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The oxygen reduction reaction (ORR) that for instance takes place at the cathode of fuel cells is one of the most examined model reactions of energy conversion. The ORR presents sluggish reaction kinetics, thus limiting the overall efficiency of these cells. Pt-based catalysts are still the widest choice though they exhibit important drawbacks such as long-term instability and intolerance to methanol crossover. In this context, engineering transition metals in the form of nano- and subnano-sites on carbonaceous supports has the potential of becoming an alternative to scarce noble metal-based catalysts. Herein, we describe a simple synthetic route towards CuII/CuI decorated N-doped carbonaceous ORR electrocatalysts. CuII/CuI nanosites are obtained by calcination in air of an ionic liquid derived noble carbonaceous support impregnated with copper(II) acetate. The strong interaction between the copper and the noble support foster the co-formation of CuII/CuI nanosites. Larger amounts of copper(II) acetate translate into larger amounts of CuI and lower Tafel slopes. The material with 4 wt% of copper catalyzes the selective reduction of oxygen through a 4-electron transfer pathway and exhibits a lower Tafel slope than commercial platinum, a minimal overpotential, and a higher limiting current density. Moreover, all materials show promising durability and high methanol stability, which makes them promising to replace noble metals for the ORR. [ABSTRACT FROM AUTHOR]

The hydrogen evolution reaction (HER) is a complex reaction involving many interdependent physicochemical steps. Highly ordered carbon nitride‐based materials, such as Na‐PHI and K‐PHI, display some of the highest activities for H2 evolution among the carbon nitride‐based materials, due to their electronic properties, but also the presence of cyanimide terminations, which favors the charge transfer for the Pt cocatalyst nanoparticles (NPs). For such highly optimized semiconductor structures, the necessity to control and improve other steps of the photocatalytic process becomes essential, in particular the poor electron transfer from the Pt NPs to the protons in solution over the Helmholtz or Stern layer. Taking highly ordered Na‐PHI as a test material, the influence of water‐dissolved alkali cations on the HER is systematically studied and it is experimentally verified that the electron transfer from the Pt NPs to the protons in solution limits the efficiency of heterogeneous carbon nitride‐based catalysts. This paper explains how hydrated alkali cations influence electron transfer and are able to boost the H2 evolution rate of the same Na‐PHI from 2401 up to 5330 µmol h−1 g−1 with an apparent quantum yield of 13% at 420 nm. [ABSTRACT FROM AUTHOR]

Polymer brushes on surfaces enable advanced material design. In the present contribution, transparent and flat photoactive polymeric carbon nitride (pCN) thin films are employed as a photoactive substrate and primer layer to grow polystyrene (PS) brushes. These films are then characterized by ellipsometry. For the first time herein is reported on the optical anisotropy of pCN thin films revealing a high positive birefringence up to 0.71 with an in‐plane nD of 2.54 making this material of high interest for photonic devices. Furthermore and rather surprising, the photografted polystyrene brushes exhibit an unusual high negative birefringence, too. This negative birefringence can be attributed to a practically complete stretching of the polymer chains throughout growth in the radical chain process. As the stretched PS brushes grafted from the pCN surfaces also provide unusual surface properties, the overall system can be of great interest for photonics, but also as mechanical coating and membranes for gas separation. [ABSTRACT FROM AUTHOR]

Multistep synthesis of novel amphiphilic polybutadiene-block-poly (L-glutamate) copolymers is described. This system can perform a coil-helix transformation without changing the morphology.

Photocatalytic H2 production via water splitting holds great potential for the conversion of solar energy into renewable and storable chemical fuels in a sustainable manner, but this up-hill reaction is mainly hindered by the water oxidation process. This reaction is sluggish and relies on high overpotentials (wasted energy), while only oxygen is generated as a low value oxidation by-product. Coupling hydrogen generation to a less unfavorable oxidation reaction creating higher value products is therefore a recommendable issue. Here we found that poly(heptazine imide) (PHI), a stable and reactive allotrope of crystalline carbon nitride, supported with highly dispersed Pt nanoparticles (PtNPs) could achieve efficient and persistent H2 and CH4 production by photocatalytic reforming of biomass derived alcohols under visible light irradiation. The results reveal that PHI with low grain boundary defects restrains the bulk charge carrier recombination and largely promotes photocatalytic efficiency. The apparent quantum efficiency (AQE) of the optimized material for visible light H2 evolution could reach values as high as 15% at 420 nm. The DFT results reveal that the activity is associated with the Tafel step rather than the Volmer–Tafel step. This study highlights the development of a new covalent scaffold for the simultaneous generation of storable and valuable chemical fuels (H2 and CH4) in a feasible photocatalytic manner. [ABSTRACT FROM AUTHOR]

