Covalent organic frameworks (COFs) are crystalline, permanently porous, two-dimensional or three-dimensional polymers with tunable topology and functionality. COFs linked with imines or ...β-ketoenamines are more chemically stable than their boron-linked counterparts, making them more promising for a broad range of applications, including energy storage devices, proton-conductive membranes, and catalyst supports. We report a general and scalable method for synthesizing imine- and β-ketoenamine-linked COFs based on the formal transimination of N-aryl benzophenone imines. These substrates are often the synthetic precursors of traditional polyfunctional aryl amine monomers and are more stable, soluble, and easy to handle and purify. The imine- and β-ketoenamine-linked COFs obtained from this approach show excellent materials quality, as characterized by X-ray diffraction and surface area analysis. The most optimized COF exhibited a Brunauer–Emmett–Teller surface area (>2600 m2/g) very close to its theoretical value (2830 m2/g). This method is amenable to both conventional solvothermal conditions and microwave heating, providing similar or even improved materials quality with shorter reaction times. The high materials quality, scalability, and availability of benzophenone imine monomers are all attractive features of this approach.
Electrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than ...batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.
Heteroatom doping and oxygen functionalizations are a promising solution to improve the energy storage performance of nanocarbon materials. The fundamental effects of doping and oxygen functionalization on the physicochemical properties of nanocarbons leading to enhanced supercapacitor performance are reviewed. This article may serve as a reference for fundamental properties and practical applications of heteroatom doped and oxygen functionalized nanocarbons.
Multi‐resonance induced by boron and nitrogen atoms in opposite resonance positions endows a thermally activated delayed fluorescence (MR‐TADF) emitter with a strikingly small full width at half ...maximum of only 26 nm and excellent photoluminescence quantum yield of up to 97.48 %. The introduction of a carbazole unit in the para position of the B‐substituted phenyl‐ring can significantly boost up the resonance effect without compromising the color fidelity, subsequently enhancing the performances of the corresponding pure blue TADF‐OLED, with an outstanding external quantum efficiency (EQE) up to 32.1 % and low efficiency roll‐off, making it one of the best TADF‐OLEDs in the blue region to date. Furthermore, utilizing this material as host for a yellow phosphorescent emitter, the device also shows a significantly reduced turn‐on voltage of 3.2 V and an EQEmax of 22.2 %.
Strong enhancement of the multi‐resonance effect in thermally activated delayed fluorescence species by a peripheral carbazole unit substitution was applied for a material with a photoluminescent quantum yield of up to 97.48 %. The maximum luminance exceeded 16 000 cd m−2 and the highest external quantum efficiency was up to 32.1 %.
Reverse osmosis (RO) based desalination is one of the most important and widely recognized technologies for production of fresh water from saline water. Since its conception and initiation, a ...significant development has been witnessed in this technology w.r.t. materials, synthesis techniques, modification and modules over the last few decades. The working of a RO plant inclusive of the pretreatment and post-treatment procedures has been briefly discussed in the article. The main objective of this review is to highlight the historical milestones achieved in RO technology in terms of membrane performance, the developments seen over the last few years and the challenges perceived.
The material properties of the membrane dominate the performance of a RO process. The emergence of nano-technology and biomimetic RO membranes as the futuristic tools is capable of revolutionizing the entire RO process. Hence the development of nano-structured membranes involving thin film nano-composite membranes, carbon-nanotube membranes and aquaporin-based membranes has been focussed in detail. The problems associated with a RO process such as scaling, brine disposal and boron removal are briefed and the measures adopted to address the same have been discussed.
•RO based desalination is one of the most important technologies for the production of fresh water.•This review highlights about important milestones in RO technology.•The material property, mainly dominates the RO process.•Few of the problems associated with RO technology is also discussed.
Freie Borylene (R‐B:) konnten bislang lediglich spektroskopisch in der Gasphase oder in Tieftemperatur‐Matrices charakterisiert werden. In der letzten Zeit gelang es jedoch, einige Mono‐ und ...Di(Lewis‐Base)‐stabilisierte Borylene zu isolieren. In beiden Verbindungen ist das Boratom durch die formale Oxidationsstufe +I gekennzeichnet, während es sich in klassischen Organoborverbindungen in der Oxidationsstufe +III befindet. Mono(Lewis‐Base)‐stabilisierte Borylene sind isoelektronisch zu Singulett‐Carbenen, und ihre Reaktivität ähnelt teilweise der von Übergangsmetallen, etwa bei der Aktivierung kleiner Moleküle (wie H2) und der Koordination weiterer Liganden. Di(Lewis‐Base)‐Borylen‐Addukte sind isoelektronisch zu Aminen und Phosphanen. Im Unterschied zu Boranen, die als Elektronenakzeptoren fungieren, sind diese Spezies elektronenreich und eignen sich als Liganden für Übergangsmetalle.
Organoborverbindungen als Carben‐ und Aminanaloga: Im Gegensatz zu klassischen Organoborverbindungen, die sich als Lewis‐Säuren verhalten und in denen Bor die Oxidationsstufe +III einnimmt, kennzeichnet Mono‐ und Di(Lewis‐Base)‐Borylen‐Addukte ein nucleophiler Charakter, und das Boratom befindet sich in der Oxidationsstufe +I. Dieses Forschungsgebiet steckt noch in den Anfängen, verspricht aber viele Entdeckungen.
