镧系元素光化学 Ⅳ 铁和铈对光还原分离铕的影响

本文在水溶液中以1:1HCOOH～HCOONa做自由基清除剂,Na_2SO_4做光还原产物Eu~(2+)沉淀剂,研究了杂质铁和含量变化对光还原分离铕的影响,并用紫外光谱证明了体系中是光反应生成的Fe和Ce~(4+)对发生氧化,致使Eu~(2+)光还原生成Eu~(2+)速度减慢,铕的收率下降。     

Study of thermal decomposition of ammonium cerium sulphate

Thermal decomposition of ammonium cerium sulphate has been studied by differential scanning calorimetry and thermogravimetry. The results show that the material decomposes in five steps in the temperature region 364–1116 K in oxygen. Based on the thermal data, elemental analysis and magnetic susceptibility measurements, sequence of decomposition has been established. The final product has been identified as CeO₂ by X-ray diffractometry. Ammonium cerium sulphate and the products of the first and the final transitions contain cerium ion in 4+ oxidation state, while the three intermediate phases have cerium ion in 3+ oxidation state. From the non-isothermal DSC studies, kinetic parameters have been computed. The isothermal data show that the dehydration process follows Ginstling-Brounshtein mechanism, while the next three steps are governed by Mampel's unimolecular law of random nucleation.

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Zusammenfassung Mittels DSC und TG wurde die thermische Zersetzung von Ammoniumzersulfat untersucht. Die Ergebnisse zeigen in Sauerstoff einen fünfstufigen Zersetzungsprozeß im Temperaturbereich 364–1116 K. Ausgehend von den thermoanalytischen Angaben, der Elementaranalyse und den Messungen der magnetischen Suszeptibilität wurde eine Sequenz für die Zersetzung erstellt. Das Endprodukt wurde mittels Röntgendiffraktion als CeO₂ identifiziert. Ammoniumzersulfat und die Produkte des ersten und des letzten Überganges enthalten Zerionen mit der Oxydationsstufe +4, während in den drei Zwischenschritten Zerionen mit der Oxydationsstufe +3 vorkommen. Anhand der nichtisothermen DSC-Untersuchungen wurden die kinetischen Parameter berechnet. Die isothermen Angaben zeigen, daß der Dehydratationsprozeß einem Ginstling-Brounstein Mechanismus folgt, während die folgenden drei Schritte durch das Mampelsche unimolekulare Gesetz der Randomkeimbildung bestimmt werden.

     

The Use of Derivative Thermogravimetry to Estimate Degree of Thermal Degradation

It is difficult to estimate the degree of thermal degradation which has taken place in complex parts composed of cellulosics and polymeric insulation unless complete failure has occurred. There is a definite need for a parameter which can quickly and easily measure the relative degree of thermal attack on organic insulation subjected to various known environmental and processing conditions. This paper reports preliminary work using derivative thermogravimetry to perform this function. Derivative thermogravimetric analysis (TGA) was used to produce a value, TGA Index, related to the peak height of the major TGA derivative signal. This TGA Index was found to correlate with the copper number of insulating paper measured after thermal degradation. The application of TGA Index to evaluation of polymer degradation after thermal shock, water absorption, and accelerated UV attack is also discussed. Finally, preliminary studies on the use of derivative TGA to evaluate coatings exposed to various outdoor environments around the country are reported.     

Metal–Organic Framework (MOF)-Derived Carbon-Mediated Interfacial Reaction for the Synthesis of CeO2−MnO2 Catalysts

CeO₂-based catalysts are widely studied in catalysis fields. Developing one novel synthetic approach to increase the intimate contact between CeO₂ and secondary species is of particular importance for enhancing catalytic activities. Herein, an interfacial reaction between metal–organic framework (MOF)-derived carbon and KMnO₄ to synthesize CeO₂−MnO₂, in which carbon is derived from the pyrolysis of Ce-MOFs under an inert atmosphere, is described. The MOF-derived carbon is found to restrain the growth of CeO₂ crystallites under a high calcination temperature and, more importantly, intimate contact within CeO₂/C is conveyed to CeO₂/MnO₂ after the interfacial reaction; this is responsible for the high catalytic activity of CeO₂−MnO₂ towards CO oxidation.     

