Support Morphology Effect on Selective Hydrogenation of 3-Nitrostyrene to 3-Vinylaniline over Pt/α-Fe2O3 Catalysts

Selective hydrogenation of substituted nitroaromatic compounds is an extremely important and challenging reaction. Supported metal catalysts attract much attention in this reaction because the properties of metal nanoparticles (NPs) can be modified by the nature of the support. Herein, the support morphology on the catalytic performance of selective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. Pt NPs supported on octadecahedral α-Fe₂O₃ supports with a truncated hexagonal bipyramid shape (Pt/α-Fe₂O₃-O) and rod-shaped α-Fe₂O₃ supports (Pt/α-Fe₂O₃-R) were prepared by glycol reduction method. Detailed characterizations reveal that the electronic structure and dispersion of Pt NPs can be modified by the supports. The Pt/α-Fe₂O₃-O catalyst exhibited superior catalytic performance for hydrogenation of 3-nitrostyrene because of its low coordinated Pt sites and the small Pt NPs size, which is benefit from the high-index exposed surfaces of truncated hexagonal bipyramid-shaped α-Fe₂O₃ support. The structural evolution during the catalytic reaction was investigated in detail by identical location transmission electron microscopy (IL-TEM) method, which found that the high cycling activity of Pt/α-Fe₂O₃-O catalyst during the cycle experiment results from the stability of Pt NPs.     

Block copolymer solution self-assembly: Recent advances,emerging trends,and applications

The self-assembly process of block copolymers (BCPs) in solution has been at the focus of extended scientific research over the past several decades owing to the astonishing morphological diversity and attainable complexity of the resulting nanoassemblies, including spheres, cylinders, lamellae, vesicles, and many other complex, bicontinuous or even hierarchical structures. The ever-increasing sophistication in the development of synthetic chemistry methods and techniques has led to a myriad of available macromolecules with varying chemical compositions, architectures, features, and properties. This assortment of characteristics has led in turn to a plethora of intriguing self-organized polymeric nanostructures, with countless possible applications in several nanotechnological fields relevant to physics, chemistry, material science, nanomedicine, and biomaterials. The present review aims to illuminate the importance and fascinating potential of BCPs solution self-assembly by highlighting recent advances and emerging trends in the field, as well as significant application-oriented progress, through characteristic contemporary examples.     

Mn3−xFexO4 Hollow Nanostructures for High-Performance Asymmetric Supercapacitor Applications

Design of hollow nanostructure and controllable phase of mixed metal oxides for improving performance in supercapacitor applications is highly desirable. Here we demonstrate the rational design and synthesis of Mn_3−xFe_xO₄ hollow nanostructures for supercapacitor applications. Owing to high porosity and the specific surface area that provides more active sites for electrochemical reactions, the electrochemical performance of Mn_3−xFe_xO₄ hollow nanostructure substantially enhanced comparing with pristine Mn₃O₄. Particularly, in 1.0 M KOH electrolyte, Mn_0.16Fe_2.84O₄ with a typical diameter of 20 nm exhibits excellent specific capacitance of 2675, 2320, 1662, 987 F g⁻¹ at current densities of 1, 2, 5, 10 A g⁻¹, respectively, which is significantly superior to those of other transition metal oxides. Besides, an asymmetric supercapacitor is assembled by using Mn_0.16Fe_2.84O₄ and activated carbon as a positive and a negative electrode, respectively. Electrochemical results indicate a high energy density of 42 Wh kg⁻¹ at a power density of 0.75 kW kg⁻¹, which makes this hollow nanostructure a highly promising electrode for achieving high-performance next-generation supercapacitors.     

Mesoporous carbons from self-assembled polymers

Polymer self-assembly provides a robust and cost-efficient nanomanufacturing platform for enabling a broad range of applications, such as microelectronics, drug delivery, and separation membranes. This review focuses on discussing the progress and opportunities of self-assembled polymer in the synthesis of mesoporous carbons (MCs), which have aroused significant research interests over the past decades. Specifically, we will discuss the two most established approaches for converting nanostructured polymers to MCs, including templating-based and direct pyrolysis-based methods. We will also review the fundamental ordering mechanisms and kinetics of these polymeric systems and discuss the recent development of engineering methods for providing on-demand control over the pore size and morphology of MCs. Additionally, this review article also includes a section focusing on the strategies to further functionalize these materials from self-assembled polymers to enhance their performance, such as chemical activation, heteroatom doping, introduction of nanoparticles into the carbon matrix, and enhancing graphitization degree of carbon walls. Finally, a brief perspective is provided about the emerging research opportunity in this exciting field.     

