Search

The electrochemical N2 reduction reaction (NRR) under ambient conditions is attractive in replacing the current Haber-Bosch process toward sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising NRR electrocatalysts. However, simultaneously boosting their NRR activity and selectivity remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M–N4–C centers as novel, defined, and effective catalysts, achieving simultaneously enhanced activity and selectivity of electrocatalytic NRR to ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn, and Cu) and pyrene units bonded by pyrazine linkages. Significantly, the 2D c-COFs with Fe–N4–C center exhibit higher ammonia yield rate (33.6 μg h–1 mgcat–1) and Faradaic efficiency (FE, 31.9%) at −0.1 V vs reversible hydrogen electrode than those with other M–N4–C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h–1 mgcat–1 and FE > 30%). In situ X-ray absorption spectroscopy, Raman spectroelectrochemistry, and theoretical calculations unveil that Fe–N4–C centers act as catalytic sites. They show a unique electronic structure with localized electronic states at Fermi level, allowing for stronger interaction with N2 and thus faster N2 activation and NRR kinetics than other M–N4–C centers. Our work opens the possibility of developing metal–nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalyst and provides an atomic understanding of the NRR process on M–Nx–C based electrocatalysts for designing high-performance NRR catalysts.

Background Acute lung injury is an important factor that leads to the death of patients with pneumonia. Previous studies have shown that nicotinamide (NAM) plays a role in reducing cell damage, so this study explored the mechanism by which NAM functions in acute lung injury. Methods We explored the mechanism by which NAM affects acute lung injury in vivo and in vitro by qRT-PCR, western blotting and ELISA. Results The results showed that NAM could significantly reduce lung injury and proinflammatory mediator accumulation. Further mechanistic studies showed that NAM could significantly inhibit the MAPK and AKT/NF-κB signaling pathways. Conclusion These results suggested that NAM may reduce the release of proinflammatory mediators by inhibiting the MAPK and AKT/NF-κB signaling pathways and ultimately alleviate lung injury.

Layered two-dimensional (2D) conjugated metal-organic frameworks (MOFs) represent a family of rising electrocatalysts for the oxygen reduction reaction (ORR), due to the controllable architectures, excellent electrical conductivity, and highly exposed well-defined molecular active sites. Herein, we report a copper phthalocyanine based 2D conjugated MOF with square-planar cobalt bis(dihydroxy) complexes (Co-O4 ) as linkages (PcCu-O8 -Co) and layer-stacked structures prepared via solvothermal synthesis. PcCu-O8 -Co 2D MOF mixed with carbon nanotubes exhibits excellent electrocatalytic ORR activity (E1/2 =0.83 V vs. RHE, n=3.93, and jL =5.3 mA cm-2 ) in alkaline media, which is the record value among the reported intrinsic MOF electrocatalysts. Supported by in situ Raman spectro-electrochemistry and theoretical modeling as well as contrast catalytic tests, we identified the cobalt nodes as ORR active sites. Furthermore, when employed as a cathode electrocatalyst for zinc-air batteries, PcCu-O8 -Co delivers a maximum power density of 94 mW cm-2 , outperforming the state-of-the-art Pt/C electrocatalysts (78.3 mW cm-2 ).

Large blue rectangular crystals of the 2D layered coordination polymer 1 have been obtained. The interest for this complex is two-fold. First, complex 1 is made of 2D layers packing along the (0–11) direction favored by the presence of lattice and coordinated water molecules. And second, nanostructures that could be derived by delamination are potentially suitable for catalytic purposes. Therefore it represents an excellent example to study the role of interlayer solvent molecules on the ultrasound-assisted delamination of functionally-active 2D metal-organic frameworks in water, a field of growing interest. With this aim, ultrasound-assisted delamination of the crystals was optimized with time, leading to stable nanosheet colloidal water suspensions with very homogeneous dimensions. Alternative bottom-up synthesis of related nanocrystals under ultrasound sonication yielded similar shaped crystals with much higher size dispersions. Finally, experimental results evidence that the nanostructures have higher catalytic activities in comparison to their bulk counterparts, due to larger metallic center exposition. These outcomes confirm that the combination of liquid phase exfoliation and a suitable synthetic design of 2D coordination polymers represents a very fruitful approach for the synthesis of functional nanosheets with an enhancement of catalytic active sites, and in general, with boosted functional properties., This work was supported by grant RTI2018-098027-B-C21 from the Spanish Government funds and by the European Regional Development Fund (ERDF). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706). Noemí Contreras Pereda’s project that gave rise to these results received the support of a fellowship from “laCaixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/ES17/11600012. Renhao Dong acknowledgements the financial support from ERC Starting Grant (FC2DMOF, No. 852909) and DFG project (SPP 1928, COORNETs).

