Imaging defects and their evolution in a metal–organic framework at sub-unit-cell resolution

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Defect engineering of metal–organic frameworks (MOFs) offers promising opportunities for tailoring their properties to specific functions and applications. However, determining the structures of defects in MOFs—either point defects or extended ones—has proved challenging owing to the difficulty of directly probing local structures in these typically fragile crystals. Here we report the real-space observation, with sub-unit-cell resolution, of structural defects in the catalytic MOF UiO-66 using a combination of low-dose transmission electron microscopy and electron crystallography. Ordered ‘missing linker’ and ‘missing cluster’ defects were found to coexist. The missing-linker defects, reconstructed three-dimensionally with high precision, were attributed to terminating formate groups. The crystallization of the MOF was found to undergo an Ostwald ripening process, during which the defects also evolve: on prolonged crystallization, only the missing-linker defects remained. These observations were rationalized through density functional theory calculations. Finally, the missing-cluster defects were shown to be more catalytically active than their missing-linker counterparts for the isomerization of glucose to fructose

Targeted synthesis of an electroactive organic framework

A new strategy for targeted design and synthesis of an electroactive microporous organic molecular sieve (JUC-Z2) is described. Experiment demonstrated that such a targeted synthesis approach to achieve phenyl-phenyl coupling was a controllable process and predominately generated two-dimensional polymer sheets, significantly different from the traditional chemical or electrochemical oxidation methods to prepare conducting polymers. Successive self-assembly leads to a lamellar organic framework comprised of stacked polymer sheets with an hcb topology. JUC-Z2 was found to have a well-defined uniform micropore distribution (similar to 1.2 nm), a large surface area (BET = 2081 m(2) g(-1)) and high physicochemical stability (> 440 degrees C). After doping with I(2), JUC-Z2 exhibits typical p-type semiconductive properties. As the first example of an electroactive organic framework, JUC-Z2 possesses a unique ability of electrochemical ion recognition, arising from the synergistic function of the uniform micropores and the N-atom redox site.State Basic Research Project[2011CB808703]; NSFC[91022030, 20771041, 20773101, 20833005]; "111'' project[B07016]; Ministry of Science and Technology[2006DFA41190]; Jilin Science and Technology Department[20106021

Research on Conflict Resolution Method of Production Evaluation Index in Flexible Manufacturing Field Based on Multiplayer Cooperative Game

Multiple local assignment rules are common in production lines with complex production elements to direct the production process. Different local assignment rules have different degrees of impact on each production evaluation index, which aggravates the conflict between each production evaluation index. In order to solve the problem of increasing conflict among multiple production evaluation indexes in complex production scheduling process, based on the mathematical model of flexible flow shop with limited buffer and public buffer (FFSP-PB), game elements such as game player, game strategy and game order are established according to the idea of multiplayer cooperative game, and design the corresponding game strategy selection method to predict and control the game behavior of each player in the problem. Then a conflict resolution method of production evaluation index based on multiplayer cooperative game is proposed to solve the conflict between multiple production evaluation indexes, and then improve each production evaluation index. Finally, according to the actual production data of a bus manufacturing enterprise based on flexible manufacturing mode, several simulation schemes are designed to analyze and verify the effectiveness and practicability of the proposed method in resolving the conflicts between production evaluation indexes, and provides a reliable new solution for the conflict resolution of production evaluation index in the field of flexible manufacturing

Enriched Finite Element Method Based on Interpolation Covers for Structural Dynamics Analysis

This work proposes a novel enriched finite element method (E-FEM) for structural dynamics analysis. We developed the enriched 3-node triangular and 4-node tetrahedral displacement-based elements (T-elements). The standard linear shape functions of these T-elements were enriched using interpolation cover functions over each patch of elements. We also introduced and compared different orders of cover functions; higher-order functions obtained higher computational performance. Subsequently, the forced and free vibration analyses were performed on various typical numerical examples. The proposed enriched finite element method generated more precise numerical results and ensured faster convergence than the original linear elements

Resistance potential of soil bacterial communities along a biodiversity gradient in forest ecosystems

