Fe3+ regulated synthesis of Fe3O4@MIL-100(Fe): nanoarchitectonics and enhanced photo-Fenton activity

The weak light absorption, low charge separation efficiency, and poor recyclability severely restrict the practical application of heterogeneous photo-Fenton catalyst MIL-100(Fe). Herein, we report the synthesis of Fe 3 O 4 @MIL-100(Fe) with tunable structures via hydrothermal growth, using Fe(NO 3 ) 3 ·9H 2 O and H 3 btc as precursors on an Ag/Fe 3 O 4 template. Notably, Fe(NO 3 ) 3 ·9H 2 O serves dual roles: it acts as a precursor for MIL-100(Fe) formation and as an oxidizing agent to remove the Ag template. The microstructure of the resulting catalyst can be precisely regulated by varying the Fe 3⁺ dosage. By optimizing the Fe(NO 3 ) 3 ·9H 2 O dosage, the optimal hollow Fe 3 O 4 /MIL-100(Fe) catalyst is obtained, which exhibits excellent dispersion, a distinct core/shell structure, a larger specific surface area (312.6 m 2 /g), a smaller average pore diameter (4.9298 nm), strong magnetic separability, and superior photo-Fenton degradation performance (95.6% within 30 min). After 4 consecutive cycles, the degradation efficiency toward Rhodamine B (RhB) remains above 90%, demonstrating outstanding cycling stability. Electron spin resonance (ESR) analysis confirms that both ·O 2 ⁻ and ·OH are the dominant reactive oxygen species responsible for the catalytic degradation reactions.