Latest ArticlesTransition-metal chalcogenides with hollow nanostructure, especially cobalt sulfides, are considered as the most promising non-precious metal catalysts for oxygen evolution reaction. However, it is difficult to synthesize oxygen-containing cobalt sulphides with hollow structure due to the different physical/chemical properties between metal sulfides and metal cobalts. Herein, we report a novel oxygen-containing amorphous cobalt sulfide ball-in-ball hollow spheres (Co-S-O BBHS) synthesized by an anion exchange method. Taking advantage of the ball-in-ball hollow structure, the amorphous Co-S-O BBHS shows superior oxygen evolution reaction (OER) electrocatalytic performance with a low overpotential of 285 mV at 10 mA/cm2, small Tafel slope of 49.67 mV/dec, high Faraday efficiency of 96%, and satisfied durability. Experiments and DFT calculations demonstrate that the introduction of oxygen and sulfur modulates the electronic structure of Co-S-O BBHS, thus enhancing the adsorption of *O (adsorbed O species on catalyst surface) intermediate, which greatly boosts the catalytic activity towards OER. This work provides a new strategy for controllable synthesis of complex hollow structures of transition-metal chalcogenides for OER.
CeO2 morphology was proposed to be a crucial factor for reducing nitrobenzene to azoxybenzene under the base-free condition. Herein, the structure-activity relationship of CeO2 catalysts was explored to improve the azoxybenzene yield. A series of CeO2 catalysts were synthesized with seven morphologies to obtain different Ce3+ proportion and various surface areas. Notably, the catalytic performance of these samples for reducing nitrobenzene to azoxybenzene enhanced with the increasing Ce3+ proportion. With the highest surface Ce3+ proportion, the Rod-CeO2 catalyst exhibited 100% conversion of nitrobenzene and 89.8% azoxybenzene selectivity in 7 h at 150 ℃ under 1 MPa CO. Moreover, the preliminary mechanistic analysis indicated that the inhabitation of azoxybenzene to by-product azobenzene resulted in the high selectivity of azoxybenzene.
Selective hydrogenation of aromatic amines, especially chemicals such as aniline and bis(4-aminocyclohexyl)methane for non-yellowing polyurethane, is of particular interests due to the extensive applications. To conquer the existing difficulties in selective hydrogenation, the Ru0-Ruδ+/CeO2 catalyst with solid frustrated Lewis pairs was developed for aromatic amines hydrogenation with excellent activity and selectivity under relative milder conditions. The morphology, electronic and chemical properties, especially the Ru0-Ruδ+ clusters and reducible ceria were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), CO2 temperature programmed desorption (CO2-TPD), H2 temperature programmed reduction (H2-TPR), H2 diffuse reflectance Fourier transform infrared spectroscopy (H2-DRIFT), Raman, etc. The 2% Ru/CeO2 catalyst exhibited good conversion of 95% and selectivity greater than 99% toward cyclohexylamine. The volcano curve describing the activity and Ru state was found. Owning to the "acidic site isolation" by surrounding alkaline sites, condensation between the neighboring amine molecules could be effectively suppressed. The catalyst also showed good stability and applicability for other aromatic amines and heteroarenes containing different functional groups.
Electrical double-layer capacitors are widely concerned for their high power density, long cycling life and high cycling efficiency. However, their wide application is limited by their low energy density. In this study, we propose a simple yet environmental friendly method to synthesize cobalt and nitrogen atoms co-doped porous carbon (CoAT-NC) material. Cobalt atoms connected with primarily pyridinic nitrogen atoms can be uniformly dispersed in the amorphous carbon matrix, which is benefit for improving electrical conductivity and density of states of the carbon material. Therefore, an enhanced performance is expected when CoAT-NC is served as electrode in a supercapacitor device. CoAT-NC displays a good gravimetric capacitance of 160 F/g at 0.5 A/g combing with outstanding capacitance retention of 90% at an extremely high current density of 100 A/g in acid electrolyte. Furthermore, a good energy density of 30 Wh/kg can be obtained in the organic electrolyte.
