原子数精确的金属纳米团簇在电催化领域的应用研究进展

金属纳米团簇(MNCs)是由几个到数百个金属原子组成,其尺寸一般小于2nm.金属纳米团簇在许多催化反应中表现出高的催化活性和选择性,这与金属纳米团簇具有高的比表面积、较多暴露的活性原子,以及与金属纳米粒子(MNPs)不同的电子结构有关.金属纳米团簇确定的组成和结构使其成为一种新型模型催化剂,对纳米团簇的催化性能研究有利...     

Atomically Precise Metal Nanoclusters: Novel Building Blocks for Hierarchical Structures

Atomically precise ligand-protected nanoclusters (NCs) constitute an important class of compounds that exhibit well-defined structures and, when sufficiently small, evident molecular properties. NCs provide versatile building blocks to fabricate hierarchical superstructures. The assembly of NCs indeed offers opportunities to devise new materials with given structures and able to carry out specific functions. In this Concept article, we highlight the possibilities offered by NCs in which the physicochemical properties are controlled by the introduction of foreign metal atoms and/or modification of the composition of the capping monolayer with functional ligands. Different approaches to assemble NCs into dimers and higher hierarchy structures and the corresponding changes in physicochemical properties are also described.     

Atomically Precise Alloy Nanoclusters

Metal nanoclusters (NCs) have a particle size of about one nanometer, which makes them the smallest unit that can give a function to a substance. In addition, metal NCs possess physical and chemical properties that are different from those of the corresponding bulk metals. Metal NCs with such characteristics are expected to be important for use in nanotechnology. Research on the precise synthesis of metal NCs and elucidation of their physical/chemical properties and functions is being actively conducted. When metal NCs are alloyed, it is possible to obtain further various electronic and geometrical structures and functions. Thus, research on alloy NCs has become a hot topic in the study of metal NCs and the number of publications on alloy NCs has increased explosively in recent years. Such publications have provided much insight into the effects of alloying on the electronic structure and function of metal NCs. However, the rapid increase in knowledge has made it difficult for researchers (especially those new to the field) to grasp all of it. Therefore, in this review, we summarize the reported chemical composition, geometrical structure, electronic structure, and physical and chemical properties of Au_n−xM_x(SR)_m, Ag_n−xM_x(SR)_m, Au_n−xM_x(PR₃)_l(SR)_m, and Ag_n−xM_x(PR₃)_l(SR)_m (Au=gold, Ag=silver, M=heteroatom, PR₃=phosphine, and SR=thiolate) NCs. This review is expected to help researchers understand the characteristics of alloy NCs and lead to clear design guidelines to develop new alloy NCs with intended functions.     

原子级精确的币金属纳米团簇在光催化应用方面的研究进展

光催化技术可以直接将太阳能转化为化学能,制造化学燃料或环境友好的产品。然而,常用的光催化剂大多为具有宽能隙的半导体材料,所需光源大多在紫外区,对太阳光的利用率不高;并且电子-空穴复合率高,导致光催化反应效率低。币金属纳米团簇具有超小尺寸（<2 nm）和分立能级,能够实现电子和空穴的分离,电子结构可调,可以通过调节其电子结构进而提高其光催化性能。同时,精确的原子级组成和结构使其成为一种在原子水平上探索光催化机制的理想模型。本文报道了基于币金属纳米团簇的光催化反应的现状,包括水分解产氢、有机污染物降解和光催化氧化胺等。通过探讨调节币金属纳米团簇的光催化性能的策略,对币金属纳米团簇光催化剂的发展前景予以展望。     

Contributions of Internal Atoms of Atomically Precise Metal Nanoclusters to Catalytic Performances

