BaO-B2O3-GeO2(BaO≤50 mo1％)三元系相图的研究

本文用X射线衍射及差热分析等方法, 研究了BaO-B_2O_3-GeO_2(BaO≤50 mol％)三元系的室温截面相图。发现了一个新的三元化合物Ba_3B_6Ge_2O_(16)(3BaO·3B_2O_3·2GeO_2)。并且研究了BaB_2O_4-Ba_3B_6Ge_2O_(16), BaGeO_3-Ba_3B_6Ge_2O_(16), BaB_2O_4-BaGeO_3三个二元系相图。它们都是共晶体系, 共晶温度分别为937±3 ℃、879±3 ℃875±3 ℃; 共晶组分分别为(BaO)_(0.42)(B_2O_3)_(0.42)(GeO_2)_(0.16), (BaO)_(0.42)(B_2O_3)_(0.24)(GeO_2)_(0.34), (BaO)_(0.50)(B_2O_3)_(0.27)(GeO_2)_(0.23)。这三个二元系组成一个三元共晶体系, 其三元共晶温度为870±3 ℃, 共晶组分为(BaO)_(0.46)(B_2O_3)_(0.27)(GeO_2)_(0.27)。     

Fast atom bombardment induced ring rupture of silatranes

During a comparison study of the fast atom bombardment (FAB) and electron impact mass spectra of 1-organyl-2,9,10-trioxa-6-aza-1-silatricyclo[4.3.3.0^1,6]dodecanes, an unusual ion peak at m/z 164 was noticed in the FAB spectra. Accurate mass measurement indicated that m/z 164 corresponds to protonated 1-[N,N-bis(2-hydroxyethyl)amino]-1-propanol (BHAP), which is produced by a ring-rupture reaction. Further experiment showed that the intensity of the [BHAP + H]⁺ ion peak increased markedly as the 7keV Ar⁰ bombardment proceeded, suggesting a FAB-induced reaction. The possible mechanism is also discussed.     

Enhancing Built-in Electric Fields for Efficient Photocatalytic Hydrogen Evolution by Encapsulating C60 Fullerene into Zirconium-Based Metal-Organic Frameworks

High-efficiency photocatalysts based on metal-organic frameworks (MOFs) are often limited by poor charge separation and slow charge-transfer kinetics. Herein, a novel MOF photocatalyst is successfully constructed by encapsulating C₆₀ into a nano-sized zirconium-based MOF, NU-901. By virtue of host-guest interactions and uneven charge distribution, a substantial electrostatic potential difference is set-up in C₆₀@NU-901. The direct consequence is a robust built-in electric field, which tends to be 10.7 times higher in C₆₀@NU-901 than that found in NU-901. In the catalyst, photogenerated charge carriers are efficiently separated and transported to the surface. For example, photocatalytic hydrogen evolution reaches 22.3 mmol g⁻¹ h⁻¹ for C₆₀@NU-901, which is among the highest values for MOFs. Our concept of enhancing charge separation by harnessing host-guest interactions constitutes a promising strategy to design photocatalysts for efficient solar-to-chemical energy conversion.     

Atomically Dispersed Iron Regulating Electronic Structure of Iron Atom Clusters for Electrocatalytic H2O2 Production and Biomass Upgrading

The integration of highly active single atoms (SAs) and atom clusters (ACs) into an electrocatalyst is critically important for high-efficiency two-electron oxygen reduction reaction (2e⁻ ORR) to hydrogen peroxide (H₂O₂). Here we report a tandem impregnation-pyrolysis-etching strategy to fabricate the oxygen-coordinated Fe SAs and ACs anchored on bacterial cellulose-derived carbon (BCC) (FeSAs/ACs-BCC). As the electrocatalyst, FeSAs/ACs-BCC exhibits superior electrocatalytic activity and selectivity toward 2e⁻ ORR, affording an onset potential of 0.78 V (vs. RHE) and a high H₂O₂ selectivity of 96.5 % in 0.1 M KOH. In a flow cell reactor, the FeSAs/ACs-BCC also achieves high-efficiency H₂O₂ production with a yield rate of 12.51±0.18 mol g_cat⁻¹ h⁻¹ and a faradaic efficiency of 89.4 %±1.3 % at 150 mA cm⁻². Additionally, the feasibility of coupling the produced H₂O₂ and electro-Fenton process for the valorization of ethylene glycol was explored in detail. The theoretical calculations uncover that the oxygen-coordinated Fe SAs effectively regulate the electronic structure of Fe ACs which are the 2e⁻ ORR active sites, resulting in the optimal binding strength of *OOH intermediate for high-efficiency H₂O₂ production.     

