Enhancement of oxygen evolution reaction by X-doped (X = Se,S, P) holey graphitic carbon shell encapsulating NiCoFe nanoparticles: a combined experimental and theoretical study

Among the two half-reactions of the electrochemical water splitting, the anodic oxygen evolution reaction (OER) is a kinetically sluggish process and usually requires noble metal oxide catalysts. Therefore, the development of highly active, noble metal-free, and durable catalysts for OER is an urgent need for sustainable applications. The encapsulation of transition-metal alloyed nanoparticles in graphitic carbon layers, with core-shell features, is a viable approach for establishing an undegradable and highly efficient catalyst toward OER. Furthermore, the reactivity of the carbon shell surface can be further improved by the electron transfers between the core alloy and carbon shell, through a control of the alloyed nanoparticle compositions, or through a chemical doping. Nevertheless, it is still not clear whether the incorporation of a chemical dopant directly into the carbon shells systematically promotes the catalytic activities toward OER. To clarify this point, we synthetize trimetallic (CoNiFe) nanoparticles encapsulated in graphitic carbon shells by pyrolysis of metal?organic frameworks. We then investigate the effect of a doped graphitic carbon shell by incorporating non-metallic elements such as sulfur, phosphorus, and selenium. The main finding is that all doped CoNiFe@C core-shell catalysts exhibit an enhanced catalytic activity toward OER in the alkaline electrolyte with a low overpotential, a small Tafel slope, and long stability, which are all being comparable to those of RuO₂ benchmark. Electrochemical impedance spectroscopy, X-ray photoelectron spectroscopic, and Raman measurements collected at different applied potentials during the OER process indicate that the doping of graphitic carbon shell significantly improves the interfacial electron-transfer kinetics and facilitates the adsorption of OH^? ion as well as promotes the formation of metal oxyhydroxide, which positively affect the OER performances. Moreover, this improvement in OER efficiency upon incorporating of a chemical doping is rationalized by the optimization of the Gibbs free energy of OER intermediates, thereby remarkably reducing the required energy input of rate-determining step, as elucidated by the density functional theory calculations.     

Wall‐ and Hybridisation‐Selective Synthesis of Nitrogen‐Doped Double‐Walled Carbon Nanotubes

Controlled nitrogen‐doping is a powerful methodology to modify the properties of carbon nanostructures and produce functional materials for electrocatalysis, energy conversion and storage, and sensing, among others. Herein, we report a wall‐ and hybridisation‐selective synthetic methodology to produce double‐walled carbon nanotubes with an inner tube doped exclusively with graphitic sp²‐nitrogen atoms. Our measurements shed light on the fundamental properties of nitrogen‐doped nanocarbons opening the door for developing their potential applications.     

Review on Undoped/Doped TiO2 Nanomaterial; Synthesis and Photocatalytic and Antimicrobial Activity

This review covers the various synthetic methods of doped and undoped TiO₂ nanomaterials, ranging from single‐doped and co‐doped to multidoped with transition‐metal ions, rare earth metal ions, and other metals and nonmetals ions. The effects of doping on the physiochemical propertiesas well as the photocatalytic and antimicrobial activities of TiO₂ nanomaterial are discussed. The results from the literature show that doping of TiO₂ shifts the absorption edge to the visible region as a result of the decrease in the bandgap due to the formation of new energy levels in the bandgap. The dopent also acts as a trapping center for electrons and holes, thereby reducing the recombination rate of charge carriers and increasing the photocatalytic and antimicrobial activity of TiO₂ nanomaterials. All multidoped TiO₂ nanomaterials show higher activity than their undoped, single‐doped, and co‐doped counterparts.     

