比较低. 亚硝酸甲酯(CH₃ONO)是一种性质活泼的气体, 可由甲醇、O₂、NO在无需催化剂的条件下获得, 其反应活性比甲醇高很多. 通过亚硝酸甲酯在常压条件下催化分解可以高效制备DMM. 本工作系统研究了不同类型分子筛的酸性对亚硝酸甲酯催化分解制备DMM的影响规律, 催化活性顺序为: NaY (97%)=HY (97%)>HZSM-5 (90%)>Hβ (89%)>NaZSM-5 (18%)>Naβ (6%), DMM选择性顺序为: NaY (53%)>HY (12%)=Naβ (12%)>NaZSM-5 (7%)>Hβ (4%)>HZSM-5 (3%), 其中NaY分子筛是一种性能优异的亚硝酸甲酯分解制备DMM的催化剂. 通过X射线衍射(XRD)、比表面及孔隙度分析(BET)、扫描电子显微镜(SEM)、吡啶红外(Py-FTIR)等结构表征手段, 发现分子筛的酸性位点是促进亚硝酸甲酯分解的活性中心, 而Na⁺和Al物种的Lewis酸是高选择性生成DMM的关键. 本工作可为DMM提供一种新的高效合成路线.     

Hyperpolarizabilities of Chelidamic Acid Complexes M_m(C_7H_3O_5N)_n (M=Cu, Ag): Theoretical Analysis

The frequency‐dependent hyperpolarizabilities of chelidamic acid complexes M_m(C₇H₃O₅N)_n (M?Cu, Ag) were investigated under the time dependent density functional theory (TDDFT) combined with the sum‐over‐states method (SOS). The relationship between molecular orbitals and nonlinear optical (NLO) properties has been explored. The results show that the charge transitions of π‐π* and 3d_M‐π* are very important to the second‐order polarizabilities, and the largest component of dynamic β is 3.84×10^?25 cm⁵·esu^?1 at 0.74 eV for Ag₂Cu₂(C₇H₃O₅N)₄. The charge transition between π‐π* is also highly crucial to the third‐order polarizabilities, and the largest component of dynamic γ is ?4.46×10^?29 esu at 0.50 eV for Ag₂Cu₂(C₇H₃O₅N)₄. The central Cu ion, as electron bridge, extends the range of delocalization and leads to an interesting phenomenon of spiroconjugation.     

基于空域非均匀傅里叶变换的傅里叶望远镜

为了在稀疏发射阵列下清晰重构目标图像,提出了一种基于空域非均匀傅里叶变换(NDFT)的傅里叶望远镜信号处理方法。依据傅里叶望远镜的发射器位置与抽取的目标空间频率关系,结合MATLAB程序特点,完成了空域非均匀傅里叶逆变换,重构了目标图像。稀疏发射阵列配置方式为:T型阵列单臂放置11个发射望远镜,连续抽取目标的8个低频信息,再抽取3个高频分量。选择不同形状和灰度分布的4个卫星作为成像目标。与补零均匀快速傅里叶变换(FFT)方法重构的图像对比发现:信噪比为100 dB时,相比补零均匀FFT方法, NDFT方法重构图像的Strehl比都有所提升,最高提升了0.159 8。     

富晶格位错的多孔铋纳米花高效电还原二氧化碳制甲酸盐※

二氧化碳转化已成为现今世界研究的热点. 本工作采用原位电化学转化的策略, 将简单溶剂热法合成的层状甲酸氧铋纳米花(BiOCOOH NFs)还原为带有大量晶格位错的多孔铋纳米花(p-Bi NFs). 研究结果表明, p-Bi NFs电催化二氧化碳转化为甲酸盐具有较小的过电位(436 mV). 在–1.8 V(相对饱和甘汞电极, vs. SCE)时, 甲酸盐的分电流密度(j_formate)高达24.4 mA•cm^-2, 法拉第效率(FE_formate)为96.7%, 且在超过500 mV的宽电位窗口内FE_formate超过90%, 并具有很好的稳定性. 该催化剂的高催化性能可归因于前驱体晶格坍塌和重构而形成特殊的多孔粗糙的微纳多级结构, 其表面富含晶格位错和缺陷等高本征活性位, 且具有较强的电子传递能力. 本研究为设计合成高性能的电催化二氧化碳还原产甲酸催化剂提供了新的思路.     