Ammonia borane H3NBH3, first reported in 1955, is isoelectronic with ethane H3CCH3, but it has much different properties owing to (i) the nitrogen and boron atoms (leading to a dipole moment), (ii) ...the protic and hydridic hydrogens, and (iii) the heteropolar dihydrogen bonding (rationalizing its solid state at ambient conditions). Ammonia borane has exceptional properties for chemical hydrogen storage and the recent years have witnessed many efforts in making it implementable for both thermolytic and hydrolytic dehydrogenations. The present article aims at (1) giving an exhaustive overview of the 1955–2016 literature dedicated to ammonia borane's fundamentals and exceptional properties, and then (2) surveying the main achievements, limitations and challenges for chemical hydrogen storage.
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•Ammonia borane H3NBH3 has attractive properties owing to the N and B atoms.•Ammonia borane has in fact exceptional properties for chemical hydrogen storage.•Ammonia borane is implementable for thermolytic and hydrolytic dehydrogenations.•An exhaustive overview of the 1955–2016 literature is given herein.•The main achievements, limitations and challenges are surveyed.
The intermolecular radical addition to the carbonyl group is difficult due to the facile fragmentation of the resulting alkoxyl radical. To date, the intermolecular radical addition to ketones, a ...valuable approach to construct quaternary carbon centers, remains a formidable synthetic challenge. Here, we report the first visible-light-induced intermolecular alkyl boronic acid addition to α-ketoacids enabled by the Lewis acid activation. The in situ boron complex formation is confirmed by various spectroscopic measurements and mechanistic probing experiments, which facilitates various alkyl boronic acid addition to the carbonyl group and prevents the cleavage of the newly formed C–C bond. Diversely substituted lactates can be synthesized from readily available alkyl boronic acids and ketoacids at room temperature merely under visible light irradiation, without any additional reagent. This boron activation approach can be extended to alkyl dihydropyridines as radical precursors with external boron reagents for primary, secondary, and tertiary alkyl radical additions. The pharmaceutically useful anticholinergic precursors are easily scaled up in multigrams under metal-free conditions in flow reactors.
•The composition of electrodeposited NiCu nanoparticles is controlled by the value of the deposition potential.•Metallic NiCu nanoparticles enriched with Ni show BOR activity comparable to metallic ...Ni.•NiCu nanoparticles demonstrate higher resistance against electrochemical oxidation and improved reducibility than Ni nanoparticles.•Surface oxidation at mild conditions results in a significant decrease of BOR currents on Ni, but slightly affects the performance of NiCu nanoparticles of certain compositions.
Development cost-effective and stable electrocatalysts for the borohydride oxidation reaction (BOR) is mandatory for the deployment of the direct borohydride fuel cells (DBFC). Ni electrocatalysts have recently been shown to outperform noble-metal (Pt, Pd, Au) catalysts at low BOR overpotentials, but their activity largely depends on the state of the Ni surface with metallic Ni demonstrating the highest activity. Here, bimetallic NiCu nanoparticles of different compositions were prepared, which demonstrate high BOR activity comparable to Ni nanoparticles in the metallic state of their surface and allow to overcome in considerable extent the negative issues related to inevitable surface passivation.
Triarylboron compounds have attracted much attention, and found wide use as functional materials because of their electron‐accepting properties arising from the vacant p orbitals on the boron atoms. ...In this study, we design and synthesize new donor–acceptor triarylboron emitters that show thermally activated delayed fluorescence. These emitters display sky‐blue to green emission and high photoluminescence quantum yields of 87–100 % in host matrices. Organic light‐emitting diodes using these emitting molecules as dopants exhibit high external quantum efficiencies of 14.0–22.8 %, which originate from efficient up‐conversion from triplet to singlet states and subsequent efficient radiative decay from singlet to ground states.
Triarylboron‐based emitters are reported that show high photoluminescence quantum yields and efficient up‐conversion from triplet to singlet states. Organic light‐emitting diodes (OLEDs) using these emitters show a maximum external quantum efficiency of 21.6 % for a sky‐blue OLED and 22.8 % for a green OLED.
Heteroatom-doped carbons have drawn increasing research interest as catalysts for various electrochemical reactions due to their unique electronic and surface structures. In particular, co-doping of ...carbon with boron and nitrogen has been shown to provide significant catalytic activity for oxygen reduction reaction (ORR). However, limited experimental work has been done to systematically study these materials, and much remains to be understood about the nature of the active site(s), particularly with regards to the factors underlying the activity enhancements of these boron–carbon–nitrogen (BCN) materials. Herein, we prepare several BCN materials experimentally with a facile and controlled synthesis method, and systematically study their electrochemical performance. We demonstrate the existence of h-BN domains embedded in the graphitic structures of these materials using X-ray spectroscopy. These synthesized structures yield higher activity and selectivity toward the 2e– ORR to H2O2 than structures with individual B or N doping. We further employ density functional theory calculations to understand the role of a variety of h-BN domains within the carbon lattice for the ORR and find that the interface between h-BN domains and graphene exhibits unique catalytic behavior that can preferentially drive the production of H2O2. To the best of our knowledge, this is the first example of h-BN domains in carbon identified as a novel system for the electrochemical production of H2O2.
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