Metal‐Free Electrocatalyst for Oxygen Reduction: Synthesis‐Controlled Density of Catalytic Centers and Impact on ORR

This work demonstrates a rapid and scalable route for the preparation of N‐doped carbon spheres of 80–120 nm via pyrolysis of polypyrrole as the only carbon and nitrogen source. The resulting porous catalyst has a nitrogen doping level of 6–8 at%. Electrochemical studies show that N‐doped C is very active toward oxygen reduction in alkaline electrolyte and the mechanism of ORR process is controlled by the surface concentration of catalytic active sites that promote either a direct four‐electron or two‐electron process. An interesting observation is that we can generate precursors for the N‐doped carbon with desirable particle size, shape and with the preferential structure (linear polypyrrole from the α? α coupling during slow polymerization or cross‐linked polypyrrole from α? β coupling during fast polymerization) that promotes the formation of favorable catalytic sites for O₂ reduction. The XPS analysis in conjunction with RDE voltammetry highlights the effect of polymer precursor synthesis on the chemical structure and a resulting electrochemical activity of the N‐doped carbon materials.     

Nitrogen,Phosphorus, and Sulfur Co‐Doped Hollow Carbon Shell as Superior Metal‐Free Catalyst for Selective Oxidation of Aromatic Alkanes

Metal‐free heteroatom‐doped carbocatalysts with a high surface area are desirable for catalytic reactions. In this study, we found an efficient strategy to prepare nitrogen, phosphorus, and sulfur co‐doped hollow carbon shells (denote as NPS‐HCS) with a surface area of 1020 m² g⁻¹. Using a poly(cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol) (PZS) shell as carbon source and N, P, S‐doping source, and the ZIF‐67 core as structural template as well as extra N‐doping source, NPS‐HCS were obtained with a high surface area and superhydrophilicity. All these features render the prepared NPS‐HCS a superior metal‐free carbocatalyst for the selective oxidation of aromatic alkanes in aqueous solution. This study provides a reliable and facile route to prepare doped carbocatalysts with enhanced catalytic properties.     

Nitrogen,Phosphorus, and Sulfur Co‐Doped Hollow Carbon Shell as Superior Metal‐Free Catalyst for Selective Oxidation of Aromatic Alkanes

Metal‐free heteroatom‐doped carbocatalysts with a high surface area are desirable for catalytic reactions. In this study, we found an efficient strategy to prepare nitrogen, phosphorus, and sulfur co‐doped hollow carbon shells (denote as NPS‐HCS) with a surface area of 1020 m² g^?1. Using a poly(cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol) (PZS) shell as carbon source and N, P, S‐doping source, and the ZIF‐67 core as structural template as well as extra N‐doping source, NPS‐HCS were obtained with a high surface area and superhydrophilicity. All these features render the prepared NPS‐HCS a superior metal‐free carbocatalyst for the selective oxidation of aromatic alkanes in aqueous solution. This study provides a reliable and facile route to prepare doped carbocatalysts with enhanced catalytic properties.     

N‐Doped Carbon Aerogel Derived from a Metal–Organic Framework Foam as an Efficient Electrocatalyst for Oxygen Reduction

Metal–organic frameworks (MOFs) are promising alternative precursors for the fabrication of heteroatom‐doped carbon materials for energy storage and conversion. However, the direct pyrolysis of bulk MOFs usually gives microporous carbonaceous materials, which significantly hinder the mass transportation and the accessibility of active sites. Herein, N‐doped carbon aerogels with hierarchical micro‐, meso‐, and macropores were fabricated through one‐step pyrolysis of zeolitic imidazolate framework‐8/carboxymethylcellulose composite gel. Owing to the hierarchical porosity, high specific surface area, favorable conductivity, excellent thermal and chemical stability, the as‐prepared N‐doped carbon aerogel exhibits excellent oxygen reduction reaction (ORR) activity, long‐term durability, and good methanol tolerance in alkaline medium. This work thus provides a new way to fabricate new types of MOF‐derived carbon aerogels for various applications.     

