Superoxide radicals dominated visible light driven peroxymonosulfate activation using molybdenum selenide (MoSe<inf>2</inf>) for boosting catalytic degradation of pharmaceuticals and personal care products

Abstract

In recent years, molybdenum disulfides (MoS2) have been widely recognized as a promising catalyst or cocatalyst in Advanced Oxidation Processes (AOPs); however, the discharge of hydrogen sulfide (H2S) after catalytic process is still a key issue that needs to be addressed. Hence, in this study, a superoxide radical (O2[rad]−) dominated visible-light-driven peroxymonosulfate activation process has been established by adopting molybdenum selenide (MoSe2) to replace MoS2 in order to dramatically enhance the catalytic degradation efficiency of three types of pharmaceuticals and personal care products (PPCPs) (e.g., ibuprofen, benzophenone-3 and carbamazepine). This enhancement is due to its exposed surface metallic Mo4+ ions, accompanied with the oxidization to Mo5+ and Mo6+ for further participating in the decomposing of PMS, as well as the photo-generated electrons playing a prominent role in reducing the Mo5+ and Mo6+ back to Mo4+. Scavenger tests and electron paramagnetic resonance (EPR) identify the O2[rad]− as the primary reactive oxygen species (ROS) in the MoSe2/PMS system, and singlet oxygen (1O2) is mainly derived from the transformation of O2[rad]−. Density Functional Theory (DFT) is used to explain the elongation of O–O bond in the PMS molecule that would facilitate the generation of sulfate radicals and hydroxyl radicals in both of MoSe2 catalyzed PMS system and cocatalyzed Fe(II) or Fe(III)/PMS systems. Ultimately, the MoSe2/PMS system is also applicable for the treatment of actual sewage. This work highlights the important role of photo-generated electrons and molybdenum ions in PMS reduction and oxidation, and establishes theoretical support for further relevant studies.