Facile Synthesis of Sub-Nanometric Copper Clusters by Double Confinement Enables Selective Reduction of Carbon Dioxide to Methane

Previous density-functional theory (DFT) calculations show that sub-nanometric Cu clusters (i.e., 13 atoms) favorably generate CH₄ from the CO₂ reduction reaction (CO₂RR), but experimental evidence is lacking. Herein, a facile impregnation-calcination route towards Cu clusters, having a diameter of about 1.0 nm with about 10 atoms, was developed by double confinement of carbon defects and micropores. These Cu clusters enable high selectivity for the CO₂RR with a maximum Faraday efficiency of 81.7 % for CH₄. Calculations and experimental results show that the Cu clusters enhance the adsorption of *H and *CO intermediates, thus promoting generation of CH₄ rather than H₂ and CO. The strong interactions between the Cu clusters and defective carbon optimize the electronic structure of the Cu clusters for selectivity and stability towards generation of CH₄. Provided here is the first experimental evidence that sub-nanometric Cu clusters facilitate the production of CH₄ from the CO₂RR.     

Spatially Responsive Multicolor Lanthanide-MOF Heterostructures for Covert Photonic Barcodes

Micro/nanoscale photonic barcodes based on multicolor luminescent segmented heterojunctions hold potential for applications in information security. However, such multicolor heterojunctions reported thus far are exclusively based on static luminescent signals, thus restricting their application in advanced confidential information protection. Reported here is a strategy to design responsive photonic barcodes with heterobimetallic (Tb³⁺/Eu³⁺) metal—organic framework multicolor heterostructures. The spatial colors could be precisely controlled by thermally manipulating the energy-transfer process between the two lanthanides, thus achieving responsive covert photonic barcodes. Also demonstrated is that spatially resolved responsive barcodes with multi-responsive features could be created in a single heterostructure. These findings offer unique opportunities to purposely design highly integrated responsive microstructures and smart devices toward advanced anti-counterfeiting applications.     

Metal–Sulfur Linkages Achieved by Organic Tethering of Ruthenium Nanocrystals for Enhanced Electrochemical Nitrogen Reduction

Inspired by the metal–sulfur (M-S) linkages in the nitrogenase enzyme, here we show a surface modification strategy to modulate the electronic structure and improve the N₂ availability on a catalytic surface, which suppresses the hydrogen evolution reaction (HER) and improves the rate of NH₃ production. Ruthenium nanocrystals anchored on reduced graphene oxide (Ru/rGO) are modified with different aliphatic thiols to achieve M-S linkages. A high faradaic efficiency (11 %) with an improved NH₃ yield (50 μg h⁻¹ mg⁻¹) is achieved at −0.1 V vs. RHE in acidic conditions by using dodecanethiol. DFT calculations reveal intermediate N₂ adsorption and desorption of the product is achieved by electronic structure modification along with the suppression of the HER by surface modification. The modified catalyst shows excellent stability and recyclability for NH₃ production, as confirmed by rigorous control experiments including ¹⁵N isotope labeling experiments.     

Longitudinal 3D Blood Flow Distribution Provided by Diffuse Correlation Tomography during Bone Healing in a Murine Fracture Model

Noninvasive monitoring of vascularization can potentially diagnose impaired bone healing earlier than current radiographic methods. In this study, a noncontact diffuse correlation tomography (DCT) technique was employed to measure longitudinal blood flow changes during bone healing in a murine femoral fracture model. The three-dimensional distribution of the relative blood flow was quantified from one day pre-fracture to 48 days post-fracture. For three mice, frequent DCT measurements were performed every other day for one week after fracture, and then weekly thereafter. A decrease in blood flow was observed in the bone fracture region at one day post-fracture, followed by a monotonic increase in blood flow beyond the pre-injury baseline until five to seven days post-fracture. For the remaining 12 mice, only weekly DCT measurements were performed. Data collected on a weekly basis show the blood flow for most mice was elevated above baseline during the first two post-fracture weeks, followed by a subsequent decrease. Torsional strength of the excised femurs was measured for all 15 mice after 7 weeks of healing. A metric based on the early blood flow changes shows a statistically significant difference between the high strength group and the low strength group.     

Metal-free and base-free decarboxylation of substituted cinnamic acids in a deep eutectic solvent

Abstract

A metal-free and base-free strategy was developed in DES to synthesize styrenes for the first time by decarboxylation of cinnamic acid derivatives, which provided a renewable and cost efficiently protocol to access various styrenes including those with functional groups such as 4-vinylphenol and 1-chloro-4-vinylbenzene.     

