Carbon Nitride Supported High‐Loading Fe Single‐Atom Catalyst for Activation of Peroxymonosulfate to Generate 1 O 2 with 100 % Selectivity

Active Center Size-Dependent Fenton-Like Chemistry for Sustainable Water Decontamination

Accurately controlling catalytic activity and mechanism as well as identifying structure-activity-selectivity correlations in Fenton-like chemistry is essential for designing high-performance catalysts for sustainable water decontamination. Herein, active center size-dependent catalysts with single cobalt atoms (CoSA), atomic clusters (CoAC), and nanoparticles (CoNP) were fabricated to realize the changeover of catalytic activity and mechanism in peroxymonosulfate (PMS)-based Fenton-like chemistry. Catalytic activity and durability vary with the change in metal active center sizes. Besides, reducing the metal size from nanoparticles to single atoms significantly modulates contributions of radical and nonradical mechanisms, thus achieving selective/nonselective degradation. Density functional theory calculations reveal evolutions in catalytic mechanisms of size-dependent catalytic systems over different Gibbs free energies for reactive oxygen species generation. Single-atom site contact with PMS is preferred to induce nonradical mechanisms, while PMS dissociates and generates radicals on clusters and nanoparticles. Differences originating from reaction mechanisms endow developed systems with size-dependent selectivity and mineralization for treating actual hospital wastewater in column reactors. This work brings an in-depth understanding of metal size effects in Fenton-like chemistry and guides the design of intelligent catalysts to fulfill the demand of specific scenes for water purification.

Enhanced Interfacial Electron Transfer by Asymmetric Cu-Ov -In Sites on In2 O3 for Efficient Peroxymonosulfate Activation

Enhancing the peroxymonosulfate (PMS) activation efficiency to generate more radicals is vital to promote the Fenton-like reaction activity, however, how to promote the PMS adsorption and accelerate the interfacial electron transfer to boost its activation kinetics remains a great challenge. Herein, we prepared Cu-doped defect-rich In₂ O₃ (Cu-In₂ O₃ /O_v ) catalysts containing asymmetric Cu-O_v -In sites for PMS activation in water purification. The intrinsic catalytic activity is that the side-on adsorption configuration of the O-O bond (Cu-O-O-In) at the Cu-O_v -In sites significantly stretches the O-O bond length. Meanwhile, the Cu-O_v -In sites increase the electron density near the Fermi energy level, promoting more and faster electron transfer to the O-O bond for generating more SO₄ ⋅^- and ⋅OH. The degradation rate constant of tetracycline achieved by Cu-In₂ O₃ /O_v is 31.8 times faster than In₂ O₃ /O_v , and it shows the possibility of membrane reactor for practical wastewater treatment.

Generation of FeIV =O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron-N-C Catalyst

Generating Fe^IV =O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the Fe^IV =O generation pathway and oxidation behavior remain obscure. Employing an Fe-N-C catalyst with a typical Fe-N₄ moiety to activate peroxymonosulfate (PMS), we demonstrate that generating Fe^IV =O is mediated by an Fe-N-C-PMS* complex-a well-recognized nonradical species for induction of electron-transfer oxidation-and we determined that adjacent Fe sites with a specific Fe₁ -Fe₁ distance are required. After the Fe atoms with an Fe₁ -Fe₁ distance <4 Å are PMS-saturated, Fe-N-C-PMS* formed on Fe sites with an Fe₁ -Fe₁ distance of 4-5 Å can coordinate with the adjacent Fe^II -N₄ , forming an inter-complex with enhanced charge transfer to produce Fe^IV =O. Fe^IV =O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidation potential.

A Site Distance Effect Induced by Reactant Molecule Matchup in Single-Atom Catalysts for Fenton-Like Reactions

Understanding the site interaction nature of single-atom catalysts (SACs), especially densely populated SACs, is vital for their application to various catalytic reactions. Herein, we report a site distance effect, which emphasizes how well the distance of the adjacent copper atoms (denoted as d_Cu1-Cu1 ) matches with the reactant peroxydisulfate (PDS) molecular size to determine the Fenton-like reaction reactivity on the carbon-supported SACs. The optimized d_Cu1-Cu1 in the range of 5-6 Å, which matches the molecular size of PDS, endows the catalyst with a nearly two times higher turnover frequency than that of d_Cu1-Cu1 beyond this range, accordingly achieving record-breaking kinetics for the oxidation of emerging organic contaminants. Further studies suggest that this site distance effect originates from the alteration of PDS adsorption to a dual-site structure on Cu₁ -Cu₁ sites when d_Cu1-Cu1 falls within 5-6 Å, significantly enhancing the interfacial charge transfer and consequently resulting in the most efficient catalyst for PDS activation so far.

Coordination Chemistry Engineered Polymeric Carbon Nitride Photoanode with Ultralow Onset Potential for Water Splitting

Construction of an intimate film/substrate interface is of great importance for a photoelectrode to achieve efficient photoelectrochemical performance. Inspired by coordination chemistry, a polymeric carbon nitride (PCN) film is intimately grown on a Ti-coated substrate by an in situ thermal condensation process. The as-prepared PCN photoanode exhibits a record low onset potential (Eonset ) of -0.38 V versus the reversible hydrogen electrode (RHE) and a decent photocurrent density of 242 μA cm-2 at 1.23 VRHE for water splitting. Detailed characterization confirms that the origin of the ultralow onset potential is mainly attributed to the substantially reduced interfacial resistance between the Ti-coated substrate and the PCN film benefitting from the constructed interfacial sp2 N→Ti coordination bonds. For the first time, the ultralow onset potential enables the PCN photoanode to drive water splitting without external bias with a stable photocurrent density of ≈9 μA cm-2 up to 1 hour.

Nickel Glyoximate Based Metal-Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Evolution

Metal-covalent organic frameworks (MCOFs) have been recently received wide attention owing to the homogeneous distribution of active metal centers that are beneficial for enhancing the application potentials. However, metal complex based functional building blocks for MCOFs synthesis are limited. Herein, two new MCOFs (Ni-Py-COF and Ni-Bn-COF) were constructed via a novel nickel glyoximate based building block. Splendid photocatalytic activity on hydrogen evolution from water and great long-term recyclability were achieved using these nickel glyoximate based MCOFs as photocatalysts. Excitingly, even without the addition of Pt co-catalyst, the hydrogen evolution rates (HER) of Ni-Py-COF reached up to 626 μmol g^-1  h^-1 , which is better than many porous organic polymers. This work not only expands the type of building units for MCOFs, but also provides meaningful insights for developing stable, efficient and earth-abundant photocatalysts toward H₂ generation.