No abstract

aromatic groups, which via columnar π-π stacking order into a periodic 3D structure (Scheme S1, Supporting Information). Their modular construct and ordered porosity makes them find use in diverse applications Here we are seeking application of 2D COFs in metal-ion batteries, which are typically made of electrodes with layered structures, for example, graphite as anode and LiCoO 2 as cathode. Owing to their graphite resembling structure, COF can serve as anode. Since their initial discovery, many 2D materials with comparable layered structures have been explored as lithium insertion-deinsertion materials. [28][29][30][31][32][33][34][35][36][37][38][39] Some of the highly desirable characteristics of a superior anode material include moderate to high surface accessibility to ensure maximum charge storage per unit area, and the other is the hierarchical porosity for favorable kinetics. Exfoliation enhances surface accessibility and active site creation in such 2D materials. [40][41][42][43][44][45][46][47][48] In this regard, COFs could have much more to offer. [49][50][51] Exfoliation in any 2D material is largely dependent on the interlayer forces holding them. Typically, the COF layers are held together by interlayer π-π interactions or in some cases via additional hydrogen bonding. [52,53] However, unlike graphite, the layers of COF are not built from fused aromatic rings. In their optimized Covalent organic framework (COF) can grow into self-exfoliated nanosheets. Their graphene/graphite resembling microtexture and nanostructure suits electrochemical applications. Here, covalent organic nanosheets (CON) with nanopores lined with triazole and phloroglucinol units, neither of which binds lithium strongly, and its potential as an anode in Li-ion battery are presented. Their fibrous texture enables facile amalgamation as a coin-cell anode, which exhibits exceptionally high specific capacity of ≈720 mA h g −1 (@100 mA g −1 ). Its capacity is retained even after 1000 cycles. Increasing the current density from 100 mA g −1 to 1 A g −1 causes the specific capacity to drop only by 20%, which is the lowest among all high-performing anodic COFs. The majority of the lithium insertion follows an ultrafast diffusion-controlled intercalation (diffusion coefficient, D Li + = 5.48 × 10 −11 cm 2 s −1 ). The absence of strong Liframework bonds in the density functional theory (DFT) optimized structure supports this reversible intercalation. The discrete monomer of the CON shows a specific capacity of only 140 mA h g −1 @50 mA g −1 and no sign of lithium intercalation reveals the crucial role played by the polymeric structure of the CON in this intercalation-assisted conductivity. The potentials mapped using DFT suggest a substantial electronic driving-force for the lithium intercalation. The findings underscore the potential of the designer CON as anode material for Li-ion batteries. Lithium Storage

Covalent organic frameworks (COFs) have structures and morphologies closely resembling graphenes, whose modular construction permits atomiclevel manipulations. This, combined with their porous structure, makes them excellent catalyst supports. Here, the high electrocatalytic activity of a composite, formed by supporting Ni 3 N nanoparticles on a benzimidazole COF, for oxygen evolution reaction is shown. The composite oxidizes alkaline water with a near-record low overpotential of 230 mV @ 10 mA cm −2 (η 10 ). This high activity is attributed to the ability of the COF to confine the Ni 3 N nanoparticles to size regimes otherwise difficult to obtain and to its low band gap character (1.49 eV) arising from the synergy between the conducting Ni 3 N nanoparticles and the π-conjugated COF. The COF itself, as a metalfree self-standing framework, has an oxygen evolution reaction activity with η 10 of 400 mV. The periodic structure of the COF makes it serve as a matrix to disperse the catalytically active Ni 3 N nanoparticles favoring their high accessibility and thereby good charge-transport within the composite. This is evident from the amount of O 2 evolved (230 mmol h −1 g −1 ), which, to the best of our knowledge, is the highest reported. The work reveals the emergence of COF as supports for electrocatalysts.