含[V2M6S6O2](M＝Cu,Ag)簇骼单元的八核簇合物的分子结构和谱学性质

报道了两个「Ｖ２Ｍ６Ｓ６Ｏ」（Ｍ＝Ｃｕ,Ａｇ）八核簇合物的合成和分子结构,讨论了它们的约外光谱,＾５１ＶＮＭＲ和电子光谱,采用动态红外光谱跟踪技术探讨「Ｖ２Ｃｕ６Ｓ６Ｏ２」簇合物的成簇机理。     

Rb2MGe3S8 (M=Zn,Cd): [MGe3S8]2–单元构型变换导致化合物从中心到非心的转变※

在本工作中, 利用高温固相法成功合成了两个碱金属硫属化合物Rb₂MGe₃S₈ [M=Zn (1), Cd (2)]. 化合物1, 2都为二维层状结构且均具备大的光学带隙, 化合物1和2的实验带隙分别为3.24和3.16 eV. 化合物1属于P-1中心对称群, 化合物2属于非心P2(1)2(1)2(1)空间群且具有一定的非线性光学(NLO)效应, 在粒径为50~75 μm时与KH₂PO₄ (KDP)相当(@1064 nm). 化合物2的激光损伤阈值为AgGaS₂的16.6倍. 化合物1, 2的分子式化学计量比相同但展示不同的对称性, 通过分析它们的晶体结构发现, 其基本构造单元[MGe₃S₈]^2–在两化合物中构型的不同导致化合物1、2对称性发生中心到非心的转变. 为了深入了解化合物2的NLO效应的起源, 基于密度泛函理论对其进行了电子能带结构和NLO极化率的理论计算.     

A grain boundary defect model for ZnO ceramic varistors by deep heat treatment

Studies on ZnO ceramic varistors by deep heat treatment at 650–900 C are reported. The current creep time curve exhibits a peak during the continuous action of a dc biasing voltage; the forwardV-l characteristic is improved rather than degraded after the action of the biasing voltage. We assume that the zinc interstitial cations Zn_i are out diffused rapidly and the concentration of Zn_i in the depletion layer is decreased rapidly during deep heat treatment; the oxygen anions O’_o could be accumulated at the grain interface if the out diffusion quantity of Zn_i is not enough to react with the O’_o; the current creep phenomenon above results from the migration of the interface O’_o by the biasing voltage. We suggest an improved grain boundary defect model for the ZnO varistors by deep heat treatment, and examine the model using the experimental data of lifetime positron-annihilation spectroscopy. Project supported by the National Natural Science Foundation of China.     

柠檬酸辅助水热法制备可见光高效去除甲基橙的Bi2WO6纳米片

以Bi(NO3)3·5H2O和Na2WO3 ·2H2O为原料,以柠檬酸为络合剂,采用辅助水热法制备了Bi2WO6纳米片,运用X射线衍射、扫描电镜、场发射高分辨透射电镜、拉曼光谱、红外光谱和紫外-可见漫反射光谱等手段对样品进行了表征,并考察了该催化剂光催化去除甲基橙反应性能.结果表明,通过调节体系的pH值可制得结晶度良好...     

CeO_2:Eu~(3+)纳米晶的水热合成和光学性能

以硝酸铈(Ce(NO3)3·6H2O)、硝酸铕(Eu(NO3)3·6H2O)、氨水(NH3·H2O)为原料和十六烷基三甲基溴化铵(CTAB)为分散剂,采用水热法制备了CeO2:Eu3+纳米晶,用X射线衍射(XRD)、X射线光电子能谱分析(XPS)、透射电镜(TEM)、傅立叶红外(FT-IR)、拉曼光谱和荧光(FL)等手段对产品的结构和光学性能进行分析和表征。测试结果表明:CeO2:Eu3+是立方萤石结构的纳米晶体,铕以Eu3+形式进入CeO2晶格中致使其晶胞参数略增,晶粒尺寸减小。相比纯CeO2,CeO2:Eu3+的紫外-可见光吸收边发生些许红移,其中CeO2:Eu3+(9.0%)纳米晶的能带隙为2.84 e V。CeO2:Eu3+纳米晶在593,612和632 nm处发橙红光,其中非直接激发(356 nm)的CeO2:Eu3+(1.0%)的磁偶极跃迁(5D0→7F1)占主导,而直接激发(468 nm)的CeO2:Eu3+(5.0%)的电偶极跃迁(5D0→7F2)强度更大,两者均随焙烧温度升高而增强。     

Temperature Induced Interpenetration Suppression of a Couple of Azo‐based Isomers with a Flexible Second Ligand

Two new azo‐based coordination compounds with a flexible second ligand, crystal 1 (composed with [Zn(adc)(eda)]_n‐1) and crystal 2 (composed with {[Zn(adc)]_0.9568(eda)}_n‐1′ and {[Zn(adc)]_0.0414}_n) have been synthesized as a couple of isomers with different reaction temperature. Adc^2? and eda represent azobenzene‐4,4′‐dicarboxylic ion and 1,2‐ethanediamine, respectively. Single crystal X‐ray diffraction measurement indicates the interpenetration of the above crystals could be suppressed by simply tuning the reaction temperature, that is, the 5‐fold interpenetration which leads to no free volume left in lower temperature synthesized compound [Zn(adc)(eda)]_n‐1 could be reduced to a 4‐fold interpenetration in higher temperature synthesized {[Zn(adc)]_0.9568(eda)}_n‐1′ which results in free volume accounting for 3.6% (31.6 ų per unit cell volume) in crystal 2 . The synthesis, crystal structure and fluorescence spectra of crystals 1 and 2 have been discussed, together with the data of elemental analysis and X‐ray powder diffraction.