A highly efficient synthesis of imidazo-fused polyheterocycles via Groebke–Blackburn–Bienaymè reaction catalyzed by LaCl3·7H2O

A highly efficient and mild protocol for the synthesis of imidazo-fused polyheterocycles via Groebke–Blackburn–Bienaymè reaction under the influence of catalytic amount of lanthanum chloride heptahydrate has been described. A wide range of nitrogen-enriched polyheterocycles are synthesized with high yields under neat conditions.     

Thermal stability of polybenzoxazines with lanthanum chloride and their crosslinked structures

Lanthanum chloride (LaCl₃) was incorporated into five kinds of benzoxazines by different preparation methods. The thermal stability and the structures of polybenzoxazines were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The evolved gases from the degradation process of polybenzoxazines were analyzed by FTIR. The results showed that the thermal stability and char yields of three kinds of polybenzoxazines containing LaCl₃ can be improved obviously. LaCl₃ has an important effect on the polymerization reactions of benzoxazines. More stable arylamine Mannich bridges were observed in the chemical structures of the polybenzoxazines. It is these structures that can effectively retard the volatilization of aniline derivatives and result in the improvement of the thermal stability of the polybenzoxazines.     

A Porous 4d–4f Heterometallic Coordination Polymer: Synthesis,Crystal Structure and Physical Properties

A 4d–4f heterometallic coordination polymer, [AgLa(pydc)₂]·3H₂O ( 1 ) (H₂pydc = pyridine‐3,4‐dicarboxylic acid), has been synthesized under hydrothermal conditions, and further characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and single‐crystal X‐ray diffraction. Complex 1 features a three‐dimensional (3D) framework containing one‐dimensional (1D) channels occupied by free water molecules, which is constructed from 1D inorganic heterometallic chains and linear pydc linkers. To the best of our knowledge, complex 1 represents a rare example of 3D open‐framework 4d–4f heterometallic coordination polymer. Moreover, after removal of the water molecules from complex 1 , the remaining material has high thermal stability and good adsorption behavior towards nitrogen gas.     

Synthesis, crystal and electronic structure, and physical properties of the new lanthanum copper telluride La3Cu5Te7

The new lanthanum copper telluride La₃Cu_5−xTe₇ has been obtained by annealing the elements at 1073 K. Single-crystal X-ray diffraction studies revealed that the title compound crystallizes in a new structure type, space group Pnma (no. 62) with lattice dimensions of a=8.2326(3) Å, b=25.9466(9) Å, c=7.3402(3) Å, V=1567.9(1) Å³, Z=4 for La₃Cu_4.86(4)Te₇. The structure of La₃Cu_5−xTe₇ is remarkably complex. The Cu and Te atoms build up a three-dimensional covalent network. The coordination polyhedra include trigonal LaTe₆ prisms, capped trigonal LaTe₇ prisms, CuTe₄ tetrahedra, and CuTe₃ pyramids. All Cu sites exhibit deficiencies of various extents. Electrical property measurements on a sintered pellet of La₃Cu_4.86Te₇ indicate that it is a p-type semiconductor in accordance with the electronic structure calculations.     

Amperometry with Two Polarizable Electrodes. Chelometric Determination of Rare Earths

Abstract

The method of determining rare earths by chelometric EDTA titration with biamperometric end-point indication using two stationary platinum electrodes was studied. The convenient pH range for the determination of lanthanum is 5.0 – 8.0, for yttrium 3.5 – 8.0 and for ytterbium 3.0 – 8.0. Rare earths have been determined in the presence of iron and thorium. Iron and thorium can be titrated at pH 1.5 – 2.0 and rare earths of the lanthanum group can be determined by successive titration at pH 5.0. Large amounts of rare earths of the yttrium group interfere with the determination of iron and thorium.     

High Sensitive Sensor Based on Carbon Nanotube Electrode for Determination of Lanthanum in the Presence of Calcon Carboxylic Acid

In this paper we have investigated the electrochemical activity of lanthanum chloride (La (III)) in the presence of calcon carboxylic acid (CCA) using a multi-walled carbon nano tube/carbon paste electrode (CNT/CPE). The peak current increases linearly with increasing of the La (III) concentration. For this purpose, a few electrochemical methods such as cyclic, differential pulse voltammetry, linear sweep and hydrodynamic voltammetry, and chronoamperometry were used. The results show that calcon carboxylic acid as a ligand was useful for determination of La (III) and was able to improve its sensitivity. Cyclic voltammetry was used for study of reduction reaction of La (III) at the surface of modified electrode. The electrochemical parameters for La (III) at the surface of CNT/CPE, such as diffusion coefficient (D/ cm² s ^?1 = 5.26 × 10^?6), the electron transfer coefficient, (α = 0. 43), and the reduction rate constant, (k/ M s^?1 = 2.33 (±0.015) × 10²), were determined using voltammetry methods, which with the detection limit of La (III) by differential pulse voltammetry was found to be 1.3 nM. The combination of CCA with CNT as mediators in carbon paste electrode showed that this electrode is capable, sensitive, and simple to quantify La (III) in real samples with an average recovery of 97.64%.     