Carbon nanomaterials in microbial sensing and bactericidal applications

The spread of antimicrobial resistance and lesser development of new antibiotics have intensified the search for new antimicrobial and diagnostic vehicles. Carbon nanomaterials (CNMs), which broadly include carbon dots, carbon nanotubes, and graphene/graphene oxide nanostructures, have emerged as promising theranostic materials exhibiting, in many instances, potent antibacterial activities and diagnostic capabilities. Ease of synthesis, tunable physicochemical properties, biocompatibility, and diverse modes of action make CNMs a powerful class of theranostic nanomaterials. This review discusses recent studies illuminating innovative new CNMs and their applications in bacterial theranostics. We particularly emphasize the relationship between the structural parameters and overall chemical properties of CNMs and their biological impact and utilization. Overall, the expanding work on the development and use of CNMs in therapeutic, sensing, and diagnostic applications in the microbial world underscores the considerable potential of these nanomaterials.     

The Proportion of Fe‐NX,N Doping Species and Fe3C to Oxygen Catalytic Activity in Core‐Shell Fe‐N/C Electrocatalyst

A bifunctional oxygen electrocatalyst composed of iron carbide (Fe₃C) nanoparticles encapsulated by nitrogen doped carbon sheets is reported. X‐ray photoelectron spectroscopy and X‐ray absorption near edge structure revealed the presence of several kinds of active sites (Fe?N_x sites, N doping sites) and the modulated electron structure of nitrogen doped carbon sheets. Fe₃C@N‐CSs shows excellent oxygen evolution and oxygen reduction catalytic activity owing to the modulated electron structure by encapsulated Fe₃C core via biphasic interfaces electron interaction, which can lower the free energy of intermediate, strengthen the bonding strength and enhance conductivity. Meanwhile, the contribution of the Fe?N_x sites, N doping sites and the effect of Fe₃C core for the electrocatalytic oxygen reaction is originally revealed. The Fe₃C@N‐CSs air electrode‐based zinc‐air battery demonstrates a high open circuit potential of 1.47 V, superior charge‐discharge performance and long lifetime, which outperforms the noble metal‐based zinc‐air battery.     

Carbon‐Supported Copper Nanomaterials: Recyclable Catalysts for Huisgen [3+2] Cycloaddition Reactions

Highly disperse copper nanoparticles immobilized on carbon nanomaterials (CNMs; graphene/carbon nanotubes) were prepared and used as a recyclable and reusable catalyst to achieve Cu^I‐catalyzed [3+2] cycloaddition click chemistry. Carbon nanomaterials with immobilized N‐heterocyclic carbene (NHC)‐Cu complexes prepared from an imidazolium‐based carbene and Cu^I show excellent stability including high efficiency at low catalyst loading. The catalytic performance evaluated in solution and in bulk shows that both types of Cu‐CNMs can function as an effective recyclable catalysts (more than 10 cycles) for click reactions without decomposition and the use of external additives.     

Optimal Configuration of N‐Doped Carbon Defects in 2D Turbostratic Carbon Nanomesh for Advanced Oxygen Reduction Electrocatalysis

The charge redistribution strategy driven by heteroatom doping or defect engineering has been developed as an efficient method to endow inert carbon with significant oxygen reduction reaction (ORR) activity. The synergetic effect between the two approaches is thus expected to be more effective for manipulating the charge distribution of carbon materials for exceptional ORR performance. Herein we report a novel molecular design strategy to achieve a 2D porous turbostratic carbon nanomesh with abundant N‐doped carbon defects (NDC). The molecular level integration of aromatic rings as the carbon source and urea units as the N source and sacrificial template into the novel precursor of polyurea (PU) promises the formation of abundant carbon edge defects and N doping sites. A special active site—a carbon edge defect doped with a graphitic valley N atom—was revealed to be responsible for the exceptional ORR performance of NDC material.     

The Crucial Role of Charge Accumulation and Spin Polarization in Activating Carbon‐Based Catalysts for Electrocatalytic Nitrogen Reduction

Cost‐effective carbon‐based catalysts are promising for catalyzing the electrochemical N₂ reduction reaction (NRR). However, the activity origin of carbon‐based catalysts towards NRR remains unclear, and regularities and rules for the rational design of carbon‐based NRR electrocatalysts are still lacking. Based on a combination of theoretical calculations and experimental observations, chalcogen/oxygen group element (O, S, Se, Te) doped carbon materials were systematically evaluated as potential NRR catalysts. Heteroatom‐doping‐induced charge accumulation facilitates N₂ adsorption on carbon atoms and spin polarization boosts the potential‐determining step of the first protonation to form *NNH. Te‐doped and Se‐doped C catalysts exhibited high intrinsic NRR activity that is superior to most metal‐based catalysts. Establishing the correlation between the electronic structure and NRR performance for carbon‐based materials paves the pathway for their NRR application.     