Sodium lignosulfonate (LS) was valorized to low molecular weight (Mw) fractions by combining solvothermal (SF) and catalytic hydrogenolysis/hydrogenation fragmentation (SHF) in a continuous flow system. This was achieved in either alcohol/H2O (EtOH/H2O or MeOH/H2O) or H2O as a solvent and Ni on nitrogen-doped carbon as a catalyst. The tunability according to the temperature of both SF and catalytic SHF of LS has been separately investigated at 150 °C, 200 °C, and 250 °C. In SF, the minimal Mw was 2994 g mol−1 at 250 °C with a dispersity (Đ) of 5.3 using MeOH/H2O. In catalytic SHF using MeOH/H2O, extremely low Mw was found (433 mg gLS−1) with a Đ of 1.2 combined with 34 mg gLS−1. The monomer yield was improved to 42 mg gLS−1 using dual catalytic beds. These results provide direct evidence that lignin is an unstable polymer at elevated temperatures and could be efficiently deconstructed under hydrothermal conditions with and without a catalyst. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) have been extensively investigated as a promising alternative for lithium ion batteries (LIBs) owing to the readily available character of sodium, lower costs of battery systems, as well as a similar working mechanism to LIBs. However, this view turns out to be oversimplified; countless reviews especially in the last years contradict each other, and it is still a challenging task to design highly performing electrode materials for SIBs. Due to the larger radius of Na+, its lower covalent character, and the resulting changes in intercalation chemistry, sodium is far from being only the bigger relative of lithium, and the difference leads to altered loading curves, and the occurrence of a multiplicity of binding sites. An in‐depth holistic understanding of the sodium storage mechanisms is needed to resolve the controversial discussions in the research community, ideally starting with unquestionable thermodynamic points. Here, taking a tutorial perspective, first the recent discussions on the storage mechanism of sodium in carbons are reviewed from an unorthodox viewpoint, namely addressing sodium uptake as a multifaceted adsorption process with an added electrochemical binding potential. This model is based on literature data. Afterward, challenges and perspectives revealed by such a model are discussed. [ABSTRACT FROM AUTHOR]

The hydrosilylation reaction is one of the largest‐scale applications of homogeneous catalysis, and Pt homogeneous catalysts have been widely used in this reaction for the commercial manufacture of silicon products. However, homogeneous Pt catalysts result in considerable problems, such as undesired side reactions, unacceptable catalyst residues and disposable platinum consumption. Here, we synthesized electron‐deficient Pt single atoms supported on humic matter (Pt1@AHAU400), and the catalyst was used in hydrosilylation reactions, which showed super activity (turnover frequency as high as 3.0×107 h−1) and selectivity (>99 %). Density functional theory calculations reveal that the high performance of the catalyst results from the atomic dispersion of Pt and the electron deficiency of the Pt1 atoms, which is different from conventional Pt nanoscale catalysts. Excellent performance is maintained during recycle experiments, indicating the high stability of the catalyst. [ABSTRACT FROM AUTHOR]

We designed a metal‐free synthesis of carbon nanofiber based on ketene chemistry using phosphorus pentoxide (P2O5) and vegetable oil. Based on the characterization of intermediates, P2O5‐oil reaction yielded most possibly alkylketenes, which polymerized into poly(ketene) with abundant enol groups. The enol groups further reacted with P2O5, forcing the poly(ketene) to assemble into a nano‐sized preassembly structure. Moderate heating transforms these structures into carbonaceaus nanofibers. This approach is applicable to other chemicals with similar structure to vegetable oil. The carbon nanofibers with P‐O‐C functionalization show relatively high graphitization degree and promising textural properties. The C‐O‐P environment accounts for 66 at % of the total P and creates a superior thermal stability. As a model application, a CDI system built of a carbon‐nanofiber‐based electrode countered by an activated carbon‐based electrode exhibited exceptional performance. [ABSTRACT FROM AUTHOR]

Following our previous studies on potassium poly(heptazine imide) (K‐PHI), that is, catalyzed photooxidative [3+2] aldoxime‐to‐nitrile addition to form 1,2,4‐oxadiazoles, we discovered that electron‐rich oximes yield the parent aldehydes instead of target products. In this work, the mechanism of this singlet oxygen‐mediated deoximation process was established using a series of control reactions and spectroscopic measurements such as steady‐state and time‐resolved fluorescence quenching experiments. Additionally, the singlet‐triplet energy gap value was obtained for K‐PHI in suspension, and the reaction scope was broadened to include ketoximes. [ABSTRACT FROM AUTHOR]

