Anaerobic formation of manganese oxides mediated by complexed iron and application in tetracycline hydrochloride degradation

Biological manganese oxides (BioMnOx) are promising materials for micro-pollutant degradation, with conventional synthesis primarily mediated by aerobic microorganisms and dependent on high-potential oxidants (e.g., O 2 , NO 3 − ). In this study, light-driven anaerobic synthesis of BioMnOx was investigated using the photosynthetic bacterium Rubrivivax benzoatilyticus , and its application in tetracycline hydrochloride (TC) degradation under anaerobic conditions was evaluated. Results showed that in the presence of potassium ferrocyanide, R. benzoatilyticus could extracellularly oxidize Mn 2+ to BioMnOx anaerobically. The ferrocyanide potassium firstly was biologically oxidized to ferricyanide potassium under photo-anaerobic conditions, and then Mn 2+ was abiotically oxidized to BioMnOx by ferricyanide potassium. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) confirmed that aqueous Mn 2+ was converted to mixed-valence Mn 3 O 4 , with concurrent co-precipitation of Mn 3 (PO 4 ) 2 . TC degradation experiments demonstrated that approximately 40.24% TC removal was achieved with 20 mg/L BioMnOx under near-neutral conditions, while acidic environments significantly enhanced its oxidation performance. The maximum TC removal efficiency of 89.10% was attained at 40 mg/L BioMnOx and pH 3. UV–Vis spectroscopy and liquid chromatography-mass spectrometry (LC-MS) detected multiple degradation intermediates of TC, confirming that TC was oxidized by BioMnOx rather than simply adsorbed. This work provides an effective strategy for the anaerobic synthesis of BioMnOx and the degradation of TC, offering new insights into the micro-pollutants removal via manganese cycling in anaerobic aquatic environments. • Light-driven anaerobic manganese oxidation pathway has been established. • BioMnOx primarily composed of Mn 3 O 4 was successfully synthesized. • BioMnOx exhibited significant TC oxidation activity under dark and anaerobic conditions. • At pH 3 and a BioMnOx dosage of 40 mg/L, the TC removal efficiency reached up to 89.10%. • LC-MS results revealed that TC was transformed into low-molecular-weight products.