Every atom of a heterogeneous catalyst can play a direct or indirect role in its overall catalytic properties. However, it is extremely challenging to determine explicitly which atom(s) of a catalyst can contribute most to its catalytic performance because the observed performance usually reflects an average of all the atoms in the catalyst. The emergence of atomically precise metal nanoclusters brings unprecedented opportunities to address these central issues, as the crystal structures of such nanoclusters have been solved, and hence very fundamental understanding of nanocatalysis can be attained at an atomic level. This minireview focuses on recent efforts to reveal the contributions of the internal atoms or vacancies of nanocluster catalysts to the catalytic processes, including how the catalytic activity can be dramatically changed by the central doping of a foreign atom, how catalytic activation and inactivation can be reversibly switched by shuttling the central atom into and out of nanoclusters, and how evolution in catalytic activity can be driven by structural periodicity in the inner kernels of the nanoclusters. We anticipate that progress in this research area could represent a novel conceptual framework for understanding the crucial roles of internal atoms of the catalysts in tuning the catalytic properties.     

多策略可控合成原子精度合金纳米团簇

合金纳米团簇作为一类新兴的多功能纳米材料已被广泛用于催化、光学传感以及生物医学成像等研究领域,而纳米团簇的可控合成和结构特征是调节纳米团簇性质并对其进一步利用的基础。尽管当前有关金属纳米团簇可控合成和结构特征的研究主要集中在单金属纳米团簇中,但有关合金纳米团簇原子精度的可控合成也取得了显著的进展。本文综述了配体保护的合金金属纳米团簇原子精度可控合成策略,包括一步合成法、金属交换、配体交换、化学刻蚀、簇间反应、原位两相配体交换以及最新的表面模体交换反应,并对相关合成策略的优缺点进行了详细的讨论和阐述。     

Atomically Precise Multimetallic Semiconductive Nanoclusters with Optical Limiting Effects

For the first time, multinuclear noble‐metal clusters have been successfully stabilized by Ti‐oxo clusters. Two unprecedented Ag₆@Ti₁₆‐oxo nanoclusters with precise atomic structures were prepared and characterized. The octahedral Ag₆ core has strong Ag?Ag bonds (ca. 2.7 Å), and is further stabilized by direct Ag?O?Ti coordination interactions. Moreover, as a result of different acidic/redox conditions in synthesis, the Ag₆ core can adopt diverse geometric configurations inside the Ti₁₆‐O shell. Correspondingly, structural differences greatly influence their optical limiting effects. The transmittance reduction activity of the clusters towards 532 nm laser shows a nearly linear concentration dependence, and can be optimized up to about 43 %. This work not only opens a new direction for multimetallic semiconductive nanoclusters with interesting optical properties, but also provides molecular models for important noble‐metal/TiO₂ heterogeneous materials.     

“非保护型”金属胶体纳米簇形成机理研究

碱-乙二醇法制备的"非保护型"金属及合金纳米簇由表面吸附的溶剂分子和简单离子实现稳定化,它们被广泛用于制备高性能复相催化剂和研究复相催化剂中的尺寸、组成、载体表面基团以及修饰剂对催化性能的影响。关于此类非保护金属纳米簇的形成过程及机理的认识尚有待进一步深化。本文采用原位快速扫描X射线吸收精细结构谱(QXAFS)、原位紫外-可见(UV-Vis)吸收光谱、透射电子显微镜和动态光散射技术研究了碱-乙二醇法合成中非保护型金属胶体纳米簇的形成过程与机理。结果表明,在碱-乙二醇法合成非保护型Pt金属纳米簇的过程中,室温下即有部分Pt(IV)被还原至Pt(II)。随着反应温度的升高,OH-逐渐取代与Pt离子配位的Cl-,在Pt―Pt键形成之前,反应体系的UV-Vis吸收光谱中可观察到明显的纳米粒子的散射信号,原位QXAFS分析表明Pt纳米簇是由Pt氧化物纳米粒子还原所形成的;在Ru金属纳米簇的形成过程中,OH-首先取代了Ru Cl_3中的Cl~-,形成羟基配合物Ru(OH) _6~(3-),后者进一步缩合形成氧化钌纳米粒子,最终Ru金属纳米簇由乙二醇还原氧化钌纳米粒子形成。由于先形成了氧化物纳米粒子,后续的还原反应被限制在氧化物纳米粒子内,使最终得到的非保护型金属纳米簇具有尺寸小、分布窄的特点。本工作所获得的知识对发展高性能能源转化催化剂、精细化学合成催化剂、传感器等功能体系具有重要意义。     

