Two-Dimensional Two-Component Plasma with Adsorbing Impurities

We study the behavior of the two-dimensional two-component plasma in the presence of some adsorbing impurities. Using a solvable model, we find analytic expressions for the thermodynamic properties of the plasma such as the n-body densities, the grand potential, and the pressure. We specialize in the case where there are one or two adsorbing point impurities in the plasma, and in the case where there are one or two parallel adsorbing lines. In the former case we study the effective interaction between the impurities, due to the charge redistribution around them. The latter case is a model for electrodes with adsorbing sticky sites on their surface.     

氰基修饰石墨相氮化碳构建高效的活性位点用于光催化还原CO2

作为影响光催化反应的关键因素,光催化剂的活性位点数量直接决定了光催化活性.传统石墨相氮化碳(g-C3N4)由于活性位点不足而表现出较弱的光催化活性.为了增加g-C3N4的活性位点数量,研究人员采取了各种策略,包括杂原子掺杂、表面改性和空位工程.其中,表面改性是增加催化剂活性位点的有效策略之一.氰基具有很强的吸电子能力,可在光催化反应中作为活性位点.然而,关于氰基作为CO2光还原活性位点的研究并不多,特别是对于氰基修饰增强g-C3N4活性的机理尚不清楚.构建多孔结构是暴露催化剂活性位点的有效措施之一.多孔结构可以有效改善纳米片的团聚,促进活性位点暴露,增大反应物与活性位点间的接触机会;并且相互连接的多孔网络可形成独特的传输通道,进一步促进载流子迁移.本文通过分子自组装和碱辅助策略合成了氰基改性的多孔g-C3N4纳米片(MCN-0.5).氰基由于具有良好的吸电子特性,促进了局部载流子分离,并充当了光催化反应的活性位点.受益于活性位点的影响,MCN-0.5表现出显著增强的光催化CO2还原活性.在不添加牺牲剂和助催化剂的条件下,MCN-0.5样品上CO和CH4产率达到13.7和0.6μmol·h–1·g–1,分别是传统煅烧法制备的g-C3N4(TCN)产生CO和CH4产率的2.5和2倍.通过盐酸处理MCN-0.5除去氰基,并没有破坏样品的形貌结构,但催化剂的光催化活性显著降低,证实了氰基活性位点的作用.光还原Pt纳米颗粒的实验结果表明,与对照样品相比,氰基修饰的样品上还原的Pt纳米颗粒更多,进一步证实了引入氰基为光还原反应提供了更多活性位点.CO2等温吸附测试结果表明,MCN-0.5对CO2的吸附能力不如对照样品,间接证明氰基能成为活性位点是由于其良好的吸电子能力促进了局部载流子分离.瞬态荧光光谱、光电化学表征结果表明,氰基修饰增强了载流子迁移和分离能力.根据理论计算和原位红外光谱提出了氰基修饰增强g-C3N4光催化还原CO2活性的作用机理.以三聚氰胺为前驱体接枝氰基的g-C3N4也表现出比体相g-C3N4明显增强的光催化还原CO2活性,这证明了氰基改性增强g-C3N4活性策略的通用性.本文通过在光催化剂材料中设计活性位点为太阳能高效转化提供了一个有效途径.     

