Pt/Fe₃O₄ Core/Shell Triangular Nanoprisms by Heteroepitaxy: Facet Selectivity at the Pt–Fe₃O₄ Interface and the Fe₃O₄ Outer Surface

Pt/Fe₃O₄ core/shell triangular nanoprisms were synthesized using seed-mediated heteroepitaxy. Their well-defined shape, facets, and ordered-assembly allowed detailed analysis of mechanism of the heteroepitaxy. At the Pt–Fe₃O₄ interface, existence of both lattice and chemical mismatch resulted in facet-selective epitaxy along ⟨111⟩ directions of two lattices. X-ray absorption fine structure measurements demonstrated that the Pt seed nanocrystals were composed of an iron-rich Pt–Fe metallic thin layer sandwiched between the Pt core and a Fe–O outer-surface. The Fe–O outer-surface of the seed nanocrystals presumably offered epitaxial sites for the following deposition of the Fe₃O₄ shell. Each tip and side of a triangular nanoprism respectively possessed a groove and a ridge, and a (111) plane parallel to the basal planes linked all grooves and ridges. This interesting (111) plane approximately bisected the triangle nanoprisms and located near the Pt-seed. The outer surface of the hybrid nanocrystals was also found to be facet-selective, that is, solely {111} facets of Fe₃O₄ lattice. These polar {111} facets allowed the surface to be only occupied with high-density iron ions, and thus offered best surface coordination for the electron donating ligands in the solution

Asymmetric Construction of a Multi-Pharmacophore-Containing Dispirotriheterocyclic Scaffold and Identification of a Human Carboxylesterase 1 Inhibitor

A catalytic asymmetric [3 + 2] cyclization of novel 4-isothiocyanato pyrazolones and isatin-derived ketimines was developed, delivering a wide range of intriguing dispirotriheterocyclic products in high yield with excellent diastereoselectivity and enantioselectivity. A chiral sulfoxide derivative of this dispirocyclic product was identified to be a promising hit of the human carboxylesterase 1 inhibitor, and the significant difference of the activity between two enantiomers emphasized the importance of this asymmetric process

Ammonia-Induced Size Convergence of Atomically Monodisperse Au₆ Nanoclusters

Developing effective synthetic protocols for atomically monodisperse Au nanoclusters is pivotal to their fundamental science and applications. Here, we present a novel synthetic protocol toward atomically monodisperse [Au₆(PPh₃)₆]²⁺ nanoclusters (abbreviated as Au₆) via ammonia-induced size convergence from polydisperse Au_<i>x</i> (<i>x</i> = 6–11) nanocluster mixture. The analogous ammonia-induced size conversion reactions starting from individually prepared Au₇ and Au₉ nanoclusters to Au₆ were traced by time-dependent ultraviolet–visible absorption and electrospray ionization mass spectra. It is observed that in both cases the size conversion is achieved through gradual release of the ion–molecule complex [NH₄AuPPh₃Cl]⁺ from the larger Au nanoclusters until the formation of thermodynamically stable Au₆ nanoclusters with the stability against the etching reaction. The role of ammonia ions in this size convergence synthesis is to accelerate the depletion of [Au­(PPh₃)]⁺ fragments from the PPh₃-protected Au nanoclusters, by the formation of the stable complex [NH₄AuPPh₃Cl]⁺

In-Plane Coassembly Route to Atomically Thick Inorganic–Organic Hybrid Nanosheets

