Polyelectrolyte Multilayer: Caged PTFE Particles in Water for Continuous, Sonochemical H₂O₂ Synthesis

The use of polytetrafluoroethylene (PTFE) particles to promote sonochemical H₂O₂ production has attracted growing interest, as cavitation bubbles formed at or near their perfluorinated surfaces provide favorable interfacial environments for generating reactive radicals from water and oxygen. However, their practical application is limited by poor dispersibility in aqueous media. Here, we report a yolk-shell particle (YSP) design, where PTFE cores are encapsulated within polyelectrolyte multilayer (PEM) shells assembled via layer-by-layer deposition of polyallylamine hydrochloride and poly(styrene sulfonate). This structure enables stable dispersion in water while maintaining exposure of hydrophobic PTFE surfaces through internal void spaces, thereby maximizing the ultrasound-driven interfacial H₂O₂ generation efficiency of PTFE surfaces. As a result, continuous sonochemical conversion of H₂O and O₂ to H₂O₂ is achieved, with a maximum concentration of 2.5 mmol·L^-1 over 12 h and a production rate of 3.34 mmol·g_cat ^-1·h^-1. Moreover, the YSP platform allows systematic evaluation of particle size and surface chemistry effects. This strategy not only enables the reuse of polymer waste as functional promoters but also facilitates the development of accessible, cost-effective sonochemical H₂O₂ generators for applications in water purification, food safety, and healthcare.