无定形硅铝负载镍催化剂上乙烯齐聚反应的活性位点结构鉴定

镍(Ni)基催化剂在低碳烯烃聚合领域具有重要的地位,也是该领域研究的热点.自Johnson等报道(J.Am.Chem.Soc.,1995,117,6414–6415)二亚胺配体络合的Ni(Ⅱ)催化剂可有效降低烯烃聚合度,降低产物中非线性烯烃的选择性,甚至可以生成α-烯烃以来,掀起了Ni基催化剂在烯烃聚合领域的研究热潮.从均相到负载型多相Ni基催化剂,从载体类型到配体性质,从Ni纳米粒子的粒径调控到金属表面价态,关于Ni活性中心的研究工作一直存在争论.本课题组之前研究结果表明,曾明确了无定形硅铝(ASA)载体负载的Ni催化剂,经惰性气氛(N2)预处理得到的一价Ni是烯烃齐聚反应的主要活性中心(J.Chem.Soc.Chem.Commun.,1991,126–127).本文进一步深入研究了不同Al2O3含量的ASA载体上Ni活性位点的结构及其在乙烯齐聚反应中的活性.27Al NMR结果表明,催化剂中的铝存在三种配位方式,分别为AlⅣ、AlⅤ和AlⅥ,其中AlⅣ含量随Al2O3含量的增加而增加.载体中铝配位方式的不同,导致其表面金属负载的金属Ni活性位点所处的结构亦不同.原位FTIR-CO和H2-TPR实验结果表明,催化剂表面存在两种不同结构分布的Ni位点,分别是接枝在弱酸性硅醇上的Ni2+阳离子和Si?(OH)?Al桥式羟基离子交换位置的Ni2+阳离子.多数研究者认为,位于离子交换位置处孤立的Ni阳离子是反应的活性中心.然而,近期有研究者提出负载在酸性硅烷醇表面孤立的Ni2+阳离子为反应的活性中心物质.本文研究发现,随着Al2O3负载量的降低,处于离子交换位置处的Ni2+离子含量逐渐减少,而处于硅醇缺陷位点处的Ni2+离子含量则逐渐增多.原位FTIR-CO分析结果表明,处于硅醇缺陷位点处的Ni2+离子物种在惰性气氛中更易于转化为活性中心Ni+.相应的催化反应结果表明,相比于离子交换位置的Ni2+物种,具有与硅醇缺陷位点相连的Ni2+离子结构更有利于表现出更高的乙烯齐聚化活性.由此可知,处于硅醇缺陷位点的Ni2+物种是乙烯齐聚反应的活性中心的前驱体.本文进一步研究了硅醇缺陷位点处的Ni2+离子物种更易于转化为活性中心Ni+的原因.H2-TPR结果表明,相比于离子交换位置的Ni2+物种,处于硅醇缺陷位点的Ni2+物种与载体之间的相互作用力更弱.C2H4-TPD结果进一步表明,具有这种相对较弱的金属载体间作用力结构的催化剂对反应物C2H4分子的吸附作用力相对更强,吸附量也相对增多,因此其乙烯齐聚的催化性能更优.本研究结果对理解活性中心结构和合理设计催化剂提供参考.     

Potential active sites of Mo single atoms for electrocatalytic reduction of N2

Single atom catalysts(SACs) with isolated metal atoms dispersed on supports exhibit distinctive performances for electrocatalysis reactions.The designable realization of well-dispersed single metal atoms is still a great challenge owing to their ease of aggregation.Here,Mo single atomic sites(Mo-N₃C)combined with some ultrasmall Mo₂C/MoN clusters(Mo-SA/Mo₂C-MoN-Cs,mean diameter <2 nm) on nitrogen-doped porous carbon were synthesized via a simple pyrolysis of bimetallic Zn/Mo metalorganic frameworks.X-ray absorption near edge spectra(XANES) in combination with various characterizations show that most of Mo species in sample exist in the form of single sites and the exact structure is Mo-N₃C.Density functional theory(DFT) calculation further shows that as the number of Ncoordination in the Mo-NxC moieties increases,the positive cha rge of Mo atoms increases.The single Mo atoms in Mo-N₃C have the best capability of N₂ adsorption,which may serve as main active sites for further electrochemical N2 reduction.     

Crystal structures of the octahedral rhenium cluster compexes Cs4[Re6S8(OH)6]·6H2O and Cs4[Re6Se8(OH)6]·8H2O

The salts Cs₄[Re₆S₈(OH)₆]·6H₂O (1) and Cs₄[Re₆Se₈(OH)₆]·8H₂O (2) were obtained by the reactions of Re₆S₈Br₂ and Re₆Se₈Br₂ with a CsOH melt with further solution of the products in water and crystallization of 1 and 2 from the aqueous solutions. The structure of the compounds was established by X-ray single crystal diffraction analysis. Compound 1 crystallizes in the orthorhombic space group Pbca with unit cell parameters a = 14.175(2) Å, b = 11.321(2) Å, c = 17.503(2) Å, V = 2808.5(7) ų, Z = 4, d _calc = 5.003 g/cm³; compound 2 crystallizes in the triclinic space group with unit cell parameters a = 9.020(4) Å, b = 9.127(4) Å, c = 10.289(4) Å, α = 79.589(7)°, β = 75.829(7)°, γ = 72.186(7)°, V = 776.8(6) ų, Z = 1, d _calc = 5.402 g/cm³. Original Russian Text Copyright ? 2007 by K. A. Brylev, Yu. V. Mironov, S.-J. Kim, and V. E. Fedorov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 6, pp. 1183–1188, November–December, 2007.     

