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The use of light as a catalytic prompt for the synthesis of industrial relevant compounds is widely explored in the past years, with a special consideration over the hydrogen evolution reaction (HER). However, semiconductors for heterogeneous photocatalysis suffer from fast charge recombination and, consequently, low solar‐to‐hydrogen efficiency. These drawbacks can be mitigated by coupling photocatalysts with an external circuit that can physically separate the photogenerated charge carriers (electrons and holes). For this reason, photoelectrochemical (PEC) production of hydrogen is under the spotlight as promising green and sustainable technique and widely investigated in numerous publications. However, considering that a significant fraction of the hydrogen produced is used for reduction processes, the development of PEC devices for direct in situ hydrogenation can address the challenges associated with hydrogen storage and distribution. This Perspective aims at highlighting the fundamental aspects of HER from PEC systems, and how these can be harnessed toward the implementation of suitable settings for the hydrogenation of organic compounds of industrial value. [ABSTRACT FROM AUTHOR]

Time‐resolved EPR (TR‐EPR) demonstrates the formation of well‐defined spin triplet excitons in carbon nitride. This permits to experimentally probe the extent of the triplet wavefunction which delocalizes over several tri‐s‐triazine units. Analysis of the temperature dependence of the TR‐EPR signal reveals the mobility of the triplet excitons. By employing monochromatic light excitation in the range 430–600 nm, the energy of the spin triplet is estimated to be ≈0.2 eV above the conduction band edge, proving that the triplet exciton lies above the corresponding singlet. Comparison between amorphous and graphitic forms establishes the singlet‐triplet inversion as a general feature of carbon nitride materials. [ABSTRACT FROM AUTHOR]

2H−MoS2 is an appealing semiconductor because of its Earth‐abundant nature, cheapness, and low toxicity. This material has shown promising catalytic activity for various energy‐related processes, but its use in catalysis for C−C bond forming reactions towards useful organic compounds is still largely unexplored. The lack of examples in organic synthesis is mainly due to the intrinsic difficulties of using bulk 2H−MoS2 (e. g., low surface area), which implies the reliance on high catalytic loadings for obtaining acceptable yields. This makes the optimization process more expensive and tedious. Here, we report the development of a 2H−MoS2‐mediated synthesis of valuable bis(indolyl)methane derivatives, using indoles and benzaldehydes as starting materials. Exploiting the Design of Experiments (DoE) method, we identified the critical parameters affecting the catalytic performance of commercial 2H−MoS2 powder and optimized the reaction conditions. Lastly, we demonstrated that the catalytic system has versatility and good tolerance towards functional group variations of the reagents. [ABSTRACT FROM AUTHOR]

The use of graphitic carbon nitride (g‐CN) for the photocatalytic radical formylation of anilines, which represents a more sustainable and attractive alternative to the currently used approaches, is reported herein. Our operationally simple method occurs under mild conditions, employing air as an oxidant. In particular, the chemistry is driven by the ability of g‐CN to reach an electronically excited state upon visible‐light absorption, which has a suitable potential energy to trigger the formation of reactive α‐amino radical species from anilines. Mechanistic investigations also proved the key role of the g‐CN to form reactive superoxide radicals from O2 via single electron transfer. Importantly, this photocatalytic transformation provides a variety of functionalized formamides (15 examples, up to 89 % yield). [ABSTRACT FROM AUTHOR]

Carbon nitride (CN) is a heterogeneous photocatalyst that combines good structural properties and a broad scope. The photocatalytic efficiency of CN is associated with the presence of defective and radical species. An accurate description of defective states—both at a local and extended level—is key to develop a thorough mechanistic understanding of the photophysics of CN. In turn, this will maximise the generation and usage of photogenerated charge carriers and minimise wasteful charge recombination. Here the influence of morphology and light‐excitation on the number and chemical nature of radical defects is assessed. By exploiting the magnetic dipole‐dipole coupling, the spatial distribution of native radicals in CN is derived with high precision. From the analysis an average distance in the range 1.99–2.34 nm is determined, which corresponds to pairs of radicals located approximately four tri‐s‐triazine units apart. [ABSTRACT FROM AUTHOR]

In recent years, the field of dual photocatalysis has become an increasingly popular tool for the functionalization of organic substrates under mild operative conditions. Single‐atom heterogeneous catalysts (SACs), where the metal atoms are stabilized by means of properly structured photoactive supports, are currently one of the frontiers of this research field. To this end, Carbon Nitrides (CNs) have emerged as ideal two‐dimensional semiconducting supports, capable of stabilizing single metal sites (for instance: nickel, iron, among other) through nitrogen‐rich structures. This Concept highlights the recent advances in the synthesis of carbon nitride‐based SACs and their applications in light‐driven dual‐catalytic processes, also providing forward‐looking opportunities within this research area. [ABSTRACT FROM AUTHOR]

