Sonochemical synthesis of Fe3O4/carbon nanotubes using low frequency ultrasonic devices and their performance for heterogeneous sono-persulfate process on inactivation of Microcystis aeruginosa.

Iron oxide nanoparticles decorated on multi-wall nanotube (MWCNTs) were successfully fabricated through a facile and rapid sonochemical method without any pre-treatment on MWCNTs. Fe3O4/MWCNTs-20 showed a uniform and fine distribution of nanoparticles in the MWCNTs. The obtained Fe3O4/MWCNTs were analysed using TEM and XPS. Notably, Fe3O4/MWCNTs were used for persulfate activation on cyanobacterial cell removal. With 20 mg/L persulfate, Fe3O4/MWCNTs showed an efficient catalytic performance after 1 h treatment. In the Fe3O4/MWCNTs hybrid catalyst, Fe3O4 helps to produce sulfate radicals and hydroxyl radicals whereas the size of the Fe3O4 clusters could affect the electron transfer for radical generation. Moreover, using high frequency low intensity ultrasound, the combination of persulfate and Fe3O4/MWCNTs-20 reduced the remaining cell number to 9.4% within 30 min treatment. In conclusion, our work demonstrated that low frequency ultrasonic devices are capable of fabricating Fe3O4/MWCNTs via a simple and time-saving route, and the obtained catalysts showed superior catalytic performance on persulfate for harmful cyanobacteria control.