Decoration of MnFe ₂ O ₄ nanoparticles on activated carbon as recoverable photocatalyst for perfluorooctanesulfonic acid degradation in water

A MnFe₂O₄/activated carbon composite (FMAC) was successfully prepared for the treatment of perfluorooctanesulfonic acid (PFOS). Structural and compositional analyses confirmed the formation of spinel manganese ferrite (FMO) nanoparticles and their uniform immobilization on the activated carbon (AC) surface. XPS results revealed the coexistence of multiple oxidation states of Mn and Fe, along with abundant oxygen-containing functional groups on the carbon support, indicating strong interfacial interactions between FMO and the AC support. Optical measurements showed that FMO and FMAC exhibit excellent visible-light absorption with a bandgap (<i>E</i> _g) of ∼2.4 eV. Electrochemical studies also demonstrated reduced charge transfer resistance and suppressed electron-hole recombination in FMAC. Vibrating sample magnetometry (VSM) also indicated a sufficient magnetic response for recovery of FMAC from aqueous media. Photocatalytic tests showed that FMAC with a content of 10 mg L^-1 accomplished significant degradation efficiency (∼94%) of PFOS in 100 ppb solution at pH 4.0 under visible light irradiation for 90 min, which was higher than both FMO and AC under similar conditions. Radical scavenging experiments indicated that holes and hydroxyl radicals played dominant roles, while superoxide radicals were negligible due to unfavorable band edge potentials. Inclusively, the enhanced performance of FMAC is attributed to improved pollutant adsorption, efficient charge separation, and strong interfacial coupling between FMO and AC.