Metal directed structural diversity of two coordination polymers and their optical and magnetic properties

Two new coordination polymers [Cu(5-NIP)₂(TBPE)] (1) (where, 5-NIP = 5-nitro isophthalic acid and TBPE = trans-4,4′-bipyridylethylene) and [Zn₄(μ3-OH)₂(5-NIP)₄(TBPE)₂] (2) have been synthesized and structurally characterized. Compound 1 features a molecular ladder type structure composed of Cu₂(5-NIP)₄ as metallacyclic platforms and TBPE as building blocks. Two nearly parallel ladders are assembled through π-π interactions between benzene rings of 5-NIP molecules, whereas a supramolecular two-fold interpenetrated square grid network results from the hydrogen bonding interactions between free carboxylates and nitrates of the 5-NIP molecules. Compound 2 forms a 3D network which is constructed from tetrameric units composed of two tetrahedral and two octahedral Zn(II) centers arranged in a coplanar fashion by two triply bridging μ3-OH groups. The electronic spectra of compound 1 reflect the distorted octahedral symmetry around the copper center in corroboration with the crystal structure data. EPR measurements again reconcile the D_4h symmetry for copper in an axially elongated octahedral geometry, in agreement with the spectroscopic studies. Magnetic susceptibility measurement reveals that compound 1 behaves like a magnetically dilute system with large spin-orbit coupling and it exhibits weak antiferromagnetic coupling at lower temperatures. Furthermore, the luminescent properties of both compounds were also determined in the solid state at room temperature.     

Spectral,Antimicrobial, and Thermal Studies of Some Transition Metal Complexes Derived from Bidentate Ligands Containing N and S Donor Atoms

Abstract

Bidentate ligands have been synthesized by the reaction of 2,4-dichlorobenzaldehyde with 4-amino-5-mercapto-1,2,4-triazole and 4-amino-5-mercapto-3-propyl-1,2,4-triazole. The ligands react with acetates of Co(II), Ni(II), Cu(II), and Zn(II) to yield 1:2 [metal:ligand] complexes. The newly synthesized compounds were characterized by elemental analyses, spectral (UV-Vis, IR, ¹H NMR, fluorescence, ESR) studies, thermal techniques, and magnetic measurements. Thermal studies of the complexes showed a multistep decomposition pattern. A square planar geometry for Cu(II) and octahedral geometry for Co(II), Ni(II), and Zn(II) complexes have been proposed. The synthesized complexes exhibit enhanced antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Aspergillus niger, and A. flavus compared to parent ligands. However, tested compounds did not exhibit any activity against Escherichia coli and Pseudomonas aeruginosa.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

不同的沉淀剂对铁酸铜催化剂水煤气变换活性和热稳定性的影响(英文)

以氢氧化钾、碳酸钠和碳酸氢钠为沉淀剂,采用共沉淀法制备3种铁酸铜催化剂,并对其水煤气变换活性和热稳定性进行了评价。测试发现,以氢氧化钾为沉淀剂制得的催化剂表现出优异的水煤气变换活性。通过X射线粉末衍射仪(XRD)、N2物理吸附(N2-physisorption)、H2-程序升温还原(H2-TPR)、CO2-程序升温脱附(CO2-TPD)和循环伏安法(CV)等技术手段研究了不同的沉淀剂对催化剂的微观结构和表面性质的影响。结果发现,氢氧化钾能有效促进CuFe2O4的生成、抑制CuO和CuFe2O4晶格的长大、促使CuO在催化剂表面的较好分散、增强催化剂的还原能力、增加弱碱性位点的数量。它们显著改善了催化剂的催化活性和热稳定性。