The interaction between water molecules and surfaces in porous systems is of huge importance in various fields including but not limited to catalysis, adsorption, and the storage or conversion of electrochemical energy. Hydrophilicity of usually non-polar carbon-based materials can be enhanced by the incorporation of heteroatoms like nitrogen but insights into the interaction mechanisms on a molecular level remain hardly achievable due to the lack of porous carbons with a defined and regular atomic construction and a suitable structure model for such substances. This makes theoretical calculations difficult. In order to illuminate the interactions between nitrogen-containing carbon surfaces and water molecules, water adsorption is studied in this work on a series of model materials with different pore structures and atomic construction. In particular, volumetric adsorption measurements and 1H solid-state NMR spectroscopic investigations in combination with theoretical calculations on water in nitrogen-rich C2N materials show a remarkably strong heat of adsorption significantly above 60 kJ mol−1, that is, far beyond what is typically considered physisorption. In such porous materials, water is becoming an integral part of the chemical architecture, and the term "zeocarbons" is therefore well deserved. From a general perspective, this study is intended to set a base for establishing the chemical principles of a new water chemistry confined in strongly interacting nanopores. [ABSTRACT FROM AUTHOR]

The inclusion of the metal free semiconductor graphitic carbon nitride (g‐CN) into polymer systems brings a variety of new options, for instance as a heterogeneous photoredox polymer initiator. In this context, we present here the decoration of the inner surface of poly(styrene‐co‐divinylbenzene) beads with organomodified g‐CN via one pot suspension photopolymerization. The resulting beads are varied by changing reaction parameters, such as, crosslinking ratio, presence of porogens, and mechanical agitation. The photocatalytic activity of so‐formed beads was tested by aqueous rhodamine B dye photodegradation experiments. Additionally, dye adsorption/desorption properties were examined in aqueous as well as in organic solvents. Photoinduced surface modification with vinylsulfonic acid and 4‐vinyl pyridine is introduced. Overall, metal‐free semiconductor g‐CN donates photoactivity to polymer networks that can be employed for dye photodegradation and acid–base catalyst transformation through facile photoinduced surface modifications. [ABSTRACT FROM AUTHOR]

Ternary materials made up only from the lightweight elements boron, carbon, and nitrogen are very attractive due to their tunable properties that can be obtained by changing the relative elemental composition. However, most of the times, the synthesis requires to use up to three different precursor and very high temperatures for the synthesis. Moreover, the low reciprocal solubility of boron nitride and graphene often leads to BN‐C composite materials due to phase segregation. Herein, an innovative method is presented to prepare BCN thin films by chemical vapor deposition from a single source precursor, melamine diborate. The deposition occurs homogenously at relatively low temperatures generating very high degree of sp2 conjugation. The as‐prepared thin films possess high transparency and refractive index values in the visible range that are of interest for reflective mirrors and lenses. Furthermore, they are wide‐bandgap semiconductor with very positive valence band, making these materials very stable against oxidation of interest as protective coating and charge transport layer for solar cells. The simple chemical vapor deposition method that relies on commonly available and low‐hazard precursor can open the way for application of BCN thin films in optics, optoelectronics, and beyond. [ABSTRACT FROM AUTHOR]

Among external stimuli used to promote a chemical reaction, photocatalysis possesses a unique one—light. Photons are traceless reagents that provide an exclusive opportunity to alter chemoselectivity of the photocatalytic reaction varying the color of incident light. This strategy may be implemented by using a sensitizer capable to activate a specific reaction pathway depending on the excitation light. Herein, we use potassium poly(heptazine imide) (K‐PHI), a type of carbon nitride, to generate selectively three different products from S‐arylthioacetates simply varying the excitation light and otherwise identical conditions. Namely, arylchlorides are produced under UV/purple, sulfonyl chlorides with blue/white, and diaryldisulfides at green to red light. A combination of the negatively charged polyanion, highly positive potential of the valence band, presence of intraband states, ability to sensitize singlet oxygen, and multi‐electron transfer is shown to enable this chromoselective conversion of thioacetates. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Conductive polymers find key applications ranging from optoelectronics and OLEDs to conductive composite materials. The synthesis of conductive polymers from monomers, such as thiophene derivatives, pyrroles and aniline, mainly relies on oxidative polymerization, and the processing of so‐formed (insoluble) polymers is a major issue that needs to be addressed. In the present work, oxidative photopolymerization of 3,4‐ethylenedioxythiophene (EDOT) by visible light employing the metal‐free semiconductor graphitic carbon nitride (g‐CN) is presented. Two main reaction pathways based on g‐CN content are described, and the formation of processable oligo‐EDOT is demonstrated. [ABSTRACT FROM AUTHOR]