Smart strategies that can decrease the side effect and enhance the therapeutic efficacy of chemotherapy are in urgent need to meet the special demands of cancer therapy. Herein, two water-soluble macrocyclic hosts, i. e., a carboxylated leaning tower[6]arene (CLT6) and a carboxylated [2]biphenyl-extended pillar[6]arene (CBpP6), are used to load chemotherapy drug oxaliplatin (OxPt) by forming inclusion complexes (OxPt⊂CLT6 and OxPt⊂CBpP6) through host-guest interactions. Interestingly, OxPt can be released from the macrocyclic cavities of these drug delivery systems (DDSs) via the competitive binding effect of spermine (SPM) because of the stronger binding abilities of CLT6/CBpP6 toward SPM as compared with OxPt, leading to enhanced cytotoxicity on SPM-overexpressed cancer cells, such as breast cancer MCF-7 cells. Moreover, compared to free OxPt, due to the low concentration of SPM in normal cells, OxPt⊂CLT6 and OxPt⊂CBpP6 demonstrated a decreased cytotoxicity on liver L02 cells, which is beneficial for reducing the side effect of anticancer drug during chemotherapy. Such a strategy might be extended to other antitumor drugs and water-soluble macrocycles with suitable cavity sizes to achieve controllable drug delivery and enhanced anticancer ability in supramolecular chemotherapy.
The design and synthesis of a phenoxazine-based metal-organic tetrahedron (Zn4L4) as biomimetic lectin for selectively recognition of glucosamine (GlcN) was reported. Different from the free phenoxazine-based ligand (L), Zn4L4 displayed the highest fluorescent intensity enhancement efficiency toward GlcN over other related natural mono- and disaccharides. Fluorescence titration demonstrated a 1:1 stoichiometric host-guest complex was formed with an association constant about 4.03×104 L/mol. 1H NMR spectroscopic studies confirmed this selectivity resulted from the multiple hydrogen bonding interactions formed between GlcN and Zn4L4. The present results suggested that rational arrangement of recognition sites in the confined space of metal-organic cage is crucial for the selectivity toward target guests.
A simultaneous C2-H arylation and C8-H alkylation of naphthalene ring has been achieved by palladium-catalyzed cascade reaction of N-(2-halophenyl)-2-(naphthalen-1-yl)acrylamides with aryl iodides, which provides an efficient method for synthesizing various aryl-substituted spirocyclic oxindoles. The protocol enables three CC bonds formation via an intramolecular Heck reaction and sequentially regioselective CH bond activation.
A new family of isostructural 3d-4f polymetallic complexes, formulated as [Cu6Ln5(μ3−OH)9 (C4H8O2N)6(C5H4ON)6(H2O)9]·(ClO4)6·(H2O)22 (Ln = Pr, 1; Nd, 2; Sm, 3; Eu, 4; Gd, 5), was successfully isolated through the simple hydrolysis reaction of 2-aminoisobutyric acid, 2-hydroxypyridine, Cu(CH3COO)2·H2O, and Ln(ClO4)3·6H2O. Notably, the [Cu6Ln5] clusters with high molecular symmetry of D3h are rare examples of 2-aminoisobutyric acid-based 3d-4f clusters. The successful theoretical modeling of 5 yielded that the Gd-Gd exchange is of order 0.2 K, whereas the Gd-Cu exchange is an order of magnitude larger. Magnetization data collected for complex 5 yield a magnetic entropy change (−ΔSm) of 19.6 J kg−1 K−1 at 3 K and 7 T, which may be attributed to the weak magnetic interactions between the component metal ions.
The N-heterocyclic carbene (NHC)-catalyzed reactions involving two-electron reaction pathway have been well-established. However, the development of NHC-catalyzed radical reactions is still in its infancy in terms of reaction types and enantioselectivity. In the past decade, several elegant NHC-catalyzed radical reactions have been developed, including NHC-catalyzed oxidation of aldehydes to esters, reductive coupling reactions using Breslow intermediate as SET reductant and NHC-catalyzed reactions via radical homoenolates, dienoaltes and trienolates. This review summarizes the recent advances in NHC-catalyzed reactions involving radical intermediates.
Metal-free anti-Markovnikov hydroalkylation of unactivated alkenes with cyanoacetate has been developed, featuring the use of a dual-component initiator containing an organic photocatalyst and a radical precursor. When combined, the two components can undergo visible light-induced single-electron transfer, and serve as a versatile and effective alkyl radical generator.
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