Adjacent single-atom irons boosting molecular oxygen activation on MnO2

Adatom Bonding Sites in a Nickel-Fe3 O4 (001) Single-Atom Model Catalyst and O2 Reactivity Unveiled by Surface Action Spectroscopy with Infrared Free-Electron Laser Light

Single-atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst's performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe₃ O₄ (001). We reveal that Ni and Au adatoms selectively bind to surface oxygen ions which are octahedrally coordinated to Fe ions. In addition, we find that the Ni adatoms can activate O₂ to superoxide in contrast to the bare surface and Ni in subsurface positions. Overall, we unveil the advantages of combining SAS and DFT for improving the understanding of single-atom catalysts.

Large-Scale Synthesis of Spinel Nix Mn3-x O4 Solid Solution Immobilized with Iridium Single Atoms for Efficient Alkaline Seawater Electrolysis

Seawater electrolysis not only affords a promising approach to produce clean hydrogen fuel but also alleviates the bottleneck of freshwater feeds. Here, a novel strategy for large-scale preparing spinel Ni_x Mn_3-x O₄ solid solution immobilized with iridium single-atoms (Ir-SAs) is developed by the sol-gel method. Benefitting from the surface-exposed Ir-SAs, Ir₁ /Ni_1.6 Mn_1.4 O₄ reveals boosted oxygen evolution reaction (OER) performance, achieving overpotentials of 330 and 350 mV at current densities of 100 and 200 mA cm^-2 in alkaline seawater. Moreover, only a cell voltage of 1.50 V is required to reach 500 mA cm^-2 with assembled Ir₁ /Ni_1.6 Mn_1.4 O₄ ‖Pt/C electrode pair under the industrial operating condition. The experimental characterizations and theoretical calculations highlight the effect of Ir-SAs on improving the intrinsic OER activity and facilitating surface charge transfer kinetics, and evidence the energetically stabilized *OOH and the destabilized chloride ion adsorption in Ir₁ /Ni_1.6 Mn_1.4 O₄ . This work demonstrates an effective method to produce efficient alkaline seawater electrocatalyst massively.

Metal-metal interactions in correlated single-atom catalysts

Single-atom catalysts (SACs) include a promising family of electrocatalysts with unique geometric structures. Beyond conventional ones with fully isolated metal sites, an emerging class of catalysts with the adjacent metal single atoms exhibiting intersite metal-metal interactions appear in recent years and can be denoted as correlated SACs (C-SACs). This type of catalysts provides more opportunities to achieve substantial structural modification and performance enhancement toward a wider range of electrocatalytic applications. On the basis of a clear identification of metal-metal interactions, this review critically examines the recent research progress in C-SACs. It shows that the control of metal-metal interactions enables regulation of atomic structure, local coordination, and electronic properties of metal single atoms, which facilitate the modulation of electrocatalytic behavior of C-SACs. Last, we outline directions for future work in the design and development of C-SACs, which is indispensable for creating high-performing new SAC architectures.

Construction of α-Fe2O3/Sulfur-Doped Polyimide Direct Z-Scheme Photocatalyst with Enhanced Solar Light Photocatalytic Activity

A novel two-dimensional α-Fe₂O₃/sulfur-doped polyimide (FO/SPI) direct Z-scheme photocatalyst was successfully constructed by a facile thermal treatment method. The effects of α-Fe₂O₃ nanosheets on the morphology, chemical structure, and photoelectronic properties of FO/SPI composites were systematically characterized by different spectroscopic means. These methods include X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, transient fluorescence spectra, and so forth. It was confirmed that the small amounts of α-Fe₂O₃ can availably facilitate exfoliation of bulk SPI, resulting in a transformation of SPI from bulk to 2D layered composite that illustrates tight interface through the coordination Fe-N bond and an all-solid-state direct Z-scheme junction. Thus, the transfer and separation efficiency of photogenerated electron/hole pairs were significantly enhanced, which greatly promoted improvement of the photocatalytic activity of the FO/SPI composite for methyl orange degradation under solar light. This work provides a new approach to constructing efficient inorganic-organic Z-scheme photocatalyst based on strong interface interaction.

Neighboring sp-Hybridized Carbon Participated Molecular Oxygen Activation on the Interface of Sub-nanocluster CuO/Graphdiyne

Activation of O₂ is a crucial step in oxidation processes. Here, the concept of sp-hybridized C≡C triple bonds as an electron donor is adopted to develop highly active and stable catalysts for molecular oxygen activation. We demonstrate that the neighboring sp-hybridized C and Cu sites on the interface of the sub-nanocluster CuO/graphdiyne are the key structures to effectively modulate the O₂ activation process in the bridging adsorption mode. The as-prepared sub-nanocluster CuO/graphdiyne catalyst exhibited the highest CO oxidation activity and readily converted 50% CO at around 133 °C, which is 34 and 94 °C lower than that for CuO/graphene and CuO/active carbon catalysts, respectively. In situ diffused reflectance infrared Fourier transform spectroscopy and density functional theory calculation results proved that the neighboring sp-hybridized C is more favorable to promote the rapid dissociation of carbonate than sp²-hybridized C without overcoming any energy barrier. The gaseous CO directly reacts with the active molecular oxygen and tends to proceed through the E-R mechanism with a relatively low energy barrier (0.20 eV). This work revealed that sp-hybridized C of graphdiyne-based materials could effectively improve the O₂ activation efficiency, which could facilitate the low-temperature oxidation processes.

