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•The advance of post-synthetic modification (PSM) of MOFs in the past five years was reviewed.•Two increasingly apparent tendencies in PSM of exploring new types and tandem reactions ...were demonstrated.•Selected examples including several from China focus on new types and tandem PSM.
In the past five years, post-synthetic modification (PSM) has become a very useful strategy in systematically functionalizing metal–organic frameworks (MOFs) by modifying the linker, metal node, pore character, and surface environment for the purpose of increasing the structural stability and introducing desired properties. In this review, we intend to demonstrate the two major trends in PSM including the mushrooming of new types of reaction and the combination of multi-steps PSM. The selected examples illustrate three promising PSM classes, post-synthetic metal exchange (PSME), post-synthetic ligand exchange (PSLE) and post-synthetic elimination and insertion (PSE&I). Combined with the well-developed covalent PSM and dative PSM, tandem PSM which constitutes of multistep and different types of reaction adds to the step-by-step improvement of catalytic activity, regulating magnetism and others. These recent advances in PSM not only open new paths to improve the function of MOFs, but also reveal the unprecedented reaction complexity of crystalline solids.
One important goal of the current electrocatalysis is to develop integrated electrodes from the atomic level design to multilevel structural engineering in simple ways and low prices. Here, a series ...of oxygen micro‐alloyed high‐entropy alloys (O‐HEAs) is developed via a metallurgy approach. A (CrFeCoNi)97O3 bulk O‐HEA shows exceptional electrocatalytic performance for the oxygen evolution reaction (OER), reaching an overpotential as low as 196 mV and a Tafel slope of 29 mV dec−1, and with stability longer than 120 h in 1 m KOH solution at a current density of 10 mA cm−2. It is shown that the enhanced OER performance can be attributed to the formation of island‐like Cr2O3 microdomains, the leaching of Cr3+ ions, and structural amorphization at the interfaces of the domains. These findings offer a technological‐orientated strategy to integrated electrodes.
A new class of bulk electrodes is designed by incorporating oxide microdomains into the so‐called high‐entropy alloys (HEAs). From these, unprecedented oxygen evolution reaction (OER) activity is achieved, with an ultralow overpotential of 196 mV and a Tafel slope of 29 mV dec−1, and with stability longer than 120 h in 1 m KOH solution at current density of 10 mA cm−2.
Supramolecular rather than covalent molecular engineering on Feringa motors can provide an alternative toolkit for tuning the properties of motorized materials through appropriate supramolecular ...structural perturbations, which are underexplored. Herein, a multicomponent supramolecular gel system is successfully prepared by employing an ultra‐low molecular weight gelator and a modulator‐Feringa motor. The electron microscopic, spectroscopic, and rheological data revealed that the morphology and mechanical properties of the gel can be tuned via a crystallographic mismatch branching (CMB) mechanism simply by adding varied amounts of motor modulators. Notably, the rotary motion of the motor is preserved in such a multicomponent gel system, and the morphology and rheology of the gel can be further altered by the motor's rotary motion that promotes the structural perturbation, resulting in seldomly seen gel‐to‐gel transition events. The work shown here offers prospects to utilize a supramolecular perturbation strategy to deliver responsiveness from molecular motors to the corresponding bulk materials.
A multicomponent supramolecular gel containing a Feringa motor as the modulator is successfully prepared. The rotary motion of the motor is preserved in such a multicomponent gel system, and the morphology and rheology of the gel can be altered by the light‐activated motor's rotary motion that leads to the supramolecular structural perturbation, resulting in seldomly seen gel‐to‐gel transition event.
A novel Z-scheme system of CeO2–Ag/AgBr heterostructure photocatalyst exhibits excellent ability to eliminate ciprofloxacin under visible light irradiation.
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•Novel Z-scheme ...CeO2–Ag/AgBr photocatalysts were prepared.•Superior photocatalytic activity for the degradation of ciprofloxacin (CIP) refractory pollutants was obtained.•The factors affecting the photocatalytic performance were investigated.•A plausible degradation pathway for CIP was proposed.•A Z-scheme photocatalytic mechanism was proposed.
In this study, CeO2–Ag/AgBr composite photocatalysts with a Z-scheme configuration were fabricated by in situ interspersal of AgBr on CeO2 and subsequent photoreduction process. The CeO2–Ag/AgBr composites exhibited enhanced photocatalytic activity for the photodegradation of ciprofloxacin (CIP) under visible light irradiation. The effects of initial CIP concentration and various inorganic salts were investigated in detail. Three-dimensional excitation–emission matrix fluorescence spectra were used to further monitor the CIP molecule degradation. Plausible degradation pathways for CIP were proposed based on LC-MS instruments. Photoluminescence, electrochemical impedance spectroscopy, and photocurrent tests indicated the rapid transfer and migration of electrons–holes can be achieved in this ternary photocatalytic system. The enhanced photocatalytic performances of CeO2–Ag/AgBr could be credited to the accelerated interfacial charge transfer process and the improved separation of the photogenerated electron–hole pairs. The existence of a small amount of metallic Ag is conducive to the formation of a stable Z-scheme photocatalytic system. This work would pave the route for the design of novel Z-scheme photocatalytic systems for application in solar-to-fuel conversion and photocatalytic water treatment.
