Precision vacancy engineering and element refilling in S-scheme C3N5/Bi2MoO6 heterojunction for efficient photo-Fenton degradation of tetracycline

The Fe–B(P, S)– C₃N₅(v)/Bi₂MoO₆ (Fe–CN_V (B, P, S)/BMO) composite was first designed as a high-efficiency photo-Fenton catalyst for tetracycline (TC) degradation. Remarkably, the optimized Fe–B–C₃N₅(v)/Bi₂MoO₆ achieves 91.9 % TC degradation efficiency with a mineralization efficiency of 81.3 % within 120 min under visible light illumination with 0.02 mM H₂O₂, exhibiting a first-order rate constant (k) of 0.01775 min⁻¹ (R² = 0.9291) and an approximately 3-fold enhancement in photo-Fenton degradation activity compared to pristine C₃N₅. Combined experimental and theoretical analyses confirm that the performance improvement primarily originates from the synergistic effects of vacancy engineering, element refilling and S-scheme heterojunction construction, which significantly promote H₂O₂ activation by enhancing charge separation and providing abundant active sites. The capture experiments revealed that the •O₂⁻ and •OH are the dominant active species to induce the degradation of TC, along with a suggested decomposition pathway according to the detected main intermediates. This further confirms that charge modulation coupled with effective reactant activation can significantly enhance the degradation efficiency of TC organic pollutants. This work offers a feasible pathway for the rational design of photo-Fenton systems towards recyclable degradation of environmental contaminants.