Efficient tribocatalysis of magnetically recyclable cobalt ferrite nanoparticles through harvesting friction energy

Friction, a common phenomenon in ordinary life, can be converted into positive and negative charges via triboelectrification and can further react with the OH- and dissolved O2 in the solution to generate some active species with strong redox ability in theory, which can be named as tribocatalysis. In this work, the efficient tribocatalysis is obtained in the magnetically recyclable CoFe2O4 nanoparticles synthesized via a hydrothermal method for Rhodamine B (RhB) dye decomposition, in which the mechanical stirring is adopted to generate the friction between the stirring rod and the nanocatalysts surface. After being stirred for 5 h, the CoFe2O4 nanoparticles can tribocatalytically decompose 91.9% RhB dye solution with a concentration of 5 mg·L−1. Due to the continuous full contact and friction between the stirring rod and the CoFe2O4 nanoparticle, the negative and positive charges are respectively retained over the contact area of the CoFe2O4 nanoparticle and the stirring rod, so as to react with hydroxide ions and dissolved oxygen to generate active species achieving the RhB dye decomposition. Subsequently, the different shapes of stirring rod experiments prove that the full contact between the CoFe2O4 nanoparticle and the stirring rod is essential for the efficient tribocatalysis. The electron spin resonance experiments confirm that both ·OH and ·O2- are the main active species. On basis of the recycling utilization experiments' results, after being magnetically-recycled for 3 cycles, the CoFe2O4 nanoparticles can still decompose 86.5% RhB dye. With these advantages of the efficient tribocatalysis and the magnetically recycle ability, CoFe2O4 nanoparticles are hopeful in dealing with dye wastewater through harvesting the ordinary friction energy in environment.