Correction to: Nature Communications https://doi.org/10.1038/s41467-020-15141-y, published online 16 March 2020. The original version of this Article did not acknowledge Renhao Dong as a corresponding author. This has now been corrected in both the PDF and HTML versions of the Article.

Highly effective electrocatalysts promoting CO2 reduction reaction (CO2RR) is extremely desirable to produce value-added chemicals/fuels while addressing current environmental challenges. Herein, we develop a layer-stacked, bimetallic two-dimensional conjugated metal-organic framework (2D c-MOF) with copper-phthalocyanine as ligand (CuN4) and zinc-bis(dihydroxy) complex (ZnO4) as linkage (PcCu-O8-Zn). The PcCu-O8-Zn exhibits high CO selectivity of 88%, turnover frequency of 0.39 s−1 and long-term durability (>10 h), surpassing thus by far reported MOF-based electrocatalysts. The molar H2/CO ratio (1:7 to 4:1) can be tuned by varying metal centers and applied potential, making 2D c-MOFs highly relevant for syngas industry applications. The contrast experiments combined with operando spectroelectrochemistry and theoretical calculation unveil a synergistic catalytic mechanism; ZnO4 complexes act as CO2RR catalytic sites while CuN4 centers promote the protonation of adsorbed CO2 during CO2RR. This work offers a strategy on developing bimetallic MOF electrocatalysts for synergistically catalyzing CO2RR toward syngas synthesis., Effective electrocatalyst is crucial in promoting CO2 reduction to address current energy/environmental issue. Here, the authors develop bimetallic layered two-dimensional conjugated metal-organic framework to synergistically and efficiently electro-catalyze CO2 to CO toward syngas synthesis.

A simple, one-step and amplified Hg2+ detection strategy based on DNAzyme motor was described here. Fluorophore labeled DNA probes and long arm DNA are immobilized on the AuNPs by Au-S bond. The fluorescent signal of DNA probe is significantly quenched by AuNPs. In the presence of Hg2+, thymine-Hg2+-thymine (T-Hg2+-T) interaction can causes the duplex structure of split E-DNA and then form an entire E-DNA. Then the E-DNA can bind with fluorophore labeled DNA to form Mg2+-dependent DNAzyme structure. With the assistance of Mg2+, the fluorophore labeled DNA can be circularly cleaved by DNAzyme and then leave from the AuNPs surface. The recycling cleavage and binding processes caused processive moving of E-DNA on AuNPs surface and significant fluorescent signal recovery. A good linear relationship was obtained between fluorescence intensity and Hg2+ concentration in the range from 0.1 nM to 5 nM. The limit of detection was calculated to be 30 pM. This strategy was successfully used for detection of Hg2+ in Chinese herbs (Atractylodes macrocephala Koidz), showing a promising practical application future.

A novel fluorescent and colorimetric strategy with enzyme-free dual amplification was developed for ultra-sensitively detection of uranyl in river waters samples. The enzyme-strand recycling and hairpin catalytic assembly (HCA) reaction were used as dual enzyme-free amplification strategies. Three hairpins labeled with fluorophore can absorb on the surface of gold nanoparticles (AuNPs) to prevent them from aggregation in salt solution and quench the fluorescent signal simultaneously. In the presence of UO22+, the HCA reaction between hairpins was induced to form rigid DNA triangles, resulting in the aggregation of AuNPs with a red to blue color change and a “turn-on” fluorescent signal. The limit of detection was as low as 0.1 pM. Importantly, this strategy provided colorimetric and fluorescent dual signals for lower false-positives and higher anti-interference ability. It was successfully used for detection of uranyl in real waters samples.

