Efficient piezocatalysis of Bi_0.5(Na_1−xK_x)_0.5TiO₃ nanoparticles: bridging the phase ratio at MPB composition and piezocatalytic activity

As a promising replacement for widely studied photocatalysis, piezocatalysis is capable of realizing organic dye degradation, water splitting, medical therapy, and many other functions by harvesting mechanical vibration energy in the surroundings. In this study, we demonstrate the excellent piezocatalytic effect of hydrothermally synthesized Bi_0.5(Na_1−xK_x)_0.5TiO₃ (BNKT) nanoparticles through both degradations of dyes and hydrogen evolution. A high kinetic rate constant k of 0.065 min⁻¹ for the degradation of rhodamine B dye was obtained from the BNKT nanoparticles with a tetragonal-rich morphotropic phase boundary (MPB) composition, overperforming the counterparts with a rhombohedral-rich MPB composition and a single tetragonal phase. The BNKT nanoparticles possessing a tetragonal-rich MPB composition yield the most pronounced piezoelectric effect among the studied compositions, albeit better band alignment with the redox potential levels in rhombohedral-rich MPB nanoparticles, thus confirming the critical role of a strong piezoresponse in promoting the piezocatalytic activities. Our work will not only shed some light on understanding the dominant mechanism of piezocatalysis, but also uncover additional degrees of freedom, namely phase ratio within a phase boundary region, to further enhance the piezocatalytic efficiency.