Toward Practical Water Decontaminations via Peroxymonosulfate Nonradical Oxidation: The Role of Cocatalyst MoS2 with Sulfur Vacancies

Abstract

Molybdenum disulfide (MoS₂) is a prevalent cocatalyst for peroxymonosulfate (PMS) activation with iron-based materials. The contribution of molybdenum atoms in cocatalyst MoS₂ to iron regeneration during PMS activation has been broadly known, though the role of sulfur atoms remains explored. Here, we applied a one-step, facile means to prepare particulate Fe₃O₄ supported by wrinkled MoS₂ with discernible sulfur vacancies (S_V), forming a flower-like Fe₃O₄–MoS₂ composite catalyst. We demonstrated, for the first time, a strong affinity of S_V to PMS, facilitating the formation of an intermediate Fe^III–PMS* while modulating the generation of pivotal nonradical species. Using an extensive characterization, we confirmed the simultaneous generation of high-valent iron-oxo species (≡Fe^IV═O) and singlet oxygen (¹O₂) during PMS activation with the Fe₃O₄–MoS₂ catalysts. In addition, we proposed that the ≡Fe^IV═O stemmed from the Fe^III–PMS* precursor, which underwent heterolytic cleavage of the O–O bonds and concomitant rearrangement of oxygen atoms. Meanwhile, ¹O₂ is excited by PMS and formed by active oxygen (O*) liberated from iron oxides. Consequently, the Fe₃O₄–MoS₂ catalysts showed impressive performance in removing typical micropollutants from real water sources, such as secondary effluent from wastewater treatment plants, tap water, and surface water stream. Our study provides new insights into a nonradical pathway for PMS activation with Sv-containing MoS₂, clearing the way for developing high-performance MoS₂ catalysts for water decontamination.