Atomically Dispersed Cu Anchored on Nitrogen and Boron Codoped Carbon Nanosheets for Enhancing Catalytic Performance

Development of the cobalt-modified boron-doped metal‑nitrogen‑carbon nanoparticles (co-BCN) for the chemiluminescent determination of the total antioxidant capacity of beverages and fruits

The development of novel detection methods is essential for total antioxidant capacity (TAC) assay in the quality of foods and dietary pharmaceuticals. Herein, a series of cobalt-modified boron-doped metal‑nitrogen‑carbon nanoparticles (Co-BCN) were prepared through high-temperature pyrolysis of the precursors. The Co-BCN shows an outstanding activity of oxidase mimics, and can activate dissolved oxygen to generate a large amount of reactive oxygen species (ROS). These ROS oxidize luminol anions rapidly and emits intense chemiluminescent (CL) radiation. The antioxidants, ascorbic acid, glutathione and cysteine can scavenge the generated ROS, thus sharply reducing the CL signal. The reduction in the CL signals show good linear relationships in the concentration range of 0.1-1.0 μmol·L-1 ascorbic acid, 1.0-10.0 μmol·L-1 glutathione, and 10.0-80.0 μmol·L-1 cysteine, respectively. The method was employed for the TAC determination in eight commercially available fruits and beverages, and the results show good agreement with those of the CUPRAC method.

Optimizing s-p Orbital Overlap Between Sodium Polysulfides and Single-Atom Indium Catalyst for Efficient Sulfur Redox Reaction

P-block metal carbon-supported single-atom catalysts (C-SACs) have emerged as a promising candidate for high-performance room-temperature sodium-sulfur (RT Na-S) batteries, due to their high atom utilization and unique electronic structure. However, the ambiguous electronic-level understanding of Na-dominant s-p hybridization between sodium polysulfides (NaPSs) and p-block C-SACs limits the precise control of coordination environment tuning and electro-catalytic activity manipulation. Here, s-p orbital overlap degree (OOD) between the s orbitals of Na in NaPSs and the p orbitals of p-block C-SACs is proposed as a descriptor for sulfur reduction reaction (SRR) and sulfur oxidation reaction (SOR). Compared to NG and NG-supported InN4 (NG-InN4) SACs, the nitrogen-doped graphene-supported InN5 (NG-InN5) SACs show the largest s-p OOD, demonstrating the weakest shuttle effect and the lowest reaction energy barriers in both SRR and SOR. Accordingly, the designed catalysts allow the Na-S pouch batteries to retain a high capacity of 490.7 mAh g-1 at 2 A g-1 with a Coulombic efficiency of 96 % at a low electrolyte/sulfur (E/S) ratio of 4.5 μl mg-1. This work offers an s-p orbital overlap descriptor describing the interaction between NaPSs and p-orbital-dominated catalysts for high-performance RT Na-S batteries.

Nanowire-like phosphorus modulated carbon-based iron nanozyme with oxidase-like activity for sensitive detection of choline and dye degradation

Choline is mainly supplemented through food intake, lack of choline would result in diseases like liver cirrhosis, hardening of the arteries, or neurodegenerative disorders. The accurate detection of choline is important for human health. Herein, a novel nanowire-like phosphorus/nitrogen co-doped carbon-based iron nanozyme (Fe-NPC) with outstanding oxidase-like activity was synthesized, and the influence of phosphorus doping on oxidase-like activity was explored. Proper phosphorus doping was found to enhance the oxidase-like activity of Fe-NPC by increasing surface defects, promoting iron loading, and modulating chemical environment of central site. The oxidase-like activity of Fe-NPC was successfully applied to colorimetric-fluorescent dual mode detection of choline, and good linear relationship in the ranges of 3-200 μM were achieved with LODs of 1.95 and 1.50 μM, respectively. The fluorescent detection was constructed based on the fluorescence quenching of silicon quantum dots (Si QDs) by quinone-imine. The quenching mechanism was attributed to FRET due to the large spectra overlap, reduced fluorescence lifetime and proper donor-acceptor distance. The successful application to the detection of choline in milk proved the practicability of the proposed sensing method. The oxidase-like properties of Fe-NPC was further used in the degradation of cationic dye methyl blue, high degradation efficiency of 74 % was achieved within 5 min under optimal conditions, proving the enormous potential of Fe-NPC for application in environment protection.

Substance migration in the synthesis of single-atom catalysts

Substance migration is universal and crucial in the synthesis of catalysts, which directly affects their existing form and the micro-structure of their active sites. Realizing migration during the synthesis of single-atom catalysts (SACs) is beneficial for not only increasing their metal loading capacity but also manipulating the electronic structures (coordination structure, long-range interactions, etc.) of their metal sites. This review summarizes the thermodynamics and kinetic processes involved in the synthesis of SACs to unveil the fundamental principles involved in their synthesis. For a better understanding of the effect of migration, the migration of both metal (including ions, atoms, and molecules) and nonmetal species is outlined. Moreover, we propose the research directions to guide the rational design of SACs in the future and deepen the fundamental understanding in the formation of catalysts.