Iron single-atom anchored N-doped carbon as a 'laccase-like' nanozyme for the degradation and detection of phenolic pollutants and adrenaline

To solve the inherent defects of laccase, the first iron single-atom anchored N-doped carbon material (Fe₁@CN-20) as a laccase mimic was disclosed. The FeN₄ structure of this material can well mimic the catalytic activity of laccase. Although Fe₁@CN-20 has a lower metal content (2.9 wt%) than any previously reported laccase mimics, it exhibits kinetic constants comparable to those of laccase, as its K_m (Michaelis constant) and V_max (maximum rate) are 0.070 mM and 2.25 µM/min respectively, which are similar to those of laccase (0.078 mM, 2.49 µM/min). This catalyst displays excellent stability even under extreme pH (2-9), high temperature (100 °C), strong ionic strength (500 mM of NaCl), high ethanol concentration (volume ratio 40%) and long storage time (2 months). Additionally, it can be reused for at least 7 times with only a slight loss in activity. Therefore, this material has a much lower price and better stability and recyclability than laccase, which has been applied in the detection and degradation of a series of phenolic compounds. In the detection of adrenaline, Fe₁@CN-20 achieved a detection limit of 1.3 µM, indicating it is more sensitive than laccase (3.9 µM).

Atomically Defined Undercoordinated Copper Active Sites over Nitrogen-Doped Carbon for Aerobic Oxidation of Alcohols

Selective aerobic oxidation of alcohols offers an attractive means to address challenges in the modern chemical industry, but the development of non-noble metal catalysts with superior efficacy for this reaction remains a grand challenge. Here, this study reports on such a catalyst based on atomically defined undercoordinated copper atoms over nitrogen-doped carbon support as an efficient, durable, and scalable heterogeneous catalyst for selective aerobic oxidation of alcohols. This catalyst exhibits extremely high intrinsic catalytic activity (TOF of 7692 h^-1 ) in the oxidation of cinnamyl alcohol to afford cinnamaldehyde, along with exceptional recyclability (at least eight cycles), scalability, and broad substrate scope. DFT calculations suggest that the high activity derives from the low oxidation state and the unique coordination environment of the copper sites in the catalyst. These findings pave the way for the design of highly active and stable single atom catalysts to potentially address challenges in synthetic chemistry.

Engineering Electron-Rich Sites on CoSe2-x Nanosheets for the Enhanced Electroanalysis of As(III): A Study on the Electronic Structure via X-ray Absorption Fine Structure Spectroscopy and Density Functional Theory Calculation

Vacancy and doping engineering are promising pathways to improve the electrocatalytic ability of nanomaterials for detecting heavy metal ions. However, the effects of the electronic structure and the local coordination on the catalytic performance are still ambiguous. Herein, cubic selenium vacancy-rich CoSe₂ (c-CoSe_2-x) and P-doped orthorhombic CoSe_2-x (o-CoSe_2-x|P) were designed via vacancy and doping engineering. An o-CoSe_2-x|P-modified glass carbon electrode (o-CoSe_2-x|P/GCE) acquired a high sensitivity of 1.11 μA ppb^-1 toward As(III), which is about 40 times higher than that of c-CoSe_2-x, outperforming most of the reported nanomaterial-modified glass carbon electrodes. Besides, o-CoSe_2-x|P/GCE displayed good selectivity toward As(III) compared with other divalent heavy metal cations, which also exhibited excellent stability, repeatability, and practicality. X-ray absorption fine structure spectroscopy and density functional theory calculation demonstrate that electrons transferred from Co and Se to P sites through Co-P and Se-P bonds in o-CoSe_2-x|P. P sites obtained plentiful electrons to form active centers, which also had a strong orbital coupling with As(III). In the detection process, As(III) was bonded with P and reduced by the electron-rich sites in o-CoSe_2-x|P, thus acquiring a reinforced electrochemical sensitivity. This work provides an in-depth understanding of the influence of the intrinsic physicochemical properties of sensitive materials on the behavior of electroanalysis, thus offering a direct guideline for creating active sites on sensing interfaces.

Cytotoxicity of ZnO Nanoparticle Under Dark via Oxygen Vacancy Dependent Reactive Oxygen Species Generation

Antimicrobial and cytotoxic effect of zinc oxide nanomaterials are popularly thought due to zinc ion leaching, but the exact mechanism of cytotoxicity is controversial and not fully understood. Recent works...

Single-Atom Catalysts: A Review of Synthesis Strategies and Their Potential for Biofuel Production

Biofuels have been derived from various feedstocks by using thermochemical or biochemical procedures. In order to synthesise liquid and gas biofuel efficiently, single-atom catalysts (SACs) and single-atom alloys (SAAs) have been used in the reaction to promote it. SACs are made up of single metal atoms that are anchored or confined to a suitable support to keep them stable, while SAAs are materials generated by bi- and multi-metallic complexes, where one of these metals is atomically distributed in such a material. The structure of SACs and SAAs influences their catalytic performance. The challenge to practically using SACs in biofuel production is to design SACs and SAAs that are stable and able to operate efficiently during reaction. Hence, the present study reviews the system and configuration of SACs and SAAs, stabilisation strategies such as mutual metal support interaction and geometric coordination, and the synthesis strategies. This paper aims to provide useful and informative knowledge about the current synthesis strategies of SACs and SAAs for future development in the field of biofuel production.