Unveiling 79‐Year‐Old Ixene and Its BN‐Doped Derivative

Polycyclic aromatic hydrocarbons (PAHs) are key components of organic electronics. The electronic properties of these carbon‐rich materials can be controlled through doping with heteroatoms such as B and N, however, few convenient syntheses of BN‐doped PAHs have been reported. Described herein is the rationally designed, two‐step syntheses of previously unknown ixene and BN‐doped ixene (B₂N₂‐ixene), and their characterizations. Compared to ixene, B₂N₂‐ixene absorbs longer‐wavelength light and has a smaller electrochemical energy gap. In addition to its single‐crystal structure, scanning tunneling microscopy revealed that B₂N₂‐ixene adopts a nonplanar geometry on a Au(111) surface. The experimentally obtained electronic structure of B₂N₂‐ixene and the effect of BN‐doping were confirmed by DFT calculations. This synthesis enables the efficient and convenient construction of BN‐doped systems with extended π‐conjugation that can be used in versatile organic electronics applications.     

Direct Solvothermal Synthesis of B/N‐Doped Graphene

Heteroatom‐doping into graphitic networks has been utilized for opening the band gap of graphene. However, boron‐doping into the graphitic framework is extremely limited, whereas nitrogen‐doping is relatively feasible. Herein, boron/nitrogen co‐doped graphene (BCN‐graphene) is directly synthesized from the reaction of CCl₄, BBr₃, and N₂ in the presence of potassium. The resultant BCN‐graphene has boron and nitrogen contents of 2.38 and 2.66 atom %, respectively, and displays good dispersion stability in N‐methyl‐2‐pyrrolidone, allowing for solution casting fabrication of a field‐effect transistor. The device displays an on/off ratio of 10.7 with an optical band gap of 3.3 eV. Considering the scalability of the production method and the benefits of solution processability, BCN‐graphene has high potential for many practical applications.     

Recent advances in covalent functionalization of carbon nanomaterials with polymers: Strategies and perspectives

Carbon nanomaterials (CNMs) have been proposed as promising nanofillers for polymer composites because of their high surface area, structural flexibility, good mechanical strength, and their unique thermal, optical, and electronic properties. However, the strong van der Waals interactions between individual nanoparticles have limited the manipulation of CNMs and restricted their use in many promising fields. The functionalization of CNMs has attracted great interest on synthesis of complex structures, and helped establish different facile, scalable, controllable and low-cost methods to graft well-defined polymers onto the surfaces of CNMs. This review highlights the advances made in recent years on the functionalization chemistry of carbon nanotubes and graphene with polymers by both the “grafting from” and “grafting to” techniques. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 622–631     

Uniform silver nanoparticles on tunable porous N‐doped carbon nanospheres for aerobic oxidative synthesis of aryl nitriles from benzylic alcohols

Tunable N‐doped carbon nanospheres from sucrose as carbon source and Tris(2‐aminoethyl)amine (TAEA) as nitrogen source by a simple and easily reproducible method were prepared. It was demonstrated that the tunable N‐doping of carbon spheres could be realized by altering the ratio of TAEA in the raw materials. The content of doped nitrogen, surface area, pore volume and pore size of carbon nanospheres were increased with the increasing of TAEA amount in the hydrothermal process. Prepared N‐doped carbon nanospheres act as solid ligand for anchoring of Ag NPs which generated via chemical reduction of Ag ions. Benzylic alcohols and aldehydes were converted into the aryl nitriles by using Ag/N‐CS‐1 nanospheres as the catalyst and O₂ as the oxidant, efficiently. This catalyst was stable and could use for 6 successful runs.     