Triple Frustrated Lewis Pair-Type Reactivity on a Single Rare-Earth Metal Center

Rare-earth metal cations have been used rarely as Lewis-acidic components in the chemistry of frustrated Lewis pairs (FLPs). Herein, we report the first cerium/phosphorus system ( 2 ) employing a heptadentate N₄P₃ ligand, which exhibits triple FLP-type reactivity towards a series of organic substrates, including isocyanates, isothiocyanates, diazomethane, and azides on a single rare-earth Lewis acidic Ce center. This result shows that the Ce center and three P atoms in 2 could simultaneously activate three equivalents of small molecules under mild conditions. This study broadens the diversity of FLPs and demonstrates that rare earth based FLP exhibit unique properties compared with other FLP systems.     

Probing Multiconfigurational States by Spectroscopy: The Cerium XAS L3-edge Puzzle

The Ce L₃ edge XAS spectra of CeO₂ and cerocene [Ce(C₈H₈)₂] were calculated with relativistic ab-initio multireference wavefunction approaches capable of reproducing the observed spectra accurately. The study aims to resolve the decades-long puzzle regarding the relationship between the number and relative intensities of the XAS peaks and the 4f electron occupation in the ground state (GS) versus the core-excited states (ESs). CeO₂ and cerocene exemplify the different roles of covalent bonding and wavefunction configurational composition in the observed intensity patterns. Good agreement is found between the calculated GS 4f-shell occupations and the value derived from XAS measurements using peak areas (n_f). The identity of the two-peaked Ce L₃ edge is fully rationalized from the perspective of the relaxed wavefunctions for the GS and core ESs. The states underlying the different peaks differ from each other in a surprisingly simple way that can be associated with 4f¹ vs. 4f⁰ sub-configurations. Furthermore, part of one of the cerocene spectral peaks is associated with 4f² sub-configurations. The pattern therefore reveals excited states that can be interpreted in terms of Ce IV and III oxidation numbers, as long assumed, with Ce II states additionally appearing in the cerocene spectrum. While this work demonstrates the rough accuracy of the conventional approach to determining n_f from Ce L₃-edge XAS, limitations are highlighted in terms of the ultimate accuracy of this approach and the potential of observing new types of excited states. The need to determine the sources of n_f by calculations, is stressed.     

铁氰化铈薄膜固载血红蛋白修饰的过氧化氢生物传感器的制备及性能

采用电化学沉积法将铁氰化铈(CeHCF)薄膜修饰于玻碳电极(GCE)表面,得到铁氰化铈薄膜修饰玻碳电极;将血红蛋白(Hb)固载于该修饰电极表面,成功制得了Hb/CeHCF/GCE过氧化氢生物传感器.考察了铁氰化铈薄膜修饰玻碳电极的氧化还原机理和制备条件,并对血红蛋白在电极上的电子传递过程进行了较为深入的研究.结果表明,铁氰化铈薄膜为血红蛋白提供了温和的固载环境,可实现血红蛋白与电极表面的直接电子转移,提高了血红蛋白的电化学活性;所制得的传感器对过氧化氢具有较高的催化响应和较强的稳定性.相关研究结果在生物医学和临床医学领域具有一定的借鉴意义.     

First-principles characterization of formate and carboxyl adsorption on stoichiometric CeO2(111) and CeO2(110) surfaces

Molecular adsorption of formate and carboxyl on stoichiometric CeO₂(111) and CeO₂(110) surfaces was studied using periodic density functional theory (DFT+U) calculations. Two distinguishable adsorption modes (strong and weak) of formate are identified. The bidentate configuration is more stable than the monodentate adsorption configuration. Both formate and carboxyl bind at the more open CeO₂(110) surface are stronger. The calculated vibrational frequencies of two adsorbed species are consistent with the experimental measurements. Finally, the effects of U parameters on the adsorption of formate and carboxyl over both CeO₂ surfaces were investigated. We found that the geometrical configurations of two adsorbed species are not affected by different U parameters (U = 0, 5, and 7). However, the calculated adsorption energy of carboxyl pronouncedly increases with the U value while the adsorption energy of formate only slightly changes (<0.2 eV). The Bader charge analysis shows the opposite charge transfer occurs for formate and carboxyl adsorption where the adsorbed formate is negatively charge while the adsorbed carboxyl is positively charged. Interestingly, with the increasing U parameter, the amount of charge is also increased.