Control over the anisotropic assembly of small building blocks into organized structures is considered an effective way to design organic nanosheets and atomically thick inorganic nanosheets with nonlayered structure. However, there is still no available route so far to control the assembly of inorganic and organic building blocks into a flattened hybrid nanosheet with atomic thickness. Herein, we highlight for the first time a universal in-plane coassembly process for the design and synthesis of transition-metal chalcogenide–alkylamine inorganic–organic hybrid nanosheets with atomic thickness. The structure, formation mechanism, and stability of the hybrid nanosheets were investigated in detail by taking the Co₉S₈–oleylamine (Co₉S₈–OA) hybrid nanosheets as an example. Both experimental data and theoretical simulations demonstrate that the hybrid nanosheets were formed by in-plane connection of small two-dimensional (2D) Co₉S₈ nanoplates <i>via</i> oleylamine molecules adsorbed at the side surface and corner sites of the nanoplates. X-ray absorption fine structure spectroscopy study reveals the structure distortion of the small 2D Co₉S₈ nanoplates that endows structural stability of the atomically thick Co₉S₈–OA hybrid nanosheets. The brand new atomically thick nanosheets with inorganic–organic hybrid network nanostructure will not only enrich the family of atomically thick 2D nanosheets but also inspire more interest in their potential applications

Atomically Thick Bismuth Selenide Freestanding Single Layers Achieving Enhanced Thermoelectric Energy Harvesting

Thermoelectric materials can realize significant energy savings by generating electricity from untapped waste heat. However, the coupling of the thermoelectric parameters unfortunately limits their efficiency and practical applications. Here, a single-layer-based (SLB) composite fabricated from atomically thick single layers was proposed to optimize the thermoelectric parameters fully. Freestanding five-atom-thick Bi₂Se₃ single layers were first synthesized via a scalable interaction/exfoliation strategy. As revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, surface distortion gives them excellent structural stability and a much increased density of states, resulting in a 2-fold higher electrical conductivity relative to the bulk material. Also, the surface disorder and numerous interfaces in the Bi₂Se₃ SLB composite allow for effective phonon scattering and decreased thermal conductivity, while the 2D electron gas and energy filtering effect increase the Seebeck coefficient, resulting in an 8-fold higher figure of merit (<i><i>ZT</i></i>) relative to the bulk material. This work develops a facile strategy for synthesizing atomically thick single layers and demonstrates their superior ability to optimize the thermoelectric energy harvesting

Fast Photoelectron Transfer in (C_ring)–C₃N₄ Plane Heterostructural Nanosheets for Overall Water Splitting

Direct and efficient photocatalytic water splitting is critical for sustainable conversion and storage of renewable solar energy. Here, we propose a conceptual design of two-dimensional C₃N₄-based in-plane heterostructure to achieve fast spatial transfer of photoexcited electrons for realizing highly efficient and spontaneous overall water splitting. This unique plane heterostructural carbon ring (C_ring)–C₃N₄ nanosheet can synchronously expedite electron–hole pair separation and promote photoelectron transport through the local in-plane π-conjugated electric field, synergistically elongating the photocarrier diffusion length and lifetime by 10 times relative to those achieved with pristine g-C₃N₄. As a result, the in-plane (C_ring)–C₃N₄ heterostructure could efficiently split pure water under light irradiation with prominent H₂ production rate up to 371 μmol g^–1 h^–1 and a notable quantum yield of 5% at 420 nm

Ionic Exchange of Metal–Organic Frameworks to Access Single Nickel Sites for Efficient Electroreduction of CO₂

Single-atom catalysts often exhibit unexpected catalytic activity for many important chemical reactions because of their unique electronic and geometric structures with respect to their bulk counterparts. Herein we adopt metal–organic frameworks (MOFs) to assist the preparation of a catalyst containing single Ni sites for efficient electroreduction of CO₂. The synthesis is based on ionic exchange between Zn nodes and adsorbed Ni ions within the cavities of the MOF. This single-atom catalyst exhibited an excellent turnover frequency for electroreduction of CO₂ (5273 h^–1), with a Faradaic efficiency for CO production of over 71.9% and a current density of 10.48 mA cm^–2 at an overpotential of 0.89 V. Our findings present some guidelines for the rational design and accurate modulation of nanostructured catalysts at the atomic scale