The chemistry of humic substances (HSs) occurs hidden from our sight, but is of key importance to agriculture and the environment, and nowadays even to medicine and technology. HSs are nowadays not only natural, but extracted and engineered, and in the past 20 years such products have been widely used in soil improvement and environment governance. In this review, we collate and summarize the applications and working principles of such HSs in agriculture and environmental ecology, mainly to elaborate the multiple roles of this functional polymer along with physical chemical quantification. Then several of the latest synthesis technologies, including hydrothermal humification technology (HTH), hydrothermal carbonization technology (HTC) and hydrogen peroxide oxidation technology (HOT) are presented, which were introduced to prepare artificial humic substances (A-HSs). The availability of reproducible and tunable synthetic A-HSs is a new chemical tool, and effects such as solubilization of insoluble phosphorus minerals, recovery of phosphorus, improvement of soil fertility for crop growth and reduction of toxicity of typical pollutants, can now be analyzed in detail and quantified. As a result, we can provide an effective chemical technology for utilizing biomass side products ("biowaste") to generate A-HSs of different types, thus realizing improvement in agricultural production and control of environmental pollution by the macro-synthesis of A-HSs-. [ABSTRACT FROM AUTHOR]

To render the sodium ion battery (SIB) competitive among other technologies, the processes behind sodium storage in hard carbon anodes must be understood. For this purpose, electrochemical impedance spectroscopy (EIS) is usually undervalued, since fitting the spectra with equivalent circuit models requires an a priori knowledge about the system at hand. The analysis of the distribution of relaxation times (DRT) is an alternative, which refrains from fitting arbitrarily nested equivalent circuits. In this paper, the sodiation and desodiation of a hard carbon anode is studied by EIS at different states of charge (SOC). By reconstructing the DRT function, highly resolved information on the number and relative contribution of individual electrochemical processes is derived. During the sloping part of the sodiation curve, mass transport is found to be the most dominant source of resistance but rapidly diminishes when the plateau phase is reached. An equivalent circuit model qualitatively reproducing the experimental data of the sloping region was built upon the DRT results, which is particularly useful for future EIS studies on hard carbon SIB anodes. More importantly, this work contributes to establish EIS as a practical tool to directly study electrode processes without the bias of a previously assumed model. [ABSTRACT FROM AUTHOR]

In photocatalysis, small organic molecules are converted into desired products using light responsive materials, electromagnetic radiation, and electron mediators. Substitution of low molecular weight reagents with redox active functional materials may increase the utility of photocatalysis beyond organic synthesis and environmental applications. Guided by the general principles of photocatalysis, we design hybrid nanocomposites composed of n‐type semiconducting potassium poly(heptazine imide) (K‐PHI), and p‐type conducting poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the redox active substrate. Electrical conductivity of the hybrid nanocomposite, possessing optimal K‐PHI content, is reversibly modulated combining a series of external stimuli ranging from visible light under inert conditions and to dark conditions under an O2 atmosphere. Using a conductive polymer as the redox active substrate allows study of the photocatalytic processes mediated by semiconducting photocatalysts through electrical conductivity measurements. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A novel method based on the use of reactive eutectic media for the extraction of cellulose nanocrystals and their functionalization with positively charged functional groups in a one-step procedure is presented. With its ability to form strong hydrogen bonds, the eutectic medium serves as a cellulose-solubilizing agent, while the presence of a Leuckart reagent provides the reactivity toward the reductive amination of carbonyl groups in the cellulose chains. In the proposed method, amorphous cellulose domains are partially dissolved by undergoing aminolysis, resulting in the formation of water-dispersible nanocellulose products with high crystallinity. [ABSTRACT FROM AUTHOR]

We report the synthesis of 1,4-dicarbonyl compounds and substituted alkenes (Mizoroki–Heck type coupling) starting from secondary and tertiary alkyl halides and vinyl acetate or styrene derivatives using visible-light photocatalysis. The protocol uses mesoporous graphitic carbon nitride (mpg-CN) as a heterogeneous organic semiconductor photocatalyst and Ni(II) salts as Lewis acid catalysts. Detailed post-characterization of the heterogeneous material has been carried out to support the proposed catalytic cycle. Apart from high functional-group tolerance, mild reaction conditions, scalability as well as easy recovery and reuse of the mpg-CN photocatalyst provide a practical solution to these widespread transformations in terms of sustainability and efficiency and this methodology is recommended for applications in academic and industrial synthesis. [ABSTRACT FROM AUTHOR]

A network of aqueous emulsion droplets that exhibits programmed and directional chemical inter-droplet communication is described. A non-reciprocal transfer of substrates between enzyme-containing aqueous emulsion droplets is realized by (biochemically) induced osmolarity gradients and concomitant concentration gradients are used to direct a multistep enzymatic cascade reaction across multiple droplets. [ABSTRACT FROM AUTHOR]