Fe-g-C3N4/ZnFe2O4 S-scheme heterojunction: A photo-Fenton-like system for efficient tetracycline hydrochloride degradation.

A novel S-scheme heterojunction constructed from Fe-doped g-C3N4 (with an optimal Fe precursor to melamine mass ratio of 0.05:5) and ZnFe2O4 exhibited high efficacy in the tetracycline hydrochloride (TCH) degradation via a photo-Fenton process under visible light with H2O2. The heterojunction demonstrated high activity, removing 96.72% of 20 mg L-1 TCH within 30 min, corresponding to an apparent rate constant (k) of 0.07191 min-1. This superior performance originated from three key factors: efficient migration of photogenerated charges, plentiful surface-active sites, and thermodynamically favorable band positions for reactive species generation. Based on the analysis of density functional theory (DFT) calculations and various experimental characterizations, the photo-Fenton-like mechanism was unveiled, which involves multiple reactive species, generated by the highly efficient photo-Fenton-like system, preferentially attacking the aromatic ring of TCH and ultimately mineralizing it. By combining systematic experimentation with in-depth mechanistic analysis, this work broadens the research avenues for S-scheme heterojunctions in photo-Fenton-like catalysis, thereby offering valuable insights into the broader field of advanced oxidation processes (AOPs).