Piezo-photocatalytic tetracycline degradation over monoclinic Y(IO3)3: mechanistic insights into piezo-promoted charge separation via DFT-electrochemistry

Tetracycline (TC) is one of the most widely used veterinary and human antibiotics, and its persistence in surface and ground waters is a growing concern for aquatic ecosystems and human health. Efficient catalytic strategies that combine light and mechanical stress are therefore needed. Piezo-photocatalysis enhances charge separation by coupling piezoelectric and photocatalytic effects under mechanical stimulation and light irradiation, yet the contribution of the piezoelectric effect to the catalytic mechanism is rarely quantified. We report yttrium iodate (Y(IO 3 ) 3 ) as a model piezo-photocatalyst for TC degradation and use a combined density functional theory (DFT)-electrochemistry framework to estimate its piezoelectric contribution under the P2 1 structural model adopted in this work. The model gives an orientation- and time-averaged internal field of approximately 18.9 V·m −1 at an effective reactor stress of 77 Pa. The predicted current (13.1 μA) is of the same order as the measured piezo-photocatalytic photocurrent (11.91 μA); this agreement is an indirect internal-consistency check and not a direct measurement of the local particle-level piezoresponse. Under coupled activation, the pseudo-first-order rate constant reached 0.037 min −1 , 1.3 times that of photocatalysis alone. An amorphous SiO 2 control under UV irradiation and 300 rpm stirring gave k = 0.00031 ± 0.00003 min −1 and only 1.8% removal after 60 min, while dark-equilibrium adsorption by Y(IO 3 ) 3 differed by only 0.4 percentage points between 30 and 300 rpm. These controls and the transport analysis indicate that mixing and adsorption cannot account for the observed rate increase. EPR measurements showed the strongest ·OH, ·O 2 − , and 1 O 2 signals under coupled activation, while GC–MS identified progressive ring cleavage to low-molecular-weight acids. Activity declined over ten cycles; because post-cycle surface, textural, and leaching data were unavailable, the deactivation mechanism remains unresolved.