Hierarchical Fe-Bi/Bi₇O₉I₃/OVs microspheres coupled with natural air diffusion electrode to achieve efficient heterogeneous visible-light-driven photoelectro-Fenton degradation of tetracycline without aeration

A novel Fe-doping three-dimensional flower-like Bi₇O₉I₃ microspheres with plasmonic Bi and rich surface oxygen vacancies (Fe-Bi/Bi₇O₉I₃/OVs) was prepared as catalysts, and further coupled with natural air diffusion electrode (NADE) to construct the heterogeneous visible-light-driven photoelectro-Fenton (HE-VL-PEF) process to enhance the degradation and mineralization of tetracycline (TC). Interfacial ≡Fe sites, OVs and Bi metal were simultaneously constructed via Fe doping, which effectively improved visible light absorption and the separation efficiency of photogenerated carriers to further accelerate the transformation of Fe(III) to Fe(II), achieving Fenton reaction recycling. HE-VL-PEF process could achieve enhanced treatment of pollutants, thanks to the synergistic effect of electro-Fenton (EF) and photo-Fenton (PF). NADE exhibited excellent H₂O₂ electrosynthesis without external oxygen-pumping equipment. Under the irradiation of visible light, Fe-Bi/Bi₇O₉I₃/OVs could achieve more photoelectrons to accelerate the transformation of Fe(III) to Fe(II) or directly activate H₂O₂. DFT calculations also clearly demonstrated that except for the fast charge separation and transfer, Fe-Bi/Bi₇O₉I₃/OVs could achieve a faster electron transport between Fe-O, facilitating Fe site acquire more electron. Consequently, the Fe-Bi/Bi₇O₉I₃/OVs in HE-VL-PEF process presented performance superiorities including excellent pollutant removal (91.91 %), low electric energy consumption of 66.34 kWh/kg total organic carbon (TOC), excellent reusability and wide pH adaptability (3–9).