Piezoelectric Activation of Peroxymonosulfate by CoMn₂O₄ for Highly Efficient Tetracycline Degradation

Advanced oxidation processes employing peroxymonosulfate (PMS) show significant promise for wastewater treatment. However, PMS activation typically relies on energy- and chemically intensive techniques due to its relatively low reactivity. Hence, the exploration of novel and energy-efficient approaches, such as the piezoelectric effect, for PMS activation is of paramount importance. Herein, we prepared a piezoelectric material (CoMn₂O₄) via a simple hydrothermal method followed by calcination. The degradation experiments of tetracycline (TC) demonstrated that CoMn₂O₄ exhibited excellent performance under ultrasound, the apparent rate constant k is 0.191 min^-1, and its degradation rate reached 83.63% after 10 min. Piezo force microscopy (PFM) tests confirmed that CoMn₂O₄ exhibited a piezotronic effect under ultrasound. In situ electron paramagnetic resonance (in situ EPR) tests revealed that PMS could be activated to form hydroxyl radicals (^•OH) and sulfate radicals (SO₄^•-) under ultrasound, which are active species for TC degradation. Consequently, CoMn₂O₄ effectively activated PMS into ^•OH and SO₄^•- active species, enabling the effective TC degradation. Moreover, biotoxicity experiments using germination tests showed that CoMn₂O₄ was capable of effectively degrading TC, thereby reducing environmental toxicity. This work not only provides mechanistic insights into piezoelectric material-activated PMS for pollutants degradation but also establishes a basis for the application of piezoelectric materials in pollutant degradation.