基于蛋白和多肽为模板的贵金属纳米簇合成研究

贵金属(Au, Ag, Pt等)纳米簇通常指的是由几个到约一百个原子组成的分子聚集体, 具有生物相容性好、超小尺寸(<2 nm)以及优异的物理化学性质, 尤其是能发出较强荧光等特点引起了人们的广泛关注. 目前多种贵金属纳米簇的合成方法已相继被报道, 且已应用于生物荧光成像、电化学发光、生物传感器以及细胞标记等多个领域. 本文共分为五部分, 首先重点介绍近几年兴起的以蛋白和多肽为模板来合成纳米簇的方法及优点, 并随后总结列举了文献中所采用的蛋白以及自主设计的多肽组分序列的类别, 随后探索了蛋白和多肽中的特定氨基酸与合成的贵金属纳米簇的荧光波长、量子产率、粒径之间的联系. 本文最后总结阐述了蛋白和多肽为模板成功合成贵金属纳米簇的先决条件并对其生物医学应用前景进行了展望.     

Carbon Monoxide: A Mild and Efficient Reducing Agent towards Atomically Precise Gold Nanoclusters

In recent years, thiolate‐protected gold nanoclusters (or thiolated Au NCs) with a core size below 2 nm have emerged as a new class of multifunctional nanoparticles because of their unique molecular‐like properties and the potential to use these properties in many practical applications. A general synthesis of Au NCs may involve the use of a strong reducing agent (e.g., sodium borohydride (NaBH₄)), which often leads to the formation of mix‐sized Au NCs if no delicate control is applied. To obtain atomically precise Au NCs, additional physical or chemical selection processes (e.g., high‐resolution separation or size‐focusing) are required, which are difficult to be scaled up or are limited to only thermodynamically stable products. By introducing a milder reducing agent – carbon monoxide (CO) – both stable and metastable thiolated Au NCs, including Au_10–12, Au₁₅, Au₁₈, Au₂₅, and Au₂₉, can be synthesized in a one‐pot manner. In addition, CO reduction also enables the synthesis of a highly luminescent Au₂₂(SG)₁₈ NC. Furthermore, the intermediates of Au NC growth can be tracked in the CO‐reduction system due to the mild and readily stoppable nature of CO reduction. Therefore, the use of CO reduction may bring new flexibilities in designing synthetic strategies and understanding the growth mechanism of atomically precise Au NCs, which could contribute to a better design of functional Au NCs, further paving their way towards practical applications in various fields.     

Partial Phosphorization: A Strategy to Improve Some Performance(s) of Thiolated Metal Nanoclusters Without Notable Reduction of Stability

Thiolates endow metal nanoclusters with stability while sometimes inhibit the catalytic activity due to the strong M−S interaction (M: metal atom). To improve the catalytic activity and keep the stability to some extent, one strategy is the partial phosphorization of thiolated metal nanoclusters. This is demonstrated by successful partial phosphorization of Au₂₃(SC₆H₁₁)₁₆ and by revealing that the products Au₂₂(SC₆H₁₁)₁₄(PPh₃)₂ and Au₂₂(SC₆H₁₁)₁₂(PPh₃)₄, with varied degree of phosphorization, both show excellent activity in the photocatalytic oxidation of thioanisole without notable reduction of stability. Furthermore, Au₂₂(SC₆H₁₁)₁₂(PPh₃)₄ exhibits better photoluminescence performance than the mother nanocluster Au₂₃(SC₆H₁₁)₁₆, indicating that partial phosphorization can also improve some other performance(s) except for the catalytic performance. The intermediates Au_22-xCu_x(SC₆H₁₁)₁₂(PPh₃)₄ (x=1, 2) in the transformation from Au₂₃(SC₆H₁₁)₁₆ (Au₂₂(SC₆H₁₁)₁₄(PPh₃)₂) to Au₂₂(SC₆H₁₁)₁₂(PPh₃)₄ were captured and identified by mass spectrometry and single crystal X-ray diffraction, which throws light on the understanding of the non-alloyed anti-galvanic reaction.     

