Preparation of highly photoluminescent carbon dots from polyurethane: Optimization using response surface methodology and selective detection of silver (I) ion

In this study, novel carbon dots were synthesized from polyurethane foam via a one-step pyrolysis method. Polyurethane foam is an interesting precursor for carbon dot synthesis because: (1) polyurethane foam waste generation is alarmingly high and (2) polyurethane is rich in nitrogen content which is important for producing highly photoluminescent carbon dots. The carbon dot synthesis parameters namely acid concentration, reaction time, and reaction temperature were modeled and optimized using Box-Behnken design (BBD) of response surface methodology (RSM). Temperature was found to be the most important parameter affecting the photoluminescence quantum efficiency of the carbon dots. The as-prepared carbon dots in aqueous solution showed a blue-green emission under UV light with a relatively high quantum yield of 33%, agreeing well with the value predicted using the RSM. The carbon dots exhibited distinct selectivity toward silver ion (Ag+) with a limit of detection of 2.8 μM. The Ag+ contents in real water samples were accurately determined with acceptable repeatability. Based on these results, the RSM is a useful tool for investigating the effects of reaction parameters on the quantum efficiency of carbon dots. Furthermore, pyrolysis was proved to be an effective means for producing label-free, highly photoluminescent carbon dots from polyurethane, enabling new, effective recycling strategy and various potential sensing applications.