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

Abstract

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 (O_V) 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.