Porphyrin/Quinoidal-Bithiophene-Based Macrocycles and Their Dications: Template-Free Synthesis and Global Aromaticity

We report the template-free synthesis and characterization of a new type of porphyrin/quinoidal-bithiophene-based conjugated macrocycle. X-ray crystallographic analysis of the dimer ( 2MC ) revealed a cyclophane-like geometry with large dihedral angles between the porphyrin and the neighboring thiophene rings, and NMR measurements and theoretical calculations confirmed a localized aromatic character of the porphyrin/thiophene rings and quinoidal character of the bithiophene linkers. Restricted rotation of the thiophene rings linked to the porphyrin unit was observed by variable-temperature NMR measurements. The dication ( 2MC²⁺ ) adopts a chair-shaped conformation to facilitate π-electron delocalization around the whole macrocycle. As a result, the molecule is globally aromatic, with a dominant 54 π conjugation pathway. The trimer ( 3MC ) also shows localized aromatic character of porphyrin rings and conformational flexibility, but its dication ( 3MC²⁺ ) is rigid and globally aromatic with a dominant 82 π conjugation pathway.     

Pathways of Methane Transformation over Copper-Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

The reaction of methane with copper-exchanged mordenite with two different Si/Al ratios was studied by means of in situ NMR and infrared spectroscopies. The detection of NMR signals was shown to be possible with high sensitivity and resolution, despite the presence of a considerable number of paramagnetic Cu^II species. Several types of surface-bonded compounds were found after reaction, namely molecular methanol, methoxy species, dimethyl ether, mono- and bidentate formates, Cu^I monocarbonyl as well as carbon monoxide and dioxide, which were present in the gas phase. The relative fractions of these species are strongly influenced by the reaction temperature and the structure of the copper sites and is governed by the Si/Al ratio. While methoxy species bonded to Brønsted acid sites, dimethyl ether and bidentate formate species are the main products over copper-exchange mordenite with a Si/Al ratio of 6; molecular methanol and monodentate formate species were observed mainly over the material with a Si/Al ratio of 46. These observations are important for understanding the methane partial oxidation mechanism and for the rational design of the active materials for this reaction.     

La3B6O13(OH): The First Acentric High-Pressure Borate Displaying Edge-Sharing BO4 Tetrahedra

La₃B₆O₁₃(OH) was obtained by a high-pressure/high-temperature experiment at 6 GPa and 1673 K. The compound crystallizes in the space group P2₁ (no. 4) with the lattice parameters a=4.785(2), b=12.880(4), c=7.433(3) Å, and β=90.36(10)°, and is built up of corner- as well as edge-sharing BO₄ tetrahedra. It represents the first acentric high-pressure borate containing these B₂O₆ entities. The compound develops borate layers of „sechser“-rings with the La³⁺ cations positioned between the layers. Single-crystal and powder X-ray diffraction, vibrational and MAS NMR spectroscopy, second-harmonic generation (SHG) and thermoanalytical measurements, as well as computational methods were used to affirm the proposed structure and the B₂O₆ entities.     

C.I.颜料红177中间体的制备工艺改进

本文较为系统地研究了铜粉催化剂加入方式对C.I.颜料红177中间体4,4'-二氨基-1,1'-二蒽醌-3,3'-二磺酸(DAS)合成过程中的乌尔曼偶联反应速率的影响规律。 研究结果表明,在55 ℃较佳反应温度下,先加入与溴氨酸钠质量比为2:5的铜粉,反应一段时间后再加入与溴氨酸钠的质量比为1:5的铜粉,与一次性加入与溴氨酸钠的质量比为3:5的铜粉相比较,综合反应时间可节省2~3 h。 另外,对于DAS中混有的铜盐,采取在制备过程中加入柠檬酸的方法予以去除,此举可提高DAS的纯度。 当铜粉与柠檬酸的质量比为6:1时,可使DAS中铜盐的含量小于0.001%。 此外还探究了蒸馏后滤液的剩余量对DAS收率的影响,结果表明,滤液的剩余量在20 mL时,DAS的收率在95%以上。 基于本文的研究结果提出,欲进一步提高该反应的收率,需要寻找更高效的催化剂。     

光电催化二氧化碳还原研究进展

CO_2是最常见的化合物,作为潜在的碳一资源,可用于制备多种高附加值的化学品,如一氧化碳、甲烷、甲醇、甲酸等。传统的热催化转化CO_2方法能耗高,反应条件苛刻。因此,如何在温和条件下高效地将CO_2转化成高附加值的化学品,一直以来是催化领域的研究热点和难点之一。光催化技术反应条件温和、绿色环保。然而,纯光催化反应普遍存在太阳能利用效率有限,光生载流子分离效率低等问题。针对上述问题,在光催化的基础上引入电催化,可以提高载流子的分离效率,在较低的过电位下,实现多电子、质子向CO_2转移,从而提高催化反应效率。总之,光电催化技术可以结合光催化和电催化的优势,提高CO_2催化还原反应效率,为清洁、绿色利用CO_2提供了一种新方法。本文依据光电催化CO_2还原反应基本过程,从光吸收、载流子分离和界面反应等三个角度综述了光电催化反应的基本强化策略,并对未来可能的研究方向进行了展望。