Constructing Nitrogen-Coordinated Single Atom Catalysts via Bond-Plucking Strategy for Oxidation of Benzene

Single-atom catalysts (SACs) with nitrogen-coordinated active centers feature unique electronic and geometric structures and thus show high catalytic activity for various industrial reactions. Searching for operable synthesis protocols to accurately devise SACs is vital but remains challenging because commonly used high-temperature pyrolysis always causes unpredictable structural changes and inhomogeneous single-atom sites. Herein, a mild bond-plucking strategy is reported to construct atomically dispersed Cu supported on graphene-liked C3N4 (g-C3N4) under lower than 100 °C, and Cu foam is used as the source of metal. When g-C3N4 closely coats the surface of Cu foam, Cu0 atoms on Cu foam transfer electrons to nitrogen on g-C3N4 due to the strong Lewis acbase interaction, simultaneously forming Cuδ+ (0 < δ < 2) and Cu─N bonds. Subsequently, g-C3N4 nanosheets are exfoliated out from the surface of Cu foam, eventually obtaining a well-defined Cu single atoms/g-C3N4 (Cu SAs/g-C3N4) catalyst with atomically dispersed Cu-N3 moieties. Cu SAs/g-C3N4 serves as a highly effective and durable catalyst toward the oxidation of benzene to phenol at 60 °C, with a conversion of 65.1% and selectivity of 97.6% after 12 h. The findings pave a new way to construct well-defined SACs at low costs, promoting large-scale production and industrial application.

Out-of-Plane Single-Copper-Site Catalysts for Room-Temperature Benzene Oxidation

Crafting single-atom catalysts (SACs) that possess "just right" modulated electronic and geometric structures, granting accessible active sites for direct room-temperature benzene oxidation is a coveted objective. However, achieving this goal remains a formidable challenge. Here, we introduce an innovative in situ phosphorus-immitting strategy using a new phosphorus source (phosphorus nitride, P3N5) to construct the phosphorus-rich copper (Cu) SACs, designated as Cu/NPC. These catalysts feature locally protruding metal sites on a nitrogen (N)-phosphorus (P)-carbon (C) support (NPC). Rigorous analyses, including X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS), validate the coordinated bonding of nitrogen and phosphorus with atomically dispersed Cu sites on NPC. Crucially, systematic first-principles calculations, coupled with the climbing image nudged-elastic-band (CI-NEB) method, provide a comprehensive understanding of the structure-property-activity relationship of the distorted Cu-N2P2 centers in Cu/NPC for selective oxidation of benzene to phenol production. Interestingly, Cu/NPC has shown more energetically favorable C-H bond activation compared to the benchmark Cu/NC SACs in the direct oxidation of benzene, resulting in outstanding benzene conversion (50.3 %) and phenol selectivity (99.3 %) at room temperature. Furthermore, Cu/NPC achieves a remarkable turnover frequency of 263 h-1 and mass-specific activity of 35.2 mmol g-1 h-1, surpassing the state-of-the-art benzene-to-phenol conversion catalysts to date.

Boron in the Second Coordination Sphere of Fe Single Atom Boosts the Oxygen Reduction Reaction

Metal single atoms coordinated with four nitrogen atoms (M1N4) are regarded as tremendously promising catalysts for the electrocatalytic oxygen reduction reaction (ORR). Nevertheless, the strong bond intensity between the metal center and the O atom in oxygen-containing intermediates significantly limits the ORR activity of M1N4. Herein, the catalytically active B atom is successfully introduced into the second coordination sphere of the Fe single atom (Fe1N4-B-C) to realize the alternative binding of B and O atoms and thus facilitate the ORR activity. Compared with the pristine Fe1N4 catalyst, the synthesized Fe1N4-B-C catalyst exhibits improved ORR catalytic capability with a half-wave potential (E1/2) of 0.80 V and a kinetic current density (JK) of 5.32 mA cm-2 in acid electrolyte. Moreover, in an alkaline electrolyte, the Fe1N4-B-C catalyst displays remarkable ORR activity with E1/2 of 0.87 V and JK of 8.94 mA cm-2 at 0.85 V, outperforming commercial Pt/C. Notably, the mechanistic study has revealed that the active center is the B atom in the second coordination shell of the Fe1N4-B-C catalyst, which avoids the direct bonding of Fe-O. The B center has a moderate binding force to the ORR intermediate, which flattens the ORR energy diagram and thereby improves the ORR performance. Therefore, this study offers a novel strategy for tailoring catalytic performance by tuning the active center of single-atom catalyst.