Co3O4@Cu-Based Conductive Metal–Organic Framework Core–Shell Nanowire Electrocatalysts Enable Efficient Low-Overall-Potential Water Splitting

In the work reported herein, the electrocatalytic properties of Co₃O₄ in hydrogen and oxygen evolution reactions have been significantly enhanced by coating a shell layer of a copper-based metal–organic framework on Co₃O₄ porous nanowire arrays and using the products as high-performance bifunctional electrocatalysts for overall water splitting. The coating of the copper-based metal–organic framework resulted in the hybridization of the copper-embedded protective carbon shell layer with Co₃O₄ to create a strong Cu−O−Co bonding interaction for efficient hydrogen adsorption. The hybridization also led to electronically induced oxygen defects and nitrogen doping to effectively enhance the electrical conductivity of Co₃O₄. The optimal as-prepared core–shell hybrid material displayed excellent overall-water-splitting catalytic activity that required overall voltages of 1.45 and 1.57 V to reach onset and a current density of 10 mA cm⁻², respectively. This is the first report to highlight the relevance of hybridizing MOF-based co-catalysts to boost the electrocatalytic performance of nonprecious transition-metal oxides.     

Magnetically Induced CO2 Methanation Using Exchange‐Coupled Spinel Ferrites in Cuboctahedron‐Shaped Nanocrystals

Magnetically induced catalysis can be promoted taking advantage of optimal heating properties from the magnetic nanoparticles to be employed. However, when unprotected, these heating agents that are usually air‐sensitive, get sintered under the harsh catalytic conditions. In this context, we present, to the best of our knowledge, the first example of air‐stable magnetic nanoparticles that: 1) show excellent performance as heating agents in the CO₂ methanation catalyzed by Ni/SiRAlOx, with CH₄ yields above 95 %, and 2) do not sinter under reaction conditions. To attain both characteristics we demonstrate, first the exchange‐coupled magnetic approach as an alternative and effective way to tune the magnetic response and heating efficiency, and second, the chemical stability of cuboctahedron‐shaped core–shell hard CoFe₂O₄–soft Fe₃O₄ nanoparticles.     

Face-Centered-Cubic Ag Nanoclusters: Origins and Consequences of the High Structural Regularity Elucidated by Density Functional Theory Calculations

Face-centered-cubic (FCC) silver nanoclusters (NCs) adopting either cubic or half-cubic growth modes have been recently reported, but the origin of these atomic assembly patterns and how they are achieved, which would inform our understanding of larger FCC silver nanomaterials, are both unknown. In this study, the cubic and half-cubic growth modes have been unified based on common structural characteristics, and differentiated depending on the starting blocks (cubic vs. half cubic). In both categories, the silver atoms adopt octahedral Ag₆, linear AgS₂ (in projection drawing), or tetrahedral AgS₃P binding modes, and the sulfur atoms adopt T-shaped SAg₃ and orthogonal SAg₄ modes. An additional T-shaped AgS₃ mode is oriented on the surface edge in cubic NCs to complete the cubic framework. Density functional theory calculations indicated that the high structural regularity originates from the strong diffusing capacity of the Ag(5d) and S(3p) orbitals, and the angular momentum distribution of the formed superatomic orbitals. The equatorial orientation of μ⁴-S or μ⁴-Ag determines whether growth stops or continues. In particular, a density-of-states analysis indicated that the octahedral silver atoms are chemically more reactive than the silver atoms in the AgS₃P motif, regardless of whether the parent NC functions as an electron donor or acceptor.     

Controllable synthesis of monodisperse nonspherical colloidal particles with cavity structures

This article reports a facile controllable approach to prepare monodisperse nonspherical colloidal particles with cavity structures by one‐pot soap‐free emulsion polymerization of styrene (St), 3‐(trimethoxysilyl)propyl methacrylate (MPS), and acrylic acid (AA). In our strategy, only by varying the feeding time of AA to the as‐polymerized St and MPS, the nonspherical latex particles with single cavity of different surface roughness and multicavity structures could be successfully synthesized. The depth and width of the cavity can be also easily controlled by adjusting the amount of MPS and AA. A possible formation mechanism is proposed on the basis of experimental results. These nonspherical colloidal particles, which have controllable cavity structures, are good building blocks or templates for the construction of functional coating and complex colloidal architectures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1645–1652