Chemical Vapor Deposition for Atomically Dispersed and Nitrogen Coordinated Single Metal Site Catalysts

Atomically dispersed and nitrogen coordinated single metal sites (M-N-C, M=Fe, Co, Ni, Mn) are the popular platinum group-metal (PGM)-free catalysts for many electrochemical reactions. Traditional wet-chemistry catalyst synthesis often requires complex procedures with unsatisfied reproducibility and scalability. Here, we report a facile chemical vapor deposition (CVD) strategy to synthesize the promising M-N-C catalysts. The deposition of gaseous 2-methylimidazole onto M-doped ZnO substrates, followed by an in situ thermal activation, effectively generated single metal sites well dispersed into porous carbon. In particular, an optimal CVD-derived Fe-N-C catalyst exclusively contains atomically dispersed FeN₄ sites with increased Fe loading relative to other catalysts from wet-chemistry synthesis. The catalyst exhibited outstanding oxygen-reduction activity in acidic electrolytes, which was further studied in proton-exchange membrane fuel cells with encouraging performance.     

Atomically Dispersed Metal Sites in MOF‐Based Materials for Electrocatalytic and Photocatalytic Energy Conversion

Metal sites play an essential role in both electrocatalytic and photocatalytic energy conversion. The highly ordered arrangements of the organic linkers and metal nodes as well as the well‐defined pore structures of metal‐organic frameworks (MOFs) make them ideal substrates to support atomically dispersed metal sites (ADMSs) located in their metal nodes, linkers, and pores. Porous carbon materials doped with ADMSs can be derived from these ADMS‐incorporating MOF precursors through controlled treatments. These ADMSs incorporated in pristine MOFs and MOF‐derived carbon materials possess unique advantages over molecular or bulk metal‐based catalysts and bridge the gap between homogeneous and heterogeneous catalysts for energy‐conversion applications. This Review presents recent progress in the design and incorporation of ADMSs in MOFs and MOF‐derived materials for energy‐conversion applications.     

手性金属配合物催化的不对称环丙烷化反应的新进展

总结了近年来关于环丙烷化反应中各种手性金属催化剂的研究进展, 包括席夫碱、噁唑啉、卟啉、联吡啶及四吡啶、羧酸酯等类型的手性化合物作为配体的金属催化剂.     

Volatile Metal Alkoxides according to the Concept of Donor Functionalization

Since the fundamental works of D. C. Bradley and R. C. Mehrotra, metal alkoxides have attracted attention because of the diversity of their low- and high-molecular-weight structures; they are also generating increasing interest as precursor compounds for solving technical materials problems. The understanding of the hydrolytic nucleation behavior is a prerequisite for the optimization of materials from sol–gel processes. For metal alkoxides to be precursors in chemical vapor deposition (CVD) processes in the preparation of inorganic oxidic materials, they should be sufficiently volatile, and sublimation should occur without decomposition at as low a temperature as possible (< 150 °C). Only recently, using the “donor functionalization” concept, was a ligand type systematically developed that unifies the advantages of both steric demands and σ-donor stabilization and so stabilizes low-molecularweight metal alkoxides. Even large metal ions of low charge (for example Ba²⁺) can thus form volatile alkoxides. O- and N-donor functions in bidentate and multidentate alkoxo ligands are particularly advantageous; hence, for example, the vanadium derivative [V(OCMe₂CH₂OMe)₃] is one of the most volatile metal alkoxides known to date. The first alkoxides of the alkaline earth metals calcium, strontium, and barium, which sublime without decomposition, have the formula [M₂{OC(CH₂OiPr)₂tBu}₄]. This article presents a critical inventory of the metal alkoxides with particular regard to the aspect of volatility. It also describes successes of the donor functionalization concept and shows—in prespective—how alkoxo ligands can be “tailor made” for metals according to their charge-to-radius ratio by further development of the concept.     

