Ultrahigh efficient degradation activity of single- and few-layered MoSe2 nanoflowers in dark by piezo-catalyst effect

We have demonstrated an ultrahigh degradation activity of the single-layer and few-layered MoSe2 nanoflowers for decomposing the Rhodamine (RhB) dye by the piezo-catalyst effect. The MoSe2 nanoflowers can successfully decompose the RhB dye by 90% in 30 s through the application of the mechanical force (e.g., ultrasonic vibration) in dark. The size of the MoSe2 nanoflowers has a diameter of less than 3 µm, which exhibits a great number of the single- and few-layers with a plentiful amount of active surface sites. The interlayer spacing between each single-layer MoSe2 is ~ 0.67 nm. The piezoresponse force microscopy (PFM), and the tunneling atomic force microscopy (TUNA), further evidence that the MoSe2 nanoflowers exhibit a significantly piezoelectric potential as created by the internal electric fields in different polarization domains of the single- and few-layered MoSe2. The observed kobs rate constant is 0.3 (ppm s−1) with an ultra-fast degradation rate of ~ 69,889 ppm L mole−1 s−1. This is the fastest degradation rate in the dark among all reported catalysts. A redox process of the MoSe2 nanoflowers as induced by mechanical force in dark have been evidenced by XPS spectra. The electron paramagnetic resonance (EPR) spin trapping with 5,5-dimethylpyrroline-1-oxide (DMPO) spectra indeed demonstrated the formation of the hydroxyl radical from the MoSe2 nanoflowers during the ultrasonic vibration in dark, which is the major reactive oxygen species (ROS) for destroying the dye molecules. This is first work to demonstrate the very efficient catalyst and redox processes by piezo-catalyst effect using the MoSe2 nanoflowers.