{Cu6(pybz)8(OH)2·I5 –·I7 –} n (1), obtained hydrothermally by using iodine molecules as a versatile precursor template, consists of a cationic framework with two types of zigzag channels, which ...segregate I5 – and I7 – anions. The framework exhibits the first observed bipillared-bilayer structure featuring both interdigitation and interpenetration. 1 displays high framework stability in both acidic (HCl) and alkaline (NaOH) solutions. 1 slowly releases iodine in dry methanol to give Cu6(pybz)8(OH)2(I–)2·3.5CH3OH (1′) and partially recovers iodine from cyclohexane to form Cu6(pybz)8(OH)2(I–)2·xI2 (1″). Differences of up to 100 times in electrical conductivity and of 4 times in nonlinear optical activity (NLO) have been measured between 1 and 1′. This compound is one of few displaying multifunctionality, electrical conductivity, NLO, and crystal–crystal stability upon release and recovery of iodine. It is also unique in the iodine release from polyiodide anions in a metal–organic framework.
This paper proposes two deep learning methods for remaining useful life (RUL) prediction of bearings. The methods have the advantageous end-to-end property that they take raw data as input and ...generate the predicted RUL directly. They are TSMC-CNN, which stands for the time series multiple channel convolutional neural network, and TSMC-CNN-ALSTM, which stands for the TSMC-CNN integrated with the attention-based long short-term memory (ALSTM) network. The proposed methods divide a time series into multiple channels and take advantage of the convolutional neural network (CNN), the long short-term memory (LSTM) network, and the attention-based mechanism for boosting performance. The CNN performs well for extracting features from data with multiple channels; dividing a time series into multiple channels helps the CNN extract relationship among far-apart data points. The LSTM network is excellent for processing temporal data; the attention-based mechanism allows the LSTM network to focus on different features at different time steps for better prediction accuracy. PRONOSTIA bearing operation datasets are applied to the proposed methods for the purpose of performance evaluation and comparison. The comparison results show that the proposed methods outperform the others in terms of the mean absolute error (MAE) and the root mean squared error (RMSE) of RUL prediction.
This article presents advances in resource allocation for downlink non-orthogonal multiple access (NOMA) systems, focusing on user pairing and power allocation algorithms. The former pairs the users ...to obtain high capacity gain by exploiting the channel gain difference between the users, while the latter allocates power to users in each cluster to balance system throughput and user fairness. Additionally, the article introduces the concept of cluster fairness and proposes the divide-and-next-largest-difference-based user pairing algorithm to distribute the capacity gain among the NOMA clusters in a controlled manner. Furthermore, performance comparison between multiple-input multiple-output NOMA (MIMO-NOMA) and MIMO orthogonal multiple access (MIMO-OMA) is conducted when users have pre-defined quality of service. Simulation results are presented, which validate the advantages of NOMA over OMA. Finally, the article provides avenues for further research on resource allocation for downlink NOMA.
In this paper, the performance of multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) is investigated, when multiple users are grouped into a cluster. The superiority of ...MIMO-NOMA over MIMO-OMA in terms of both sum channel capacity and ergodic sum capacity is proved analytically. Furthermore, it is demonstrated that the more users are admitted to a cluster, the lower is the achieved sum rate, which illustrates the tradeoff between the sum rate and maximum number of admitted users. On this basis, a user admission scheme is proposed, which is optimal in terms of both sum rate and the number of admitted users when the signal-to-interference-plus-noise ratio thresholds of the users are equal. When these thresholds are different, the proposed scheme still achieves good performance in balancing both criteria. Moreover, under certain conditions, it maximizes the number of admitted users. In addition, the complexity of the proposed scheme is linear in the number of users per cluster. Simulation results verify the superiority of MIMO-NOMA over MIMO-OMA in terms of both sum rate and user fairness, as well as the effectiveness of the proposed user admission scheme.
The in situ tracking of the pyrolysis of a binary molecular cluster Zn7(μ3‐CH3O)6(L)6ZnLCl22 is presented with one brucite disk and two mononuclear fragments (L=mmimp: ...2‐methoxy‐6‐((methylimino)‐methyl)phenolate) to porous carbon using TG‐MS from 30 to 900 °C. Following up the spilled gas product during the decomposed reaction of zinc cluster along the temperature rising, and in conjunction with XRD, SEM, BET and other materials characterization, where three key steps were observed: 1) cleavage of the bulky external ligand; 2) reduction of ZnO and 3) volatilization of Zn. The real‐time‐dependent phase‐sequential evolution of the remaining products and the processing of pore forming template transformation are proposed simultaneously. The porous carbon structure featuring a uniform nano‐sized pore distribution synthesized at 900 °C with the highest surface area of 1644 m2 g−1 and pore volume of 0.926 cm3 g−1 exhibits the best known capacitance of 662 F g−1 at 0.5 A g−1.
Supercharged: The in situ pyrolysis and real‐time progressive phase evolution of a binary zinc molecular cluster are tracked. The supercapacitive porous carbon, which is obtained under 900 °C, has a record capacitance of 662 F g−1 at 0.5 A g−1.
Metal–organic framework (MOF) glasses are a fascinating new class of materials, yet their prosperity has been impeded by the scarcity of known examples and limited vitrification methods. In the work ...described in this report, we applied synergistic stimuli of vapor hydration and thermal dehydration to introduce structural disorders in interpenetrated dia -net MOF, which facilitate the formation of stable super-cooled liquid and quenched glass. The material after stimulus has a glass transition temperature (T g) of 560 K, far below the decomposition temperature of 695 K. When heated, the perturbed MOF enters a super-cooled liquid phase that is stable for a long period of time (>104 s), across a broad temperature range (26 K), and has a large fragility index of 83. Quenching the super-cooled liquid gives rise to porous MOF glass with maintained framework connectivity, confirmed by EXAFS and PDF analysis. This method provides a fundamentally new route to obtain glassy materials from MOFs that cannot be melted without causing decomposition.
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