Abstract Higher biodiversity is often assumed to be a more desirable scenario for maintaining the functioning of ecosystems, but whether species‐richer communities are also more disturbance‐tolerant remains controversial. In this study, we investigated the bacterial communities based on 472 soil samples from 28 forests across China with associated edaphic and climatic properties. We developed two indexes (i.e., community mean tolerance breadth [CMTB] and community mean response asynchrony [CMRA]) to explore the relationship between diversity and community resistance potential. Moreover, we examined this resistance potential along the climatic and latitudinal gradients. We revealed that CMTB was significantly and negatively related to species richness, resulting from the changes in balance between relative abundances of putative specialists and generalists. In comparison, we found a unimodal relationship between CMRA and richness, suggesting that higher biodiversity might not always lead to higher community resistance. Moreover, our results showed differential local patterns along latitude. In particular, local patterns in the northern region mainly followed general relationships rather than those for the southern forests, which may be attributed to the differences in annual means and annual variations of climate conditions. Our findings highlight that the community resistance potential depends on the composition of diverse species with differential environmental tolerance and responses. This study provides a new, testable evaluation by considering tolerance breadth and response asynchrony at the community level, which will be helpful in assessing the influence of disturbance under rapid shifts in biodiversity and species composition as a result of global environmental change

Phase-dependent microstructure modification leads to high thermoelectric performance in n-type layered SnSe2

International audienceMicrostructure control is crucial for thermoelectrics since it is intimately related to the scattering mechanism of both electrons and phonons. Herein, we propose a new strategy to modify microstructure by phase regulation that simultaneously induces high carrier mobility and low lattice thermal conductivity. As demonstrated in layered SnSe2, the addition of Cu can induce a phase transition from space group P3¯m1 to P63mc. Due to the enlarged formation energy of stacking faults in the later phase, the stacking fault density is greatly reduced after heat treatment that leads to an increased grain size. Accordingly, the carrier mobility of SnSe1.97Br0.03–3 % Cu sample is enhanced by 100 % at room temperature. Furthermore, the reduction of stacking fault density is accompanied by the formation of pores in the matrix, which results in low lattice thermal conductivity. As a result, a record peak zT of 1.13 for SnSe2-based materials is achieved at 773 K, and the attained ZTave of 0.62 is a record-high value among n-type polycrystalline layered materials working in intermediate-to-high temperature region. This work provides a feasible strategy to decouple the electron and phonon transport in layered thermoelectric compounds by phase-dependent microstructure modification. © 202

Investigating the Influence of Mesoporosity in Zeolite Beta on Its Catalytic Performance for the Conversion of Methanol to Hydrocarbons

Hierarchically porous zeolite Beta (Beta-MS) synthesized by a soft-templating method contains remarkable intracrystalline mesoporosity, which reduces the diffusion length in zeolite channels down to several nanometers and alters the distribution of Al among distinct crystallographic sites. When it was used as a catalyst for the conversion of methanol to hydrocarbons (MTH) at 330 °C, Beta-MS exhibited a 2.7-fold larger conversion capacity, a 2.0-fold faster reaction rate, and a remarkably longer lifetime in comparison to conventional zeolite beta (Beta-C). The superior catalytic performance of Beta-MS is attributed to its hierarchical structure, which offers full accessibility to all catalytically active sites. In contrast, Beta-C was easily deactivated because a layer of coke quickly deposited on the outer surfaces of the catalyst crystals, impeding access to interior active sites. This difference is clearly demonstrated by using electron microscopy combined with electron energy loss spectroscopy to probe the distribution of coke in the deactivated catalysts. At both low and high conversions, ranging from 20% to 100%, Beta-MS gave higher selectivity toward higher aliphatics (C₄–C₇) but lower ethene selectivity in comparison to Beta-C. Therefore, we conclude that a hierarchical structure decreases the residence time of methylbenzenes in zeolite micropores, disfavoring the propagation of the aromatic-based catalytic cycle. This conclusion is consistent with a recent report on ZSM-5 and is also strongly supported by our analysis of soluble coke species residing in the catalysts. Moreover, we identified an oxygen-containing compound, 4-methylbenzaldehyde, in the coke, which has not been observed in the MTH reaction before