Hierarchical multilevel synergy of piezoelectricity-photocatalysis-defect engineering in ZnS for boosting peroxymonosulfate activation: A sustainable strategy for azo dye degradation

The persistent presence of refractory organic pollutants in aquatic ecosystems remains a global challenge, owing to their structural stability, bioaccumulation potential, and the toxicity of their transformation products. To address this issue, a hierarchical multilevel synergistic system (denoted as the ZP system) is constructed based on simple single-component ZnS coupled with peroxymonosulfate (PMS) for the efficient degradation of direct black G (DBG). This system integrates three synergistic mechanisms: piezoelectricity-photocatalysis-defect engineering synergy, catalyst-PMS activation synergy, and adsorption-degradation synergy. The cooperative process involves: (i) synergistic separation of photogenerated charges through the piezo-photocatalytic effect and sulfur vacancies (V S ) in ZnS; (ii) amplification via a ZnS-V S -PMS interaction, where continuous electron consumption establishes a self-sustaining “excitation-depletion-re-excitation” cycle; and (iii) an adsorption-degradation cycle that enriches pollutants near active sites and regenerates adsorption sites during degradation. ZP system maintains high removal efficiency (>85 %) over a broad pH range (2–8). Moreover, ZP system achieves complete DBG removal within 20 min in various real water matrices (pond, tap, and river water) under the Xenon lamp irradiation, and exhibits a great application potential under natural sunlight and simulated flowing water. Compared with the original DBG, the toxicity of degradation products was significantly reduced, with the cell viability of 96.8 %. Radical trapping experiments and electron paramagnetic resonance spectroscopy identify h + , •SO 4 − , •OH, and •O 2 − as the dominant reactive species. Moreover, the ZP system exhibits excellent biocompatibility with negligible hemolysis, underscoring its environmental friendliness. This work highlights the promise of a simple single-material-based multilevel synergy as a scalable, cost-effective, and adaptable strategy for sustainable water purification.