Biomass‐derived Nitrogen and Phosphorus Co‐doped Hierarchical Micro/mesoporous Carbon Materials for High‐performance Non‐enzymatic H2O2 Sensing

Nitrogen and phosphorus co‐doped hierarchical micro/mesoporous carbon (N,P‐MMC) was prepared by simple thermal treatment of freeze‐dried okra in the absence of any other additives. The 0.96 wt % of N and 1.47 wt % of P were simultaneously introduced into the graphitic framework of N,P‐MMC, which also possesses hierarchical porous structure with mesopores centered at 3.6 nm and micropores centered at 0.79 nm. Most importantly, N,P‐MMC carbon exhibits excellent catalytic activity for electrocatalytic reduction of H₂O₂, resulting in a new strategy to construct non‐enzymatic H₂O₂ sensor. The N,P‐MMC‐based H₂O₂ sensor displays two linear detection range about 0.1 mM–10 mM (R²=0.9993) and 20 mM–200 mM (R²=0.9989), respectively. The detection limit is estimated to be 6.8 μM at a signal‐to‐noise ratio of 3. These findings provide insights into synthesizing functional heteroatoms doped porous carbon materials for biosensing applications.     

O2 dissociative adsorption on the Cu‐, Ag‐, and W‐doped Al(111) surfaces from DFT computation

The O₂ adsorption and dissociation on M‐doped (M = Cu, Ag, W) Al(111) surface were studied by density functional theory. The adsorption energy of adsorbate, the average binding energy and surface energy of Al surface, and the doping energy of doping atom were calculated. All the doped atoms can be stably combined with Al atoms, while being slightly embedded in the surface to a certain depth. The TOP‐type surfaces are the most stable doped surfaces for O₂ adsorption, which is related to the orbital hybridization between the adsorbate and the surface atoms, the electronegativity, and the orbital energy level of the doping atoms. Moreover, the O atoms and doping atoms contribute significantly to the density of states (DOS), especially the O‐p orbital electrons and the d orbital electrons of doping atoms. The degree of O₂ dissociation is related to the doping atoms on Al surfaces, and the doping atoms actually resist the dissociation of O₂. W atoms have the best resistance effect on the O₂ dissociation as compared with Cu and Ag atoms, especially W‐1NN surface, which has both large barrier energy and reaction energy.     

Dual Graphitic‐N Doping in a Six‐Membered C‐Ring of Graphene‐Analogous Particles Enables an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Graphene‐based materials still exhibit poor electrocatalytic activities for the hydrogen evolution reaction (HER) although they are considered to be the most promising electrocatalysts. We fabricated a graphene‐analogous material displaying exceptional activity towards the HER under acidic conditions with an overpotential (57 mV at 10 mA cm^?2) and Tafel slope (44.6 mV dec^?1) superior to previously reported graphene‐based materials, and even comparable to the state‐of‐the art Pt/C catalyst. X‐ray absorption near‐edge structure (XANES) and solid‐state NMR studies reveal that the distinct feature of its structure is dual graphitic‐N doping in a six‐membered carbon ring. Density functional theory (DFT) calculations show that the unique doped structure is beneficial for the activation of C?H bonds and to make the carbon atom bonded to two graphitic N atoms an active site for the HER.     

Homogenous Boron‐doping in Self‐sensitized Carbon Nitride for Enhanced Visible‐light Photocatalytic Activity

We report a solvothermal approach for the preparation of homogeneously B‐doped self‐sensitized carbon nitride (B‐SSCN) composed of a core of B‐doped carbon nitride microspheres and a covalently linked shell of s‐triazine oligomers. Compared to the undoped structure, the obtained B‐SSCN photocatalyst exhibits an enhanced visible‐light activity, excellent stability for photocatalytic hydrogen generation due to a reduced band‐gap, enhanced charge‐separation efficiency, and better surface reactivity of B‐SSCN. This work provides a new strategy to uniformly insert heteroatoms into the polymeric carbon nitride framework for the development of metal‐free photocatalysts towards efficient production of solar fuels.