Fig. 4. (A) Absorption spectra of SA after reaction with Fe²⁺/H₂O₂, in the absence and presence of Mn₃O₄ NPs. SA alone, and SA reacted with Fe²⁺ or H₂O₂ were used as control. (B) Dependence between the elimination of ˙OH and concentration of Mn₃O₄ NPs and CeO₂ NPs (mean ±S.D., **p < 0.05; n.s., not significant).