Optimized synthesis of Mn3O4−[Ce(Ⅲ)]x adsorbent for enhanced Sb(V) removal from aqueous solutions: role of Ce/Mn redox couples and oxygen vacancies

Antimony pollution poses significant risks to aquatic environments due to its high toxicity and persistence. Herein, a novel Mn3O4−[Ce(Ⅲ)]x adsorbent was developed by optimizing the molar ratio of MnO and Ce(NO3)3 for efficient Sb(V) removal. The preparation involves a Ce(Ⅲ)/Ce(IV) redox-driven process, where Ce(Ⅲ) oxidation by O2 generates Ce(IV), which oxidizes Mn(Ⅱ) to Mn(Ⅲ/IV), accelerating the formation of spinel Mn3O4, while Ce species form Ce2O3/CeO2, and lattice mismatch creates Mn−O−Ce heterojunctions with oxygen vacancies. Batch experiments showed that Mn3O4−[Ce(Ⅲ)]x=0.25 achieved a high adsorption capacity of 191.46 mg·g-1 under the optimal conditions (pH =3.0, reaction time = 2.0 h, dosage = 1.0 g/L, temperature = 30 ℃), owing to its high specific surface area (57.34 m2/g) and pHpzc (8.29), as well as oxygen vacancies and lattice defects. Regarding coexisting ions, the inhibitory effect of anions followed the order PO43– > SiO32– > CO32– > SO42– > Cl–, whereas cations showed minimal interference. Notably, the adsorbent maintained 85.41% removal after seven cycles with NaOH being the most effective eluent. Comprehensive characterization revealed that chemisorption dominates the process, primarily through proton transfer and coordination reconstruction, leading to the formation of CeMnSbO5 and stable Ce/Mn−O−Sb inner-sphere complexes via electrostatic attraction, ligand exchange, hydrogen bonding, and the dual redox pair synergy (Ce(Ⅲ/IV) and Mn(Ⅲ/IV)). Among these, the Ce(Ⅲ)/Ce(IV) redox couple plays a dominant role in regenerating active sites and suppressing toxic Sb(III) formation. Collectively, these findings demonstrate that Mn3O4−[Ce(Ⅲ)]x=0.25 is a highly promising adsorbent for efficient Sb(V) removal in water treatment applications.