Synthesis of Pd-Rh Core-Frame Concave Nanocubes and Their Conversion to Rh Cubic Nanoframes by Selective Etching of the Pd Cores

Construction of Single-Crystalline Hierarchical ZSM-5 with Open Nanoarchitectures via Anisotropic-Kinetics Transformation for the Methanol-to-Hydrocarbons Reaction

We report an anisotropic-kinetics transformation strategy to prepare single-crystalline aluminosilicate MFI zeolites (ZSM-5) with highly open nanoarchitectures and hierarchical porosities. The methodology relies on the cooperative effect of in situ etching and recrystallization on the evolution of pure-silica MFI zeolite (silicalite-1) nanotemplates under hydrothermal conditions. The strategy enables a controllable preparation of ZSM-5 nanostructures with diverse open geometries by tuning the relative rate difference between etching and recrystallization processes. Meanwhile, it can also be extended to synthesize other heteroatom-substituted MFI zeolite nanocages. Compared with conventional ZSM-5 microcrystals, nanocrystals, and nanoboxes, the ZSM-5 nanocages with single-crystalline nature, highly open nanoarchitectures, and hierarchical porosities exhibit remarkably enhanced catalytic lifetime and low coking rate in the methanol-to-hydrocarbons (MTH) reaction.

Observation of Surface Ligands-Controlled Etching of Palladium Nanocrystals

Selective adsorption of ligands on nanocrystal surfaces can affect oxidative etching. Here, we report the etching of palladium nanocrystals imaged using liquid cell transmission electron microscopy. The adsorption of surface ligands (i.e., iron acetylacetonate and its derivatives) and their role as inhibitor molecules on the etching process were investigated. Our observations revealed that the etching was dominated by the interplay between palladium facets and ligands and that the etching exhibited different pathways at different concentrations of ligands. At a low concentration of iron acetylacetonate (0.1 mM), rapid etching primarily at {100} facets led to a concave structure. At a high concentration (1.0 mM), the etch rate was decreased owing to a protective film of iron acetylacetonate on the {100} facets and a round nanoparticle was achieved. Ab initio calculations showed that the differences in adsorption energy of inhibitor molecules on palladium facets were responsible for the etching behavior.

Bimetallic Nanocrystals: Structure, Controllable Synthesis and Applications in Catalysis, Energy and Sensing

In recent years, bimetallic nanocrystals have attracted great interest from many researchers. Bimetallic nanocrystals are expected to exhibit improved physical and chemical properties due to the synergistic effect between the two metals, not just a combination of two monometallic properties. More importantly, the properties of bimetallic nanocrystals are significantly affected by their morphology, structure, and atomic arrangement. Reasonable regulation of these parameters of nanocrystals can effectively control their properties and enhance their practicality in a given application. This review summarizes some recent research progress in the controlled synthesis of shape, composition and structure, as well as some important applications of bimetallic nanocrystals. We first give a brief introduction to the development of bimetals, followed by the architectural diversity of bimetallic nanocrystals. The most commonly used and typical synthesis methods are also summarized, and the possible morphologies under different conditions are also discussed. Finally, we discuss the composition-dependent and shape-dependent properties of bimetals in terms of highlighting applications such as catalysis, energy conversion, gas sensing and bio-detection applications.

Janus Nanocages of Platinum-Group Metals and Their Use as Effective Dual-Electrocatalysts

Janus nanocages with distinctive platinum-group metals on the outer and inner surfaces can naturally catalyze at least two different reactions. Here we report a general method based on successive deposition and then selective etching for the facile synthesis of such nanocages. We have fabricated 11 different types of Janus nanocages characterized by a uniform size and well-defined {100} facets, together with porous, ultrathin, asymmetric walls up to 1.6 nm thick. When tested as dual-electrocatalysts toward oxygen reduction and evolution reactions, the Janus nanocages based on Pt and Ir exhibited superior activities depending on the thickness and relative position of the metal layer. Density functional theory studies suggest that the alloy composition and surface structure of the nanocages both play important roles in enhancing the electrocatalytic activities by modulating the stability of key reaction intermediates.

Atomic-Level Manipulations in Oxides and Alloys for Electrocatalysis of Oxygen Evolution and Reduction

As chemical reactions and charge-transfer simultaneously occur on the catalyst surface during electrocatalysis, numerous studies have been carried out to attain an in-depth understanding on the correlation among the surface structure and composition, the electrical transport, and the overall catalytic activity. Compared with other catalysis reactions, a relatively larger activation barrier for oxygen evolution/reduction reactions (OER/ORR), where multiple electron transfers are involved, is noted. Many works over the past decade thus have been focused on the atomic-scale control of the surface structure and the precise identification of surface composition change in catalyst materials to achieve better conversion efficiency. In particular, recent advances in various analytical tools have enabled noteworthy findings of unexpected catalytic features at atomic resolution, providing significant insights toward reducing the activation barriers and subsequently improving the catalytic performance. In addition to summarizing important surface issues, including lattice defects, related to the OER and ORR in this Review, we present the current status and discuss future perspectives of oxide- and alloy-based catalysts in terms of atomic-scale observation and manipulation.