Recently, the field of dual photocatalysis has grown rapidly, to become one of the most powerful tools for the functionalization of organic molecules under mild conditions. In particular, the merging of Earth‐abundant nickel‐based catalytic systems with visible‐light‐activated photoredox catalysts has allowed the development of a number of unique green synthetic approaches. This goes in the direction of ensuring an effective and sustainable chemical production, while safeguarding human health and environment. Importantly, this relatively new branch of catalysis has inspired an interdisciplinary stream of research that spans from inorganic and organic chemistry to materials science, thus establishing itself as one dominant trend in modern organic synthesis. This Review aims at illustrating the milestones on the timeline evolution of the photocatalytic systems used, with a critical analysis toward novel applications based on the use of photoactive two‐dimensional carbon‐based nanostructures. Lastly, forward‐looking opportunities within this intriguing research field are discussed. [ABSTRACT FROM AUTHOR]

Practical‐scale on‐site production of hydrogen peroxide (H2O2) via two‐electron (2e−) oxygen reduction reaction (ORR) relies on efficient, robust, and selective electrocatalysts. Among them, carbon‐based materials are cheap, abundant, durable, and their surface properties can be tuned to favor the 2e− ORR pathways, resulting in higher efficiency and facilitating possible scale‐up towards commercially appealing levels. Here, we demonstrate that the selective installment of carboxyl groups on the surface of N‐doped graphene yielding a material named graphene acid (N‐GA) promotes the catalytic 2e− ORR, achieving a H2O2 faradaic efficiency (FE) as high as 70 % in acidic media (pH=0.96) and a H2O2 productivity in long term bulk electrolysis that could reach 107.8 mmol gcatalyst−1 h−1 under optimized conditions. Extended XPS analysis and density functional theory (DFT) calculations revealed that surface carboxylic acid functional groups play a significant role in achieving the high activity of N‐GA for 2e− ORR. [ABSTRACT FROM AUTHOR]

Oxidized active carbon (oAC) catalyses the formation of polysubstituted quinolines from o‐vinyl anilines and aldehydes. The reaction proceeds in a cascade manner through condensation, electrocyclization and dehydrogenation, and gives access to a wide range of quinolines with alkyl and/or aryl substituents as demonstrated with 40 examples. The metal‐free catalytic procedure allows a heterogeneous protocol for the synthesis of various polysubstituted quinolines. The mechanistic studies imply that both the acid and quinoidic groups in oAC are integral for the catalytic manifold. [ABSTRACT FROM AUTHOR]

HNO3‐oxidized carbon nanotubes catalyze oxidative dehydrogenative (ODH) carbon–carbon bond formation between electron‐rich (hetero)aryls with O2 as a terminal oxidant. The recyclable carbocatalytic method provides a convenient and an operationally easy synthetic protocol for accessing various benzofused homodimers, biaryls, triphenylenes, and related benzofused heteroaryls that are highly useful frameworks for material chemistry applications. Carbonyls/quinones are the catalytically active site of the carbocatalyst as indicated by model compounds and titration experiments. Further investigations of the reaction mechanism with a combination of experimental and DFT methods support the competing nature of acid‐catalyzed and radical cationic ODHs, and indicate that both mechanisms operate with the current material. [ABSTRACT FROM AUTHOR]

Electrocatalytic oxygen reduction (ORR) is an emerging synthetic strategy to prepare H2O2 in a sustainable fashion. N‐doped graphitic carbon with embedded cobalt nanoparticles was selected as an advanced material able to selectively trigger the ORR to form H2O2 with a faradaic efficiency of almost 100 % at very positive applied potentials. The production of H2O2 proceeded with high rates as calculated by bulk electrolysis (49 mmol g−1 h−1) and excellent current densities (≈−0.8 mA cm−2 at 0.5 V vs. reversible hydrogen electrode). The totally selective behavior depended on the combination of concomitant material features, such as the textural properties, the nature of the metal, the distribution of N moieties, the acidic environment, and the applied potential. [ABSTRACT FROM AUTHOR]

Sustainable energy and the environment are one of the central priorities for our society, triggering a massive capital investment on research to define new trajectories for bypassing fossil fuel dependence and move to clean energy and consequent pollution abatement. The last decade has witnessed the rise and establishment of nanomaterials as frontrunners for a real societal impact of key processes under investigation, such as sustainable hydrogen production and CO2 conversion to fuels. The enormous progress achieved has been made possible by the opportunity to better understand materials at the nanoscale through the use of more powerful characterization techniques and advanced synthetic strategies. The lesson learned is that appropriately engineered multicomponent nanomaterials may hold the key to the routine industrial establishment of new greener concepts of energy production, with strong repercussions to the quality of life. [ABSTRACT FROM AUTHOR]

Appropriate and fine-tuned treatments of amorphous carbon (AC) involving aqua regia or concentrated HNO3 lead to oxidised carbon materials (oAC) which are able to catalyse 2,2'- and 3,3'- homocouplings of various functionalised indoles with outstanding activity. This newly developed carbocatalysed Csp²-Csp² bond formation can be achieved under mild thermal conditions. The study on the scope of the reaction revealed that the reaction can be extended to the homocoupling of other substrates of high synthetic interest such as 2-naphthol, 2-functionalised benzofurans and benzothiofurans. The characterisation of oAC with XPS together with ad hoc experiments aimed at blocking the active site revealed that the presence and distribution of C=O functionalities is critical and correlates well with the catalytic activity. Such experiments provide solid support for elucidation of the mechanism, suggesting a quinone nature of the active C= O groups, which are spontaneously regenerated by oxygen. This is confirmed by the fact that 2,3-dichloro- 5,6-dicyano-1,4-benzoquinone (DDQ) is able to promote the coupling in a stoichiometric fashion. [ABSTRACT FROM AUTHOR]

