Fig. 3: Mechanism, structural characterizations, and US-activated piezocatalysis of mKNN PNPs.

a Fluorescence images of blank and mKNN MNs. mKNN MNs showed reduced fluorescence particularly at the tips. Scale bars, 600 μm. b Schematic illustration of US-activated piezocatalysis of mKNN PNPs loaded in dissolvable MNs. c TEM images and corresponding EDS mapping results of mKNN NPs. Scale bars, 100 nm. d HR-TEM image of mKNN PNPs. Scale bar, 5 nm. e XRD patterns of mKNN ceramic and PNPs. f The spontaneous polarization vectors of mKNN materials with R-O-T phase coexistence. g XPS spectra of O 1s for mKNN PNPs. h SS-PFM amplitude curve and phase loop of mKNN PNPs. i, j Electronic band structure (i) and density of states (j) of mKNN PNPs determined by DFT calculations. k UV-vis diffuse reflectance spectra of mKNN PNPs. l, Schematic illustration of electron and hole generation, transfer, and utilization in mKNN PNPs for piezocatalysis. m Degradation of Rho B by mKNN PNPs under US stimulation. n Piezocurrents of KNN, mKNN, and non- piezoelectric Nb₂O₅ PNPs under periodic US stimulation. o FEA simulation of surface piezo-potential distribution of a mKNN PNP under the acoustic pressure generated by wf-UMP. p EPR spectra of DMPO-^•OH and DMPO-^•\({{\mbox{O}}}_{2}^{-}\) over mKNN PNPs under US stimulation.