Neutral Nitrogen Donor Ligand-based MOFs for Sensing Applications

Neutral nitrogen donor (N-donor) ligand-based MOFs, with their enticing features inclusive of facile synthesis, labile metal-ligand bond, framework flexibility, atomic level tunability renders them appealing in molecular recognition-based studies. Intriguingly, the flexibility in such systems (owing to weaker metal-nitrogen bonds) promote maximization of host-analyte interactions, which is critical for the manifestation of a signaling response. Such host-analyte interactions can be tapped by discerning any change in the physical properties associated with the system, such as optical, fluorometric, chemiresistive, magnetic, dielectric constant, mass. This minireview presents a brief discussion on the various types of signal transduction pathways unveiled hitherto using neutral N-donor ligand-based MOFs and the fundamental insight into the signal‘s origin. Moreover, an elaborate compilation of the recent examples in this field has been presented. Also, the untapped prospects have been highlighted, which may serve as a beacon to drive future research.     

Intercalation of Highly Dispersed Metal Nanoclusters into a Layered Metal Oxide for Photocatalytic Overall Water Splitting

Metal nanoclusters (involving metals such as platinum) with a diameter smaller than 1 nm were deposited on the interlayer nanospace of KCa₂Nb₃O₁₀ using the electrostatic attraction between a cationic metal complex (e.g., [Pt(NH₃)₄]Cl₂) and a negatively charged two‐dimensional Ca₂Nb₃O₁₀^? sheet, without the aid of any additional reagent. The material obtained possessed eight‐fold greater photocatalytic activity for water splitting into H₂ and O₂ under band‐gap irradiation than the previously reported analog using a RuO₂ promoter. This study highlighted the superior functionality of Pt nanoclusters with diameters smaller than 1 nm for photocatalytic overall water splitting. This material shows the greatest efficiency among nanosheet‐based photocatalysts reported to date.     

“缓”然一新——深蓝里的金属防腐*

缓蚀剂和缓蚀涂层能够在金属表面形成一层致密保护膜,从而达到延缓金属腐蚀的目的。其具有成本低、可操作性强、缓蚀效果好、寿命长等优点,成为海洋工程防腐中一类重要的材料。围绕海洋工程中钻井平台、风力发电机、航空母舰和核潜艇等中易发生腐蚀的部位介绍化学缓蚀剂及缓蚀涂层的结构、性质,并突出其重要作用。     

羟甲基功能化吡唑金属羰基化合物的合成及催化性质

研究了3(5)-羟甲基-5(3)-甲基吡唑(L~1),4-羟甲基吡唑(L2)及双(3-羟甲基-5-甲基吡唑)甲烷(L3)与羰基钨(钼)的反应,合成了一系列以单齿及双齿氮配位的羰基金属衍生物LW(CO)5(L=L1或L2)和L3M(CO)4(M=Mo或W)。通过核磁、红外及X射线单晶衍射分析,对这些化合物进行了详细的结构表征。结果表明,这些化合物往往通过O-H…O,N-H…O及O-H…OC-M等氢键作用,形成一维或二维金属有机超分子结构。并且依赖于配体中羟甲基所处的不同位置,这些金属有机超分子表现出明显不同的结构特征。初步的催化活性测试表明,这些新化合物在苯乙炔三聚反应中具有明显的催化活性。     

Synthesis and Structural Characterization of Alkali Metal Guanidinates

Reactions of 1,3-diisopropylcarbodiimide with alkali metal amides, MN（SiMe3）2 （M=Li or Na） in hexane or THF produced the alkali metal guanidinates { （i-PrN）2C [N（SiMe3）2]Li }2 （1） and { （i-PrN）2C[N（SiMe3）2]Na（THF） } 2 （2） in nearly quantitative yields. Both complexes 1 and 2 were well characterized by elemental analysis, IR spectra, ^1H and ^13C NMR spectra, and X-ray diffraction. It was found that the guanidinates adopt different coordination modes in these complexes.