Kinetically Controlled Growth of Fine Gold Nanofractals from Au(I) via Indirect Galvanic Replacement Reaction

Two of the most important features of Au nanostructures, size and shape, are significantly affected by the reduction kinetics of the relevant metal precursors. Because of the high standard oxidative potential of gold ionic species, AuCl₄^– in particular, Au fractals formed via various chemical or electrochemical approaches often have very coarse branches with diameters varying from tens of nanometers to submicrometers, even though extensive chemicals and/or complicated processes have been deployed to control the reduction kinetics. Herein we report an indirect galvanic replacement (IGR) strategy where the electrons generated in a galvanic replacement reaction from anode oxidation are channeled out to a separate conducting film on which the cathodic metal can be deposited. Reduction of Au­(I) ionic species with relatively low standard oxidative potential has been conducted with the IGR experimental setting. 2D finely hyperbranched Au fractals (4.0 nm in diameter and a few micrometers in length) with high structural integrity were produced. Controls over the deposition density, location, and microfeatures of Au nanofractals were demonstrated through a mechanistic study. In addition, the thus-prepared Au nanofractals were also thoroughly tested in electrochemical sensing of H₂O₂

Synthesis, Self-Assembly, Transformation, and Functionalization of Nanoscale Artificial Allophane Spherules for Catalytic Applications

Mesoporous materials with large surface area and chemical inertness are of great importance, and currently prevailing synthetic approaches involve usages of micelles as pore-directing agents to create such mesopores. In this work, allophanes, which are hollow aluminosilicate spherules of 3.5–5.5 nm in size, have been synthesized and assembled simultaneously for the first time in a controlled manner to generate mesoporous spherical allophane assemblages (MSAAs) with diameters of 445 ± 40 nm, specific surface area as high as 1032 m²/g, pore volume 1.104 mL/g at <i>P</i>/<i>P</i>₀ = 0.975, and average mesopore size at 3.4 nm. Furthermore, the thus-prepared MSAA could be doped with transition metal ions to create a series of isomorphous derivatives; they could also be converted to aluminum-based hierarchical assemblages of layered double hydroxide easily. Different from the conventional channel-like mesopores, the new mesoporosity attained in MSAA is easily accessible because their mesopores are generated from the interparticle spaces of spherical building units of hollow spherules. Therefore, the mesoporous MSAA provides an excellent platform for construction of integrated nanocatalysts. Highly dispersed noble metal nanoclusters such as Pt, Au, and Pd could be deposited on the surface or in the interior mesopores of the MSAA. Excellent activity and stability of MSAA-based catalysts for Suzuki couplings and electrochemical sensing of H₂O₂ have been demonstrated using Pd/MSAA and Au/MSAA nanocomposites, respectively

Metal–Hydroxide and Gold–Nanocluster Interfaces: Enhancing Catalyst Activity and Stability for Oxygen Evolution Reaction

By engineering the interaction between the transition metal ions (M = Mn²⁺, Co²⁺, and Ni²⁺) and the nanorod-shaped assemblages of Au nanoclusters (AuNCs), a series of tubular AuNCs@M­(OH)₂ core–shell nanocomposites are produced in which numerous AuNCs are embedded beneath a thin layer of metal hydroxide with thickness below 4 nm and where the AuNCs within the same assemblage are partially connected with each other. Because of the synergistic effects from the abundant presence of the AuNCs–M­(OH)₂ interfaces, the AuNCs@M­(OH)₂ (M = Co and Ni) nanocomposites demonstrate evidently enhanced activity for oxygen evolution reaction (OER) in alkaline condition. Overpotentials of 0.350 and 0.375 V have been obtained at the current density of 10 mA cm^–2 in 0.1 M KOH for the AuNCs@Co­(OH)₂ and AuNCs@Ni­(OH)₂, respectively. And at the overpotential of 0.42 V, the current density of AuNCs@M­(OH)₂ (M = Co and Ni) nanocomposites is more than 10 times of those generated by their respective metal hydroxides. Compared with monophasic transition metal hydroxides, the AuNCs@ M­(OH)₂ nanocomposites, especially the AuNCs@Ni­(OH)₂, possess excellent OER catalytic stability

Simultaneous Synthesis and Assembly of Noble Metal Nanoclusters with Variable Micellar Templates

Simultaneous synthesis and assembly of Au, Pt, and Pd nanoclusters (NCs; with sizes ≤3 nm) into mesoscale structures with defined boundaries are achieved using their metal halides, cetyl­trimethyl­ammonium bromide (CTAB), and thiourea (Tu). Geometric shape, hierarchical organization, and packing density of resultant assemblages vary depending on metal precursors and CTAB concentration. For example, rod- or tube-like assemblages are formed from Au NCs, giant vesicles and/or dandelion-like assemblages from Pt NCs, and rhombic/hexagonal platelet assemblages from PdS NCs and Pd NCs. These assemblages inherit pristine shapes from their respective variable micelles of CTA⁺–metal halide complexes. Owing to dynamical nature, the assembled NCs demonstrate various structural reforming behaviors. The metal halides, which serve as counterions of positively charged surfactant heads, screen the electrostatic repulsion among the surfactant molecules as well as the micelles, providing the driving force for the formation of soft templates. Meanwhile, the formation of NCs can be addressed from the perspective of nucleation and growth kinetics. The unique protecting role of surface sulfur, controlled release of S^2– from Tu, and formation of NCs of metal sulfides as intermediates together lead to a relatively low rate-ratio of growth to nucleation and thus limit the size of product NCs. Our preliminary study also indicates that the assembled noble metal NCs have high catalytic activity and recyclability. In this regard, the present approach not only provides a facile means to construct NC-based metal catalysts but serves also as a simple way to visualize interaction and evolution of micelles of CTA⁺–metal halide complexes

