High-entropy oxide for peroxydisulfate activation: Collaboration between oxygen vacancies and pore structure

The activation of peroxydisulfate (PDS) with polymetallic components and entropy-stabilized structures of high-entropy oxides (HEOs) to eliminate organic pollutants is becoming increasingly attractive. In this paper, the orthogonal HEOs-(FeCuMnCoNi)O_x of Pbam (55) space group has been proven to be an excellent catalyst for PDS activation. By stepwise regulating the synthesis of precursors, HEOs-500 with abundant oxygen vacancies can be formed by calcining the precursors at 500 °C for 2 h. The solid solution properties of HEOs-500 result in a low total ion leaching (0.289 mg/L). The lower calcination temperature (500°C) gives it a richer specific surface area (19.79 m²/g), which is 11.24 times larger than the HEOs-800 calcined at 800 °C. A method for evaluating the catalytic activity of HEOs using the product of relative content of oxygen vacancies (ROVs) and relative specific surface area (RS) is proposed. The ROVs * RS showed a significant positive correlation (R² > 0.98) with the quasi-first order reaction constants of quinolone antibiotics degraded by the HEOs/PDS system. The high catalytic activity of HEOs was realized, which could completely degrade levofloxacin (LFX) within 60 min. The efficient adsorption and activation capacity of (Mn Co) adsorption sites on the (201) crystal face of HEOs-500 for PDS. Free radical oxidation pathways (·OH and SO₄·^-) and non-free radical oxidation pathways (¹O₂) were shown to be responsible for the rapid degradation of LFX in the HEOs-500/PDS system. This work validates the superior prospect of HEOs catalysts in activating PDS for tail water remediation.