Waste Polystyrene-derived Sulfonated Fluorescent Carbon Nanoparticles for Cation Sensing

Polystyrene, one of the most widely-produced plastics worldwide, is non-biodegradable and has unsustainable life-cycles with only a small fraction recycled presently. Hence, there is considerable effort underway to explore new methods to give post-consumer polystyrene waste a new lease-of-life as functional materials. In this study, we report the synthesis of the first polyanionic fluorescent carbon nanoparticles from sulfonated waste polystyrene food containers via an environmentally-benign route in water. By virtue of their sulfonate groups, these biocompatible and fluorescent nanoparticles show a number of distinct behaviours in the presence of different main group and transition metal cations. Al3+ brings about both fluorescence enhancement and nanoparticle precipitation, whilst fluorescence quenching was observed for paramagnetic and toxic transition metal cations, with Cu2+ eliciting the most sensitive fluorescence response (LoD=26 mu M). These fluorescence intensity perturbations are likely a consequence of direct metal cation coordination to the exposed sulfonate groups on the nanoparticles. Our findings suggest the potential of using post-synthetically modified waste plastics to produce a family of luminescent carbon materials for environmental sensing of these hazardous cations.