<i>Z</i>‑Selective Synthesis of γ,δ-Unsaturated Ketones via Pd-Catalyzed Ring Opening of 2‑Alkylenecyclobutanones with Arylboronic Acids

Pd-catalyzed 1,2-addition (instead of 1,4-addition) of arylboronic acids to 2-alkylenecyclobutanones followed by β-carbon elimination from the resulting palladium cyclobutanolates to afford γ,δ-unsaturated ketones was developed. The desired γ,δ-unsaturated ketones were obtained in good to excellent yields with <i>Z</i>/<i>E</i> selectivities of up to >99:1 and a broad spectrum of functional group tolerability

Synthesis of β‑Aminoenones via Cross-Coupling of In-Situ-Generated Isocyanides with 1,3-Dicarbonyl Compounds

An efficient and practical strategy for the synthesis of β-aminoenones from a three-component reaction was developed. Ethyl bromodifluoroacetate serves as a C1 source in this strategy, forming isocyanides in situ with primary amines. This reaction represents the first example of utilization of readily available starting materials to generate isocyanides in situ and sequentially fully converted to β-aminoenones, avoiding the generation of byproduct imines and overinsertion products. The mechanism study suggested that this method involves activation of two C­(sp³)–F bonds and the formation of isocyanides, which might nourish both isocyanide chemistry and fluorine chemistry

Substituent-Controlled Chemoselective Cleavage of CC or C_sp²–C(CO) Bond in α,β-Unsaturated Carbonyl Compounds with H‑Phosphonates Leading to β‑Ketophosphonates

An unprecedented substituent-controlled chemoselective cleavage of CC double bond or C­(sp²)–C­(CO) bond along with aerobic phosphorylation of α,β-unsaturated carbonyl compounds with H-phosphonates through a radical process has been disclosed. The current strategy provides an access to β-ketophosphonates under mild conditions with a wide substrate scope

Synthesis of 2‑Arylimino-6,7-dihydrobenzo[<i>d</i>][1,3]oxathiol-4(5<i>H</i>)‑ones via Rh₂(OAc)₄‑Catalyzed Reactions of Cyclic 2‑Diazo-1,3-diketones with Aryl Isothiocyanates

A convenient and efficient synthesis of 2-arylimino-6,7-dihydrobenzo­[<i>d</i>]­[1,3]­oxathiol-4­(5<i>H</i>)-ones was developed via a Rh₂(OAc)₄-catalyzed reaction of cyclic 2-diazo-1,3-diketones and aryl isothiocyanates in acetone at 60 °C. This reaction uses readily available stable cyclic 2-diazo-1,3-diketones as a starting material and generates the desired products in good to excellent yields (78–93%). The reaction proceeds under mild reaction conditions, produces only N₂ as the byproduct, and features a broad substrate scope. A plausible mechanism for this reaction is also discussed

Synthesis of 2‑Arylimino-6,7-dihydrobenzo[<i>d</i>][1,3]oxathiol-4(5<i>H</i>)‑ones via Rh₂(OAc)₄‑Catalyzed Reactions of Cyclic 2‑Diazo-1,3-diketones with Aryl Isothiocyanates

A convenient and efficient synthesis of 2-arylimino-6,7-dihydrobenzo­[<i>d</i>]­[1,3]­oxathiol-4­(5<i>H</i>)-ones was developed via a Rh₂(OAc)₄-catalyzed reaction of cyclic 2-diazo-1,3-diketones and aryl isothiocyanates in acetone at 60 °C. This reaction uses readily available stable cyclic 2-diazo-1,3-diketones as a starting material and generates the desired products in good to excellent yields (78–93%). The reaction proceeds under mild reaction conditions, produces only N₂ as the byproduct, and features a broad substrate scope. A plausible mechanism for this reaction is also discussed

Functionalized TiO₂ Nanoparticles Tune the Aggregation Structure and Trapping Property of Polyethylene Nanocomposites

The interfacial region between a nanoparticle and the polymer matrix is considered to have an important effect on the properties of nanocomposites. In this experimental study, the tuning effects of surface-modified TiO₂ nanoparticles on the aggregation structure and trapping property of the nanocomposites are investigated. The addition of TiO₂ nanoparticles increases the number of spherulites and decreases their sizes. It is also found that TiO₂ nanoparticles can suppress the mobility of chain segments in the interfacial region, suppress crystallization, and reduce the crystallinity, depending on the surface modification and loading levels of nanoparticles. On the basis of the conclusions, the model of a spherulite and the interface is established and the trap distribution of the interface is analyzed according to the results of TSC measurements. It is assumed that there is a strong correlation between traps and the charge transport of nanocomposites, and the mechanism of charge transport is discussed with respect to the results of the volume conductivity measurement. It is believed that this study would provide an important hint to the research of the interface between nanoparticles and the polymer matrix in future research