<p>Metformin (MET), recognized as the most extensively consumed pharmaceutical globally, exhibits minimally metabolized and is predominantly excreted unchanged. To remove MET from water, this study synthesized Fe₃O₄@MnO₂ (FM) catalysts, which could be easily recoverable using magnets. Notably, Fe₃O₄ nanospheres, characterized by their superior crystallinity, significantly altered the morphology and structure of the externally wrapped MnO₂. This modification resulted in an expanded surface area and an increased number of active sites. Furthermore, ultrasound (US) was employed to assist in peroxymonosulfate (PMS) activation, ensure effective dispersion of FM-5, and enhance the homogeneity of the reaction system. The synergistic application of US and FM-5 successfully activated PMS, achieving a remarkable MET degradation efficiency of 98.89% within 80&#xa0;min, predominantly via a pathway governed by ·O₂⁻ and ¹O₂. The FM-5/US/PMS system demonstrated robust adaptability under various environmental conditions. An analysis of the correlation mechanism revealed enhanced MET decomposition under alkaline conditions, thereby broadening the pH adaptation range of FM-5/US/PMS. Using density functional theory (DFT) calculations and HPLC–MS detection to propose degradation products, this study identified a product with comparatively lower toxicity. This work could offer a reference for further development of high performance and eco-friendly catalyst.</p> Graphical Abstract <p></p>