活化分析

本文是《分析试验室》定期评述中“活化分析”课题的第二篇文章,它对我国活化分析领域在1988年9月～1990年10间的工作进展作了较全面的评述。内容包括活化分析在地球化学、宇宙化学、生命科学、环境科学、工业材料、考古、司法等领域中的应用;活化分析方法学中的化学预处理与放射化学处理;自动化方法;仪器、设备与计算机软件;以及近两年涌现出的一批新课题与新方法。     

无脂链磺化酞菁铜多层膜体系：电子非弹性平均自由程的研究

磺化酞菁铜多层膜体系是利用Langmuir-Blodgett技术制备的有序有机分子膜,它对于XPS测试有很好的稳定性,本文在固定电子出射角的条件下利用XPS方法研究了不同厚度的膜样品中Cu_((2(?))_(3/2))、Ni_(1(?))、S_(2p)峰强度的变化规律,讨论了膜内分子有序排列引起的散射效应对电子平均自由程的影响。     

Thermionic emission from giant fullerenes

The kinetics of cluster formation in supersonic jets is examined by numerical integration of the master equation system. Some general characteristics of cluster kinetics could be formulated. Excellent agreement between experimental curves of p-cresol (H₂O)_{0, 1, 2, 3} formation as function of H₂O pressure and the corresponding calculated curves were obtained assuming successive cluster formation. From the kinetic curves, an unambiguous assignment of cluster size was possible which agreed with mass-resolved REMPI measurements. The fit of the rate coefficients shows the formation of p-cresol (H₂O)₁ to be faster than p-cresol (H₂O)₂ and p-cresol (H₂O)₃.     

Nb掺杂调控CoSeS多级纳米结构用于增强析氢反应

电催化析氢(HER)是清洁制氢的一种有效途径,对于氢经济和氢能产业的发展具有重要意义.金属掺杂是提高电催化剂本征活性的有效方法,导电基底的采用也有利于电荷传输和催化性能的整体提高.尽管已有关于硒化物作为HER催化剂的相关报道,但是合成条件有限、导电性、本征活性的影响,其电催化性能仍有提升的空间.此外,在酸性电解液中的腐...     

Self-assembled lamellar nanochannels in polyoxometalate-polymer nanocomposites for proton conduction

The construction of nanostructured ion-transport channels is highly desirable in the design of advanced electrolyte materials,as it can enhance ion conductivity by offering short ion-transport pathways.In this work,we present a supramolecular strategy to fabricate a nanocomposite electrolyte containing highly ordered lamellar proton-conducting nanochannels,by the electrostatic self-assembly of a polyoxometalate H_3 PW_(12)O_(4 O)(PW) and a comb copolymer poly(4-methlstyrene)-graft-poly(N-vinyl pyrrolidone).PW can effectively regulate the self-assembling order of polymer moieties to form a large-ra nge lamellar structure,meanwhile,introducing protons into the nanoscale lamellar domains to build proton transport channels.Moreover,the rigid PW clusters contribute a remarkable mechanical reinforcement to the nanocomposites.The lamellar nanocomposite exhibits a conductivity of 4.3 × 10~(-4) S/cm and a storage modulus of 1.1 × 10~7 Pa at room temperature.This study provides a new strategy to construct nanostructured ion-conductive pathways in electrolyte materials.     

Cu分隔开的Pd单原子用于乙炔选择加氢:Cu担载量的影响

大量乙烯中少量乙炔的去除是化工生产中的重要过程之一,理想途径是将其选择加氢生成乙烯.负载型Pd催化剂因具有很高的乙炔转化率而被广泛用于该过程,但乙烯选择性很低,同时会使原料气中的乙烯被加氢,造成原料气的浪费.采用其它元素对Pd纳米粒子表面修饰,覆盖部分活性位,可以在一定程度上提高乙烯选择性,但是会大大降低Pd的利用率.因此,制备兼具高活性和高选择性且经济实用的催化剂,仍是这一过程亟待解决的主要问题之一.我们的前期工作中,将Pd与IB族金属(Au,Ag,Cu)分别结合制备得到了一系列含Pd的合金单原子催化剂(SAC),发现它们在大量乙烯存在条件下的乙炔选择加氢反应中表现出优异的催化性能.其中,Pd的用量仅为ppm级别,大大提高了Pd的利用率.作为IB族最为廉价的金属,Pd与Cu形成的合金SAC在提高Pd原子利用率的同时,能够进一步降低催化剂的经济成本.然而,当形成合金SAC时,Cu/Pd原子比例的极限值仍然不确定.本文通过固定Pd的担载量,采用简单的等体积共浸渍的方法,制备了一系列不同Cu/Pd原子比例的氧化硅负载的双金属催化剂.首先,我们采用程序升温还原(TPR)和X射线衍射(XRD)对催化剂的还原能力和双金属纳米粒子的尺寸进行了考察.进一步,采用X射线吸收光谱(XAS,包括EXAFS和XANES)对双金属催化剂中Pd的配位环境进行了分析.最后,结合它们在大量乙烯存在条件下的乙炔选择加氢反应中的催化性能,对形成合金SAC时Cu/Pd原子比例进行了讨论.TPR结果显示,Cu与Pd结合时会促进双金属纳米粒子的还原.XRD结果表明,随着Cu含量的降低,双金属纳米粒子的尺寸明显减小.XANES结果证实,当Pd与Cu结合时,Pd会带有部分负电荷,这也与Pd的电负性大于Cu相一致.通过对EXAFS拟合结果进行分析,我们发现当Cu/Pd的原子比例≥40/1时,Pd原子可以被Cu原子完全分隔开,形成含Pd的合金SAC,使其在大量乙烯存在条件下的乙炔选择加氢反应中表现出优异的催化性能.通过对还原温度的考察,我们发现还原温度由250 oC升高到400 oC时,对同一催化剂的催化性能影响不大;EXAFS拟合结果显示,对比分别经过250和400 oC还原后的催化剂,Pd的配位环境变化不明显,这可能是导致催化性能相似的主要原因.