Synthesis of Metallic Nanocrystals: From Noble Metals to Base Metals

Metallic nanocrystals exhibit superior properties to their bulk counterparts because of the reduced sizes, diverse morphologies, and controllable exposed crystal facets. Therefore, the fabrication of metal nanocrystals and the adjustment of their properties for different applications have attracted wide attention. One of the typical examples is the fabrication of nanocrystals encased with high-index facets, and research on their magnified catalytic activities and selections. Great accomplishment has been achieved within the field of noble metals such as Pd, Pt, Ag, and Au. However, it remains challenging in the fabrication of base metal nanocrystals such as Ni, Cu, and Co with various structures, shapes, and sizes. In this paper, the synthesis of metal nanocrystals is reviewed. An introduction is briefly given to the metal nanocrystals and the importance of synthesis, and then commonly used synthesis methods for metallic nanocrystals are summarized, followed by specific examples of metal nanocrystals including noble metals, alloys, and base metals. The synthesis of base metal nanocrystals is far from satisfactory compared to the tremendous success achieved in noble metals. Afterwards, we present a discussion on specific synthesis methods suitable for base metals, including seed-mediated growth, ligand control, oriented attachment, chemical etching, and Oswald ripening, based on the comprehensive consideration of thermodynamics, kinetics, and physical restrictions. At the end, conclusions are drawn through the prospect of the future development direction.

Facile solvothermal preparation of Fe3O4–Ag nanocomposite with excellent catalytic performance

Functional nanocomposites demonstrate excellent comprehensive properties and outstanding characteristics for numerous applications. Magnetic nanocomposites are an important type of composite materials, due to their applications in optics, medicine and catalysis. In this report, a new Fe₃O₄-loaded silver (Fe₃O₄–Ag) nanocomposite has been successfully synthesized via a simple solvothermal method and in situ growth of silver nanowires. The silver nanowires were prepared via the reduction of silver vanadate with the addition of uniformly dispersed Fe₃O₄ nanoparticles. Structural and morphological characterizations of the obtained Fe₃O₄–Ag nanocomposite were carried out using many characterization methods. As a new composite catalyst, the synthesized magnetic Fe₃O₄–Ag nanocomposite displayed a high utilization rate of catalytically active sites in catalytic reaction medium and showed good separation and recovery using an external magnetic field. The facile preparation and good catalytic performance of this Fe₃O₄–Ag nanocomposite material demonstrate its potential applications in catalytic treatment and composite materials.

A new Fe₃O₄–Ag nanocomposite was prepared via solvothermal method, demonstrating potential application in catalytic degradation of wastewater treatment and composite materials.

Acetylene in Organic Synthesis: Recent Progress and New Uses

Recent progress in the leading synthetic applications of acetylene is discussed from the prospect of rapid development and novel opportunities. A diversity of reactions involving the acetylene molecule to carry out vinylation processes, cross-coupling reactions, synthesis of substituted alkynes, preparation of heterocycles and the construction of a number of functionalized molecules with different levels of molecular complexity were recently studied. Of particular importance is the utilization of acetylene in the synthesis of pharmaceutical substances and drugs. The increasing interest in acetylene and its involvement in organic transformations highlights a fascinating renaissance of this simplest alkyne molecule.

Seed-Mediated Growth of Colloidal Metal Nanocrystals

Seed-mediated growth is a powerful and versatile approach for the synthesis of colloidal metal nanocrystals. The vast allure of this approach mainly stems from the staggering degree of control one can achieve over the size, shape, composition, and structure of nanocrystals. These parameters not only control the properties of nanocrystals but also determine their relevance to, and performance in, various applications. The ingenuity and artistry inherent to seed-mediated growth offer extensive promise, enhancing a number of existing applications and opening the door to new developments. This Review demonstrates how the diversity of metal nanocrystals can be expanded with endless opportunities by using seeds with well-defined and controllable internal structures in conjunction with a proper combination of capping agent and reduction kinetics. New capabilities and future directions are also highlighted.

Platinum Cubic Nanoframes with Enhanced Catalytic Activity and Durability Toward Oxygen Reduction

We report the synthesis and electrocatalytic properties of Pt cubic nanoframes with ultrathin ridges less than 2 nm in thickness. The nanoframes were synthesized through site-selected deposition of Pt onto the corner and edge sites of Pd nanocubes, followed by selective removal of the Pd cores via chemical etching. The Br^- ions chemisorbed on the side faces of a Pd nanocube played a critical role in enabling the siteselected deposition. In addition, the kinetics of deposition and the diffusion of Pt adatoms was optimized by carefully controlling the injection rate of the Pt precursor and the reaction temperature, respectively, to obtain the frame-like structure. When benchmarked against a commercial Pt/C comprised of Pt particles 2-3 nm in size, the Pt frame/C catalyst exhibited not only enhanced mass activity toward oxygen reduction, but also substantially improved catalytic durability. In an accelerated durability test, the Pt frame/C catalyst showed a mass activity more than 6× greater than for the Pt/C reference after 20 000 cycles of repeated potential sweeping. This improvement can be largely attributed to the frame-like structure, which is unique in suppressing both the detachment and aggregation of catalytic particles owing to the significantly enhanced interaction with carbon support.