Herein, a fast and visible colorimetric method for bisphenol A (BPA) detection was developed using hemin-functionalized reduced graphene oxide (H–rGO) composites and aptamer. The aptamer can be stably adsorbed on the surface of H–rGO, preventing H–rGO from salt-induced aggregation. However, in the presence of BPA, the aptamer can bind with BPA; this results in the aggregation of H–rGO. Consequently, the supernatant contains a little H–rGO and shows light blue color after the chromogenic reaction. The color difference can be used for the quantitative detection of BPA. The designed aptasensor displayed a linear response for BPA in the range from 5 nM to 100 nM with a detection limit of 2 nM. This colorimetric aptasensing platform offered great advantages, including label-free conditions and visible result readout platform, for quick screening of BPA for on-site analysis and in-house diagnosis.

2D conjugated metal–organic frameworks (2D c‐MOFs) are emerging as electroactive materials for chemiresistive sensors, but selective sensing with fast response/recovery is a challenge. Phthalocyanine‐based Ni2[MPc(NH)8] 2D c‐MOF films are presented as active layers for polarity‐selective chemiresisitors toward water and volatile organic compounds (VOCs). Surface‐hydrophobic modification by grafting aliphatic alkyl chains on 2D c‐MOF films decreases diffused analytes into the MOF backbone, resulting in a considerably accelerated recovery progress (from ca. 50 to ca. 10 s) during humidity sensing. Toward VOCs, the sensors deliver a polarity‐selective response among alcohols but no signal for low‐polarity aprotic hydrocarbons. The octadecyltrimethoxysilane‐modified Ni2[MPc(NH)8] based sensor displays high‐performance methanol sensing with fast response (36 s)/recovery (13 s) and a detection limit as low as 10 ppm, surpassing reported room‐temperature chemiresistors., Surface‐modification of phthalocyanine‐based two‐dimensional conjugated metal‐organic framework (2D c‐MOF) films by grafting aliphatic alkyl chains is developed for achieving high‐performance polarity‐selective chemiresistive sensing toward humidity and polar alcohols.

Rechargeable sodium-iodine (Na-I2 ) batteries are attracting growing attention for grid-scale energy storage due to their abundant resources, low cost, environmental friendliness, high theoretical capacity (211 mAh g-1 ), and excellent electrochemical reversibility. Nevertheless, the practical application of Na-I2 batteries is severely hindered by their poor cycle stability owing to the serious dissolution of polyiodide in the electrolyte during charge/discharge processes. Herein, the atomic modulation of metal-bis(dihydroxy) species in a fully conjugated phthalocyanine copper metal-organic framework (MOF) for suppression of polyiodide dissolution toward long-time cycling Na-I2 batteries is demonstrated. The Fe2 [(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Cu] MOF composited with I2 (Fe2 -O8 -PcCu/I2 ) serves as a cathode for a Na-I2 battery exhibiting a stable specific capacity of 150 mAh g-1 after 3200 cycles and outperforming the state-of-the-art cathodes for Na-I2 batteries. Operando spectroelectrochemical and electrochemical kinetics analyses together with density functional theory calculations reveal that the square planar iron-bis(dihydroxy) (Fe-O4 ) species in Fe2 -O8 -PcCu are responsible for the binding of polyiodide to restrain its dissolution into electrolyte. Besides the monovalent Na-I2 batteries in organic electrolytes, the Fe2 -O8 -PcCu/I2 cathode also operates stably in other metal-I2 batteries like aqueous multivalent Zn-I2 batteries. Thus, this work offers a new strategy for designing stable cathode materials toward high-performance metal-iodine batteries.