Ni/MWCNT及镧改性Ni/MWCNT催化CO2甲烷化反应的性能

以多壁碳纳米管(MWCNT)为载体, 通过浸渍法制备了负载型镍催化剂和稀土镧改性的镍催化剂, 并对其二氧化碳甲烷化的催化性能进行了研究. 借助比表面积测试、程序升温还原(TPR)、X射线衍射(XRD)和X射线光电子能谱(XPS)等表征手段研究了稀土镧的添加对Ni/MWCNT催化剂结构和表面组成、催化剂还原性能以及CO₂甲烷化反应性能的影响. 结果表明: 稀土镧改性的Ni/MWCNT较Ni/MWCNT催化剂具有更好的CO₂甲烷化活性, 镧组分的加入提高了催化剂表面的镍物种浓度和分散度, 弱化了氧化镍与载体MWCNT之间的相互作用, 促进了氧化镍的还原, 同时提高了表面镍物种的电子密度, 增加了对反应物的吸附能力, 从而提高了其CO₂甲烷化活性. 制备过程中稀土镧的添加次序对催化性能有较明显的影响, 其活性顺序为先浸渍镧后浸渍镍制备的催化剂活性明显好于先浸渍镍后浸渍镧制备的催化剂.     

氧化镧表面反应性对甲烷和氧分子活化的影响

以氧化镧催化剂在甲烷氧化偶联(OCM)反应中的结构敏感性实验研究为基础, 采用周期性密度泛函理论(DFT)计算研究氧化镧(001), (110)和(100)3个晶面及OCM反应物分子甲烷和氧在其上的吸附、 活化和解离. 结果表明, 氧化镧(001), (110)和(100)3个晶面的表面能大小顺序为(110)>(100)>(001), 3个晶面的价带和导带间隙大小顺序为(110)<(100)<(001), 即(001)是3个晶面中最稳定的晶面, 而(110)则是最活泼的晶面. 甲烷分子在氧化镧(001), (110)和(100)晶面上的吸附很弱(0.03 eV), H—CH₃解离吸附能分别为2.16, 0.68和0.90 eV, 解离反应的难易性与晶面的活性顺序一致; 而氧分子在氧化镧(001), (110)和(100)晶面上的分子吸附能分别为-0.04, -0.31和-0.12 eV, 解离吸附能分别为1.22, 0.53和1.52 eV, 即氧化镧晶面结构对氧分子吸附具有明显的影响, 其中, (001)晶面上吸附最弱, (110)晶面上吸附最强, 以致O—O在(110)晶面上可以较低能垒(0.53 eV)解离, 形成亲电的过氧物种. 由于氧分子在氧化镧表面的吸附较甲烷分子强, 因此, 氧化镧在OCM反应中结构敏感性应与氧分子的吸附和活化密切相关. 甲烷和氧分子在氧化镧表面上活化的本质源自于电子自表面流向甲烷和氧分子的反键轨道, 且表面结构的改变会导致不同强度的电子流动驱动.     

钙钛矿型LaCoO3电化学储锂的形貌调制效应

采用不同方法制备了块状(Bulk)、 纳米球状(NPs)及三维有序多孔(3DPF)钙钛矿型LaCoO₃电极材料, 并考察了材料的形貌、 结构与电化学储锂之间的相关性. 结果表明, 不同形貌的电极材料均呈钙钛矿型晶体结构, 但电化学储锂性能却表现出巨大差异: 在500 mA/g的电流密度下, 块状、 纳米球状及三维有序多孔LaCoO₃电极经350次循环后放电比容量分别为157, 579和648 mA·h/g. 电化学性能的迥异主要归因于所制备的纳米及多孔结构使活性材料与电解液之间的接触面积增大, 反应活性位点明显增多, 传质电阻降低, 从而使电子传输和Li离子的嵌入/脱嵌过程得到显著改善.     

Photocatalytic degradation of azophloxine on porous La2Ti2O7 prepared by sol-gel method

Cetyltrimethyl ammonium bromide (CTAB) was used in a sol-gel route to synthesize porous lanthanum titanate. The materials are composed of perovskite La₂Ti₂O₇ in monoclinic system. The addition of CTAB does not cause phase transformation, but leads to a slight decreasing tendency of La₂Ti₂O₇ crystallite size. Both the pore volume and pore size distribution range are enlarged after using CTAB. The sample obtained with 4 g CTAB has the maximum BET specific surface area of 42.4 m²/g. When the amount of CTAB is less than 4 g, the increase in photocatalytic degradation efficiency is almost in linear relationship to the amount of CTAB. The reaction rate constants are 0.0032, 0.0116 and 0.0237 min⁻¹ on the La₂Ti₂O₇ samples obtained using 0, 2 and 4 g CTAB. The functional groups in azophloxine molecule are decomposed during photocatalytic oxidation with extending irradiation time.