Synergetic contribution of enriched selenium vacancies and out-of-plane ferroelectric polarization in AB-stacked MoSe2 nanosheets as efficient piezocatalysts for TC degradation

In this study, ultrathin MoSe2 nanosheets (MoSe2 NSs) with enriched selenium vacancies (Se-vacancies) were prepared via a HNO3-assisted exfoliation strategy. The features of the synthesized catalysts were characterized via SEM, TEM, XRD, EPR, Raman spectroscopy, XPS, BET, EIS, PFM and contact angle tests. The results showed that the optimum MoSe2 NSs-10 with an enlarged specific surface area had superior hydrophilicity and conductivity. Meanwhile, MoSe2 NSs-10 showed typical butterfly-shaped amplitude curves and 150° polar domain switching, which confirmed its out-of-plane ferroelectricity. This out-of-plane polarization originated from the unique AB stacking mode of the MoSe2 NSs, contributing to the polarization enhancement. These superior properties of MoSe2 NSs-10 were responsible for its enhanced piezocatalytic degradation efficiency of tetracycline (TC) compared with that of pristine MoSe2 nanoflowers (NFs). Under ultrasonic irradiation, 93.9% TC was degraded by MoSe2 NSs-10 within 30 s, which was over 3.6-fold higher than that by the MoSe2 NFs. Additionally, the active species trapping tests and electron spin resonance (ESR) measurements proved that both hydroxyl radicals (·OH) and superoxide radicals (·O2−) participated in the degradation of TC as major active species. The degradation pathways of TC over the MoSe2 NSs-10 piezocatalytic system were proposed based on HPLC-MS analysis. This work provides a new approach for improving the piezocatalytic performance of MoSe2 piezocatalysts towards antibiotic wastewater treatment.