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Developing a high-performance activator is crucial for the practical application of peroxymonosulfate-based advanced oxidation processes (PMS-AOPs). High-entropy oxides (HEOs) have attracted increasing attention due to their stable crystal structure, flexible composition and unique functionality. However, research into the mechanisms by which HEOs function as PMS activators for degrading organic pollutants remains insufficient, and the relationship between entropy and the catalytic performance of HEOs has yet to be clarified. In this study, we synthesized NiMgZnCuCoO x with different levels of entropy as PMS activators for acetaminophen (APAP) degradation, and observed a significant effect for entropy on the catalytic performance. Sulfate radicals (SO 4 • ‒ ) were identified as the primary reactive oxygen species (ROS), while hydroxyl radicals (•OH) and singlet oxygen ( 1 O 2 ) act as secondary ROS during APAP degradation. Both the Co 2+ contents and the oxygen vacancy concentration in NiMgZnCuCoO x are found to increase with the entropy. An increase in the Co 2+ sites leads to more activation sites for PMS activation, while excessive oxygen vacancies consume PMS, producing weak oxidation species, and affect the electron-donating ability of Co 2+ . Consequently, the NiMgZnCuCoO x with middle level of entropy exhibits the optimal performance with APAP degradation rate and mineralization rate reaching 100% and 74.22%, respectively. Furthermore, the degradation intermediates and their toxicities were assessed through liquid chromatography-mass spectrometry and quantitative structure-activity relationship analysis. This work is expected to provide critical insight into the impact of the HEOs entropy on the PMS activation and guide the rational design of highly efficient peroxymonosulfate activators for environmental applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

During the manufacturing of pharmaceutical compounds, solvent mixtures are commonly used, where the addition of a cosolvent allows for the tuning of the intermolecular interactions present in the system. Here we demonstrate how a similar effect can be accomplished using a room temperature ionic liquid. The pharmaceutical compound acetaminophen is studied in 21 common ionic liquids composed of a 1-n-alkyl-3-methylimidazolium cation with 1 of 7 anions. Using the acetate anion, we predict a large enhancement in solubility of acetaminophen relative to water. We show how this is caused by a synergistic effect of favorable interactions between the ionic liquid and the phenyl, hydroxyl and amide groups of acetaminophen, demonstrating how the ionic liquid cation and anion may be chosen to preferentially solvate different functional groups of complex pharmaceutical compounds. Additionally, while the use of charge scaling in ionic liquid force fields has previously been found to have a minute effect on ionic liquid structural properties, we find it appreciably affects the computed solvation free energy of acetaminophen, which in turn affects the predicted solubility.