A Robust and Efficient Pd₃ Cluster Catalyst for the Suzuki Reaction and Its Odd Mechanism

The palladium-catalyzed Suzuki–Miyaura coupling reaction is one of the most versatile and powerful tools for constructing synthetically useful unsymmetrical aryl–aryl bonds. In designing a Pd cluster as a candidate for efficient catalysis and mechanistic investigations, it was envisaged to study a case intermediate between, although very different from, the “classic” Pd(0)­L<i>_n</i> and Pd nanoparticle families of catalysts. In this work, the cluster [Pd₃Cl­(PPh₂)₂(PPh₃)₃]⁺[SbF₆]⁻ (abbreviated <b>Pd</b>_<b>3</b><b>Cl</b>) was synthesized and fully characterized as a remarkably robust framework that is stable up to 170 °C and fully air-stable. <b>Pd</b>_<b>3</b><b>Cl</b> was found to catalyze the Suzuki–Miyaura C–C cross-coupling of a variety of aryl bromides and arylboronic acids under ambient aerobic conditions. The reaction proceeds while keeping the integrity of the cluster framework all along the catalytic cycle via the intermediate <b>Pd</b>_<b>3</b><b>Ar</b>, as evidenced by mass spectrometry and quick X-ray absorption fine structure. In the absence of the substrate under the reaction conditions, the <b>Pd</b>_<b>3</b><b>OH</b> species was detected by mass spectrometry, which strongly favors the “oxo-Pd” pathway for the transmetalation step involving substitution of the Cl ligand by OH followed by binding of the OH ligand with the arylboronic acid. The kinetics of the Suzuki–Miyaura reaction shows a lack of an induction period, consistent with the lack of cluster dissociation. This study may provide new perspectives for the catalytic mechanisms of C–C cross-coupling reactions catalyzed by metal clusters

Strong Surface Hydrophilicity in Co-Based Electrocatalysts for Water Oxidation

Developing efficient and durable oxygen evolution electrocatalyst is of paramount importance for the large-scale supply of renewable energy sources. Herein, we report the design of significant surface hydrophilicity based on cobalt oxyhydroxide (CoOOH) nanosheets to greatly improve the surface hydroxyl species adsorption and reaction kinetics at the Helmholtz double layer for high-efficiency water oxidation activity. The as-designed CoOOH-graphene nanosheets achieve a small surface water contact angle of ∼23° and a large double-layer capacitance (<i>C</i>_dl) of 8.44 mF/cm² and thus could evidently strengthen surface species adsorption and trigger electrochemical oxygen evolution reaction (OER) under a quite low onset potential of 200 mV with an excellent Tafel slope of 32 mV/dec. X-ray absorption spectroscopy and first-principles calculations demonstrate that the strong interface electron coupling between CoOOH and graphene extracts partial electrons from the active sties and increases the electron state density around the Fermi level and effectively promotes the surface intermediates formation for efficient OER

Design of N‑Coordinated Dual-Metal Sites: A Stable and Active Pt-Free Catalyst for Acidic Oxygen Reduction Reaction

We develop a host-guest strategy to construct an electrocatalyst with Fe-Co dual sites embedded on N-doped porous carbon and demonstrate its activity for oxygen reduction reaction in acidic electrolyte. Our catalyst exhibits superior oxygen reduction reaction performance, with comparable onset potential (<i>E</i>_onset, 1.06 vs 1.03 V) and half-wave potential (<i>E</i>_1/2, 0.863 vs 0.858 V) than commercial Pt/C. The fuel cell test reveals (Fe,Co)/N-C outperforms most reported Pt-free catalysts in H₂/O₂ and H₂/air. In addition, this cathode catalyst with dual metal sites is stable in a long-term operation with 50 000 cycles for electrode measurement and 100 h for H₂/air single cell operation. Density functional theory calculations reveal the dual sites is favored for activation of O-O, crucial for four-electron oxygen reduction