Highly efficient sono-piezo-photo synergistic catalysis in bismuth layered ferroelectrics via finely distinguishing sonochemical and electromechanochemical processes

Ultrasonic stimulation induced polarization behaviors in ferroelectric materials have been extensively explored in catalytic degradations. However, the ultrasonic wave similarly can realize dye degradation by the sonocatalysis behavior, which is always neglected in most reports on in-situ ultrasound-induced piezoelectric catalysis, so that people might overestimate piezocatalytic contributions. For this, we designed a series of visible light sensitive bismuth layered ferroelectric materials (BLFMs), M_0.5Bi_2.5Nb₂O₉ (MBN, M = Li, Na, and K). It is found that the cavitation-induced degradation rates of Rhodamine B (RhB) strongly depend mechanical stirring speeds under a fixed ultrasonic power, which gradually increases with it, and reaches 77.9% (500 rpm and 3 h). Under lower stirring speed and reaction time (< 50 rpm and 2 h), the cavitation effect is almost negligible, only piezocatalysis behavior occurs, which can be used as a key condition to distinguish the piezocatalysis and sonocatalysis. In particular, the degradation rate constant of Na_0.5Bi_2.5Nb₂O₉ catalyst reaches up to 4.943 × 10⁻² min⁻¹ by the coupling of sonocatalysis, piezocatalysis and photocatalysis, which is much higher than that of single photocatalysis (0.491 × 10⁻² min⁻¹), piezocatalytic (1.6 × 10⁻³ min⁻¹), and sonocatalysis (0.756 × 10⁻² min⁻¹). These results may provide a feasible strategy of further improving catalytic degradation efficiency, and accurately determining the sonocatalysis and piezocatalysis contribution.