Synergetic Manipulation Mechanism of Single-Atom M-N4 and M-OH (M = Mn, Fe, Co, Ni) Sites for Ozone Activation: Theoretical Prediction and Experimental Verification

Enhanced catalytic ozonation via FeBi bimetallic catalyst: Unveiling the role of zero-valent Bi as an oxygen vacancy-mediated electron reservoir

A series of bimetallic carbon catalysts (FeM@C, M = Bi, Ce, Co, Ni, Mn) were synthesized via pyrolysis of metal-organic framework (MOF) precursors, among which FeBi@C exhibits exceptional catalytic ozonation performance, achieving 90.73 % oxalic acid removal within 30 min and retaining 84 % of its initial activity over eight consecutive cycles. Advanced characterizations, including EPR, and in-situ Raman spectroscopy, revealed that oxygen vacancies (OV) serve as active sites for ozone adsorption, leading to the formation of reactive oxygen species (ROS) and ≡ Fe-O-O- peroxo intermediates. The post-reaction XPS analysis indicated significant shifts in binding energies and changes in the proportions of oxygen species, revealing the unique Fe-Bi synergy. The Fe2p spectra showed a decrease in Fe2+ content and a negative shift in binding energy, indicating an active Fe2+/Fe3+ redox cycle. The Bi4f spectra confirmed the presence of zero-valent Bi, which acts as an "electron reservoir", continuously donating electrons to enhance Fe2+/Fe3+ redox cycle and promote ozone activation. This unique mechanism, where zero-valent Bi sustains the electron transfer cycle, significantly enhances both the catalytic efficiency and long-term stability of the FeBi@C system, distinguishing it from conventional bimetallic catalysts. This work provides a novel strategy for designing high-performance catalysts for environmental remediation.

State-Of-The-Art Structural Regulation Methods and Quantum Chemistry for Carbon-Based Single-Atom Catalysts in Advanced Oxidation Process: Critical Perspectives into Molecular Level

Advanced oxidation processes (AOPs) by carbon-based single-atom catalysts (SACs) are recognized as an attractive scientific frontier for water treatment, with the outstanding benefits of ultra-effective and anti-interference capability. However, most of the research has paid more attention to the performance of SACs, while the in-depth understanding of catalytic regulation by molecular interaction is relatively deficient. This critical review delves into deciphering the catalytic mechanism through a micro-level, which makes it more convenient to interpret apparent catalytic phenomena. It first summarizes basic theories of quantum chemistry, which provide mechanism interpretation and prediction for molecular-oxidation systems. Additionally, corresponding oxidation pathways of common oxidants are underscored. Following the oxidants, state-of-the-art regulation methods are discussed with special attention to involved molecular interactions and pollutants. Particularly, the preliminary insights into the "oxidant-catalyst-pollutants" internal relationships are provided to help construct the SAC-AOP system from a molecular standpoint. Meanwhile, some cutting-edge laboratory devices and pilot-scale engineering are presented to illustrate the ultimate purpose of scientific molecular exploration. Eventually, relative challenges of SACs-AOPs upon the design of catalytic systems and investigation methods are provided. This review aims to promote the large-scale potential of SACs-based AOPs in practical water treatment by emphasizing the pivotal role of micro-insights.