Die Nutzung von auf festen Substraten gezogenem oder abgeschiedenem Graphen bietet wesentliche Vorteile, wenn man mithilfe von Funktionalisierungsprozessen fein abgestimmte Strukturen für die Elektronik und “intelligente” Materialien erzielen möchte. In diesem Aufsatz konzentrieren wir uns zunächst auf die Natur und die Eigenschaften von Graphen auf Substraten in Abhängigkeit von den jeweiligen Herstellungsverfahren. Anschließend analysieren wir die maßgebliche Literatur zur Funktionalisierung von Graphen auf einem Substrat. Insbesondere werden wir radikalische Reaktionen, Cycloadditionen, Halogenierungen, Hydrierungen und Oxidationen vergleichend diskutieren. Dabei werden wir besonders auf die Frage eingehen, wie die Reaktivität von Graphen durch seine Morphologie beeinflusst wird (d. h. Anzahl von Lagen, Defekte, Substrat, Krümmung usw.). Die kovalente Modifizierung von substratfixiertem Graphen ermöglicht eine präzise Steuerung seiner chemischen Struktur und eine Öffnung der Bandlücke für elektronische Anwendungen. Die Reaktivität wird dabei durch die Art und Morphologie des Graphens, das Substrat und mechanische Kräfte bestimmt. Für das Arbeiten mit funktionalisiertem Graphen auf einem Substrat sind eine Analyse dieser Parameter und ein Vergleich der verschiedenen Funktionalisierungswege nötig. [ABSTRACT FROM AUTHOR]

The utilization of grown or deposited graphene on solid substrates offers key benefits for functionalization processes, but especially to attain structures with a high level of control for electronics and 'smart' materials. In this review, we will initially focus on the nature and properties of graphene on substrates, based on the method of preparation. We will then analyze the most relevant literature on the functionalization of graphene on substrates. In particular, we will comparatively discuss radical reactions, cycloadditions, halogenations, hydrogenations, and oxidations. We will especially address the question of how the reactivity of graphene is affected by its morphology (i.e., number of layers, defects, substrate, curvature, etc.). [ABSTRACT FROM AUTHOR]

The development of new electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at physiological pH is critical for several fields, including fuel cells and biological applications. Herein, the assembly of an electrode based on carboxyl-functionalised hydrophilic multiwalled carbon nanotubes (MWCNTs) filled with Fe phases and their excellent performance as electrocatalysts for ORR and HER at physiological pH are reported. The encapsulated Fe dramatically enhances the catalytic activity, and the graphitic shells play a double role of efficiently mediating the electron transfer to O2 and H2O reactants and providing a cocoon that prevents uncontrolled Fe oxidation or leaching. [ABSTRACT FROM AUTHOR]

Two novel synthetic strategies to covalently link a metallocene electron-donor unit to a chlorin ring are presented. In one approach, pyropheophorbide a is readily converted into its 131-ferrocenyl dehydro derivative by nucleophilic addition of the ferrocenyl anion to the 131-carbonyl group. In another approach, the corresponding 131-pentamethylruthenocenyl derivative is synthesised from 131-fulvenylchlorin by a facile ligand exchange/deprotonation reaction with the [RuCp*(cod)Cl] (Cp*=pentamethylcyclopentadienyl; cod=1,5-cyclooctadiene) complex. The resulting metallocene-chlorins exhibit reduced aromaticity, which was unequivocally supported by ring-current calculations based on the gauge-including magnetically induced current (GIMIC) method and by calculated nucleus-independent chemical shift (NICS) values. The negative ring current in the isocyclic E ring suggests the antiaromatic character of this moiety and also clarifies the spontaneous reactivity of the complexes with oxygen. The oxidation products were isolated and their electrochemical and photophysical properties were studied. The ruthenocene derivatives turned out to be stable under light irradiation and showed photoinduced charge transfer with charge-separation lifetimes of 152-1029 ps. [ABSTRACT FROM AUTHOR]

Ein Hoch auf den Träger: Die Cycloisomerisierung von 2 ‐ Alkinylanilinen zu Indolen wird durch kationische Au ‐ Nanopartikel (NPs) auf einem Kohlenstoffträger katalysiert. Elektronisch neutrale und elektronenreiche 2 ‐ Arylindole wandeln sich durch oxidative Homokupplung weiter in 3,3′ ‐ Biindole um; dieser Schritt wird ebenfalls glatt durch Au ‐ NPs auf Kohlenstoff katalysiert, aber ebenso, wenn auch langsamer, durch den Kohlenstoffträger alleine. [ABSTRACT FROM AUTHOR]

Review: 660 refs. [ABSTRACT FROM AUTHOR]