Enhanced photo-fenton degradation of Rhodamine B by Ce-doped NH2-MIL-101(Fe,Ce): the joint effect of singlet oxygen and free radical species

Abstract

The promoting effect of bimetallic sites in metal–organic frameworks (MOFs) provides a promising yet underexplored approach for improving photo-Fenton catalytic efficiency. Herein, a series of cerium-doped NH₂-MIL-101(Fe,Ce) catalysts were synthesized via a facile solvothermal method. By adjusting the cerium doping ratio, the optimal NH₂-MIL-101(Fe,Ce10%) exhibits outstanding catalytic performance for potassium monopersulfate triple salt (PMS) activation under visible-light irradiation, achieving 99.7% degradation of Rhodamine B (RhB) within 90 min. Notably, its corresponding pseudo-first-order kinetic rate constant (0.06312 min⁻¹) is 4.26 times higher than that of pristine NH₂-MIL-101(Fe). Multiple characterizations (XRD, FT-IR, XPS, SEM, BET) and photoelectrochemical analysis (UV–vis DRS, PL, TPR, EIS) demonstrate that cerium doping introduces structural defects and establishes dual redox cycles (Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺), which slightly widens the band gap, but accelerates interfacial charge transfer, and promotes the activation of PMS. Free radical capture experiment and electron paramagnetic resonance (EPR) spectroscopy unambiguously confirm that singlet oxygen (¹O₂), sulfate radicals (SO₄^·−), and hydroxyl radicals (·OH) function as equally important and cooperative reactive species, collectively driving the degradation process. The catalyst presents favorable stability over five consecutive cycles and exhibits strong tolerance to common coexisting anions. This work elucidates the origin of enhanced photo-Fenton activity in bimetallic Fe–Ce MOFs and provides a strategy for the rational design of high-efficiency catalysts for water treatment.