Enhanced Peroxydisulfate Activation with Crystalline Iron-Based Ternary Chalcogenides (Fe2GeS4) for Organic Micropollutant Degradation

Peroxydisulfate (PDS)-based processes are an effective approach for eliminating emerging organic micropollutants (MPs) in (waste)water treatment. Iron-based homogeneous systems are known for their availability, technical and economic feasibility, and relatively nontoxic nature; however, these systems suffer from drawbacks that limit their application. Herein, an iron-based ternary chalcogenide material, Fe₂GeS₄ nanocrystals (FGS NCs), was used to activate PDS for the removal of bisphenol A (BPA). The FGS/PDS system achieved complete removal of BPA at circumneutral pH with a high reaction stoichiometric efficiency (7.8%), outperforming common PDS activators, such as Fe(II), pyrite, zerovalent iron, and black iron oxide. The synergistic enhancement in PDS activation could be attributed to the improved Fe(III)/Fe(II) cycle due to the reduced sulfur and divalent germanium species in the olivine FGS NCs. This finding was confirmed by mechanistic investigations and chromatographic, spectroscopic, and density functional theory studies. Both high-valent iron-oxo (Fe^IV) species (dominant) and sulfate radicals (auxiliary) contributed to BPA transformation, where the solution chemistry (pH, temperature, substrate dose, and anions) influenced the removal of BPA from the FGS/PDS system. Evaluation of the performance of the FGS/PDS system in real water matrices (river water, groundwater, and secondary effluents) revealed its long-term stability and efficiency in removing multiple MPs, including acetaminophen, N,N-diethyl-m-toluamide, perfluorooctanoic acid, 4-chlorophenol, benzotriazole, and ethylparaben. Overall, these findings highlight the potential of FGS/PDS for effective MPs removal in (waste)water treatment.