No abstract

Herein we report the effect of different nucleobase pair compositions on the association-induced fluorescence enhancement property of Thioflavin T (ThT), upon binding with 20 base pair long double-stranded DNA (dsDNA). Analysis of binding and decay constants along with the association (K ass ) and dissociation (K diss ) rate constants obtained from the fluctuation in the fluorescence intensity of ThT after binding with different DNA revealed selective affinity of ThT toward AT-rich dsDNA. Molecular docking also substantiates the experimental results. We also observed that addition of orange-emitting ethidium bromide (EtBr) to cyan-emitting ThT−DNA complexes leads to bright white light emission (WLE) through Forster resonance energy transfer. Additionally, the emission of white light is far greater in the case of intra-DNA strands. Besides endorsing the binding insights of ThT to AT-rich dsDNA, the present investigations open a new perspective for realizing promising WLE from two biomarkers without labeling the DNA.

COFs represent a class of polymers with designable crystalline structures capable of interacting with active metal nanoparticles to form excellent heterogeneous catalysts. Many valuable ligands/monomers employed in making coordination/organic polymers are prepared via Heck and C-C couplings. Here, we report an amphiphilic triazine COF and the facile single-step loading of Pd0 nanoparticles into it. An 18–20% nano-Pd loading gives highly active composite working in open air at low concentrations (Conc. Pd(0) <0.05 mol%, average TON 1500) catalyzing simultaneous multiple site Heck couplings and C-C couplings using ‘non-boronic acid’ substrates, and exhibits good recyclability with no sign of catalyst leaching. As an oxidation catalyst, it shows 100% conversion of CO to CO2 at 150 °C with no loss of activity with time and between cycles. Both vapor sorptions and contact angle measurements confirm the amphiphilic character of the COF. DFT-TB studies showed the presence of Pd-triazine and Pd-Schiff bond interactions as being favorable.

Covalent organic frameworks (COFs) are crystalline organic polymers with tunable structures. Here, a COF is prepared using building units with highly flexible tetrahedral sp3 nitrogens. This flexibility gives rise to structural changes which generate mesopores capable of confining very small (<2 nm sized) non‐noble‐metal‐based nanoparticles (NPs). This nanocomposite shows exceptional activity toward the oxygen‐evolution reaction from alkaline water with an overpotential of 258 mV at a current density of 10 mA cm−2. The overpotential observed in the COF‐nanoparticle system is the best in class, and is close to the current record of ≈200 mV for any noble‐metal‐free electrocatalytic water splitting system—the Fe–Co–Ni metal‐oxide‐film system. Also, it possesses outstanding kinetics (Tafel slope of 38.9 mV dec−1) for the reaction. The COF is able to stabilize such small‐sized NP in the absence of any capping agent because of the COF–Ni(OH)2 interactions arising from the N‐rich backbone of the COF. Density‐functional‐theory modeling of the interaction between the hexagonal Ni(OH)2 nanosheets and the COF shows that in the most favorable configuration the Ni(OH)2 nanosheets are sandwiched between the sp3 nitrogens of the adjacent COF layers and this can be crucial to maximizing their synergistic interactions.

Metal-organic frameworks (MOFs) have attracted significant attention as solid sorbents in gas separation processes for low-energy postcombustion CO capture. The parasitic energy (PE) has been put forward as a holistic parameter that measures how energy efficient (and therefore cost-effective) the CO capture process will be using the material. In this work, we present a nickel isonicotinate based ultramicroporous MOF, 1 [Ni-(4PyC)·DMF], that has the lowest PE for postcombustion CO capture reported to date. We calculate a PE of 655 kJ/kg CO, which is lower than that of the best performing material previously reported, Mg-MOF-74. Further, 1 exhibits exceptional hydrolytic stability with the CO adsorption isotherm being unchanged following 7 days of steam-treatment (>85% RH) or 6 months of exposure to the atmosphere. The diffusion coefficient of CO in 1 is also 2 orders of magnitude higher than in zeolites currently used in industrial scrubbers. Breakthrough experiments show that 1 only loses 7% of its maximum CO capacity under humid conditions.