Tuning the Coordination Environment of Carbon-Based Single-Atom Catalysts via Doping with Multiple Heteroatoms and Their Applications in Electrocatalysis

Carbon-based single-atom catalysts (SACs) are considered to be a perfect platform for studying the structure-activity relationship of different reactions due to the adjustability of their coordination environment. Multi-heteroatom doping has been demonstrated as an effective strategy for tuning the coordination environment of carbon-based SACs and enhancing catalytic performance in electrochemical reactions. Herein, recently developed strategies for multi-heteroatom doping, focusing on the regulation of single-atom active sites by heteroatoms in different coordination shells, are summarized. In addition, the correlation between the coordination environment and the catalytic activity of carbon-based SACs are investigated through representative experiments and theoretical calculations for various electrochemical reactions. Finally, concerning certain shortcomings of the current strategies of doping multi-heteroatoms, some suggestions are put forward to promote the development of carbon-based SACs in the field of electrocatalysis.

Regulating electron configuration of single Cu sites via unsaturated N,O-coordination for selective oxidation of benzene

Developing highly efficient catalyst for selective oxidation of benzene to phenol (SOBP) with low H2O2 consumption is highly desirable for practical application, but challenge remains. Herein, we report unique single-atom Cu1-N1O2 coordination-structure on N/C material (Cu-N1O2 SA/CN), prepared by water molecule-mediated pre-assembly-pyrolysis method, can efficiently boost SOBP reaction at a 2:1 of low H2O2/benzene molar ratio, showing 83.7% of high benzene conversion with 98.1% of phenol selectivity. The Cu1-N1O2 sites can provide a preponderant reaction pathway for SOBP reaction with less steps and lower energy barrier. As a result, it shows an unexpectedly higher turnover frequency (435 h−1) than that of Cu1-N2 (190 h−1), Cu1-N3 (90 h−1) and Cu nanoparticle (58 h−1) catalysts, respectively. This work provides a facile and efficient method for regulating the electron configuration of single-atom catalyst and generates a highly active and selective non-precious metal catalyst for industrial production of phenol through selective oxidation of benzene.

La-Cu based heterogeneous perovskite catalyst for highly selective benzene hydroxylation under mild conditions

Direct hydroxylation of benzene towards phenol with high conversion and selectivity remains a great challenge. We report herein an efficient La₂ CuO₄ perovskite catalyst for one-step oxidation of benzene using hydrogen peroxide under mild conditions. The catalyst was characterized using XRD, TEM, XPS, TG-DTA, and other advanced techniques. The one-pot hydroxylation reaction carried out at 60 °C under optimum reaction conditions in the presence of catalytic material shows benzene to phenol transformation with 51% conversion with >99% selectivity with 65 percent peroxide efficiency, respectively. The influence of reaction conditions such as temperature, amount of oxidant, reaction time and mode of addition of the oxidant was crucial in selectivity optimization.

Dual-Atom Metal and Nonmetal Site Catalyst on a Single Nickel Atom Supported on a Hybridized BCN Nanosheet for Electrochemical CO2 Reduction to Methane: Combining High Activity and Selectivity

Atomically dispersed nitrogen-coordinated transition-metal sites supported on graphene (TM-N₄-C) offer promising potential for the electrochemical carbon dioxide reduction reaction (CO₂RR). However, a few TM-N_x-C single-atom catalysts (SAC) are capable of reducing CO₂ to multielectron products with high activity and selectivity. Herein, using density functional theory calculations, we investigated the electrocatalytic performance of a single TM atom embedded into a defective BCN nanosheet for CO₂RR. The N and B atom co-coordinated TM center, namely, TM-B₂N₂, constructs a symmetry-breaking site, which strengthens the overlapping of atomic orbitals, and enables the linear CO₂ to be curved and activated, compared to the weak coupling of CO₂ with the symmetric TM-N₄ site. Moreover, the TM-B₂N₂ sites play a role of dual-atom active sites, in which the TM atom serves as the carbon adsorption site and the B atom acts as the oxygen adsorption site, largely stabilizing the key intermediates, especially *COOH. The symmetry-breaking coordination structures shift the d-band center of the TM atom toward the Fermi level and thus facilitate CO₂ reduction to hydrocarbons and oxygenates. As a result, different from the TM-N₄-C structure that leads to CO as the major product, the Ni atom supported on BCN can selectively catalyze CO₂ conversion into CH₄, with an ultralow limiting potential of -0.07 V, while suppressing the hydrogen evolution reaction. Our finding suggests that introduction of a nonmetal active site adjacent to the metal site provides a new avenue for achieving efficient multi-intermediate electrocatalytic reactions.