Degradation-upcycling of all-carbon backbone water-soluble polymers into fluorescence carbonized polymer dots via intense ultrasonic cavitation.

The conversion of all-carbon backbone polymer waste into valuable carbon materials represents an ideal route to address polymer pollution and advance resource circularity. However, conventional degradation methods are challenging to deconstruct stable all-carbon backbones and trigger molecular configuration transformation. Here, we report a one-step degradation-upcycling strategy based on highly localized intense ultrasonic cavitation (IUC) generated by a spherical cavity focused ultrasound transducer (SCUT) operating at 650 kHz under a high hydrostatic pressure of 10 MPa. Rapid C-C backbone cleavage and in situ conversion of water-soluble all-carbon backbone polymers (including polyvinyl alcohol (PVA), polymethacrylic acid (sodium salt) (PMAA), and polyvinylpyrrolidone (PVP)) into functional carbonized polymer dots (CPDs) have been realized. Taking PVA as an example, a near-complete depolymerization with maximum molecular weight reduction of 96.45 % was achieved. Meanwhile, the generated CPDs exhibit tunable fluorescence and excellent antibacterial properties, realizing the transformation from polymer waste to value-added resources. Mechanistic analysis revealed that under the highly concentrated shock waves, high temperatures, and free radicals generated in IUC, degradation-upcycling of these polymers was achieved through a cascade strategy of 'mechanical scission - radical oxidation - graphitization'. Observations of rapid degradation and transformation of the all-carbon backbone to sp2 graphitic carbon derived from the IUC under high hydrostatic pressure have broadened understanding of sonochemical polymer processing and shaped a new way for polymer waste treatment, showing significant scientific value and application potential.